As far as I am aware... the 4-speed auto in the HHR is the same that is used in the Malibu... and it can handle plenty of power in stock form. I'm sure JoeR knows better than I (from experience) but you could probably add an aftermarket transmission cooler and have plenty of durability.

 

The delay in PE is usually a little less, more like 4.0 - 4.5 sec. GM does that for fuel mileage and emission. Eliminating the delay will make the car more responsive, especially if timing is advanced some with it.

During a longer power pull, COT (catalyst over temp) will considerably enrichen the mixture towards about 10:1, where high 12's will make the best NA power.

Tuning both of the above will increase power through most of the curve, about 5 HP in some places, and up to about 15 HP if really tuned well.

Transmissions: Mine is a 5-speed. Over a year now without any problems, but I don't abuse it either. The stock clutch, however, is not up to the task of the added torque. Without any abuse I was getting slippage right away and had to put a heavier unit in (SPEC Stage 3+).

 

The auto trans will hold up pretty good for the extra power. A good tune should up line pressures some and a cooler would help.

 

I've been told by Bill Hahn who has extensive experience with our drive train, that our auto is good up to about 325hp. In my quest for 400hp, he assured me that I will need to have it rebuilt to higher specs. The trans is the one of the reasons auto SS's are tuned down for 1st & 2nd.

Many here, not Joe, talk about all of their gains, but have no dynos to show for it. I do. My tune alone got me about 18hp. Intakes did little, though the GMPP did give me more low end power. The nitrous gave me 40hp with a 50 shot and ~60hp with a 75 shot.

The key to anything is abuse. I don't take my car to the track all the time, when I have it, so an occaisional shot of nitrous is not a big issue. The shop that did my install says that as long as I go no higher than a 75 shot, I should never have an issue. Once I get my HHR back with the turbo installed though I won't be using the nitrous until I do some beefing up of the engine, if I ever use it again.

 

Speaking of abuse, I had a friend that had a nitro setup in his (then new '82 or '83) Camaro. He used it a lot street racing, and needed new piston rings after 6 or 7 months...

 

I've heard it said best this way...

"Nitrous is like a hot chick with herpes... you want to hit it but you are afraid of the consequences."

 

Good analogy...

Mike, if you're going for 400 HP, more power to you... literally!!

But expect reliability to go down big time!! Working with a few extremely modified Cobalts around here, the first Achilles’ heel" will be the inherent strength of the piston ring lands. I've seen a number of failures there. If you're going for those kind of numbers, consideration should be given to forged pistons. Last night I helped a guy pull his engine, highly modified, that literally blew out the sleeve in #2, big time!!

I agree that at those levels, the auto trans may reach its own limits of reliability.

Bottom line.... Wanna play?? Get ready to pay!!

 

Haha JoeR... I know how it goes with the LSJ. We spent last winter rebuilding one because the driver decided to have a little too much fun before being deployed overseas. It was a great learning experience, I'm just glad I didn't have to foot the bill.

 

I know I'll have to do a bunch of internal work; already discussing what will need to be done. It will be in stages. Tranny first, then rear disc brakes, motor, then more boost & retune. Remember, this will rarely see any track time. Still gonna be a driver. I'll not get much use of all the HP, just wanna know I can if I wanna!

This will all take about four years. At least that's the goal. Stage 3 next year, following year the tranny, then brakes & motor, then Stage 4!

 

Kind of Like Dog Years are Those "Hahn Years" .....