Im puttin an L98 into my '84 Bird. I searched for L98 build ups but couldnt find much. I was wondering what cam specs, intakes, etc. combined make for a good horsepower rating AND daily drivability.

 

Checkout the TPI board.

 

TPI or carb?

Define "good HP 'rating'" and "daily drivability" (what you want to get, in exchange for what you're willing to give up). Those mean vastly different things to different people.

 

You are very correct, that was quite broad. I would love to be somewhere above 300 HP adn the drivability isn't so much a factor as long as it is street legal and doesn't require anything more than 93 octane fuel. What I was really looking for is just an example of how much power difference you get from an L98 with a different cam and some other slight mods. And TPI is what I am putting in. Thanks to you both!

 

You can't make much more power with a cam and slight mods, the TPI manifold is already maxed out from the factory.

Really the only thing you can do to TPI is add headers and exhaust. Everything else is a major waste of money and you will not gain anything.

The only thing you can doto the engine is get some really good heads. But thats a waste of money because you will not really gain much.

If you want more power the only thing you can do is trash the TPI manifold and swap on a different MPFI intake, or go carb.

 

as far as that goes i like to think its a bunch of BS about not much power with TPI let me put it this way i have a 87 Pontiac Trans AM GTA with the L98 and i rebuilt it and put a bigger cam did alittle bit of head work ported whatever needed to be. the only thing suspension i have done is LCA's with 255/50/16 Fuldas and i just ran my car on sunday and i ran 13.7 at 100mph with a 1.9 60' so what was that about you cant make power if thats not making power you just let me know!!!!! oh did i mention that my car isnt even tuned ill let you know after i get DFI and tuned to see what it will do

 

Let me get this straight, you think 13.7 is fast? Hell swap a carb on there any you will be .5sec faster.

 

If you don't mind, what cam?

 

13.7 is GREAT.....for a TPI engine. 13.7 isnt that fast. TPI is a horrible form of induction for a performance engine, plain and simple. As soon as people change the intake, to anything other than TPI (stealthram, etc) its great.

 

I'm running a stock TPI intake with SLP headers and a ZZ4 cam.

The difference is tremendous. The power band moved up a bit, overall it revs a little higher, just enough to notice.

...as much as I love TPI, I can't see puttin' much more into the motor without pullin' the TPI.

 

ME Leigh,,, how many TPI cars have you tweaked or worked on to arrive at the above conclusion?

TPI will respond to mods just like any other engine. If they were maxed from the factory I could have never routinely dropped stock 350TPIs running in the 14.8 range to run mid 13s (back in the late 80s early 90s). The MAF cars were slower stock than the SD cars, but they ran near identical modified times. It took next to nothing to get either of them to run 13.8s with slicks.

I would only swap cams in the MAF cars back then (never swapped heads). Back in the 80s and early 90s,, trickery was about all we had going for us and the MAF cars would take A LOT more changes and give better throttle response than the modified SD cars. Now, with the support available for chip burning, either system can be made to work well past what you could get away with back then on the MAF system, stock chip, and trickery.

Also,, the stock plenum and base intake responds EXTREMELY well to porting,, but the intake system has it’s limitations. You get into diminishing returns around the 350 horse mark with a basically stock system. Even with the more extensively modified and aftermarket GM based TPI systems,,, once you have an engine with the potential to make around 450 horses with a carb, the short runner intake systems could give you an edge as long as you don’t mind running more cam, more gear and more stall converter. If you don’t want to run a lot of cam, gear, or stall speed,,,, and like brutal throttle response that only a long tube runner intake system can give (on the smaller displacement engines),,, then there is plenty that can be done with the basic TPI design.

 

I dont think I followed your post well, are you for or against TPI? I have worked on lots of TPI cars, and like you said there is a wall you hit at a certain point. No amount of tweaking on the stock system is going to help that. Once you switch to something like the stealthram, etc. you are no longer TPI, like most people say. Tuned Port is all about the Tuned Runners, etc. You change manifolds and that is gone. No doubt in my mind that any engine will benefit from the loss of TPI, and the gain of a carb. Because of emmisions, and other reasons, some people just cant take advantage of this "upgrade"

 

That’s why I stay away from posts like these. There’s not a short answer and I can be confusing when I try to give one. Engine / car combinations are endless but for every given combination (engine and car) there is an optimal runner length and size. If you ask am I for or against, TPI,,, I'm for long tube runners / TPI in specific applications. However, for full assault vehicles the optimal intake runner length may be 5” with a 2” area opening (short runner intake/carb),, for a stock 305 with 2.73 gears and a 1400 stall,, a 15” runner length with a 1.5” opening (stock TPI) might be optimal.

I’ve worked on and tuned a lot more carbed vehicles than fuel injection (like 20 – 30 times more), but there are situations that a “tuned” LTR system will perform better than a short runner intake system or carb. A stock LG4 car to TPI swap comes to mind,, and I have pulled TPI systems that I had tweaked on basically stock 350 TPI engines and swapped to a carb and the car slowed down. Not until gears and higher stall converter were added did the car run faster than the tweaked TPI,,, and if the guy had added just the stall to the TPI combination,,, I’m sure it would have been just as quick. I never did,, nor do I now considered myself an EFI guy. I’ve tuned carbs on a couple 9second cars, a number of 10 second cars, and too many 11 second and under cars to remember,, so it didn’t slow down because I can’t tune a carb or time an engine. So there are applications that I know for a fact a carb can not match a tuned runner system.

 

Yes i agree TPI is good for stock, or very mild engines. But once you start adding cams, heads... It starts losing very quickly.

 

Do you care to edit your post making it look like you're quoting me saying that I can't tune a carb or time an engine or are you just being funny? Because I can be a riot myself.

 

CHP did and article on a 12 second TPI camaro a while back, tho money wise, compared to a carb, or converted LT1 intake, its a waist of time.

 

I think that before you start saying what an intake can and can't do, you need to have all the specifics.

Imagine that Joe guy has stock L98. He finds a really good deal on a set ported al. vette heads and a mild cam. Maybe he's been sitting on a nice 3.27 or 3.70 9 bolt. Dad's got an old grinder in the shed. He posts here asking if it's worth porting the TPI.

First off, those simple mods will still return great results even with the stock TPI. If ya start porting the TPI, you can see even better improvements. It's all about how much you consider "fast". You'd be doing someone a dis-service telling them it's not worth it and that the TPI is junk.

...now if someone says there planning on doing an engine build-up, they have several thousand dollars, and they say they want to leave the TPI, they yes, ya gotta tell 'em that they should probably use another intake.

Like I mentioned earlier, I have an L98 with a stock TPI. ZZ4 cam, SLP 1.75 headers, and stock rebuilt heads. I have a built 700r4 with a shiftkit and a 2200 dayco convertor. The car is so much faster than stock it's not even funny. Now that's not to say I wouldn't have even MORE power with maybe a HSR, but I'm sure not what I would consider slow. Once I get into the block and heads, the TPI will go, but for the meantime it's certainly not "done".

 

I did it, but i have to admit it was pretty damn funny taking it out of context.

 

Thanks,, it was funny,, but not as funny as the one I had planned