Help--too much torque (or not enough driving skills)!

[Chevy]

I bought my first project car, a 1968 camaro, in 2004. It was a drag race car with 350, big cam, Edelbrock 1706 carb, 186 heads, muncie M21, and 12 bolt rear with 4.10:1 gear.

I started putting it right for Pro-Touring and eventually SCCA Solo II here in Hawaii. Currently the car runs a 355 with stock bottom end, AFR 190 street heads (10:1 CR), Holley Stealth Ram intake with Commmander 950 and 58 mm throttle body, Comp Cams valvetrain, including: XFI hydraulic roller camshaft (210/218 duration at 0.050" lift with 0.560"/0.555" max lift), 1.6 full roller rockers, stainless valves, inch and 5/8ths headers into a 2.5" exhaust, aluminum flywheel, TKO-600, aluminum driveshaft, the 12 bolt has been stuffed with a 3.73:1 rear gear (eaton Posi). For suspension i did the DSE coilover converstion up front with the adjustable Konis, DSE power steering (adapted to a TPI serpentine belt accessory drive), DSE 3" drop springs with adjustable Konis out back, and a manual Baer disk break set-up with 13" rotors front and 12" rear. I'm running aluminum 17" wheels with 245s up front and 275s out back (Goodyear Eagle GSD3s). battery relocated to rear, aluminum radiator set back 1.5 inches for better weight distribution. Car sits at 4.5" ride height (header limited). Konis are adjusted all the way around to one click out from stiffest.

I just finished the cam swap and Holley Stealth Ram install and have a tune that is dialed in enough to drive on the street. I have a wide band O2 sensor and digital AFR gauge on the dash for tuning. The Camshaft was chosen for torque in autocrossing and street driving. According to the CamQuest software with some conservative entry of my data, the engine should make 442 lb feet of torque at 4000 RPM and 401 HP at 5500 RPM. Torque is 400 by 2000 RPM. These are similar to numbers that Holley publishes with their Commander Software for tuning purposes and the tunes where pretty close to spot on out of the box so it seems that is the ballpark.

Here is the problem--the car makes so muck torque i am having trouble driving it. I started SCCA in December 2007 and have been learning to drive as i go, trying to be smoother and faster each time out. I started to move up from the bottom of the rankings and i'm afraid the new car set-up is going to put me right back at the bottom.

When taking off in first, i find it very difficult to not spin the tires. If you are going balls out on a track it might be OK until you have to come off the gas--but in street traffic when taking off at a stop light and then trying to feather back off the gas so as not to rear end the vehicle in front of you, the car surges forward, then if you let off the gas it jerks or bucks very hard due to the torque braking. I have the Commander 950 software running and am looking at my throttle position sensor when i am doing this, and i have a relatively light foot (TPS is 1 closed and 172 for WOT, i am applying values of ~10 when this is happenning). I have found for the street the only way to drive it is to let traffic leave me to create a gap, then take off aggressively in first, then go to second almost immediately, then go to third and essentially allow the car to idle along in traffic (idle is 850 RPM). In third, the ammount of torque on tap is diminished enough relative to the load that i can come on and off the gas (again, i'm talking 3-5% of WOT) with controllable surges rather than violent bucking. Traffic around me still think i'm an idiot because the car bucks with even the slightest progressive addition of gas (i looked at my datalogs and i'm talking TPS values of around 5--roughly 2-3% of WOT).

I haven't had it flat out yet but if i can control it i expect low 4 s 0-60 times (3200 lb car).

If i can't be smooth on and off the throttle then i'd rather not race it in my next Solo II competition this weekend...i'll take my street car (2001 Trans Am WS6) rather than be embarrassed...

I know there are others here making lots more torque and power and driving on the street and in competition, so can someone help me either in my driving technique or some tweak to the set-up to be able to drive this thing?

Thanks in advance for your insight!

[David Pozzi]

I don't recall how good your Goodyear F1 tires are, but you probably need something even better for autocross. Hoosier radial slicks are the best, but very expensive. Khumo's v710's are cheap and almost as good, but ultimately they will probably be 1 second slower on a minute long course compared to the Hoosiers.
Your shocks sound way too stiff. Try them at 7 "half turns" up from full soft, or Consult DSE if you got the shocks from them.

To reduce shock when you let off the gas, increase idle speed, try 1000 or 1200rpm.

A good part of your problem is due to the Aluminum Flywheel, I have used the GM "15lb" flywheel which is actually 19lbs. It seems to be a good middle ground type of flywheel.

Check your linkage and see if you can slow the throttle ratio down so you have better pedal control. Reducing timing at the problem rpm can reduce torque, but I'd rather see you fix the suspension and make use of the torque.

First gear is always going to be spin-city but try to make second gear work. Tune the handling for second gear if that's the gear you will be in most of the time. First gear will have much more oversteer due to the engine torque both on and off the gas. This can help you wiggle the car through the tighter slower corners where you have to use first gear anyway.
David

P.S.
If you run the Trans-Am, do your braking in a straight line, and very early, get back on the gas very lightly allowing the front end to rise a bit THEN enter the corner. Don't dive into a corner hard while braking, the front end will wash out throwing you off-line. The front lower A arm bushings are very soft on 4th gen F bodies, this causes front end overload when you push it in a corner under braking, also the cars lean too much, but the TA leans a bit less than a Camaro.

[Chevy]

I don't recall how good your Goodyear F1 tires are, but you probably need something even better for autocross. Hoosier radial slicks are the best, but very expensive. Khumo's v710's are cheap and almost as good, but ultimately they will probably be 1 second slower on a minute long course compared to the Hoosiers.
Your shocks sound way too stiff. Try them at 7 "half turns" up from full soft, or Consult DSE if you got the shocks from them.

To reduce shock when you let off the gas, increase idle speed, try 1000 or 1200rpm.

A good part of your problem is due to the Aluminum Flywheel, I have used the GM "15lb" flywheel which is actually 19lbs. It seems to be a good middle ground type of flywheel.

Check your linkage and see if you can slow the throttle ratio down so you have better pedal control. Reducing timing at the problem rpm can reduce torque, but I'd rather see you fix the suspension and make use of the torque.

First gear is always going to be spin-city but try to make second gear work. Tune the handling for second gear if that's the gear you will be in most of the time. First gear will have much more oversteer due to the engine torque both on and off the gas. This can help you wiggle the car through the tighter slower corners where you have to use first gear anyway.
David

P.S.
If you run the Trans-Am, do your braking in a straight line, and very early, get back on the gas very lightly allowing the front end to rise a bit THEN enter the corner. Don't dive into a corner hard while braking, the front end will wash out throwing you off-line. The front lower A arm bushings are very soft on 4th gen F bodies, this causes front end overload when you push it in a corner under braking, also the cars lean too much, but the TA leans a bit less than a Camaro.

David,
that is Super helpful! I already came to one of the recommendations you made and i went with a lighter spring on the throttle body so it doesn't snap shut as aggressively and i can be more progressive both on and off of it. This alone seems to have made second gear usable as you suggested. One of the ways i controlled this behavior with the carb was with suboptimal timing as you suggsted as well, but i agree--i'd rather not go there again if i have to. I thought about bumping the idle RPM up, and have already raised it 500 RPM from the 850 it was at initially 900 now. I'll try another 100 RPM as you suggest.

My Konis are single adjustable with 4 clicks of adjustability. Currently they are at 75% stiff all the way around. Do you think they should be at 25%? They are wrapped with the DSE springs which are 550 lbs/in in the front and the DSE drop springs out back.

I'm saving up for tires and was looking hard at the Kumhos.

I want to make sure i understand your aluminum flywheel comment. Is the aluminum flywheel allowing the engine to rev too fast because of the lower moment of inertia, causing it to race off, and that is why you are suggesting a heavier flywheel, which would make the car smoother both by slowing how fast the engine revs up and also by slowing the reduction of RPMs when coming off the gas, again smoothing the behavior out in oder to keep a better balanced car during autocrossing?

You're absolutely correct about the TA--it hates to enter a corner with any trail braking at all. I haven't tried actually acellerating into the corner as you suggested, but will give it a whirl next time the Camaro is down. I think i have enough from what you've given me to be able to race the Camaro this weekend.

Thanks a ton David, the less experienced of us really appreciate the insight you provide.

[David Pozzi]

Chevy,
Id ask DSE what settings to use, they have all this worked out and you should take advantage of their experience with those shocks. I forgot your konis were the DSE and not the regular steel street type Konis which use the 7 half-turn std setting. It would help a lot if someone could take "good" photos of your car cornering, try to capture when it leans the most, and a few shots of it accelerating and braking to get an idea of how much rise and fall the front suspension has.

Your front springs are on the soft side for autocross with sticky tires, ( but a great street rate, so you may have to do some compensating with extra shock stiffness. I ran a 550 front rate with slicks on my 67, and it overloaded the rear springs creating too much rear squat.

The Kumho V710 is a great tire, last long and is cheap. When or if you get to the point where you are running for a championship or something more competitive, then I'd spend the extra money for some Hoosiers, but they will cost a lot more.

Yes, you have it exactly right, the aluminum flywheel allows the engine to apply more deceleration torque to the rear axle causing the rear to break loose, especially if the rev's are high and you lift off the throttle quickly. If you are turning into a corner at this point, the rear will slide around. I had this effect with my 67, but with 10" slicks all around, there was only a problem when in first gear, and I had 4.56 gears. I could use it on purpose at times to get the rear to come around on super tight corners. A heavier flywheel will help slow acceleration and deceleration, not alot but enough to be more controlable. I used the GM "15" lb flywheel both on my 67 and my wife's 73 Camaro, it works well, it's light but not too light.

Check your brakes, we had the Baer 13" kit and the rear pads would grab like no tomorrow on the first brake application causing massive rear lockup! This was using the pads that came with the kit. Switching to a better quality pad changed it completely. I think the large mass of the front rotors caused a delay in heating compared to the rear brakes, the provided pads must have had a big difference in friction between cold and hot too. We use the Hawk HP+, but they take too long to warm up for autocross, the first brake application they don't work well, they work, but you can feel them "come in" during the first brake application. After one run, they continue to work OK. The Hawk HP's are probably OK, but we haven't tried them.

Your TA, you don't need to really accelerate into the corner, but ease off the brakes allowing the front suspension to rise taking the load off the outside front tire. Braking hard and turning at the same time won't work on those cars. We ran a 2002 Camaro SS and learned that very quickly. They don't have enough positive caster, can't achieve over 3/4 deg neg camber, and have pretty soft lower A arm bushings.
David

[Chevy]

Chevy,
Id ask DSE what settings to use, they have all this worked out and you should take advantage of their experience with those shocks. I forgot your konis were the DSE and not the regular steel street type Konis which use the 7 half-turn std setting. It would help a lot if someone could take "good" photos of your car cornering, try to capture when it leans the most, and a few shots of it accelerating and braking to get an idea of how much rise and fall the front suspension has.

i have asked before and gotten the old "use whatever feels best" response...but it may of been whomever i got on the phone. I just sent Stacy an email and will post here whatever she says.

Yes, you have it exactly right, the aluminum flywheel allows the engine to apply more deceleration torque to the rear axle causing the rear to break loose, especially if the rev's are high and you lift off the throttle quickly. If you are turning into a corner at this point, the rear will slide around. I had this effect with my 67, but with 10" slicks all around, there was only a problem when in first gear, and I had 4.56 gears. I could use it on purpose at times to get the rear to come around on super tight corners. A heavier flywheel will help slow acceleration and deceleration, not alot but enough to be more controlable. I used the GM "15" lb flywheel both on my 67 and my wife's 73 Camaro, it works well, it's light but not too light.

Thanks!

Check your brakes, we had the Baer 13" kit and the rear pads would grab like no tomorrow on the first brake application causing massive rear lockup! This was using the pads that came with the kit. Switching to a better quality pad changed it completely. I think the large mass of the front rotors caused a delay in heating compared to the rear brakes, the provided pads must have had a big difference in friction between cold and hot too. We use the Hawk HP+, but they take too long to warm up for autocross, the first brake application they don't work well, they work, but you can feel them "come in" during the first brake application. After one run, they continue to work OK. The Hawk HP's are probably OK, but we haven't tried them.

I use the Hawk HPs on the 4th gen...love them, although they make a lot of dust which means a lot more cleaning on a street car.

Thanks Again!

[andrewb70]

Since you have an adjustable EFI system I would tune out some power. Do a data log of a typical autocross and see what RPM and MAP values are being used most often. Go to the spark table and bump back your timing a little. You can leave the WOT values alone so that when you really go for it you have all the engine power on tap. Another thing you can do is use a stock LT1 throttle body. It will bolt right up to the Stealth Ram but has smaller 52mm throttle blades. I doubt that the smaller throttle body will hurt the maximum output a great deal but it will greatly improve (slow down) the initial tip in. This will make it easier to modulate the throttle.

Andrew

[Chevy]

Since you have an adjustable EFI system I would tune out some power. Do a data log of a typical autocross and see what RPM and MAP values are being used most often. Go to the spark table and bump back your timing a little. You can leave the WOT values alone so that when you really go for it you have all the engine power on tap. Another thing you can do is use a stock LT1 throttle body. It will bolt right up to the Stealth Ram but has smaller 52mm throttle blades. I doubt that the smaller throttle body will hurt the maximum output a great deal but it will greatly improve (slow down) the initial tip in. This will make it easier to modulate the throttle.

Andrew

yeah, i wish i had the HSR throttle body...i bought my ram used and this is what it had with it, a BBK/Edelbrock body. I guess i need to start saving for that one too...hadn't thought of how much it would affect the tip-in.
Thanks!

[andrewb70]

yeah, i wish i had the HSR throttle body...i bought my ram used and this is what it had with it, a BBK/Edelbrock body. I guess i need to start saving for that one too...hadn't thought of how much it would affect the tip-in.
Thanks!

You do not need the HSR throttle body. The Holley and the BBK are both 58mm which is too big for what you are trying to do with the car. No need to "save up." Get this:

http://cgi.ebay.com/ebaymotors/Chevr...QQcmdZViewItem

Andrew

[David Pozzi]

Andrew, a good thought about tip-in with a large butterfly, a small opening at low rpm's probably makes a big difference in air flow.
David

[andrewb70]

Andrew, a good thought about tip-in with a large butterfly, a small opening at low rpm's probably makes a big difference in air flow.
David

I talked to Doug Flynn at Holley today and he felt that using a stock throttle body would really be helpful. The stock LT1 throttle body has dual 48mm blades, not 52mm as I thought.

Andrew

[Norm Peterson]

Slowing down that initial tip-in was the first thing I thought of even before I finished reading your first post.

It sounds like the very same issue I had at autocross and during certain aspects of normal street driving with my Accel SuperRam on a 355 of quite similar specs. I solved it by swapping the carburetor-style throttle cable attachment (a simple pin at some radius out on the throttle shaft arm) out for a more OE EFI-conventional sector arrangement that the throttle cable winds around. I just made the sector eccentric to the throttle shaft so that the cable initially unwinds off a small radius that gradually increases. I did have to make up my own cable for length and end fittings. It does involve a small amount of welding directly to the throttle shaft arm, so you do need to be concerned about putting too much heat into the metal for that part of the job.

My fabrication isn't all that pretty, but it absolutely made a night and day difference in the driveability. I can get a picture or two for you tonight or tomorrow if it isn't pouring outside.

FWIW, the SuperRam has a dual 58 mm throttle body, claimed to be good for 1000 cfm.


Norm

[Chevy]

Slowing down that initial tip-in was the first thing I thought of even before I finished reading your first post.

It sounds like the very same issue I had at autocross and during certain aspects of normal street driving with my Accel SuperRam on a 355 of quite similar specs. I solved it by swapping the carburetor-style throttle cable attachment (a simple pin at some radius out on the throttle shaft arm) out for a more OE EFI-conventional sector arrangement that the throttle cable winds around. I just made the sector eccentric to the throttle shaft so that the cable initially unwinds off a small radius that gradually increases. I did have to make up my own cable for length and end fittings. It does involve a small amount of welding directly to the throttle shaft arm, so you do need to be concerned about putting too much heat into the metal for that part of the job.

My fabrication isn't all that pretty, but it absolutely made a night and day difference in the driveability. I can get a picture or two for you tonight or tomorrow if it isn't pouring outside.

FWIW, the SuperRam has a dual 58 mm throttle body, claimed to be good for 1000 cfm.


Norm

Another great idea! Thanks Norm, i'd love to see some pictures if you got 'em.

[Norm Peterson]

58 probably is too big for most 355's for most purposes. But you really can make it work.

I'll take a few pics, but it may be a couple of days before I can either get them up here or e-mailed out individually. My laptop is out for repair, my landline is out of service (so no dial-up backup), and I'm not coming in to the office on a weekend without getting paid to do so.


Norm

[Norm Peterson]

Here's a couple of pictures. There isn't as much progression as I remembered. Thinking a little more, there was a good bit of "stiction" with the carb-style arrangement that went away entirely. Someting like the cable force ended up having a large force component radial to the throttle arm.

Had to make the whole thing, including the little "fences" to keep the cable centered. The cable was sourced at a bicycle shop.

The car hasn't been driven in a while.


Norm

[Chevy]

It turns out the throttle position sensor was adjusted to provide a value of either 0 or 1 at the "no gas" position and the software needs it to be above 5 in this position.

What was happening was at initial throttle application, when i was pushing in the range of 0 to 5 on the TPS, the car was trying to keep RPM steady at the idle value--it was taking timeing out and using the Idle Air Control motor to take air out as well. Once i crossed over the 5 value it was surging forward because it was no longer pulling air and timing out; the values jumped up to where they should have been. I fixed this by adjusting the TPS and it dramatically improved the torque situation, especially in the higher gears.

First gear is still very torguey but way more drivable.

Thanks for all of the help, the input from the board made a big difference in sorting this out.