Place to talk about Chassis tuning?

[want-a-be]

How many people here would be intereted in a place to talk about chassis/suspension tuning on the Dart Board?

Just asking cause most of the forums I lurk in have very active talks about it. Making the power is only part of the problem of going faster. Getting it to the ground is the next problem that most don't seem to think about until after they have made the power. But they go hand in hand when you are wanting to speed up a lot.

Thing is,...:rolleyes: alot of guys seem to know about screwing parts together to build an engine,...but ask them about how to tune the chassis to get their new found power to the ground and their eyes tend to glaze over. :eek:

Just a thought.

Don

[Dart Vader]

I was wondering when you were going to post this to the forum general for review!

I would certainly be willing to create an area for it here, but it would have to get a decent amount of use. If people would want to discuss it here (more than just 3 or 4 threads), please chime in.

[want-a-be]

By the looks of the traffic on this one, named Racing, you might be able to simply rename it. Might be worth a try.

Don

[lun40119]

I hate talking about Chassis stuff........but it is something I need to learn. I did talk to Don, and will be laying down chalk lines so I can report back to the drill seargent where IC is. I had another racing buddy here in the valley tell me last week that if I was inlove with my car I should marry it...............if I want it to hook CUT it!!!!!!!

[BERT]

I would be interested in a chassis tuning bit! I can probably come up with a few silly questions to contribute. Prolly a good Idea;)

[want-a-be]

I'm no expert on anything,...but I'm more then happy to help out if/when I can.

Don

[want-a-be]

How was the reading I sent you on this subject Jake?

Don

[Kemper007]

Sounds good!

[lun40119]

Great reading Don, need to chalk out the car and get you the ic length. Then develop a plan for getting the car to work on the track. Thanks again.

[want-a-be]

No problem at all Jake. The method we talked about is a very easy way to find out where everything is. From knowing that knowledge you can start making some tuning decisions.

Don

[lun40119]

I mention that I really don't like suspension crap!!!!!!!!!

[lun40119]

Ok, I guess I will be the first to get things started. I don't have great videos to post yet, but will as soon as I get started. Just for a basic rundown here is what the car consists of. 1967 Chevelle 3520 with me. Engines is a SBC with around 600hp at 7200 and 550ftlbs at 5500. Trans is a reverse pattern TH-400 with a transbrake. Stock ratio. Converter is an 8" from ATI that stalls 5500 on the brake. Rear end is a Strange engineering Dana 60 with 4.56 gears. Upper Arms are Billet adjustables, lowers are tube with urethane mounts, and I also have the control arm connectors form Hotchkis. Front suspension is Global West uppers and lower, with Hotchkis springs and Bilstein Shocks all the way around. If there is anything I missed lemme know. Here is the problem.

I only have 10 or so passes on this car with this new combo. I have tried launching it anywhere from 4500-5500 rpm. What I thought it was doing was just spinning off the line. So I started taking air out and the 60's went down, so I put some back in. After viewing the video in good quality, it is actually shaking the tires really badly. It also seems like it is separating way too quickly. On one run it appears to bounce the rim off the track. It does pick the tires but as soon as it shakes the tires (5-10ft) they come back down. At the hit, the rear of the car goes right, then left, and then right. Its busy!!!!!!

I want to try a stiffer wall tire, and launching it even lower in the rpm band, but I don't think I should have to. Any thoughts??????????????

http://i172.photobucket.com/albums/w26/bells67/th_2009HotRodPowerTourBristolTN.jpg (http://s172.photobucket.com/albums/w26/bells67/?action=view&current=2009HotRodPowerTourBristolTN.flv)

[want-a-be]

Jake,
This is going to be some long posts. So I'm going to break them up into a few different posts.

Some of the information you are going to need before you can start tuning around these problems are the Instant Center (IC) length and how high it is off the ground. You’ll also need to know the height of the Center of Gravity (CG). Since I’m no engineer with a strong math back ground then I usually use the height of the cam center line location for the height of the CG. This is usually in line with the shaft of the water pump.

Since you have some adjustment on the chassis mount of your top bar you might be able to tame things down a bit. But you still need to measure things out to make an informed decision.


Don

[want-a-be]

This is an easy and cheap way to measure the IC and its height. You’ll need a tape measure, carpenters square, chalk line, some soap stone and some concrete big enough for the car and to mark up next to it.

1: Next to the car take the chalk line and snap a line that’s as long as the car is. This simulates the ground, and all measurements will be transferred to it. Give yourself some room to expand the drawing.

2: Measure the wheel base and use the soap stone and transfer that to the chalk line.

3: Measuring the height of the 4 link bars bolt center lines (CL) from the ground. Do the ones on the rear end first. Once you know these transfer them to the chalk line drawing. Using the square to measure from ground up to the rear end mount bolt CL.

4: Measuring the bars chassis mount distance from CL of the rear end to the CL of the forward mounting bolt. If you have multiple chassis adjustments on the top holes then measure them also. If the bars are straight forward then this is close to the measurement of the bars. But if they are mounted like yours Jake (triangulated 4 link) then you need to know how far in front of the rear end the mount is. There should be a difference in length. Transfer these measurements to the ground level of the chalk line drawing.

5: Measure the height of the forward chassis mount of the top and lower bars. If you have multiple chassis adjustments on the top holes then measure them also. Use the square to transfer these height measurements to the respective bars mount lengths.

6: Use the chalk line to connect the current respective bar mounts together. Make sure that you make the lines long enough. The upper and lower bar lines need to intersect when they are extended out past the chassis mounting points. That is the Instant Center point of the 4-link. Measuring the IC to the ground is the Height of the IC.

7: Measure the height of the water pump shaft center line. This is an assumed height of the cars Center of Gravity (CG). Go to the front wheel mark on the ground level chalk line. Use the square to transfer that height. Use the chalk line to snap a line between the
CG height at the front wheel CL to the ground level CL of the rear end. This is usually referred to as the Neutral line.

Knowing this data will allow us to talk more about tuning your chassis. Some rear end mounts will be forward of the axle CL. When this is true you need to make those changes also. But for the most part this will be close enough to get us started.

Don

[want-a-be]

I'm no author by any means. So if any of this need further Explanation let me know

Don

[lun40119]

Here is another vid that I found on youtube........doesn't show the whole run and it is hard to see what the tire is doing..........but gives you alittle more to look at..........its at about the 55sec mark. If you start and stop it at the launch and catch it at the right frame, you can see how effed up the tire is at the launch. Looks like its on the rim. Not really sure why the guy didn't finish the whole run.


http://www.youtube.com/watch?v=h-FvbCIc7cw&feature=related

[want-a-be]

Took forever to download the vid through my 2 tin cans and a string of an internet service but I finely took the time to view it. Vacation this week so I had some time.

From the vid I have to ask,...what springs and shocks are you running up front? Might as well ask about the rear shocks and springs while I'm at it.

Looks like you may need a bit more preload on the passenger side. Doing the lower link bars like we have talked about might help that if your uppers aren't adjustable.

Don

[lun40119]

Don, uppers are adjustable. The vehicle's suspension came with the TVS from Hotchkis. They are progressive rate springs with Bilstein shocks. I am sure that it isn't the most optimized setup for drag racing, but it sure does handle nice. Sorry bout the length of the vid, I didn't take that, it is just some guy on youtube that I found.

[Awesome Bill]

All that chalk stuff, lines on the floor, measure this and that is not even needed on a car that is already built. We just stuffed a 535ci Torque Monster in a back half 80 Camaro car with ladder bars 1 ft longer than I normally used last Friday. We put it on the front end rack stuck the driver in the car, checked the toe and gave it 3 flats of preload. No sway bars, anti roll bars, instant center, ftb-ratio nothing. Went to the track and run a 8.92@151 with 32° timing and shifting @ 6600 rpm and went threw the trap @ 7200rpm. Converter has 20% slippage. CAR WENT STRAIGHT AS AN ARROW! Point is, what is the car doing @ the track? then counter that for going straight! Thats all you need. If you apply more power even after the car has been scaled, then you have to reset the chassia for torque steer. Anti roll bars do fix this when power adders are used. But every time you make more power, then you have to adjust for it! So learn how to tune your car!

A good chassis board is needed, but you would need someone who can first tune a chassis and knows what he is doing as the moderator or you will have the biggest MESSED up I did this or that CHASSIS board going. First get a moderator to answer the very easy questions, then you have a place people who do not know what to do to go to!

[want-a-be]

All that chalk stuff, lines on the floor, measure this and that is not even needed on a car that is already built.



You're kidding, right?

Soooo....when a tube chassis car gets built we can just start off with both bars parallel and go racing. No reason to know trivial things like the ic of the 4 link, or it's height because it doesn't make any difference. :rolleyes: Man there has been a lot of people really wasting their time in persuit of this information. :eek:

Don

[lun40119]

All that chalk stuff, lines on the floor, measure this and that is not even needed on a car that is already built. We just stuffed a 535ci Torque Monster in a back half 80 Camaro car with ladder bars 1 ft longer than I normally used last Friday. We put it on the front end rack stuck the driver in the car, checked the toe and gave it 3 flats of preload. No sway bars, anti roll bars, instant center, ftb-ratio nothing. Went to the track and run a 8.92@151 with 32° timing and shifting @ 6600 rpm and went threw the trap @ 7200rpm. Converter has 20% slippage. CAR WENT STRAIGHT AS AN ARROW! Point is, what is the car doing @ the track? then counter that for going straight! Thats all you need. If you apply more power even after the car has been scaled, then you have to reset the chassia for torque steer. Anti roll bars do fix this when power adders are used. But every time you make more power, then you have to adjust for it! So learn how to tune your car!

A good chassis board is needed, but you would need someone who can first tune a chassis and knows what he is doing as the moderator or you will have the biggest MESSED up I did this or that CHASSIS board going. First get a moderator to answer the very easy questions, then you have a place people who do not know what to do to go to!


So what did this car weigh????? I am trying to get this car to work at full wieght, 3520 with me, with a stock length, non tubbed, gm style 4 bar on a 10.5 tire. There is work to be had. Checked some receipts and this thing only has a 4.10 in it. I put a 4.56 in the 12 bolt that I broke, so I ordered this Strange Dana, apparently I ordered it with a 4.10. This problem in the first 60' is going to get worse with a 5.13 in it.............I need to get a handle on it, or practice my excuses when the 4-bangers drive by..................

Crap man, anyone can get a car to hook and run straight, when there is an 18" tire under it.........

[want-a-be]

Jake,

When you get those measurments let me know. We can get a direction from the information you gather. You can't manage what you can, or haven't, measured.

If anyone else needs some help speak up or for ever hold your peace...lol.

Later bud, Don

[lun40119]

I will soon as I get the talon out of the shop.............need the room on the floor. Finishing up the 327 for my little bro tonight. Talk to you soon.

[Kemper007]

I would have the same problem with my car when I had the extension on the shocks to loose, causing the tire to hit to hard and create a bounce. Stiffing up the extension on the shock helped my situation. But you are hitting the tires with a lot more power than i am and with a brake. Heres a little acticle I found years ago that has always worked for all my stock retaining suspension cars. Hope it helps. Oh yeah I love the way your car sounds coming out of the box! :D
Note: that loose can mean either extension or compression.

What to watch for...

There is a standard progression of events that occur as a doorslammer launches. Watching each of these events and at what point in time they occur gives you the clues you need to dial in your suspension. The key is to making these events all happen at the right "time" is your shock valving controls.

Mike Canter of Outlaw Pro-Mod fame had this jewel of a post post years ago that I saved where he detailed the following sequence that you should watch for:

"This should be the sequence of events seen on the video. Right at launch the front should start to come up before any forward movement or the car.

The rear of the car with this added weight transferred from the rising front will lift very little but it should not go down (squat). An inch or two is normal and can be best seen by looking at the relationship between the top of the slicks and the rear fender lip.

This one or two inches of rise will indicate that the rear of the car is lifting and pushing harder on the tires while the front weight is being transferred (for every motion there is an equal and opposite motion).

If the front of the car does not rise first then the front shocks are too stiff or the rear shocks are not stiff enough.

If the rear of the car squats right away then the rear shocks are too loose.

I have found through slow motion video tape that if the rear shocks are too loose the rear tire actually bounces on the initial hit and will break loose almost right away. I stood next to the car pointing the camera right at the rear tire. It was amazing to watch. I kept on tightening the rear shocks until it stopped which was just below mid point of the adjustment. From all that I have seen the rear shocks should never be adjusted less that half way because of rear squat and tire bounce."

[lun40119]

Thanks for the read fella, I think a good place for me to start is with a set of double adjustable shocks in the front and rear. My car is so stiff it doesn't really allow for a good weight transfer. Thanks again for the information.

[Nova67ss]

Chassie talk is a good talk, lots to learn and U go faster without more HP. :D

[want-a-be]

Alot of people can build an engine,....getting it down the track effeciently can be another story.

Don

[Awesome Bill]

Don, once the car has been professionally built, then it leaves the shop and goes to the end user and he puts all his stuff into the car and brings it back and then its scaled? Really come on! You can only really move about maxx 50lbs of spring weight around without upsetting both ends of the car, the ladder bar mounts, or 4 link bars are installed and the ic comes in where ever the builder says it does and then there is 3-6 holes to play with. Then the builder says you have to scale it and never ask anything about what power the application will handle! Yeah thats really scary.

Anti roll bars make it easier than ever to have a tuned chassis. So once the car is built and welded you really can only do so much. To scale a car once it is complete will do little to nothing! Because of the 50+ professionally cars that I have set up after they come from a $500.00 to $2500.00 scale job that was done and don't go straight tells me they should really tune the chassis for the power and application @ the track is the only way to do it. I have seen brand new cars from the chassis builder never even come close to a clean pass and so have you, WHY? Becuase they don't know what they are doing for the application @ the track and power used that day.

A properly built chassis, "all welds, bars, shocks, 4 link, ladder bar, bar placements etc" once installed, the cars basic ability to handle power is very limited and turing a shock position or moving common spring weight around is only good for low HP engines. Put a 400 shot of NOS or a blower on your freshly scaled drag car and watch it run itself right into the wall with the steering wheel turned hard to the left.

I seen a brand new Tim MaGainess scaled Car with a 3000hp + blower engine drive to the left every time the owner run the car. I told The owner to step the power up and he told me the chassis was scaled and could not be messed with. He Called Tim and tells him his car won't go straight. Tim tells him to quit being a pussycat and give it some power! Very few I have told that to understands what Tim told him!

The back wheels drive the car when a lot of power is applied. I have personally seen cars crossing the finish line with the front wheels off the track! The little front tires can only do so much.

So if your talking basic drag racing cars with under 700hp, any chassis will handle that and most likely you will wind up breaking the left axle and once broken you will say" wonder why it done that" and the car will go dead straight. Power up the car and then tell me what it does.

Bar placement, anti roll bars and power all have to be adjusted @ the track for the power used that day. Once the basic chassis tuning, not a scale rip off job, is done, the customer can make small tunning adjustments for 25-50-100hp changes and the car will be dead straight every time. Getting the car there is the problem. Use a 100shot of NOS and the car goes straight, Use a 250shot of NOS and the car turns so fast right the driver usually has to abort.

So what your suggesting is that once scaled always scaled! If you believe that your not as sharp as I thought. You have to counter engine torque steer to the drive train torque steer with the proper preload if needed for the power used @ that day. I don't care what the 4 bathroom scales says and what weight is on the static car. It means little to nothing on race car sitting still. When the day of the race and tons of power is applied, thats when you know your scale job was useless. The left or right direction and how severe it is determines what is needed to be applied on the day of the race. Unless ofcourse you drive into oil!

There are some many other areas of chassis tuning once on race day that have to be factored in when the power is applied, that everyone gets lost and don't know what to do when the car does not go straight. Frontal lift messes with the chassis, gear ratios have huge bearings on preload and torque converters will change a cars ability to run straight. Most people don't even think of that. So when you hollar you have to scale your car and thats the key, I hate to say it but your badly confused!

Go ahead and post any question or response you like, I will be ready!

[want-a-be]

Bill,

I really don't have the time to answer all your post, nor go through this whole thread and read my comments.

I agree with what your saying. But I don't think I have said anything about 4 corner weights, any wheight of the car, or trying to move 50 pounds around.

I'm not sure where that came from.

Don

[want-a-be]

Did a quick scan of my posts and didn't see anywhere that I was asking about weight. Jakes weight is what it is. He can only do so much with it. But the ic of his 4 bar system has some adjustment to it. He should be able to adjust around on it for a better acting car. But before he moves anything he needs to know where the ic is. Hence the chalk on the floor.... It's a good cheap way to find out where you are actually at.

Sure,..I could help Jake out better if I were at the track with him,...but he is about 10 hours North of me. Not going to happen unless he drives down here, or I'm in his neck of the woods.

The funny thing about engine builders is,...not all of them know how to tune the chassis to get their hp down the track properly. I, and a few others around here, would like to think I can tune both.

Not implying that you can't Bill. I'm just saying what I've seen.

[lun40119]

Glad I get to talk to people that know how to help...........Cause I don't have a clue. :eek::eek::eek:

[want-a-be]

LOL,.....can't help until you get everyone elses car out of your way so you can measure everything up on yours. Looks like the snow will be flying in your neighborhood before that happens. But if I can help out any at all, I'm more then happy to.

I do have to mention that I think it's odd that this one thread has over 500 views and noone seems to have any questions about their chassis problems. First chassis forum I've ever been a part of that everyones stuff is running flawlessly,...lol

Don

[camrat68]

It isn't so much that we all have a perfectly working chassis, but that --like Jake-- most of us haven't done the measuring to be able to even start asking the right questions......
But with that many views, we are paying attention and trying to learn.;)

[want-a-be]

It isn't so much that we all have a perfectly working chassis, but that --like Jake-- most of us haven't done the measuring to be able to even start asking the right questions......
But with that many views, we are paying attention and trying to learn.;)

Easy numbers to get in your spare time, they can usually be taken in about an hour. Thing is though,...usually most racers have plenty of time to do it in the winter when everyone is going through withdraws from their addiction to speed. Racing ought to be illegal....it's more addictive then any drug out there, and once hooked you always want more. Seems to cost more also...lol

Yea, your right about the views,... this many hits should equate to some interest.

Don

[Awesome Bill]

I would have the same problem with my car when I had the extension on the shocks to loose, causing the tire to hit to hard and create a bounce. Stiffing up the extension on the shock helped my situation. But you are hitting the tires with a lot more power than i am and with a brake. Heres a little acticle I found years ago that has always worked for all my stock retaining suspension cars. Hope it helps. Oh yeah I love the way your car sounds coming out of the box! :D
Note: that loose can mean either extension or compression.

What to watch for...

There is a standard progression of events that occur as a doorslammer launches. Watching each of these events and at what point in time they occur gives you the clues you need to dial in your suspension. The key is to making these events all happen at the right "time" is your shock valving controls.

Mike Canter of Outlaw Pro-Mod fame had this jewel of a post post years ago that I saved where he detailed the following sequence that you should watch for:

"This should be the sequence of events seen on the video. Right at launch the front should start to come up before any forward movement or the car.

1. The rear tires hit first, not the front end coming up first, so that is not correct, actually with improper air pressure, the car backs up slightly then launches forward. I guess when his post was made he did not have slow mo! The engine most likely with the torque actually tries to lift the left front if the right rear set up is not correct.

The rear of the car with this added weight transferred from the rising front will lift very little but it should not go down (squat).

2. Now this is bull crap right hear, every rear travels downward not upward, being 4 link or ladder bar, you can count on every rear going downward, it has to!
What you and your buddy here forgot to mention is that with a 4 link car, the rear slams downward on a 4 pivot connection and the chassis line in the rear will move very little because of the spring and chassis set up. along with the professional build of the car. We are not talking stock 4 link!

With a ladder bar car, the rear separates and run the geometry pattern from 3 o'clock to about 4-5 o'clock to put it in laymans terms, and the chassis line will actually go up but the rear still slams down because the shorter 4 link bar, (ladder bar and 2 position connection), and proper chassis set up.

An inch or two is normal and can be best seen by looking at the relationship between the top of the slicks and the rear fender lip.

This one or two inches of rise will indicate that the rear of the car is lifting and pushing harder on the tires while the front weight is being transferred (for every motion there is an equal and opposite motion).

If the front of the car does not rise first then the front shocks are too stiff or the rear shocks are not stiff enough. You have to determine first of all if you have double adjustable shocks both front and rear? This is the only easy way to really tune your chassis. Granted some times you have to speed up extension or slow it down as well as allow compression time or slow it down. Depends on the car and power on what it does after the initial hit of the power.

We only allow about 1" of shock travel on powerful cars to keep the front end down and not coming over on us. Been there a few times.

If the rear of the car squats right away then the rear shocks are too loose.

I have found through slow motion video tape that if the rear shocks are too loose the rear tire actually bounces on the initial hit and will break loose almost right away.
The way to counter that is give the dish rag tire more air pressure to stablize the side wall! Once the sidewall of the tires give in to tire wrap, I don't care what tune up you have on the car, its over and tire shake just gets worst. Tire shake always comes from not enough side wall for torque and power verses weight and inertia.

I stood next to the car pointing the camera right at the rear tire. It was amazing to watch. I kept on tightening the rear shocks until it stopped

When you stiffen the extension up, this lesson load on tire and causes tire spin with power that the now decreased tread patch can hold. This is called reaction for a bad action especially with power. Now stockers like we are talking about with 500-600 hp, Ray Charles could tune a stock chassis for as long as basic guidelines and proven methods were used.

which was just below mid point of the adjustment. From all that I have seen the rear shocks should never be adjusted less that half way because of rear squat and tire bounce." This is the most stupid statement of all. What we have found and actually can get just about any car down a track is that track conditions are not the same. Slippery track, soft shock, good bite, hard shock! Easy to remember also. All in all there is no such thing as a one tune job leaves the chassis shop and its correct. Some times we get close and others you have to test and tune. But basic air bags, sway bars and stock suspension cars are well capable of low to mid 9's with no problems. You just have to know how to react to the cars reactions. There is no real 1 answer.

You can tell a cars ability to go straight most times buy the burn out, once the tires get a little traction and heat, the car should go perfectly straight to the line. If the back ends even begins to go to the left, the car should not be run and be fixed before racing. It will go to the right when power is applied. Now if the ass end goes to the right in the burn out, most likely we have someone that has some power and when applied, the car will run straight. Any one know why? A lot can be learned from just the burnout!

Every one has their own set ups that work and I am not saying you have to do this a certain way, what I am saying as long as power is increased each time, the car almost can not react the same way. You have to adjust for power and torque let alone torque converter stall speeds. Makes a world of difference.

Here is a simple power verses chassis ability to handle power goes. If the back end goes to the left and drives the car right, keep preloading the right rear until the car leaves straight and even. If the cars rear goes to the left, keep it the same and just keep adding power, it will get straight. Or take preload away from the right rear tire! You can do little with springs and extension rates so its best to use air bags on stock coil spring cars or traction devices for spring cars.

[lun40119]

http://i172.photobucket.com/albums/w26/bells67/LauchGLD.jpg


Does this picture show how bad the 60's really are?????? Cant get better than a 1.54 right now.

[want-a-be]

Nice looking shot of the car. Did you change anything on the suspension at all?

Don

[lun40119]

No bar, and took the bumpers out and launched with no brake......60's still suck though.

[Awesome Bill]

you could use a little more air to keep the tire from rolling over but with street tires and harder side walls, its tricky especially if you do not know how to work shocks, air bags and anti roll bars. Car looks good and even so you can only add a little air to the tires. Most times ¼ lb at a time until it blows the tires off then back up ½ lb from there. You can work with shocks to plant the harder side wall from air pressure and get it to work but you should go on a good test and tune day. Write everything down. Nice street car for sure.

[lun40119]

Thanks Bill......

[Awesome Bill]

his chassis is pretty much fixed along with all other stock 4 link bar cars. He can ajust preload if he has adjustable top bars and can pull some preload to the right rear if he was twisting the front end out of shape but that is not the problem here. His tire is getting to much hit so he could stiffen the extension up a tad or add air pressure. Even could install 2 air bags, does the same thing. The side wall has to be able to withstand the torque of the weight versus engine, gear, tire dia etc. His sidewall is being loaded to the point of distortion. If he had more power, it would tire shake for sure! IC is where all Chevelles are Stock location!

[lun40119]

I have some vids from a different angle, and it does shake the back of the tire pretty badly. I have been talking to a guy with the same car as mind (lots more power though), and I am going to put Strange DA shocks on all 4 corners with a different set of springs up front. I have less than 15 passes on this thing, so I am still learning.

[want-a-be]

Here is some good reading on this topic. I'll post a few quotes from this link also.

http://www.rehermorrison.com/blog/?p=158

The simple truth is that even the most powerful engine can’t produce winning results in a bad chassis. As an engine builder, my area of expertise is horsepower - but as a racer, I know that it’s the total combination that counts....

That’s why I cringe when someone asks me what a particular engine will run in a given chassis. There is simply no way that I can give an accurate answer. I’ve seen customers who have bought identical Super Series engines run times that differ by nearly four tenths of a second in similar cars. I’ve looked at the dyno sheets, and I know there isn’t more than one percent difference in power - so what accounts for the huge variations in e.t.? It all comes down to chassis and setup....

Just a simple change of rear tires can make a big difference in performance. In the Super-type heads-up eliminators, the goal is to eliminate tire spin and hit a perfect .400 light, so the cars are often “overtired” to produce a no-spin, dead-bog launch. The downside of this approach is that you have to carry these big tires all the way down the track, and they act like huge flywheels that the engine must accelerate. That’s not a problem if you have enough power to run the number, but if your goal is to run a Quick 16 show, then the smallest tires that will hook up the horsepower are almost certain to produce quicker elapsed times.....

Some racers mistakenly believe that computer programs that predict quarter-mile performance are infallible, but my experience suggests otherwise. Back in the days BC (Before Computers) we used a power-speed calculator to predict elapsed times and speeds....

The fact is that we race cars, not laptops. We race them on good tracks and on bad tracks,.....

And there is a bit more to read.

Don

[want-a-be]

The chassis threads seem to be drawing some readers. Almost 6000 views for only a few threads and posts in them.

Don