clegg

I am building a 55 Chevy truck. A stock LQ4 is now mounted in there. I am contemplating using the stock manifolds. I am possibly considering installing a cam with a mild lope. I am reusing the stock intake with the injection.
How much gain would there be with long tube headers compared to the stock but ported manifolds?

tfi racing

iTrader: (2)

Depends on a few factors,I'll guess the headers alone may be worth 15-20 real world hp...

R290

Changing the cam requires tuning on the ECM. I'm sure there are a few threads in here about a 6.0 and LS6 cam.


tfi racing said it, 15-20 with some 3" exhaust pipe out the back. Your engine is a big air pump, so with some free flowing exhaust there is some power to be gained.


I'm a bit behind you, just pulled the donor LQ4 from an 06 van. The end sound is more of a concern with me then the extra HP as mine is going to be for cruising, maybe a drag or two just to know what it will do. I like the idea of the Dynomax VT muffler, get the open pipe when needed and no drone when cruising.
Need to find someone that is using them before I go that route.

Dan Estrada

Interesting. I'm searching here for general info because I am putting an LQ4/4l85e put in my '55.2 big window Chevy truck. It came out of a wrecked Isuzu van with 81,000 miles. Cylinders were lightly honed, new rings, main, cam & rod bearings, all new gaskets of course. Trans was rebuilt also. It's a frame-up rodstoration project I am having done now. Was going to do it myself then life got in the way and realized if I dont get help it'll be an aborted project. It will also have a Ford 8.8 rearend.

Mine will be stock as I plan to use it as my daily driver when I retire at the end of 2017 (we'll see). Using stock exhaust off a C5 Corvette, they ought to flow plenty since a stock Vette runs a lot more horsepower than my engine will. We're guessing somewhere over 300hp, but that's plenty compare to the little 283 (with a weak cylinder) that was in there!

Here are mods made to the exhaust manifolds. We'll be using 2-1/2" all the way back with flow-through style mufflers and an "H" pipe or "X" pipe. I'm going stock but if there's much advantage to be gained with the X over H approach, please let me know.

Here's a photo of one exhaust manifold. I plan on doing some clean up, remove the EGR mount and will have them Jet Hot coated. I've no experience with it but I hear it won't discolor with het cycles even after time.

70lsgto

iTrader: (2)

for what its worth my dad races a 74 gto with 98 5.7 ls with a mild cam with manifolds it ran 11.98.....with stainless long tubes it ran a best of 12.19, mostly 12.20s, weve tried jets timing ect, the stock manifolds arent bad!

70lsgto

iTrader: (2)

ok another example,1970 chevelle my friend had 454 auto stock manifolds, he had me put on hooker super comp headers 2 1/8 primary tubes 3 1/2 colectors 1 tube goes outside frame $730 .........it ran no faster et, or mph not at all. it was a mild motor but nothing?

Cheese Weasel

Putting Super Comp headers on a mild engine is very probably a parts mismatch. There are a lot of potential reasons why you didn't see any gain (maybe the engine wasn't using more air than the manifolds could move, maybe the downstream muffler[s] were restrictive, it's very likely [IMHO] that the manifolds weren't the biggest bottleneck, etc, etc.). It all depends on the combination, & running headers that are too large can actually DECREASE your engine's power/ETs a bit. The entire combination has to match.

You can read a little bit about that right here - and, if you want to see an example of that being taken to an extreme, you can see that in this article. (Wild, huh?)

Going from memory, the test results for LS headers I've seen over the last few years is this:

• Shorty headers seem to be roughly equivalent to manifolds - sometimes a small gain (on the order of 4 or 5 HP) sometimes none;

• Mid-length headers (depending on the design) will sometimes provide a gain of 7 - 10 HP - and not infrequently, more like 5 - 8 HP;

• Long-tube headers provide the best return for your money/effort - those gains seem to be around 20 -25 HP.

(Please keep in mind that these numbers of course vary somewhat depending on engine size, camshaft, state of tune, etc.)

Personally, I'm not sure that I'd even bother with the shortys or the mid-length headers (unless maybe it was a mild street build where space was really a factor, like a Vega/Chevette/Monza/etc.)

(EDIT: Another mildly-technical header design article from Hot Rod magazine is available right here.)