Header & heat shield

[Tru-Craft]

I'm building a big valve head per Bob's design, 1.82/1.50 Chevy valves, solid lifter cam and Roller rockers. This will go on my 265 chevy piston Opel block.
While waiting for a bunch of parts from OGTS, I wanted to look at the header design.
I have an old Pace-Setter header 4 into 1 design and 2" exhaust.
Is this header any good for this big valve head, with a 38 DGAS?
What other exhaust header options would be better?

Also I was thinking of making a heat shield that would cover the #2 & #3 header tubes and run under the intake manifold. It would be made to keep an air gap of about a 1/2" from the tubes, to help keep heat away from the intake manifold.
Made out of 1/16 AL or SS?
It would bolt on with the header bolts.
Any thoughts about this?
Lyle

[davegt27]

I have an old Pacesetter header 4 into 1 design and 2" exhaust.
Is this header any good for this big valve head


yep better then nothing


Davegt27

[jeff denton]

While researching how late intake valve closing can supercharge the cylinder, an interesting site also went into the latest rage in "step headers". The first section of tubing is the smallest, next section is a step bigger, third is another step bigger going into the collector. Looked kind of neat, the theory sounds plausible... I'm glad you brought this up, let's all think on this.
My pacesetter (came on the junk car that became Speedway GT) really looked like a decent design, I kind of refabbed the collector flange bigger and wrapped it in header wrap. The new Jet Hot coating seems to be the new rage in header finish/heat retention. I went 2-1/2' all the way, from the collector it curves up through the corner of the floor/tunnel into the passenger floor area, into a Flowmaster, then comes back a bit and out the body between the door jamb and rear tire. A rather short, fat system, wrapped all the way in header wrap. Looks good, if I must say so myself. But don't do this on a street car...
I'm into trying to keep heat where it belongs, and away from things like intake manifolds. One thing I did was cut off all that excess material off the bottom of the intake, that whole big area that used to mate up to the original exhaust manifold. There's a lot of grinding to do! That left room for an air gap, some fancy (expensive) space age reflective material was then formed over the top of the wrapped header in the area of the intake. It looked cool, must be cool too, huh? Couldn't hurt. I, too thought a metal shield here would be a good idea, but it hasn't happened yet. Go ahead and make a prototype for me to copy!! I wonder if aluminum would be OK for this. I have lots of scrap highway signs, sometimes the bullet holes in them fit the project.... If you want to go SS, a neat place to get scraps is a bus company. One I know changes out dinged panels all the time, they had a pile of 'em last time I visited. Some have nice curves, ribs rolled in, even louvers sometimes. Neat scrap...

[GTJIM]

On a street engine the 4 into 2 into 1 header is arguably more "useful" as it is not quite so subject to power peaks and tends to give a smoother and wider torque curve than the 4 into 1 "regular racing" four tube header that looks like one side of a V8 header system.

Oh! With a "sprint" exhaust manifold that is exactly what Opel designed for their "Hi-perf" street motors ........ even the original Heat-box exhaust manifold is designed to that principle.

So a good "tri-y" or 4-2-1 system is a good bet for the street when designed for the application. The length of the first four pipes can be tuned for top end the next pair of pipes for the lower mid-range and the collector & tail pipe be big enough to be "free-flow" and long enough to enhance the low end torque. Opel knows!

The "racing" 4 into 1 is best for tuning to a narrow rev range and suits a car which predominantly runs in the particular rev range - that is how I see it!

[GTJIM]

Originally Posted by jeff denton While researching how late intake valve closing can supercharge the cylinder, an interesting site also went into the latest rage in "step headers". The first section of tubing is the smallest, next section is a step bigger, third is another step bigger going into the collector. Looked kind of neat, the theory sounds plausible... I'm glad you brought this up, let's all think on this.

Saw another, similar, set-up which had a smaller diameter "stub" leading from the exhaust flange and out about 2" or 3" This was surrounded by a larger pipe which was concentric with it - sort of one inside the other! The larger pipe carried on into the header and the whole thing just looked like a "large bore" header system as the "stub" was concealed by the bigger tube ..... more thinking!

[jeff denton]

Oh, yeah, the anti-reversion header! That was a very short-lived fad years ago. Its theory was covered in Hot Rod Mag once, I can't say I've ever actually seen one. I wonder what happened to that idea?

[soybean]

Originally Posted by Tru-Craft Also I was thinking of making a heat shield that would cover the #2 & #3 header tubes and run under the intake manifold. It would be made to keep an air gap of about a 1/2" from the tubes, to help keep heat away from the intake manifold. Made out of 1/16 AL or SS? It would bolt on with the header bolts. Any thoughts about this? Lyle

What about sandwiching some gasket material between the AL or SS using pop rivets, then bolting it on with the header bolts? Jarrell

[GTJIM]

A nice bit of formed stainless sheet with "surplus" ceramic heat resisting tiles stuck on might be real trick! I think you have the technology at Cape Kennedy!
Just watch it on re-entry though .........

[hrcollinsjr]

I didn't notice what kind of intake manifold you are using, but the problems I had with the two Pacesetter headers that I've installed was clearance between the front pipe and the intake. I just don't think you have a whole lot of room for a heat shield. I had a sprint manifold coated with a heat retaining coating and plan to have a intake manifold coated with a heat barrier type of coating. I don't know how effective they are but what the heck it's only money.

Harold

[Tru-Craft]

Thanks for the responses. So a 4-2-1 header is better, for a broad power band! With my modified motor, head, carb, modified intake manifold, hot cam, combination, it should produce power from about 2,800-6,500rpm. Will the 4-1be better?
Gil is working on a header for the GT again! Maybe we should put our 2 cents in on a group design!!
I will make a cardboard pattern up for the header heat shield tonight.
I'm not as concerned about the #1 & #4 header tubes, they are pretty far away from the intake manifold. What should I use for extra insulation?
Header tape?

Any ideas?

[spdkilz02]

does anyone have a pic of the step design header?

[spdkilz02]

what would be the ideal sizes to use for the header...the car would have a 2 1/4" exhaust pipe on it.

[Tru-Craft]

Jeff, I have lots of AL & SS steel sheet scraps laying around. Will play with a design tomorrow, I'm slow at work!
I think the air gap and a way to get the heat out and around the manifold is the key!
I had a thought! What about coating the bottom of the heat shield and manifold with the ceramic clay used for pottery?
Would it stick?
Could it be fired on the S.S?
Its cheap at least!

[GTJIM]

Originally Posted by spdkilz02 what would be the ideal sizes to use for the header...the car would have a 2 1/4" exhaust pipe on it.

The "ideal" size depends upon many variables: cylinder size; cam overlap & duration; compression ratio; valve size; type of porting; etc. etc. etc.
So there in no easily available "ideal"

What is available may be a better question:

1) Stock "intake stove" exhaust manifold - with 1 3/8" to 1 5/8 secondary pipes; a 2" system withRally Bobs recommended 2 1/2" loop up over the diff.
This is least effort and least expense with remarkably good results.

2) Early "Sprint" exhaust replacing the stock manifold - all else the same.
A bolt on upgrade that gives results

3) Later European fuel injection exhaust - bigger flange and secondary pipes.
Good for larger capacity motors 2.0L - 2.2L

4) "nobody's" maliable iron tube replacement for the cast iron "Sprint" manifold
Better flow ? Can be made so sould be available.

5)Aftermarket 4-1 tube header Not all created equal see some posts with search!

6) Tri-y or 4-2-1 basically an enhanced copy of the standard "Sprint"

7) Custom 4-1 tubing header

Up to you and your wallet to decide what is most appropriate for you ...

A couple if interesting bits attached:

http://headerdesign.com/extras/examples.asp

[RallyBob]

Originally Posted by Tru-Craft Thanks for the responses. So a 4-2-1 header is better, for a broad power band! With my modified motor, head, carb, modified intake manifold, hot cam, combination, it should produce power from about 2,800-6,500rpm. Will the 4-1be better? Gil is working on a header for the GT again! Maybe we should put our 2 cents in on a group design!! I will make a cardboard pattern up for the header heat shield tonight. I'm not as concerned about the #1 & #4 header tubes, they are pretty far away from the intake manifold. What should I use for extra insulation? Header tape? Any ideas?

FWIW, I've had better results with 4-1 designs. They just have to be properly sized for your engine.

4-2-1 designs are not necessarily better for our engines regardless of the general consensus out there, BUT, they are more forgiveable in terms of choosing tubing diameter and length so they are generally thought to be 'better'. In other words, if you get the 4-2-1 design 'wrong', it won't hurt power as much as getting the 4-1 design wrong.

So there is no 'catch-all' 4-1 design for all CIH Opels. A 1.9 street engine with 6300 rpm redline will need a very different design from a hot 2.2 street engine with a 7000 rpm redline. My 2 cents....

Bob

[spdkilz02]

interesting...ill have to get the motor done and take it to a well known exhaust guy around me and see if he cant come up with something that would be best suited for my application...

[Paul]

The most common mistake all but a few of the best header designers make... the primary tubes and collector are too large in OD.

For a stock 1.9 up to about 125 or so HP the primary and collector need to stay fairly small. Bigger is not always better. Too big hurts gas flow, wave propagation and really kills torque. Even the tubes on the Pacesetter 1.5" primary and 2.5" collector are too big.

Primary tube lengths will vary based upon peak torque RPM.

[spdkilz02]

see i was thinking about 1.5" tubing for the header, and then into a 2" collector, with a 2.25" exhaust on the car...but my manta is going to have a 2.0 with bigger valves, ported head, DSD, and the 2.0 pistons....so that size should be about just right for it i think...

[GTJIM]

Make those sizes the Outside diameter of the pipes ....... remember that a 2.0 is LESS than half the size of a 305 Chevy! Have a look at the headers used for them on the street - that should give you a fair idea. Good Luck~

[jeff denton]

That's exactly how we looked at it. The pacesetter header pipes were the same size as the ones on our old hobby stock car w/ 302 engine, so figured they were plenty big. To need anything bigger you'd have to build a really good breathing engine and turn it really fast... Which is always the goal but you have to be realistic!

[tekenaar]

Originally Posted by GTJIM The "ideal" size depends upon many variables: cylinder size; cam overlap & duration; compression ratio; valve size; type of porting; etc. etc. etc. So there in no easily available "ideal" What is available may be a better question: 1) Stock "intake stove" exhaust manifold - with 1 3/8" to 1 5/8 secondary pipes; a 2" system with Rally Bobs recommended 2 1/2" loop up over the diff. This is least effort and least expense with remarkably good results. 2) Early "Sprint" exhaust replacing the stock manifold - all else the same. A bolt on upgrade that gives results 3) Later European fuel injection exhaust - bigger flange and secondary pipes. Good for larger capacity motors 2.0L - 2.2L 4) "nobody's" maliable iron tube replacement for the cast iron "Sprint" manifold Better flow ? Can be made so sould be available. 5)Aftermarket 4-1 tube header Not all created equal see some posts with search! 6) Tri-y or 4-2-1 basically an enhanced copy of the standard "Sprint" 7) Custom 4-1 tubing header Up to you and your wallet to decide what is most appropriate for you ... A couple if interesting bits attached: http://headerdesign.com/extras/examples.asp

While true that the later 'Sprint' manifold has a bigger flange, the exhaust ports at the flange are NO LARGER!! than the '75 'Sprint' manifold! The exhaust holes in the matching late gasket ARE larger, but I've always wondered why the late 'Sprint' flange ports were not enlarged to match the gasket.

Trust me, they are the same size, stock, as the '75s.

[tekenaar]

BTW, while we're on the subject of heatshields, the later FI CIH engines, both 4- and 6-cylinder types, had heatshields from the factory. Before I bought my Bitter, I didn't know that. My Bitter has the factory heatshield, bought and installed it after the fact, and I fabricated one from a Honda 4-cylinder for the '75 Sprint manifold on my 2.4 engine.

Living in Texas, I've become a real proponent of heat shields, especially on 'non-crossflow head' engines like our CIHs.

[spdkilz02]

Otto, that looks really clean on the 2.4 with the honda heatshield...makes it look like its supposed to be there...

[tekenaar]

Originally Posted by spdkilz02 Otto, that looks really clean on the 2.4 with the honda heatshield...makes it look like its supposed to be there...

That's exactly what I strive for when I fabricate . . . "How would the factory have done it?!"

[spdkilz02]

heck if i know...they prolly should have had u there for you to show them the way...the things you do to some of the opels looks so much better then what they did to them in the factory...