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Headers vs. manifold

Mastiff

Mastiff

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I found some very old threads on this topic, but I'd like to open it again.

Right now I have Doug Thorley headers. They've been great in that I've never had a leak issue, and the finish is still fine after 15-20 years on the truck. I only have a few complaints at the moment. The minor ones are that changing the plugs is harder than it needs to be, and that the flange probably hits the shackle at flex, but I could live with those. The main issue at the moment is that I need to get the crossover pipe above my front driveshaft, and since they headers are so long, this is not possible. Duals are not really practical for various reasons.

So anyway, I wonder if there really are any noticeable gains for those of us who operate in truck mode: low RPM, mildly built engines, not drag racing, etc. I don't care about a few horsepower near redline. Opinions?

And is a factory style (AIR enabled, insta-rust finish) the only option for manifolds? A quick look on Summit only showed a Dorman OEM replacement.
 
depends on your mill and what you want from the rig... but it's generally not "a few hp at redline" on anything over stock.. it's THE first performance mod to make to a motor..

I know the troupe of "I hate headers, manifolds rule!" guys will come in now ***coughyougetwhatyoupayforcough****... but I'll take some quality headers over manifolds ANYDAY on something I'm trying to get performance out of, whether looking for bottom end torque, or hp..
 
Headers all the way, especially since you have a good set it sounds like. Manifolds are quieter though, if thats an issue.
 
I've been searching for dyno results for my headers, but am having a hard time. What do you suppose the percentage increase in HP and torque is below 2500 RPM? From what I'm reading, long tubes are what you need for torque.
 
Don't know exactly how applicable this is, but from a Toyota site, the improvement is significant at 2500 on their 5.7L engine:

attachment.php
 
I'd caveat that Toyota data to say that the exhaust manifolds we are dealing with are what, 50 year old technology? IMO newer stuff is LESS likely to see the same gains as old simply due to the fact that manufacturers are investing the time and money to get more performance without affecting customer experience, and that just wasn't (or couldn't be) done when the Gen1 SBC came about.

The reason for long tube headers (and the Tri-Y's) is to increase torque, so the shorter you go, the smaller your returns will be, especially in low end.

From what I've seen, the 1-5/8" primaries are actually a bit much for a 350 that is optimized for low end, 1-1/2" should be the better choice, but not many options in that size.

Properly matched with the engine, there is zero question headers are better than manifolds on a SBC strictly in terms of performance.
 
Well, now I'm back to my pipe/driveshaft interference conundrum... :rolleyes:
 
Did you look at the hedman thread? It's got a really good number of photos of them installed, which probably have good reference points for you to get an idea if they will put the outlets where you need them.

Here you go: http://coloradok5.com/forums/showthread.php?t=213472&page=3&highlight=hedman+stainless 69830's

I've been looking for a formula to calculate the exhaust gas temp as it travels through pipe. With that ability you'd most likely get at least a very good idea of how long a header needs to be for maximum effect.
 
I have an lq4 in my K5 and I'm still running manifolds, they are GTO manifolds so they do flow alittle better than the truck manifolds. But I'm a manifold guy, give them some attention with some sanding drums and gasket match them to the head.

Heck smooth down the outsides and powder coat them and they look pretty sharp.
 
Chevy305 said:
Run your exhaust dual past the end of the transfer case and then cross it over there like I did. I used a dual in/dual out muffler but you get the idea:

http://coloradok5.com/forums/showpost.php?p=3327637&postcount=1254
Click to expand...

Looks good. My problem is that it's pretty tight on the passenger side to get past the tcase, and that's the side where I routed all my rubber fuel hose and new fuel filter for my TBI conversion.

I'll take another look though, since I'm running out of options. Maybe if I clean that up more and convert more of the runs to steel I can make it work.

I'll try to snap a pic tomorrow so everyone can know what I'm talking about.
 
Thorley makes any pipe specifically for your application including the bung for the 02 sensor, it bolts up and fits very nice and it's stainless. I'll take a pic and post it.
 
sreidmx said:
Sorry about the bad pics I am leaving for work.

fea11f951998b7c1a401482d20a99af9.jpg
Click to expand...

That looks like my setup. You can see how the headers exit quite far back and it's not really possible to get over the shaft. My run looks like this except that I didn't make the little arch down and the shaft hits on droop. With that little arch down, that's the lowest place on the belly. I'd rather avoid it, but it's an option.
 
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