if you have the cast iron maniflods they don`t flow as well as you think did a lil` research on those the factory tublar headers out flow the cast by a lot and the more you can flow exhaoust out IE headers/tuned exhaust the better the engine can scavage it the better it runs.....

yup....just swapped the muffler and enlarger to 2.5" after the muffler for the very short distance..........


thanks for all the compliments guys.........like i've said before.....i won't trade my flowmaster for anything! best 72.99 i've spent (i know its different if you have 2 mufflers)

Hmmm..I was planning on doing a smaller pulley, but 3.4, not 3.2...maybe I'll skip the headers.

Thanks! I have a little more recon to do, but I may call to ask you a little more about it.

I agree, but I'm not sure it will. The Flowmaster guy was pretty sure that the supercharger would change the sound...possibly not for the better. Call him...he was great (just call the tech line off the website and ask for Dan).

Good to know...thanks.

Don't let them scare you off headers. You will make your sweetest gains with them, and the sound quality improves significantly.
I have no problem with lost boost or decreased low end torque.
If anything, there is much more torque now across the entire rpm band and my boost still goes into the orange of my boost guage with just a 3.4" pulley. I can't see any significant drop in boost.
There is only about 5 - 10hp difference beween the 3.4 & 3.2 pulley sizes and knock retard can more than kill that, so stay with the 3.4" and don't worry about doing anything but good by going to headers.
I can't speak for Roques SLP headers because they have smaller tube sizes and my guess is that they were designed mostly for normally aspirated cars to try to keep the low end torque but I think they might compromize back pressure.
The TOG headers are least restriction and better suited to the SC L67 engines.

Without a PCM headers and less then a 3.4 pulley will not help the car significantly as my dynos have shown. The SLP and the TOG'* flow more than the engine can put out so i don't think its an issue of diameter. In fact INTENSE tried to develop even larger size headers (called big dog headers) for their mp112 thinking the engine would breathe better with them only to find out that they didnt help at all because the smaller headers will more than adequate. I'm not saying headers are not worth getting, just that it probably should not be a first mod. The money that is spent on those can increase the performance significantly by putting a 3.4, intake, and rockers on. Maybe even OR pushrods.

the stock boost gauge only goes to 7psi. A 3.4 will push boost up to almost 11. Headers will drop PSI by 2 lb'* dropping it to 9, rockers will drop it another lb to 9. Still more than the stock gauge shows so it will always be in the yellow. Each lb of boost equates to about 12-15 HP but KR will negate some of this (or all if you go to small without supporting mods)

On a bonneville, 3.4 should be the lowest you go without a pcm. even with a pcm you may gain more by keeping the 3.4 and advancing timing instead of dropping to a 3.2.

I have dual magnaflows on my GP STE, and it has the little 3.1L engine, and it sounds very good IMO, so I think it would sound even better with the 3.8. Yeah, its no V8, but remember its only .2L smaller than that northstar, it can make some noise too. I bought my Magnaflows on ebay for $105 shipped for both. I probably could've gotten them cheaper, but that was a good deal to me so I just got them from a "Buy it Now" auction. I'm sure if you looked around, you could get them for even cheaper. And, they are supposed to outflow Flowmasters by quite a bit.

Shawn

My stock gauge goes to 10 psi. Before I installed the 3.4" it would never go beyond the orange line or 7-8 psi. After the 3.4" it would go half way into the orange or 9 - 9.5 psi. Now with the headers it still goes into the orange the same as with just the 3.4" pulley.
Go figure. :?
I know it should drop but maybe it'* just the gauge.

Are you saying that if you install the 3.2", providing you don't get any Knock retard, that by gaining back 2 psi you will gain another 20 hp over the 3.4" ?? I don't think so.

I'm pretty sure that stock boost from a 3.8 is 6.5lbs. The gauge while showing 10 really only reads 7-8 as max. The best way to test for boost, other than a dyno is to use a scan tool and subtract barometric pressure from manifold absolute pressure and multiply by .49. I would not expect 20hp from a 3.2 over a 3.4. I would however expect 20hp from headers and a 3.2 over a 3.4 w/o headers. I am just stating opinion from the facts I have gathered doing actualyl testing and dynoing MY car after each mod to see whats produced and whats not. Feel free to mod your car however you like.

I have to say, I believe you are correct...you've been testing your car all along, so you've seen the results...either your car is a lemon (which I don't think) or you know what you're talking about. Either way, in the end I will be getting a PCM anyway...after every other mod is done, so it can be programmed to understand what the heck is going on (and to remove the governor or push it up to a speed I'll never hit)...no sense in me getting one sooner if I'm going to put larger wheels/tires on, or anything like that (and that may be one of my last mods). Plus I need another car as a backup while this one is experiencing down time...that'* what is holding up quite a few of my mods. :? With one car in the family, we need it so much it'* hard to work on it.

Anyway Todd, I can't wait to see what happens to your car when you get a new PCM ...should be very fun. I love watching your progress because we kind of joined around the same time, and we have a lot of the same plans (and the same car, obviously :P ).