Thinking of going with old skool cast exhaust manifold

[badmix]

Was thinking of getting a set from LMC or else where or if anyone has better source.

1) What gains or losses will I see going from full length headers to manifolds

2) Should I see reduced heat in engine bay due to thicker material of cast

3) Im guessing ill need muff shop move the collector up to the manifolds.


Can anyone see pro and cons to me doing this.

Here are my reasons

1) Dont have to tighten header bolts up every 3 months

2) wont rust away like my Heddman headers do

3) could be quieter

4) gain low end torque

5) Possible less heat in engine bay, less heat around starter.

 

[dyeager535]

You'll lose across the board, except for potential longevity and heat.

Independent dyno tests I've seen on non-high performance 302's and 350's show a loss of (in either motor test I saw) roughly 40hp and/or 40ft lbs of torque with a stock manifold, across the board, not high, mid, or low RPM either.

Headers are probably THE biggest single gain you can make, for the money that a pair of headers cost.

Hedman is starting to release sets of stainless steel ones BTW. And last I checked, GM was still selling cast stainless steel tubular manifolds for the 350's...

 

[Slapperbar]

Get coated headers and use Stage 8 fasteners. I did it on my S-10 w/a 350 and no problems.

 

[Wasatch K5]

I think headers are a PITA.

I don't question that they make the engine perform better, but it seems the performance comparison is always to a stock setup with restrictive single exhaust. Certainly a well made dual exhaust system mated to cast iron manifolds will be better than stock (and not as good as with headers).

The cast iron manifolds typically don't leak, either at the collector or at the cylinder head.

 

[dyeager535]

Based on the design of the manifolds, the restrictions/gains have more to do with dumping 4 cylinders into one chamber, with only one exit...meaning every exhaust pulse but the one closest to the dump is colliding with the others. You can't build velocity that way.

Even in headers short tubes don't perform as well as long tubes, so the collector forward is where most of the gains are made obviously. Even in long tubes you have equal and unequal length runners, where the equal length runners typically make even more power (however slight) than unequal lengths.

Obviously an exhaust system is just that, you need to tune the components to each other. Great headers with a weak muffler, or vice versa, is still going to hinder performance.

 

[BadBob]

Get coated headers and use Stage 8 fasteners. I did it on my S-10 w/a 350 and no problems.

Agreed, only I think Stage 8 fasteners are junky. I'm pretty fond of the ones Breslin makes. They're bolts that are drilled, with the end split, and have a threaded splitter pin you tighten to spread the ends and lock them in place:
little article on them

 

[Slapperbar]

I've seen those. I don't like the small threaded bit inside to strip or rust togeather. However, they would work.

 

[AJMBLAZER]

What the heck where those non-emissions engine manifolds GM made back in the TBI days? I want to call them Ramshorns but that was the Corvette or something back in the 60's wasn't it? Basically were a cast iron header GM used in their commercial, non-emissions vehicles.

 

[toomany]

I went from full length headers to stock manifolds on my '77 K20. I noticed a loss in power, but not as big as you would think.

The motor was a 355 with a Comp Cam in it (don't rember the specs, but it wasn't too agressive), Edelbrock Performer EPS intake and a Holley carb. Headers had dual Flowmasters and so did the maifolds.

The power loss was in the higher RPM's (4000+), you could tell it wasn't breathing as easy. Didn't notice much change in the bottom end.

As far as the heat goes, the manifolds would keep more heat in them. But, once they got hot, they would stay hotter longer. The thicker metal would retain the heat longer. However with as open as these trucks are...I don't think it would be much of an issue. In my Camaros I noticed higher under hood temps with headers. The starter would benifit, as the tubes wouldn't be close to it.

On the bolts, I've never used Stage 8's (but have been meaning to get some for the Camaros) or the Breslin kind. But on the K5, I drilled the heads for safety wire. Sure it takes more time to remove/install, but it has been working just fine for the last 2 years. I have only needed to replace the header gaskets once, and that was because I was doing a motor swap. I honestly don't know why more people don't do this. If you have the supplies for safety wire...then this might be an option to consider.