[oldman66gto]

Does anyone know of what advantages the "HO" exhaust manifolds have over "Stock" exhaust manifolds?

I have the 9777646 (left) HO manifolds on my '66 GTO, which has a 428 in it.

I am curious if there is much gain over "stock"?

Thanks in advance for your input & knowledge.

Just an ol man trying to learn

[burd]

Read HPP article, it’s a 2 parter, they do manifolds and exhaust at the track to see what’s best

[oldman66gto]

Originally Posted by burd

Read HPP article, it’s a 2 parter, they do manifolds and exhaust at the track to see what’s best

Sorry, I'm not familiar with the "HPP" article. What are you referring to?
Thanks,

Allan

[Joe-Touring]

Here’s a good read to get your started:

https://www.sdperformance.com/moreTech.php?newsID=39

[b-man]

On a stock or near stock mild engine you gain maybe 8 horsepower switching from standard passenger car log style exhaust manifolds to the streamlined HO / Ram Air exhaust manifolds.

All of the early GTO 389 4-barrel 325 hp (1964) and 335 hp (65-66) engines as well as the Tri-Power GTO 389s (348 hp 1964, 360 hp 65-66) had log exhaust manifolds. It’s not like they didn’t hold their own on the street in factory trim.

So of course the high performance manifolds do offer a performance advantage but on a mostly stock engine you have to be the judge of whether or not spending in the neighborhood of $600 for the manifolds and down pipes to match is worth it to you for 8 horsepower. Of course they look neat but again with some people’s budgets they’re not worth it.

[Scarebird]

Not to mention they weigh twice as much too.

[oldman66gto]

Originally Posted by Joe-Touring

Here’s a good read to get your started:

https://www.sdperformance.com/moreTech.php?newsID=39

Hey Joe,

A great read, and intersting numbers in the comparision.
I wish I knew what cam is in this engine, but it runs so well, & I'm not pulling it apart to find out. I am, however going to enjoy it for what it is, and it "ain't no slug"!

Thanks for the information.

Allan

[tempest1964]

“Sorry, I'm not familiar with the "HPP" article. What are you referring to?”
Thanks,

Allan

Allan,
To answer your question, HPP is High Performance Pontiac magazine. I thought it was a great rag. Plenty of tech and performance articles that were how to and informational. Unfortunately it died a suddden and painful death a few years back.

[burd]

HPP also does a strip day article swapping of a bunch of headers to see increases.

[mrmark1957]

1973 GTO , 406" automatic 3.23 posi setup with stock #13 heads and Summit 2801 cam. The stock exhaust manifolds with 2" full exhaust and AP turbo mufflers ran 15.2 sec @90 mph. Engine done by 4500 rpm. I changed the exhaust over to Ram Air reproduction manifolds with 2.5'' openings and 2.5 inch full exhaust with Dynomax Super Turbo mufflers. Car ran 14.7 @94 mph and pulled right to 5000 rpm shift point. Power speed calculator said engine went from 250 to 285 net horsepower. Driving it has much more throttle response and a nicer sound.

[oldman66gto]

Great information! Thanks for posting!