Exhaust Experiences

[WrenchP]

Hey Everyone,

I am building a 91 k5 and I think I have a little bit of a conundrum. The story is, my stock manifolds leak pretty bad. I think this is do to the PO hacking off everything behind the cat and letting all that weight of the original cat rest on the manifolds and the trans cross member. After putting the truck back together (Engine swap (TBI for TBI) and 700R4 to SM465 swap), I installed the original manifolds, ditched the cat, added a Flowmaster 40 series muffler, a hanger, and a tip that aims the exhaust down and out the drivers side. This is a temporary solution to the exhaust.



I am using a phased approach to this truck as I am not sure what my end goals are yet. This phase is running, driving, reliability. I want to rebuild part or all the exhaust and I am torn between manifolds and headers. My goal is reliability more than anything but it is hard to justify the cost of getting stock replacements when cheap headers aren't any difference in cost. The problem I am having with the decision is that I don't want to buy new parts and have similar problems. Additionally, I think that engine upgrades would be another phase down the line. I have Aluminum heads and a Megasquirt II box that I would like to use. If I did headers, it would meet later goals.

I need some help from the knowledge bank here. Would I be wasting my time with budget headers? Would I be trading exhaust leaky manifolds for exhaust leaky headers? What is a good header for these trucks?

 

[HankScorpio]

My experience with cheap headers has been pretty bad. They leak. On my current 454 swap I went with stock replacement manifolds. Expensive headers work better than cheap ones.

 

[mrk5]

Pretty much the only way I do headers these days it to pay for good ones. Nice 3/8" thick flanges at the heads and ceramic coated. The last set I got for my 454 were Sanderson headers and I haven't had to touch them since installing 4 years and 12,000 miles ago.

 

[6872xtc]

From my personal experience, you are in a difficult position. I figured out how to deal with cheap headers in the late eighties and through the nineties. However, they can be a pain when dealing with clearance on the front driveshaft and right shackle bolts. The other problem is all of the heat into the fuel lines on the right side.
When I put my '90 Jimmy onto it's current chassis, I bought expensive, center dump Sanderson headers since I have an ORD engine crossmember. They have been several kinds of problems. The collectors leaked, messed with the O2 sensor, and now the left one cracked next to the factory weld where the 4 tubes converge into the collector.
I bought headers because none of the manifolds that I have are large enough ports for my Edelbrock aluminum heads.
So now I am on the hunt for a new solution. This obviously isn't much help for you except to hopefully tell you that there are several factors to consider here.

 

[Burt4x4]

Phase building only get's you so far.. I had good luck with Headman but the flanges are not thick to prevent warp in the long term..
One trick is to cut the flange appropriately so that each exhaust mounting surface "group" is not affected by it's neighbor. This works well with thinner flanges

Flange warping is what causes header leaks so thicker the better.... bigger gaskets are hit & miss so ..... ?

High Temp RTV is your friend

Burt

 

[Wes Harden]

I always liked annealed copper header gaskets. once they are properly tightened with good quality headers, maintenance free. $$$ not only buy a good flange, you also get a better design. might be the difference in plug wires burning up or not.

 

[Joel Wilson]

Latest rig I have had was an 85 but I have always run true dual exhaust with glasspacks. Going from stock exhaust to duals with glasspacks, you will notice a difference in power throughout the entire curve, and an H pipe will give you top end HP, but tend to crack at the welds. Not bad, but a little. I was also doing a lot of heavy towing with that rig so it would the frame would torque a bit in granny low. All headers I have seen or run have had problems with collector gaskets. As such, I have a set of 82 Corvette manifolds that are pretty beefy, center dump with a donut gasket. I have to have AIR fittings for my 77 so I am limited. The Corvette manifolds will give me a 2 1/4 or 2 1/2 exhaust and still meet smog. I am just waiting for some slower time at work to be able to get the Jimmy to the shop.

 

[WrenchP]

Thanks all for the input! I appreciate the experience.

 

[Blue85]

I've never solved the issue of header bolts backing out of the heads, but they do make locking fasteners for that (to be fair, I had the same issue with manifolds). I just tighten them up from time to time (and carry a couple of spares because I did lose one once). The biggest frustration for me was always the collector gaskets blowing out. I used aluminum gaskets, locking bolts, high-temp silicone, etc. I've had the "header buddies" for a couple of years now without the issue returning. These are kind of a ball and socket joint, but the "socket" part is just a standard collector, so it's very cost effective compared to buying ball and socket headers.

 

[ZooMad75]

If the choice is cheap headers or oem quality replacement manifolds for the same price, get the manifolds.

I know manifolds don't look as cool as headers but dealing with exhaust leaks due to cheap headers will have you wishing you went the other way.

Let's also face the fact that a stock TBI 350 is not going to have any major gain in power over the stock manifolds. So why go through the effort and deal with the leak problems and poor fitment of cheap headers?

It was said in the first post you are looking for reliability, right? Like others have said poor fitting, leaky cheap headers are going to keep the reliability in question with random check engine lights due to exhaust leaks. Or overheating the fuel lines, or hitting the shackle bolts on the front springs, or the bolts coming loose, ect.

 

[dyeager535]

I went with Stainless Hedmans that were a known fit on our trucks. I've realized that on my previous setups, the leaks were my fault. If the exhaust isn't hung properly (GM somewhat mitigates this on manifolds with the springs holding the y-pipe to manifolds, they also hang the exhaust solidly) you have a lot of leverage (and twisting) put on the headers and their mountings. Since I went with the new headers, and used a couple of good hangers that are actually stiff enough to hold the pipe solidly, I've had zero issues.

I noticed even with the ball sockets that are supposed to be better, I ended up flaring the mating piece trying to use force to fix the leaks the exhaust moving causes.

I did coated headers (also Hedman), and they lasted years, but I don't drive a ton. They also discolored fairly quickly. I'd not go with cheap headers unless it was an experiment and you knew you'd replace them later. Headers cause a host of issues IMO (plug access, heat, longevity, y-pipe, etc), up to you if the tradeoff is worth it.

Headers may or may not flow enough to screw with how it runs. TBI heads may be restrictive enough better exhaust won't be noticed, but if that's the case, neither would any gains.