GMan 3MT

iTrader: (4)

This is going to be an odd question, but here it goes...

I race in a class with a horsepower/torque limit (260hp/310tq). My car dyno'd at 275/324. You're allowed to restrict the intake and exhaust, no ecm tuning allowed.

With a 38mm restrictor between the throttle body and the intake, I pulled my numbers down to a legal 248/310.

Car is a '86 is a stock rebuilt LT1/T5, 3.42 T2R. Stock LT1 manifolds (required), 3" exhaust to a flowmaster at the back of the car.

I doubt I'll do anything this year, but I'd like to start planning for next year to get the number a bit closer to the limit. Question is, how can you drop TQ without affecting HP as much? More free flowing exhaust? More restrictive muffler?

Orr89RocZ

iTrader: (20)

Since this limit only looks at peak numbers, yes you can shift the curve around

But no ecm tuning is a stupid rule and going to make it more difficult. How are you suppose to race a motor thats not tuned? And expect it to last?

Anyway, the intake manifold design and header design can work together to get the desired power numbers. Long runner intake is tuned to produce high peak trq numbers. Short runners broaden the curve but reduce peak trq numbers.

To cut torque and not lose hp you need to shorten runner length. Headers can get shorter in length to reduce the scavenging at lower rpm to reduce peak trq.

Also playing with cam events can shift power around

Since you have an lt1 with already short runner, you kinda are forced to look at cam and exhaust changes. With stock manifolds there isnt much to lose there, however exhaust tube lengths may be changes to get numbers down. Open exhaust of improper tuned length can hurt scavenging and reduce torque but still can affect hp

Could try a small break-in rocker arm on exhaust side to reduce lift. May change power curve in a helpful manner. Like a 1.3 ratio

Easiest thing would be to alter ign timing at peak trq rpm. Just pull 10 and you'll keep same hp and dial trq however you want

GMan 3MT

iTrader: (4)

It's a fairly budget series. The no tuning rule is to try keep costs down. The guy that can afford to spend hours on a dyno dependent on each track would have an advantage.

Since the rest of the engine must be stock, cam, heads, rockers, piston etc (sorry if I neglected to mention that), there really shouldn't be much 'need' to tune like you would if headers or cam swaps were allowed.

I'm pretty fortunate to have to dial back the numbers. The 4.6 Mustang guys can't even realistically reach the 310 limit.

So swapping to no muffler or a less restrictive muffler should give a bit less hp/tq? I can move to a bigger restrictor plate if it bring down both hp/tq.

Orr89RocZ

iTrader: (20)

Good thing about tuning aspect is you can DEtune a car by overly richening and pulling timing in spots where theres too much power and not hurt anything else.

Tuning non obd2 94-95 ecms is really cheap and easy

But sounds like your only choice is to experiment with the exhaust after the manifolds and throttle restriction. But likely both hp and trq will be changing

Twin_Turbo

iTrader: (25)

How are they going to check if you did something to the ECM? Are they phusically going to pull it out?

GMan 3MT

iTrader: (4)

A year or so ago they did change the rules (thankfully) to allow you to tune out the emissions and vats stuff that can be removed or bypassed by other means.

Right now, they really don't have a way to check to see if you tune it. They also don't have a tear down rule like SCCA. I hope NASA doesn't get to the point where you have to buy a sealed pcm and hand you a box of pistons after they tear down your engine at tech. So yeah, it could be real easy to run a bunch of illegal stuff if you like to cheat in order to win a plastic trophy.

Anyways, one of the carb 5.0 guys has a homemade supertrap style muffler. The inserts look similar to these, heck they might even be these...
http://www.carchemistry.com/2-disk-insert-3-diameter/

Before I go chasing that rabbit, just wanted to know if I was heading in the right direction. Free up the exhaust flow (less back pressure) by removing the muffler and add some of those in the link above to keep the noise down and pull tq down. Of course would be matched fine tuned with a intake restrictor.

Vanilla Ice

Can you tighten the exhaust and add some lift through rockers? That should give you the effect needed.

novaderrik

put a throttle stop on it to give less throttle opening when getting dyno tested, also maybe have the car nice and heat soaked with some thick oil in the pan when doing the testing- which, honestly, better reflects what the car will be doing during a race than running it cold..

bjankuski

What class is this? Is this the mustang/camaro challenge? I would like to look up the rules and see what can be done. The restricter plate is a poor choice because it has less effect on TQ and more effect on HP at the upper end. That is why you only lost 14 ftlbs of torque but 27 HP with the 38mm plate. Tuning is the way to go.

GMan 3MT

iTrader: (4)

Yeah, it's for NASA's Camaro-Mustang Challenge.
Rules... starting at section 7.9
https://nasa-assets.s3.amazonaws.com...cial_Rules.pdf

bjankuski

Thanks for the rules, seems like a grey area to me. I assume when they say no recurve of the ignition they mean for added power. I would see if they would allow a recurve (reduction in timing) to limit torque while still allowing stock timing latter in the curve?

This class does interest me, I was looking at the cars at Road America this year and debating how I could field a competitive car for this class.

mcgarnicle

iTrader: (14)

You're back! Lets continue the chronicles of Knocker haha


https://www.thirdgen.org/forums/memb...ad-race-5.html

ploegi

Just a muffler is going to have very little, if any, affect on your numbers....... Could dial back timing via the distributor a bit.