hey there. anyone who's done strong research on the L98 motor knows that the TPI intake manifold is too small to fully support the 350 at higher RPMs. with this, and daily drivability, in mind, I wanted to build an L98 for my 88 camaro with outstanding, almost rediculous, midrange torque. I just finished reading john lingenfelter's book on modifying a small block chevy, and while it's answered many questions, it didnt give any instructions on how to figure duration, head flow or intake flow given a specific engine displacement and desired performance range. I've designed an engine using an LT4 hotcam and the stock TPI system on my desktop dyno that gets 475 ft/lbs of torque at 2500 rpms, which is beyond my standard of torque, but it's at much too low of an engine speed for a daily driver or a drag car.

my question is this: if i want to build a 350 with the tpi system on it for crazy amounts of torque, given the intake's size and intake length, what rpm range does it have the most efficient airflow velocity, secondly, what size head would you suggest using, and third, what duration cam should i look for? I dont mind a choppy idle one bit. in fact i prefer it. when i asy midrange performance with rediculous amounts of torque, i mean between 2-5k rpms having torque levels that reach above 440 ft/lbs. keep in mind, this is definately a budget build. Im not looking for crazy horsepower, just midrange torque and i do not want to change the intake to a superram or stealthram or anything of that nature because in my opinion its not needed unless you plan on tuning the engine for top performance over 4500 rpms. I also do not what to stroke the engine to a 383, as i had originally planned. it seems foolish to do so if i can get acceptible torque from a cheaper, more fuel efficient engine.

just to throw it out there, my educated guess after reading that book would lead to the combination of a set of 185cc aluminum heads using a roller cam of 215-230 duration with as high a lift as possible with about 10.4:1 compression and a lobe seperation of about 112 or 113 and 1 5/8" exhaust headers. constructive critisism is welcome.

thanks guys!

 

If you are going to hop it up, you could go to 11:1 compression max. I went with 10:8:1 and no problems. LS of 112 or 113 would be good for the street. I would go with 1 3/4 SLP headers. See sig.

 

The TPI intake will never really allow for what you want. It would have been the perfect design for a gm truck, with the torque it creates at low rpms, itwould be great for towing. But unfortuneatley that torque is there to get you off the line so fast you dont pay attention to the lack of power up top. Most aftermarket intakes will give you more upper rpm power, raising up that torque range, but at the same time you're gonna have to trade some torque for that hp

Will

 

the tpi systems hould still be able to supply good airflow till at least 4000 rpms i would think. i mean, i'll be running a T-56 tranny with pretty close gear ratios, so a wide power band is not absolutely required. of course, the wider the power band the more useful the engine, but i have to find a compromise somewhere. if i designe that engine with an aftermarket intake like the stealthram on it then i'll be forced to focus on mostly high end power, which would require more expensive parts and machining to allow an small block to operate at higher speeds for very long. light to light wouldnt be a problem, but im a "better safe than sorry" kinda guy when it comes to my money and my cars. so you guys dont think it's possible to move that powerband up into the 2k-5k area? even just 2k-4k? i dont know exactly what the flow is lik eon the GM tpi system, but i would almost say it's stupid to think it's not usable at all for a high performance application given a lower operating rpm range.

nobodys got any particular advice on how to move this band up or some information on the flow numbers for a TPI system?

 

oh, aklim. also in the book it said that using iron heads you were limited to like 9.6 compression or something, and i think it said top compression for an engine running aluminum heads was 10.8. ive wondered sinse readin that how it is that hondas run on pump gas at 11.5:1 and some sports bikes are running 12 and 12.5:1 compression. what are your thoughts?

 

Well, you can go 12:1 but you risk detonation. Also depends on the cam profile and how you cool the engine.

 

forget the tpi idea. Yes you can have an engine that makes a lot of torque and then shift at 4000 rpms. But why not just either use a stealth ram or a super ram, make just as much torque at 4000 rpms, but have an engine that pulls to 6000 and makes gobs more in terms of horsepower. Any way you look at it tpi is going to choke the hell out of your motor