Too Much Torque, Now What?

[Supercharged111]

Stupid car refuses to let me off with just 1 dyno per season. This time it's just too damn hot. I started with a 5 minute cruise on the dyno, then made 3 unrestricted pulls just for funsies. It ripped off 292whp and 329wtq with a properly flat torque curve. I was pumped, holy hot damn this motor rips and I inadvertently kick ass at building motors too! :lol: I then proceed to install last year's plate (38mm) and ripped off 270whp, then 272 just to make sure it wasn't a fluke. Whoops. So I toss in my smallest plate, a 36mm, and made 262whp. Sweet, I can deal with that amount of ballast. Oh by the way, what was the torque on that pull (I've always been short on torque)? 322 you say? FML. As I investigated further, I see I dropped all of 7 ft/lb via restrictor plate (because it peaks at 2000 RPM) so clearly plating down will not quell the torque and hp is already where I want it. I have a dual 2.5"-3" single aftermarket y-pipe installed. What impact will a factory y-pipe have? I need to lose 12 ft/lb and, preferrably, enough hp to not necessitate a CMC 1 restrictor plate. How many of you LT1 guys are running bigger y-pipes and not busting the torque? My car has always pulled happily to the rev limit, but I know Ryan Rahjes' Camaro nosed off hard after peak and I've always suspected the factory y-pipe to be the cause. On the other hand, I can't race period the way it sits now. I rebuilt it last year in the garage with a 3 stone hone, factory never-been-blowed-up pistons, rods, and crank (which I had polished). I used name brand rings, main and rod bearings and a Felpro gasket kit which, as I recall, includes a .038" head gasket with the factory being close to .030" so nowhere in that process should I have gained an unreasonable amount of torque. It's as if the motor broke in a second time, I figured it'd pooch out gradually but apparently I don't suck as bad as I thought at rebuilding motors. In light of this, I'm going to press again this season for the RCR for dyno pulls to start at 3000 RPM. My torque had dropped to 315 by then and would be raceable in the RPM range we actually operate in. Here's the sheet from today, the 3 pulls represent unrestricted, 38mm plate, and 36mm plate.

[Pranav]

I slipped up on contributing to the RCR for the 3k starting point last year, but I have stacks and stacks of dyno charts showing my 3 built LT1s making "peak" torque just off 2k RPMs when the real measurent past 3k is 10ft lbs lower. My only motor that didn't make peak torque below 3k RPMs was my first, used motor that had bad compression on one or more cylinders from the start; that motor was just below both HP/tq limits with zero restrictor. I will scan them all and submit them with you.

My only advise is to try again on a different dyno, maybe try starting in the colder end of the temp range and keep pulling to see if it goes up or down from there.

I had the same problem you had on a not so humid day; had to shove in a 36mm plate to barely make the numbers, a few months later on a different dyno I am way low on HP/tq after feeling like everyone was pulling in me big time, and found it really needed a 42mm. Two dynos later I'm still on that 42mm plate.

[Pranav]

Also running pulls without a plate is a waste of time and a good way to start stripping out your TB bolt holes on the intake.

Just warm it up and get your three pulls on the same plate you have run previously, or what you think will get you the correct numbers next time.

[Supercharged111]

Also running pulls without a plate is a waste of time and a good way to start stripping out your TB bolt holes on the intake.

Just warm it up and get your three pulls on the same plate you have run previously, or what you think will get you the correct numbers next time.

LOL, as you type that I was considering a stud swap into my intake. I've been all over the place with this thing, from unrestricted and short on torque to now what seems like a damn cheater motor. Every season that TB comes on and off multiple times, but last year it made as much with a 44mm plate as it did unrestricted and this year the damn thing is straight up breathing fire. Like I told the guy running the shop, my car LOVES the dyno. My current train of thought is to slap in a stock y pipe I just acquired and ditch the underdrive crank pulley. Between that and the scant few lb/ft a restictor drops, I can probably be legal again. Best case scenario though, I'm toying with the thought of dual exhaust minus an x/h pipe. Maybe I'd be dollars ahead to buy and install a Dynojet in my house?

[GlennCMC70]

Changing valve lash will help some. I forget which way make the torque go up or down. I've done it and it works.

I have asked for the rpm start change since I have been in CMC ('05). As a former director I will tell you that data is king. You must bring it.

[Supercharged111]

I'm bringing a thumb drive to the dyno next time, forgot to this time. I'll have all the data they can stand to look at. Any idea how much torque I can lose by going back to a stock y pipe?