I own an '88 IROC I purchased at the beginning of the summer. It's got the L98 350 and my only mods thus far is a Dynomax 3" cat-back and Dynomax 3" high-flow cat I took off my LT1 Formula.

I want to upgrade the exhaust manifolds next as it's obvious the stock piece's are a HUGE restriction. I've narrowed it down to MAC or possibly even SLP's (if I can find them at a good price). The MAC's are 1 5/8" which I feel is more than enough to handle 425-450 HP - probably the most I'd want to make with this car anyways as it's recently become my daily driver and with gas price's being what they are, I don't want to go too crazy.

Since I have no previous experience with these 3rd gen Fbody car's and their TPI motor's, I'd just like to know how much HP/Torque I can expect to pick up with either of these header system's installed.

Many thanks in advance, and if there's any advice or suggestions you'd like to give me related to the subject, I'd appreciate it.

 

All f-bodies respond greatly to headers. The Gen II and III motors will typically see greater power gains with a header install over a TPI motor but the gains you will see will be great. You could see 15 solid hp or more depending on your other mods.

 

The stock Headers a huge restriction but unless your getting Shorty style headers get 1 3/4" headers, theyre better for the larger 350.

What model(part NO.) Headers are you getting?

 

Thanks for the response.

My only other mod's so far is the rest of the exhaust. I've also removed the smog-pump and advanced the timing a bit.

15HP ? I hope that's at the wheels I picked up way more than that on my LT1 when I installed a BORLA cat-back. I hope a HEADER upgrade on this L98 will give me atleast 20-25 HP.

 

MAC

I can't/wont go with Long Tubes as I'm not willing to loose low-end torque. Torque is what makes these 3rd gen's so much fun to drive around in. Besides, my car's pretty low to the ground and a set of LT's wouldn't last very long before I hit them over a speedbump or something.

I know SLP offers 1 3/4" shorties but the price is a bit too steap for me at this time. Granted, they are stainless steal, but I think they're just too expensive for what they are. Again, if I'm lucky enough to find them at a good price, I'll go with them since they're stainless steel and I'll never have to worry about them rusting out on me (I drive this car all year round)

 

Youv'e definitely got the right stuff

didn't know youre car was lowered and youre right, those SLP's are overpriced, those 2055's are great, might help a family friend install them this weekend.

 

So does anyone here have experience with MAC headers ?

I've done a search and I know a lot of people seem to love the Hooker design, especially it's y-pipe, but the MAC's seem pretty good as well.

They claim a 21 HP increase AT THE WHEELS and the ypipe looks pretty good too.

(seen here)

If anybody can chime in on their experience with MAC or SLP's or can give me a reason why I should choose another brand instead, let me know.

P.S. If anyone knows the cheapest place to buy either one, let me know too (money's tight right now)

Thanks again.

 

get the ceramic coated hookers! I had both at one time the slp headers fit really good never had a problem with the y-pipe or anything until I got my heads anyway the hookers are very good for the money and having the ceramic coating added makes them hard to beat. (I wish my headers had the coating

 

I haven't heard of any third gens with MAC products, but people with LS1's seem to like them or so it seems on LS1tech.com. Keep in mind that 21 RWHP is probably at 5600 rpm or some crazy rpm where there is no horsepower I'd be really impressed to see it make a solid 15 or so thorugh areas of the powerband(or lack of one I say go with the Hookers there a proven good product and there is tons of info here on this site about install, places to buy, etc. But if your sold on the MAC's then buy them they look very high quality from the picture, and they come with the Y pipe like the Hookers. Post back here if you get them, I haven't heard anything about them and am interested.

 

When I installed the SLP 1 5/8" Tri-Y headers on my car it was the biggest seat of the pants improvement I made. The caveat to this is that I had already made some improvements to the intake system. So the pickup was bigger than just changing out the headers.

I do agree with the above post in that you should pick up at least 15 HP. Maybe more. With a good free flowing exhaust system it will inhance what ever changes you make upstream.

 

I lost .4 and gained 2 mph in the 1/4 just with Hooker 2055's.

 

i just got my mac headers from my local speed shop they are like 470 on the web site and i got them for 423$ but i dont have my car running yet so i cant tell you if they work good, but they went right in and fit perfectly i just had to jack the motor up on the right side but i was told they worked real nice so i thought id try'em

 

Nice. Let me know what you think of them after you're up and running. I guess I'll make my decision AFTER I here back from you as you appear to be the only person to post that has the MAC's.

Glad to hear the install went smoothly.
Let me know your thoughts after you drive it.

Thanks.

 

hey why would a set of longtubes hurt low end?

 

There's a huge debate as to which are better. Long tubes, shorties or mid-length's. Different people will have different opinions. The debate has been done to death with no real conclusion.

Neither side is going to be "convinced" the other side is right so it's a debate that will never end.

I am a firm believer that an exhaust system on a STREET car, has to have at least some back-pressure in order to build up torque at the lower RPM's.

There is such a thing as "too big" an exhaust on a street car.

A lot of people will say the best exhaust, is no exhaust at all. They say that any back-pressure at all in the exhaust is bad and you'll lose power. That's true, but only to an extent. It's all about WHERE that increase in power comes in.(low - mid - upper RPM's)

If you really want to see for your self, unhook the y-pipe from you're headers/manifolds and take it out for a spin. Your low-end torque will be almost non-existent.

When I first got my LT1, I decided to run open headers just to see what it was like. I too was under the impression that "no back-pressure is best" as everybody had told me and I was amazed at the results.

With open headers, I literally was NOT able to spin the tires. I'm not kidding either.

Put the exhaust back on and I could spin the tires for an entire city block. I didn't need a dyno to tell me I just lost all my low-end torque. It was obvious.

I've seen dyno after dyno showing that while LT's have a definete edge in the higher RPM's over shorties, from 3500 and below, shorties produce WAY more torque.

My advice to anybody is that unless your building up a motor with 500+ HP, 1 3/4 or even 1 5/8 shorties are the best way too go as they emphasize HP/Torque in the lower - mid range which is exactly where a street car is 99.9% of the time

This is especially true with these TPI motor's since they were designed to perform best from just off idle to 3500RPM.

Will you get a HP increase/torque increase by going to LT's over the stock manifolds ? Absolutely. But you won't be making as much torque as you would with shorties.

This is all my opinion mind you, one which I've formed through year's of experience working on my car's and my friend's cars.

I know a lot of people will argue with me, but that's to be expected.

For the record, I run LT's on my LT1.

I switched from shorties to LT's and did notice a pretty big difference up top compared to my Edelbrock's but that was also because I had heads/cam etc. etc.

I picked up a maximum 14RWHP at peak RMP (6500) but at the cost of loosing an average 24 lb's of torque from 2500 through to 4500 compared to the old Edelbrocks.

Bottom line:

Any aftermarket exhaust is better than stock and all will increase your car's power output.

Question is, WHERE do you want the power to be increased in the RPM range ? Upper RPM ? Go with LT's
Low-mid range ? Go with shorties.

Both designs have their pro/cons. Be honest about what you want to do with the car and make your decision based on that.

LT's - best for 500+ HP street/strip cars
shorties - best for daily driven cars (*up to 450HP)

 

LT1FUN. I have seen dyno tests and other reports that support your theory about long tubes versus shorties.

Regarding back pressure the exhaust manufacturors have a recommendation for exhaust pipe sizes for the various cubic inches versus horsepower. The ones I have seen are almost all identical.

 

i got my car running saturday but unfortunitly when i started it up i had the slave cylinder line on the header and it melted it so once i get that fixed i will take it out and tell u what i think of the headers, it sounded really nice though with very quick throtle responce im not sure if thats from the headers or the new cam and rockers

 

not going to get into a whole long post to start this off but there i sa lot of information about backpressure on this board. more often then not backpressure isn't what is causing the loss in low end it's velocity. and you can have veloicty without having more backpressure.

I would also think that with shorties vs longtubes the long tubes should give more low end with everything else being equal. you know same mods on the car as well as same pimary and collector diamater. a little of it has to do with exhuast pulse tuning and how it effect scavaging. if the rpms are low a longer exhuast helps out with tuning the exhuast to that rpm while shorter exhuast would tune to a higher rpm. kind of the like the TPI intake with really long runners it works best for more of the low to mid range right?

that might be part of the reason you couldn't spin the tires when you took your y pipe off also. maybe it wasn't due to backpressure but due to scavaging being like crap. first off now the left bank can't help create a low pressure zone for the right bank anymore to help pull the exhuast out. also each cylinder itself will not help exhuast out on any other cylinder if you have really short collectors on your header/manifold.
it's part of scavaging. one exhuast pulse creates a low pressure zone behind it. without the y pipe that low pressure zone can not create a low pressure zone for the pulse that comes on the next cylinder bank so now it's like running two 4 cylinder motors as far as your exhuast is concerned. but true duals will work right? that is cause the exhuast pulse is able to stay within the enclosed space keeping that low pressure zone. open header pulse leaves the exhuast stays in it's own primary creating a low pressure zone behind it but that low pressure zone doesn't affect any other cylinders till it can hit the collector. when it hits the collector it's too short to make much of a difference so that low pressure zone from one exhuast pulse just goes straight out the pipe without really helping any other cylinder out. at least with long tube headers you might be able to gather some effects at low rpms due to sound wave tuning and at higher rpms due to some pull maybe?

the object of scavaging is to create a LOW pressure zone (kinda defies the word backpressure doesn't it) at the valve to help pull out the next exhuast pulse

a weird way to think about it also is like an intake. forget abotu backpressure and stuff like that. they both work on the same basic idead of pressure differences and pulses. sure one might be going in and one might be going out but that is relative to what you are looking at. but if you try thinking of it like that it helps with understanding some of this velocity and all that crap

sorry I made this a little longer then I planned but see there might be other variables other then just the ones you described as to why you lost power with the open headers and it isn't so simple as just backpressure.

 

also out of curiosity what size primary/collector on the shorties and what size on the long tubes