Team Camaro Tech banner
Cancel
Create thread New Garage Forums

Exhaust crossover, Hurt head flow?

Jump to Latest
1 - 15 of 15 Posts
C

cody

· Registered
Joined
·
925 Posts
Discussion starter · #1 ·
I am thinking about purchasing some Big Block chevy edelbrock aluminum oval port heads, they make a performer, and a performer rpm. The difference is that the rpm doesn't have the crossover funcitonal, Now they are both 110cc combustion chambers. To get my desired 10.5-1 compression, i need a version that they make, which is an 1 1/2 angle rolled head, that reduces the chamber cc to 100cc which is perfect for the pistons that i have, the draw back is that you can only get the angle milled 100cc head in the performer version, which has the hole in the exhaust port for the exhaust crossover. Now i am using the air gap manifold which has the blocked crossover, but my question is, won't the hole in the exhaust port mess up the flow of the gases, and make the gases get caught in sort of a whirlpool in the hole (for the crossover)?? I want to get the most power out of this engine, i am thinking of buying these heads and getting the holes welded closed, because i am going to have them ported so they will be apart anway. Any opinions?

------------------
http://www.geocities.com/codybouc/firebirdpage.html
 
Save
Reply Quote Like Like
Discussion starter · #3 ·
Save
Reply Quote Like Like
#4 ·
A lot of people make a big deal of flow bench numbers when it's actually air velocity through the port that counts. Here's a link to the Reher Morrison tech page. http://www.rehermorrison.com/techTalk/

Check out article #16 "Flow Bench Fallacies" you'll get a better understanding on how port shapes are more important than flow numbers. This should answer your question.
George
 
#5 ·
Is the x-over hole in the E-brock heads cast in place or drilled??

I ask b/c my W/P's cast-iron Merlin ovals is cast closed with a centerpunch divet so that we can use a drill to open it up for use if wanted.

I bet that it is drilled so then you probably can just plug the hole with either a hex plug or short, small headed bolt back in the far reaches of the port.

I HAVE NEVER SEEN THE HEADS SO MAY BE WAYYYY OFF HERE!!! pdq67
 
Discussion starter · #7 ·
Yeah, but how well does the exhaust actually flow out of the head, with a big old hole in the port, that has to hurt the performance, i just can't see how a big hole in the port could barely affect how well the exhaust flows out of the head

------------------
http://www.geocities.com/codybouc/firebirdpage.html
 
Save
Reply Quote Like Like
#8 ·
The crossover port is an emission item. The exhaust gases flow through those ports, through the intake manifold, heating the intake manifold to improve vaporization which reduces emissions. It's not a threaded hole. Many people block them off in order to keep the intake manifold cooler, improving horsepower. These ports have nothing to do with intake and exhaust port flow to the combustion chamber. As the other guy said, if you put the rpm manifold on, fugetabowdit, you'll have a built in block off plate.
May I digress: When researching edelbrock heads for my '79 Camaro (355 cid), the edelbrock folks told me the only difference between the performer and the performer rpm heads were that the rpm heads didn't have the exhaust crossover which is why they are not street legal. So I bought the performer heads and blocked off the crossover. An added bonus was that that made my exhaust sound just a little bit rougher...and I like that!

------------------
2000 Corvette hardtop black, 6 speed, Halltech Tric cold air intake w/nylon MAF ends, Corsa Touring cat back exhaust w/pro tips, Taylor wires, 1/4 mile: 12.918 @ 111.29 mph on stock EMT's 330 rwhp, 342 rwt on MTI's dyno, 3075 lbs

79 Camaro 355 CID, Edelbrock intake, Edelbrock 600 cfm carb, Edelbrock performer 64 cc alum cyl heads, comp cams extreme energy 262 cam, erson roller rockers, hooker headers, Mallory Comp 9000, 3.42 posi, 700R4 rebuilt w/ B&M kit, 2400 stall converter w/ TCI lockup kit

67 Camaro, 327 w/ a 'glide , waiting on "funding"

[This message has been edited by need-for-speed (edited 01-26-2003).]
 
Save
Reply Quote Like Like
Discussion starter · #9 ·
No offense, but i am aware of all that info, also i don't see how it would change the way your exhaust would sound. another thing is that your exhaust goes out of the chamber not into it, but i still don't see how a hole in the port doesn't disrupt the flow of the exhaust, plus wouldn't there still be exhaust in the passage way inside the head, where the crossover is????????? I am seriously thinking of having it welded closed before i have them ported.

------------------
http://www.geocities.com/codybouc/firebirdpage.html
 
Save
Reply Quote Like Like
#10 ·
Cody
Yes the openings in the port will cause some turbulence. Just how much I don't know. The symetrical bowtie heads that are used on prostocks have two head bolt holes that go through the intake ports. They put the head bolt in then screw in a plug at the top of the intake runner. They do this to get all the intake runners equal in length. The disruption in the flow is said to be negligible. I have heard of people melting down cast pistons in a cast iron skillet and filling these chambers on iron heads. However I wouldn't try this on an aluminum head. You might stand to gain a few HP filling these up but I don't think it's worth all the effort on a street driven car JMO. Good Luck George
 
#11 ·
Blocking the stock crossover passage does change the sound of the exhaust. Blocking the passage gives the car a "raspier" sound. I have heard this (complaints)from guys with restored early vettes equipped with stock dual exhaust that have blocked the passage. The mellowing effect from the stock crossover in the underside of the intake is similar to the mellowing effect from an "H" pipe in a typical aftermarket performance exhaust/header setup.

-Mark.
 
#12 ·
I think the turbulence created by the crossover passage would be minimal because of the way gasses flow through the port. When going "around a bend" gasses tend to stick to the inside of the curve (the port floor). At least that is the way it works on the intake side. Since the hole is on the outside of the bend I don't think it would have much effect.

Also, when the passage is a "dead end" the passage just builds up to the same pressure as the rest of the port and stays there because there isn't any flow. Even if the passage was open to the intake, I think at higher RPMs the velocity of the gasses going through the port would be so high that I think it would "ignore" the crossover anyway. (kind of like an X pipe at high rpm, the exhaust just shoots right by and it has no real effect)

Just my opinion.
 
Discussion starter · #14 ·
Save
Reply Quote Like Like
#15 ·
pdq, my bad, I was reading too fast

Cody, no offense taken. My thinking is that since the crossover would be deadheaded by your RPM manifold, they're would be no flow but I see your point about exhaust gases flowing past an open hole, not a smooth surface.
As stingr69 said, the crossover acts as a mini H-pipe and since my '79 doesn't have a crossover in the exhaust system, blocking off the crossover in the intake completely eliminated all exhaust crossover...I like the choppy sound.
 
Save
Reply Quote Like Like
1 - 15 of 15 Posts
About this Discussion
14 Replies
6 Participants
Last post:
need-for-speed
Team Camaro Tech
posts
2.4M
members
90K
Since
1998
A forum community dedicated to 1st generation Chevy Camaros owners and enthusiasts. Come join the discussion about performance, builds, restoration, modifications, classifieds, troubleshooting, reviews, and more!
Full Forum Listing
Explore Our Forums
Bench Racing Engine Body Shop Performance Brakes, Suspension & Steering