Exhaust Upgrade ?

[tdangle]

I have a 70 C20 350 with TH350 and 4.11 gears. The engine (for now) is stock. Is there a worthwhile increase in performance to change the exhaust manifolds to headers? Mine has the ram type that curve up from the ports vs the log type that go down and straight across.

Thanks

[storm9c1]

On a stock engine, I would leave the ramhorns there. They are simple and reliable, and flow fine on any small block under 5000 RPM. If you have single exhaust, converting to a dual is a good upgrade.

Not a big fan of headers on street vehicles -- too much additional heat in the engine compartment, unreliable coatings, prone to cracking, etc. The factory setups use cast iron for a reason and it's not just cost.

For the SBC stock manifolds, ramhorns are the best of them all until the LT1 manifolds came out in the mid-90s. And then of course the LS manifolds after that.

[tdangle]

Originally Posted by storm9c1

On a stock engine, I would leave the ramhorns there. They are simple and reliable, and flow fine on any small block under 5000 RPM. If you have single exhaust, converting to a dual is a good upgrade.

Not a big fan of headers on street vehicles -- too much additional heat in the engine compartment, unreliable coatings, prone to cracking, etc. The factory setups use cast iron for a reason and it's not just cost.

For the SBC stock manifolds, ramhorns are the best of them all until the LT1 manifolds came out in the mid-90s. And then of course the LS manifolds after that.

That's what I was thinking about headers being more of a problem than a help. I do have a dual exhaust with dumps in front of the rear axle. I was just looking to confirm or dispute that I should have headers.

[GRX]

Agree with above. Headers really only increase performance if your engine has a restriction. Very unlikely with a stock build.

[68c10owner]

Headers ALWAYS show a increase in performance and sometimes fuel economy. But some manifolds, like the ram horn manifolds are pretty decent. You would see a small amount of power increase and maybe some mileage. Not sure the outcome is worth the money in your case.

BTW, years ago I had a nasty heat soak issue in my old chevelle. This was a stock 283 with standard style exhaust manifolds. When I swapped to headers I never had another issue and did not notice any additional heat in the engine compartment.

[GRX]

"ALWAYS" is such a definitive word. May be true under certain circumstances if one were to drive at WOT under full acceleration all the time. Even then there are too many variables. There is a lot to be said for a properly tuned exhaust system.

[68c10owner]

Originally Posted by GRX

"ALWAYS" is such a definitive word. May be true under certain circumstances if one were to drive at WOT under full acceleration all the time. Even then there are too many variables.

Headers are more free flowing than manifolds so yes, ALWAYS is correct. Headers dont just make more power at WOT. That makes no sense. You even said it yourself, headers will make more power if there is a restriction. All traditional manifolds that came on these old trucks are restrictive. Some less than others but all are more restritive than headers. This is common sense, not rocket science. Dont over think it.

[GRX]

Yes, *if* there is a restriction. Not overthinking at all. The science is simple. "Free flowing" does not always equate to increased efficiency. Modifying exhaust gas velocity without proper planning can detract from scavenging effects, thereby reducing fuel efficiency and power.

[68c10owner]

Originally Posted by GRX

Yes, *if* there is a restriction. Not overthinking at all. The science is simple. "Free flowing" does not always equate to increased efficiency. Modifying exhaust gas velocity without proper planning can detract from scavenging effects, thereby reducing fuel efficiency and power.

Well now for sure you are over thinking it. Correct, the velocity is important but nobody is saying to run a 13/4 tube header with a 3" exhaust on a stock engine. You are jumping pages here. Manifolds are restrictive, plain and simple, and going to a standard street header will increase performance over all. Selecting proper tube size is important.

[storm9c1]

"Manifolds are restrictive" -- OK, let's say ramhorns can free flow at 800CFM (just pulling that number out of the air, I'd have to research this to be exact). And let's say the headers you suggest will free flow at 1100CFM. Awesome right? Well stock engines don't push anything close to 800CFM (there are calculators for this online), so neither component will cause restriction at stock engine CFM (since free flow means max throughput without any measurable backpressure). And that CFM is measured at WOT, and nobody drives at WOT 100% of the time.

Sure, some headers may have large CFM gains over stock manifolds. And some manifolds are restrictive from the factory. But there is research out there showing the header gains over ramhorns on a stock engine with a stock exhaust system isn't very significant. Google "ramhorns versus manifolds" and make sure the results are posted with full exhaust systems. Header-only dyno tests are not the same and those with full exhaust.

Some of the marketing hype is dubious because most advertised header dyno tests usually happen with no mufflers or exhaust systems! As soon as you add mufflers and bends and intermediate pipes, you create backpressure, and now any gains, even though small, are nullified no matter which way you look at it.

I know there is more to exhaust systems than CFM (velocity, scavenging, cooling down of gasses, exhaust pulse tuning, etc etc), but for simplicity, I am just talking CFM since the majority of the gains and losses come down to that value.

This is a good discussion but headers just don't belong on a stock-ish engine. You will pay the price in reliability (cracks, leaks, paint burning off, rust-through, etc), heat issues, fitment, and clearances. And my opinion (which is only one man's opinion), is that headers only belong on race engines with side dumps and no other exhaust restrictions. Otherwise the supposed gains are lost by a long margin with mufflers and everything else in a normal street exhaust system.

And yes, I overthink everything. Nothing wrong with anyone doing that. I'm a critical thinker. I learn more that way. And it's my job as an engineer.

[68c10owner]

Originally Posted by 68c10owner

But some manifolds, like the ram horn manifolds are pretty decent. You would see a small amount of power increase and maybe some mileage. Not sure the outcome is worth the money in your case.

Originally Posted by storm9c1

"Manifolds are restrictive" -- OK, let's say ramhorns can free flow at 800CFM (just pulling that number out of the air, I'd have to research this to be exact). And let's say the headers you suggest will free flow at 1100CFM. Awesome right? Well stock engines don't push anything close to 800CFM (there are calculators for this online), so neither component will cause restriction at stock engine CFM (since free flow means max throughput without any measurable backpressure). And that CFM is measured at WOT, and nobody drives at WOT 100% of the time.

Sure, some headers may have large CFM gains over stock manifolds. And some manifolds are restrictive from the factory. But there is research out there showing the header gains over ramhorns on a stock engine with a stock exhaust system isn't very significant. Google "ramhorns versus manifolds" and make sure the results are posted with full exhaust systems. Header-only dyno tests are not the same and those with full exhaust.

Some of the marketing hype is dubious because most advertised header dyno tests usually happen with no mufflers or exhaust systems! As soon as you add mufflers and bends and intermediate pipes, you create backpressure, and now any gains, even though small, are nullified no matter which way you look at it.

I know there is more to exhaust systems than CFM (velocity, scavenging, cooling down of gasses, exhaust pulse tuning, etc etc), but for simplicity, I am just talking CFM since the majority of the gains and losses come down to that value.

This is a good discussion but headers just don't belong on a stock-ish engine. You will pay the price in reliability (cracks, leaks, paint burning off, rust-through, etc), heat issues, fitment, and clearances. And my opinion (which is only one man's opinion), is that headers only belong on race engines with side dumps and no other exhaust restrictions. Otherwise the supposed gains are lost by a long margin with mufflers and everything else in a normal street exhaust system.

And yes, I overthink everything. Nothing wrong with anyone doing that. I'm a critical thinker. I learn more that way. And it's my job as an engineer.

Well, I`m just a dumb truck driver but I already addressed the ram horn manifolds.

Headers dont belong on just a race car. Every engine be it stock or modified can benefit from a free flowing exhaust not only in HP gains but mileage gains as well. It`s a proven fact. They are not a direct bolt on. In some cases there is tuning involved after installation. Not everyone has the issues you describe. I installed my first set of headers 23yrs ago and have yet to have any crack or rust out. Even the cheap one. The paint, well I`ll give you that. It sucks.

Bottom line is the OP has to decide what he wants to do. Rams horn manifolds are much better than the standard log manifold and gains would be small but there would be gains. I`ve done my share of exhaust mods on Harleys with stock engines to radical strokers and while they arent the same as a sbc engine the theories are the same and there was always a increase in power until the exhaust became too free flowing. That would not be the case with a set of 1 1/2 or 1 5/8 street headers on a stock engine.

[GRX]

Have had this very same discussion with customers for years. They often spend weeks researching how their air pump takes in air, yet how it escapes is over-thinking. So the biggest set of headers they can find are installed, even for a mild 2-bbl engine, because a manufacture sponsored hot rod mag article said so.

[Grumpy old man]

There is just no drastic benefit to install headers over rams horn exhaust manifolds for the daily street driven truck be it SB or BB the increase is insignificant at best !


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[68c10owner]

Originally Posted by GRX

Have had this very same discussion with customers for years. They often spend weeks researching how their air pump takes in air, yet how it escapes is over-thinking. So the biggest set of headers they can find are installed, even for a mild 2-bbl engine, because a manufacture sponsored hot rod mag article said so.

Are you posting without even reading what I wrote? I think you are getting too hung up on my "over thinking" comment. Never did I say to run the biggest headers you can find. This round and round crap is getting old over here lately. too many "experts" want to argue a meaningless point, which actually proves my point. Carry on folks, enjoy.

[GRX]

> "too many "experts" <

No expert here. Though a few decades machining & building anything from small engines to industrial diesels, and pretty much anything in between including countless v8s, does provide a measure of insight.

[Eddie H.]

I'm not an engineer, or a rocket scientist, but I worked as a mechanic 40 plus years, and have built my share of hot rods. I have ran headers as well as ram horns on SBC Chevys over the years. In theory, I guess headers might offer some performance gains, but honestly, from my experience, I have never been able to tell any difference at all.

[clinebarger]

Headers have their place, On high performance engines. A Good set of Quality Headers cost a minimum of $500....You will never see a return on investment with a stock SBC truck engine.

Have the Ramhorns surfaced, blasted & coated if you want something that looks nice, Dual 2 1/4" pipes with some good mufflers....Enjoy years of maintenance free operation while leaving very little performance gains left on the table with a stock 3/4 ton Truck engine.

[AcampoDave]

.......and besides, ramhorns are just plain cool lookin'. When you route your plug wires out of sight down behind the block like the old 283's, you get an uncluttered view of the motor. My ramhorns are painted with Rustoleum cold galvanizing compound. Strangely enough, it doesn't burn off.

[GRX]

^^ nice looking 283. Always did like that look with the wires tucked under the ramhorns.

[toolboxchev]

Originally Posted by AcampoDave

.......and besides, ramhorns are just plain cool lookin'. When you route your plug wires out of sight down behind the block like the old 283's, you get an uncluttered view of the motor. My ramhorns are painted with Rustoleum cold galvanizing compound. Strangely enough, it doesn't burn off.

Cool motor, looks clean!

[mike16]

if you gotta do something worth braggin about, FI corvette rams horn exausts are 2.5 inch diameter outlets.

repro's are available but are not cheap,

origonals are best left to the resto crowd please

[AcampoDave]

Originally Posted by mike16

if you gotta do something worth braggin about, FI corvette rams horn exausts are 2.5 inch diameter outlets.

repro's are available but are not cheap,

origonals are best left to the resto crowd please

Yeah, I ran a set of those that were imported and cheap (both in price and quality) on a 350 for a while until they cracked after a few years. I think the tru-rams from Speedway Motors are probably what I'd want these days if were were going to go a bit on the more spendy side.
Thanks for the compliments on my ol'283 too guys. It's still running smooth as a sewing machine even after 30 years and a boatload of miles. I treated it to a new timing chain, freezeplugs and an oil pump several years back but it looks like I'll be replacing the rear main soon. What the heck, maybe I'll paint it grey when I do it so it'll look factory correct.