Cast Exhaust Manifolds (Approximately)

[Orange Crate]

After 57 years my 2.5" stock exhaust manifold cracked. Wow what a shame, these things really woke up my 406 but looked stock. Oh well on to the fix. I ordered a set of 2.5" cast units from Summit. So here are the pics comparing them to what is left of the stock pieces. I have a saying that things made in the Pacific Rim are "approximations" of the real thing. Close but.....these new ones are not going on my truck. First pic is...well yea that happened. Second pic is the "new" high performance? Third pic is the old single exhaust port. One of these things is not like the other.....On this engine I need every square millimeter of flow (No I am not going with headers). Now I am looking at the TruRam set. Anybody have a set of those? I have AC so I think these will interfere with the new Alan Grove brackets I just put on.

[Ziegelsteinfaust]

I got 2 sets of the Dorman ram horns from Summit, and they looked good. With just being rougher then factory versions, but no misaligned ports like yours.

If by true ram horns you mean the polished ones you can get from speedway that look rounded, and swoopy.

I gave my dad a set of those, and they looked very nice to me

[Orange Crate]

Thanks for the input I'll have to call them about the port size/design. I was looking at these as a substitute for the original Corvette manifolds. The obstruction that can be seen in the port isn't misalignment it is how they are cast. The port on the other end is cast the same way and also the other manifold in the set is cast exactly the same. It seems odd that the manifold is a 2.5" high performance unit but with a complete face plant in the port design, again it is an approximation of the real functional high performance piece. The original Corvette manifolds can flow pretty well up to about 4000 rpm which is fine for the way I build my engine to tow. I have an RV cam that is "all in" at 5000 rpm, so there is no need to have big flow numbers above that as you get with headers.

[Orange Crate]

Originally Posted by Ziegelsteinfaust

I got 2 sets of the Dorman ram horns from Summit, and they looked good. With just being rougher then factory versions, but no misaligned ports like yours.

If by true ram horns you mean the polished ones you can get from speedway that look rounded, and swoopy.

I gave my dad a set of those, and they looked very nice to me

Does your Dads truck have AC? Any pictures of the install on that truck?

[Ziegelsteinfaust]

Originally Posted by Orange Crate

Does your Dads truck have AC? Any pictures of the install on that truck?

They were used on hot rods, amd a 50's truck. None of them had fitment issues or had AC.

[AcampoDave]

Wow, those are even worse than the ones I had. Mine had smaller ports than the o.e.m two inchers and they cracked pretty quickly anyhow. I only have a 283 now so I just want back to oem 2". But wow those....what a shame.

[Orange Crate]

A slight update on this issue. I have searched and called just about every vendor of these "reproduction" manifolds and they all seem to have the very restrictive bolt support cast inside the ports EXCEPT one....I called Corvette Central and they have their own molds for the manifolds. But just like everyone else they have casting supply issues which basically means they don't have stock. I did talk to a guy there that actually had a set on his desk for his own car and he confirmed that the ports are correct and open. I'll have to wait until the end of the month for their restock to come in. I'll believe it when I see it.... I decided not to go with the manifolds in the picture above after finding out this info from CC.

[MySons68C20]

If it were me I would braze them up and continue....I have had great success with brazing and feel it would work well for you.

[Orange Crate]

Thanks but, the strength limits of brazing (especially at higher temps) is why I will stay away from that option.

[Orange Crate]

Ok, another update. I received the cast manifolds from CC and I am not impressed. These defects are in both of the manifolds I ordered and in the same place so I am guessing that the mold is the cause, maybe not? The concern is that the porosity will cause cracking during heat cycles. The pick is pointing to the deepest "pit". This area sees the highest temp and gas velocity so probably the absolute worst place for any kind of defects, pitting, porosity. I guess I could look for a foundry in the US that can cast these with better quality? This isn't high technology, casting iron is probably 1000 years old? Why can we not do this in this country anymore?

[cadillac_al]

Maybe send them back as defective and they could send you a better set? They can't all be low quality casting can they? I wouldn't be happy with those either. If CC only has low quality castings then I would look for good used ones on ebay and grind that hump out of them and maybe port them too.

[Orange Crate]

Originally Posted by cadillac_al

Maybe send them back as defective and they could send you a better set? They can't all be low quality casting can they? I wouldn't be happy with those either. If CC only has low quality castings then I would look for good used ones on ebay and grind that hump out of them and maybe port them too.

Yes, I started the process to return them, but they are already out of stock (within a week). I'll have to wait another six weeks to get replacements. I'm guessing that they only cast a very small number of these at a time. I predict that the replacements will be just as bad or worse. There isn't anyone at CC checking the "quality" of these parts, they come in the door from china and ship right back out to customers. Also CC does not care, they said " return them or don't, that's it"

[Willshook]

A few things.

Almost all casting is done outside of the US given the looser regulations.

Are you worried about the casting flaws ending up in failure of the part? I don't see anything in those flaws that would lead to a crack. I wouldn't be worried about anything like exhaust velocity or flow...anything other than a bone stock mild SBC is going to want more scavenging that even the best stock-type casting can deliver.

There are "hot rod" style cast manifolds that are pretty and have better flow - Sanderson and I think Hooker make these.

Finally, obviously there are a ton of these available used...and headers are obviously a choice

[Orange Crate]

Originally Posted by Willshook

A few things.

Almost all casting is done outside of the US given the looser regulations.

Are you worried about the casting flaws ending up in failure of the part? I don't see anything in those flaws that would lead to a crack. I wouldn't be worried about anything like exhaust velocity or flow...anything other than a bone stock mild SBC is going to want more scavenging that even the best stock-type casting can deliver.

There are "hot rod" style cast manifolds that are pretty and have better flow - Sanderson and I think Hooker make these.

Finally, obviously there are a ton of these available used...and headers are obviously a choice

The pictures shown above do not really show the true depth of the porosity. The picture with the pick is pointing to the deepest pit and it is deep. Again I think that this could definitely be a source for cracking during heat cycles. The 406 I built really woke up when I changed over to the 2.5" outlet manifolds from the stock 2" so I know that flow for this engine is critical to getting the most out of it. I had port matched the 2.5" manifolds before installing them. The Dart heads will flow a lot more but I like a stock look so....Again, not doing headers....

[Dead Parrot]

I put a set of these: https://www.holley.com/products/exha.../parts/8525HKR

on my mostly stock 350 when swapping away from headers. So far working fine about 18 months later. Don't know how well they compare performance wise to your former set of rams horns.

They also come in ceramic coated but the recommended break in process was not friendly with a 30 mile drive home from the exhaust shop.

[Orange Crate]

Originally Posted by Dead Parrot

I put a set of these: https://www.holley.com/products/exha.../parts/8525HKR

on my mostly stock 350 when swapping away from headers. So far working fine about 18 months later. Don't know how well they compare performance wise to your former set of rams horns.

They also come in ceramic coated but the recommended break in process was not friendly with a 30 mile drive home from the exhaust shop.

Thanks. I need center dump...I bit the bullet and ordered one exact reproduction (read expensive) manifold cast in the USA. I still have one original on the left side. So the cost of one exact reproduction is a little more than the two cheap china crap ones. I was thinking that I could have one as a spare. BUT I have to wait until mid January for the next batch. Sometimes it seems like nothing is easy.....

[dagnabbitt]

Originally Posted by Dead Parrot

I put a set of these: https://www.holley.com/products/exha.../parts/8525HKR

on my mostly stock 350 when swapping away from headers. So far working fine about 18 months later. Don't know how well they compare performance wise to your former set of rams horns.

They also come in ceramic coated but the recommended break in process was not friendly with a 30 mile drive home from the exhaust shop.

Those are really cool, especially for a truck where center dump is not an option.

[Orange Crate]

OK, so I changed my mind. I'm going to TIG braze the cracked piece. All this messing around with really really poor quality parts has put a bee in my bonnet! I still have the very expensive manifold on order, but it won't even be cast until the end of Dec. I need to get back to tuning my FI so I ordered brazing rods from Muggy Weld (https://www.muggyweld.com/product/72-electrode/). I did a bunch more reading on brazing and talked to their tech guy and it sounds like this might work? Anyhoo stay tuned for the next exciting chapter of " I can't believe people actually put that crap on their trucks" Seriously, who says " I don't care about quality or performance"? When I get the new piece I'll have a spare.

[dagnabbitt]

Sounds like fun! Don't forget to post some pics!

[Accelo]

There are a lot of used ones around. GM even sold them for a long time. They were also installed on many Corvettes. And yes, with Air-conditioning. A 1965 365HP 327 could be had with AIR.
Search for 3797901 and 3797902 or your casting number.

https://www.ebay.com/sch/i.html?_fro...7901&_osacat=0

[LS short box]

Don't know if this would work for you but maybe better than brazing would stick welding with nickel rod?
On a few of my hod rod project with GM rear ends I have the axle tubes which are mild steel welded to the cast iron center section for added strength.
I am far from a good welder so I take it to a local "pro" welding shop. As I understand to weld cast iron correctly the area to be welded has to be warmed up first. They use a torch. Then they weld using nickel rod and then wrap the welded area in insulation for a very slow cooling down.
Looking at your cracked manifold I'm guessing they would drill holes at each end of the crack. Then "V" out the crack with a grinding disc. After pre heating weld.
Just my .02.

[Orange Crate]

Originally Posted by LS short box

Don't know if this would work for you but maybe better than brazing would stick welding with nickel rod?
On a few of my hod rod project with GM rear ends I have the axle tubes which are mild steel welded to the cast iron center section for added strength.
I am far from a good welder so I take it to a local "pro" welding shop. As I understand to weld cast iron correctly the area to be welded has to be warmed up first. They use a torch. Then they weld using nickel rod and then wrap the welded area in insulation for a very slow cooling down.
Looking at your cracked manifold I'm guessing they would drill holes at each end of the crack. Then "V" out the crack with a grinding disc. After pre heating weld.
Just my .02.

That would be a great repair if I knew it would last. These manifolds are thin in the area that cracked and I just don't think melting the base metal will hold up. With brazing you don't melt the base material.

[4u2nv]

I'm real close to buying this 350 with the rams on it , I don't know if they are aftermarket or not , do these give just as good of performance as headers ??

[Willshook]

Originally Posted by 4u2nv

I'm real close to buying this 350 with the rams on it , I don't know if they are aftermarket or not , do these give just as good of performance as headers ??

The impact of headers is directly proportional to the power level of the engine and the exhaust system behind them.

So if the engine is making less than about .6 HP/CID then there's some impact; more than that then the impact increases significantly.

If you've got a 1" y'd exhaust behind the headers, then again - not much gain. if you've got 2-1/2" duals behind it, then definitely more.

TANSTAAFL

[dagnabbitt]

Originally Posted by 4u2nv

I'm real close to buying this 350 with the rams on it , I don't know if they are aftermarket or not , do these give just as good of performance as headers ??

I think that they do. Someone on here did an airflow calculation that indicated that of all the ram horns they made, the 2.5" Corvette ones are the only ones that actually are as good as having headers. That's all I needed to hear: I hate constantly messing with headers.

I have them with 2.5" pipes and mufflers, as the above poster notes, that helps. No restrictions from header to tailpipe.