I was reading thru the '05 March edition of GM High Tech, and checked out their "10 best mods for any engine." Well, on page 36, the first motor/example they give is the L98/LB9 motor. Everything seems well, but, there was one thing that took me by suprise, the exhaust part. They say, and I quote:

You are going to hit a horsepower brick wall with a 3-inch exhaust system on a 3rd-gen F-body. A Mufflex 4-inch single exhaust system, here equipped with an Edelbrock Victor Series muffler, will equal or exceed a dual 3-incher's performance with no custom fabrication.I was really surpised to read that. I didn't know, or even thought, that a single 4" pipe would be a good upgrade for a stock, or slightly modified L98 motor. Here you were giving us the low down on your custom dual 3" exhaust system, which really kicks azz, and now I read that all you "really need" is a single 4"....what's up with that????

Also, I decided to check out SLP's web site, and I see that they FINALLY have an exhaust system for '82-'92 F-bodies. The site says that it has 3" diameter intermediate pipes and 304 stainless steel high luster tailpipes with round angle-cut ends, but does that mean it's a true dual 3" exhaust system? Cause "intermediate" pipes sounds like the two pipes that come from the headers then join into the y-pipe to me. Or am I wrong in thinking that? And if I'm right, then what size is the rest of the system?

Anyway, sorry for the long post, I was just tripping out on the 3 different, (including yours), systems contrast each other.

Which do you think is the best way to go?


Edit: I went back and did a "search" to find Twilightoptics' old post....I forgot you were thinking of going with a single 4" pipe, and for some reason thought you wanted a single 3".

Something I've come to realize with GM High Tech is that their claims are..... generious to say the least. I first modeled my old combo with the Holley Stealth Ram after their HSR IROC combo which ran 12.3 in the quarter and the best I could muster was a 13.7. With a bit of head work and a much bigger cam I could only muster 13.0.

Those guys also put n20 in the rubber maf bellows and preceeded to melt the crap out of it running down the track!

As for exhaust, the 4" setup was going to cost another 2-300$ more than making my own dual 3". If you run the area of a circle formula.... The areas smallest to largest are single 3", dual 2.5", single 4", dual 3".


I think I lost a little torque with the new cam/exhaust combo, but power is up. I don't think there is a "best way" its more what the engine wants/what you want/$$$$........ I'd have probably been fine with dual 2.5" but I wanted a dual 3" to show off, aswell as it being a challenge to me to build. Say there is another 15 horse by downsizing to a 4" or dual 2.5"..... so be it, but if I put anything more than a 350 in or run some forced induction someday, I know I wont have to touch the exhaust.


I don't see a dual setup on SLP's website but the Intermediate pipe... is the pipe from the cat, back to the axle (sometimes over axle to the muffler). The picture that has the info you posted, is just a single 3" setup.


If I went too big, it's too late now. But I don't think it's THAT big a difference. I mean, did they actually run a dual 2.5", single 4", and dual 3" on that same engine to see? 4" is overkill on a stock l98, IMHO.

But hey, I've only got 285 HP with an 11:1 AFR :: rolleyes :: I will be heading back to actually tune wot on the dyno shortly. Should be over 300. Means close to 400flywheel which is about 30 short of what I was going for.

I could have sworn I seen "dual exhaust" in the SLP site, but I guess maybe I misunderstood and read dual exhaust tips for the single pipe to muffler with dual exhaust. :confused:

Well since you did mention your combo, and theirs, do you think mine would work, and about what ets do you think it'd run? I'm planing on rebuilding my 91 Camaro's short block back to stock specs, but I'd like to add TPIS' Mini-Ram set up. The heads are stock, but have been ported and polished. I'd like to go with a bigger cam, but then that'd mean having to spend more money on valve springs, etc., then if the cam is too big, then that'd also mean I'd have to buy different pistons, and I don't have the money to throw around like that. My cam, according to my buddy whom I bought the car from, said that it's not the stock cam, but similar with a "grind" on it. My buddy, as good a guy he is, doesn't know a whole lot about engines. I'm assuming he meant that the cam is bigger then stock, but smaller then .500" lift to work with the stock valve springs. Also, as much as I'd like to go with a bigger cam, I don't want to have to spend more money for a chip/computer tunning. Reason being that I want to go with a ProCharger in the future, and would like to only tune the computer once, instead of 2 or 3 times.

So, with a stock short block, ported and polished stock heads, and a TPIS mini ram, do you think it'd be a major improvement? And what 1/4 mile times do you think it'd run. My buddy said that it was already running mid to low 13s the way it was. Or do you think I should re-think my combo? Thanks!

I agree with what Twilight says. 4" is definately too large for a stock LB9/L98.

My only experience so far is upgrading from the stock RS L03 exhaust to a 3". Picked up alot above 3000rpm but lost a little below it felt like.

I think a dual 2.5" system is good for anything up to 500hp quite easily. I think my a 3" system becomes questionable above 400hp.

My '91 already has a single 3", so I guess I'm good to go, just not sure what brand the muffler is, I think my buddy said something like "CVX"...I remember it sounded similar to honda's "CRX" name tongue.gif

LXS, I've been working with my combo, as well as my friend Mike's 383 AFR Miniram. While the miniram is a good intake, it REALLY likes to spin the rpms. It doesn't have a very long runner design so going from TPI you'll lose alot of torque. If you aren't going to change heads or cam, I wouldn't wasted the $1300 on the intake.

For what it's worth, my combo has as much torque with the HSR as his 383 with the miniram. Which is unusual because he's got the bigger cubes/stroke that should be making more torque.

http://thirdgen.org/techbb2/showthread.php?s=&threadid=273727&highlight=%2Btpi+%2Bshootout

Page 1 and 2 show comparisons with the intakes. And this is on a semi modified small block. (They did get the tpis numbers backwards on the miniram vs tpi dynograph but you should be able to figure out which one is which. High HP is miniram, High Torque is TPI)

If you plan to charge it, save that miniram money because once you force it, it's not going to make much difference having that intake.


It's hard to say what times you'd run. Alot of it has to do with the launch. I'd guess actually high 13's. I had tpi with a comp xe 262 cam, semi ported 416 heads that ran 14.0@97. When I put the HSR on, which is a better manifold, IMHO, I didn' improve ANY in the 1/4.

So then I guess, if I'm going to build the motor for performance, then I'd be better off totally building it up? Meaning, heads, cam, intake/fuel injection, and possible stroking?
How would the car run if I were to use the stock tpi then add a ProCharger? When I talked to the guys at TPIS, they said that if I were to stroke and/or supercharge the motor with the stock tpi, I'd have too much unsuable torque with very little horsepower. If that holds true, then which way is the best to go?

I don't have the experiance in forced induction. Do some searches and see what numbers people are putting down with prochargers. I'd make sure to run an intercooler. It's ALWAYS best to set a goal, and go for that, rather than nickel and dime yourself to hell upgrading the next thing, when something brakes, etc.

With the charger on the tpi, if you had a rear that could take it, I wouldn't be suprised to see some air under those front tires! I would probably build the engine for lower compression so you can run much higher boost, give it a nice cam (I'm sure Harold could help you out when you decide the route you want to go) and the port/polished heads should be good. I like ported 416 heads myself.