This is not a Corvette question but there's a wealth of experience here so I thought I'd ask.

I have a 68 Cutlass with a Ramjet 350 crate engine and a Tremec TKO 600 5 speed. This car has what look like standard 5.7 Vortec manifolds and a dual 2.5" stainless exhaust with Borla mufflers, no H pipe. I noted that the RJ350 installation guide mentions that all their development was done with headers and a crossover pipe - 1.75" long tube w/3" collectors. I know that mild 350 would most likely fall on it's face with them on it. The only reason I am even looking at exhaust options is a longer story regarding tuning but my intent over the winter is to swap out that GM MEFI 4a with a Terminator X and I just thought is there were a simple solution to help it breathe a little better I should look into it.

Not so simple. I even spoke with Hedman this morning and they had no good options for me which should be giving me a big hint. The only thing I found that has the right fit are Hooker Small Block Chevrolet Exhaust Manifolds Part # 8525HKR and those look like they wouldn't be much different from what I have if at all. You can see the difference between the two - the driver side exits straight down under #5 and #7 where the passenger side exits at a 45 degree angle behind #8.

A couple questiona I have are - any experience with those Hookers ? Think it's worth bothering with an H pipe ?

At any rate, here's what I have. The casting # says 5013 730 425 but I can't find that referenced anywhere. Look up an exhaust manifold for a '98 GMC 1500 and bingo - for a 5.7 Vortec they look the same.

Any comments or ideas appreciated. Maybe somebody has dealt with this. Thanks

 

I would think Chevelle headers would be fine. Why not?

 

Another option would be to take the exhaust manifolds off and send them to a company who does Ceramic Coating as a business. They sand blast them as part of the preparation before applying the coating material and then make them whatever color you want them. A Nice Black Ceramic coating might look good on that engine. The best part is the Ceramic Coatings really do reduce the temperature of the engine compartment.

Your exhaust system looks like it is in a fairly tight area and squeezing a set of headers would be a tight job. Your exhaust manifolds look like they flow enough to keep up with the job. Headers in tight spaces is a frequent cause of Corvette Fires. A steel bodied car might let you squeeze them in with tighter tolerances.

This will make the exhaust manifolds look better and last longer as they coat the outside of the pipe and then the inside as well before curing the material. I have Hedman Long tube headers and they looked so nice when new. The headers and the silver ceramic coating are now more than 20 years old and look it. The headers are in great shape and were very well made. The ceramic coatings failed soon after being put on my high compression 427. The top few inches burned the coating off on the inside of the pipe. There is a section of the pipes used in the headers where from the exhaust burned the pipe near the same spot on all 8 pipes. I will have my next set of headers coated by a company who offers different Ceramic Coatings Temperature levels. They make a material that is used on NASCAR and can handle the higher temperatures of a high compression engine. I was quoted prices in the $200-300 for coating my headers with the higher temperature rated ceramic coatings a couple years back.

 

If I read your post correctly you said your engine would "fall on its face" with headers. I would doubt that. even with the 1.75" primarys. I would bet it will run better. maybe not enough to justify the cost but it should be better with headers that without.
Pat

 

pigfarmer
On my 68 with a RamJet 350 I put 64-65 downpipes and 2.5" Smoothies from Speedway. Doesn't seem like your frame construction would allow that perhaps you can search for some rear exit 2.5" manifolds? I also swapped out the MEFI but I went to the EZ-EFI 2.0 retrofit kit for TPI engines.
https://www.corvetteforum.com/forums...post1598237479

 

The ceramic coating is an excellent suggestion I had not thought of - thanks ! That sounds pretty good to me - functional and aesthetic. Those rusty logs look like crap and I am certain there are a couple of local places that could do that for me. I'll look into the Holley manifolds a little more as they look awfully close to what I have- it might be more cost effective.

Hedman did suggest a pair of 68290 long tube headers and said they'd likely fit but that I'd have clearance issues for the plug on #5. They also suggested a pair of shorties but like the ram's horns that center dump is problematic right over the cross member.

If I'm looking at block huggers/shorties then any gains over the manifolds are minimal. I'd prefer to avoid the hassle of installing LT headers with fitment and clearance issues because I doubt this mild 350 is going to see any great benefit that's worth the effort. Hedman agreed with that. This is my nice weather daily driver, the exhaust is tucked up very neatly and sounds great as is.

 

Post #40 from that thread was very interesting: Dyno results - headers vs rams horn manifolds

I watched an old Engine Masters Episode with similar results: They make a good case for manifolds for mild builds.

It's a long story but this all started not because I was looking to make more power or noise I was just curious about the tune and then found that note in the RJ350 installation guide. If it were straightforward to drop in a simple set of headers I probably would but it doesn't seem to be.

I am not familiar with that EZ-EFI but will take a look, always nice to look at options. I did look into 0411 ECMs but that does not look like the way I want to go. Holley is pricey but it is something that is current and supported.

Didn't go looking for an Olds or a Ramjet, I spent about two years looking for a driveway beater project in a hundred mile radius, then one day I tripped over this thing virtually in my back yard. It's in the garage not the driveway - too shiny

 

How about sending the manifolds out to "Extrude Hone", to get them opened up, a little, then get them coated?

 

pigfarmer
You made me curious. Check out these 2.5" sbc REAR-EXIT manifolds..... seems like the Circa-1984 SBC Blazer used rear exit manifolds... if you want to do more searches.
I went to ramhorns after 30-some years of headers. I'm quite happy with that decision since not really doing anything but cruising and they're tight.
Those are so relatively inexpensive that if you cannot find them coated you could check into that.

https://www.speedwaymotors.com/Hooke...SABEgKYtPD_BwE

 

I did have a look at Extrude Hone but that's pricey, it would probably be about $800 and their website actually tells you to look into headers for that reason Having the existing manifolds blasted & ceramic coated is about $200 and I like that, so says the nice lady on the phone.

@carriljc I did see something like those already coated from Hooker https://www.holley.com/products/exha...arts/8525-3HKR They are very similar to the existing manifolds but would still require some fitting & welding. Definitely an option on the table.

I found a family owned custom exhaust shop not too far from here - THAT was a surprise. Finding one of those nearby anymore is like looking for Bigfoot and last time I did that Ronald Reagan was the President. At a minimum I could have that H pipe I also want done and have an annoying slight leak fixed. I'll take a ride down there in the next few days and see what they have to say.

 

pigfarmer
I like those.
I'm glad I went with the coated smoothies on mine. They still look good almost 7 years later and have not had any leakage problems.
If those are 2.5" and your existing exhaust is 2" it might be worth swapping? Is the rest of your exhaust 2.5"

 

Many, but Not all shops have capability to make "Mandrel-Bent" curves. If you're not familiar with mandrel-bent versus the alternative, suggest look around web pics. Most will choose mandrel-bent.

 

The exhaust is 2.5" s/s.

I will have info with me on those smoothie manifolds as well as the Hedman 68290 and 68390 when I go speak to these guys, just because. If they make them I'll have to figure out how to finish them.

I have no objection to headers as long as they don't create fitment or ground clearance issues, or even those manifolds really if they are a more practical option. In some fashion I'll improve what's there and get it breathing a little better before I get into the EFI management.

 

Just. Put headers on it and be done with it. It's your best option. Millions of sets have been put on cars so it Can be done.

 

Looks far from a driveway beater project! Nice looking Olds ya got there!

 

I didn't realize that the Extrude-Hone process was that expensive!

 

As others have noted I think SB Chevelle Headers would fit. It is the same chassis.
With that said, a ramjet 350 does have vortec heads , which flow even better than stock 70s ones, so the cam must be even milder than a 350HP L46 cam.
Yes it is only 196/205" duration @ .050"
That duration is virtually identical to the old mild L48 cam. But this is a hydr roller with more lift.
Mild duration cams do not add much horsepower with headers, there just is not enough overlap for headers to help much.
They would not hurt, but the installation issues just make it a pain-but-no-gain situation.
So why bother?

Ceramic coat the stock manifolds and it will look great.
Or get some of the short block hugger headers.
They are short tubes not long tubes, but tube length is irrelevant in your situation.
The smoother bends may help HP a couple, and they look good!

 

Chevelle headers will fit. Anything with vortex heads leaves substantial horsepower and torque on the table . Perhaps the most overrated heads you can get.
And now the vortex guys will go crazy. The only thing they provide is a small combustion chamber. They have tiny valves you need to modify them to handle even a small cam. I don't know why they became popular. Flame on.

 

improved port Velocity.

 

Velocity means Little without flow.