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So..I have a set of the better TPI manifolds and a set of 2460 Hooker headers. Would be going with a Magnaflow Y-pipe or Doug's D901 for the hookers. Car already has 3in exhaust system cat-delete that will butt up to which ever one I choose. So how much power would i lose staying with the manifolds vs the headers? Pretty much stock L98 350 running TBI. If it's not a lot of difference id like to stay with manifolds for obvious reasons. What do you guys think or what are your experiences. In the past I've always went with headers but I'm not racing this one.
Not to hi-jack your thread Dustin but can some one elaborate on the tpi manifolds? There are different options? The reason I ask is I have a spare 88 parts car with a complete tpi. Other than my 87 not having the same emissions crap the 88 has I didn't know there was a better set of manifolds, of course I was just assuming.
Headers will always out-flow exhaust manifolds. You'd probably gain around 15 horsepower with headers.
Of course there are drawbacks as well. Headers dissapate a lot more heat into the engine compartment, are notorious for leaking, and don't tend to last as long as exhaust manifolds. I have the '84 HO exhaust manifolds, but I'm not going drag racing with this car...
Nothing wrong with manifolds on a street car, especially if you want stock stealth. With the right kind of work, they will support a surprising amount of power, especially on "torque" engines like "stock" 350's. I ran a race car with manifolds, and - trust me - they flowed. Now, you may not want to do a lot of work to them, I had to, but it is possible. If you are not racing, and don't want to mess with header bolts, gasket leaks...… just wanna drive, stick with them. Header power is most noticeable at higher rpm, and a shorty header has a relatively small range of power advantage....
there are two styles ,one is about 1 and 7/8 to 2" (usually on lb9 automatic cars) and the ones on the hotter LB9 5 speed and L98 cars are closer to 2 1/4" ,
there are exceptions and specifics on years applicable,search deeper for the exact definitive answers,many on here know the exact information you need.
Last edited by 1986BANDIT; 08-17-2019 at 04:46 PM.
Nothing wrong with manifolds on a street car, especially if you want stock stealth. With the right kind of work, they will support a surprising amount of power, especially on "torque" engines like "stock" 350's. I ran a race car with manifolds, and - trust me - they flowed. Now, you may not want to do a lot of work to them, I had to, but it is possible. If you are not racing, and don't want to mess with header bolts, gasket leaks...… just wanna drive, stick with them. Header power is most noticeable at higher rpm, and a shorty header has a relatively small range of power advantage....
I have had more problems with manifolds than headers. Both my G20 van and my Express vans cracked both manifolds before 100K. Also pulled apart a 305 on an old 84 ElCamino and the passenger side manifold fell apart into 3 pieces.
There are models that are prone to poor performance and breakage due to the design needed to make them fit, but the 3rd gen f body manifolds are not known for such problems....
Nothing wrong with manifolds on a street car, especially if you want stock stealth. With the right kind of work, they will support a surprising amount of power, especially on "torque" engines like "stock" 350's. I ran a race car with manifolds, and - trust me - they flowed. Now, you may not want to do a lot of work to them, I had to, but it is possible. If you are not racing, and don't want to mess with header bolts, gasket leaks...… just wanna drive, stick with them. Header power is most noticeable at higher rpm, and a shorty header has a relatively small range of power advantage....
I tend to agree with 427. That exhaust thread we were a part of Chaz posted that somewhere he saw a flow chart and there was not much difference between "shorties" and the HO manifolds as long as you have the good y pipe with a 3" exhaust.. I think there is no question you will get more HP from the headers but for what you do with your car you will get more satisfaction if you go with the HO manifolds.
if anyone can find a good place that does the extrude honing process,some very serious flow gains could be had and be virtually undetectable from the outside.
the same benefit applies to tpi runners,tpi base etc.the extrude honing pumps an abrasive slurry through the ports and removes material evenly and smoothly.
Bonehead performance quoted me $910 to extrude hone my 3 piece mpfi intake manifold plus shipping. just to get an idea of the cost. I decided I could do enough with my Dremel.
Yeah that type of work on manifolds is really only for somebody with a certain goal and the finances to back it. Like spec racing where you must run a manifold but its open to what can be done to it.
There are models that are prone to poor performance and breakage due to the design needed to make them fit, but the 3rd gen f body manifolds are not known for such problems....
The Elcamino was a LG4 and had the same manifolds as a mid 80s F-car. I replaced them with F-car shorty headers in that car. Plug access was 10x better and it had a definate power increase. Worked really well when the Q-jet/Performer intake swapped 85 LB9 long block went into it too.
Given the option headers over manifolds any day. The last car I helped setup for a friend has shorties. Just swapping the shorties even made the car sound better.
07-21-2019, 01:52 AM
