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Old 01-05-2009, 07:22 PM
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SBC cast iron Exhaust manifold performance

I am trying to decide which cast iron exhaust manifold to run with my sbc 330hp crate motor in my 49 Ford pickup set up with a Jag xj6 IFS. After trying essentially every available header set (none will fit on the drivers side), I come down to a choice between the 2" curved dump rams horn (straight dump will not fit therefore no 2 1/2" rams horn), the under the plug log style or the over the plug log style. Does anyone have data or comparison performance info on these different manifolds? Since the truck is being setup to tow a car trailer, mid range torque is really more important than high rpm hp. I understand that I could custom build headers but that is more effort than I want to expend on exhaust.

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Last edited by 49willard; 01-05-2009 at 08:02 PM.
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Old 01-05-2009, 07:52 PM
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The 2" rams horn style will probably be your best bet, unless shorty headers are out of the question.



Larry
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Old 01-05-2009, 08:44 PM
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well the best performing mid range stock manifolds i have found to use is the up sweped center dupscause any time you get a manifold that goes up right off the head is going to be a peformance gain. so i would try to find some late camaro or firebird manifolds tha have the up swept center dumps. i say use center dumps because you get better scavanging of the cylinders which will icrease your torque curve in the mid and higher rpm. the center dumps are more tuned then using a back dump also. rule of humb is you want to have all your exaust runners to be as close to the same length as possible for best back pressure scavanging of the motor.

Last edited by talon0713; 01-05-2009 at 08:46 PM. Reason: typo...
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Old 01-05-2009, 09:33 PM
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According to Randy Brzezinski of Brzezinski Racing Products, the nest best thing to Corvette Ram's-Horn manifolds are late '60's under-the-plug log-style manifolds. They have larger runners than more recent manifolds.

Brzezinski sells modified manifolds. David Vizard confirms in his book, How to Build Max Performance Small Block Chevy Engines on a Budget, that Brzezinski modified manifolds achieved about 65% of the performance gains of headers on his dyno. Vizard couldn't duplicate that but says he was able to approach it with just basic porting. Matching the manifold ports to the gasket & opening up the outlet about .125" to .25." Naturally, you can't reach very far into the manifold, but if you smooth out what you can reach you can make gains. Vizard says his porting was worth on average about 15hp on an engine like your 330hp crate engine, with some seeing as much as a 22hp gain.

Brzezinski's site at http://www.castheads.com/index.php has prices, dyno charts, and exhaust manifold FAQs if you'd like to check it out.

Last edited by BinderDriver; 01-05-2009 at 09:50 PM. Reason: Spelling
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Old 01-06-2009, 02:22 AM
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I actualy prefer the under the plug manifolds simply because the others are a PITA to keep your plug wires from getting burned. I also think that with a bit of die grinder work that they would work about as good as any rams horns.
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Old 01-06-2009, 11:55 AM
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Get something that fits and EXTRUDEHONE it.

Sanderson probably makes something. This is a common installation.
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Old 01-06-2009, 09:27 PM
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These are cheap enough to still afford extrude honing.
http://cgi.ebay.com/ebaymotors/CHEVY...mZ330298465397

These are nice but probably wont fit.
http://www.speedwaymotors.com/SandB-...olds,5425.html

http://www.speedwaymotors.com/SandB-...olds,3823.html
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Old 01-06-2009, 10:42 PM
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The curved rams horn as on the ebay listing is what I currently have mounted on the motor in the chassis and it fits. A straight down rams horn dump will not worK such that the other two selections unfortunately would not fit either. It is interesting that a company in Texas that has done chevy in XJ6 transplants for many years can use (but it is very tight per a conversation with them) the straight down rams horn. I have not been able to see their installation but I suspect that the motor in the XJ6 sits just a bit further back than it does in my F-1 and I am as far back as I can go without cutting into the firewall which I have chosen not to do.
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Old 01-06-2009, 11:29 PM
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If the Chevy II manifolds fit, why don't you just stick with them? Randy Brzezinski doesn't rate them very highly for his purposes, but then his purposes revolve around selling stock-appearing parts that'll give a circle track racer an edge and still slip by a tech inspector. On the other hand, it doesn't sound like you're overly concerned with squeezing every last bit of HP out of your motor. So use 'em as is. If you feel like putting in a couple of hours of effort, just open the manifold ports to match the gaskets, grind the floor of the port down to form an anti-reversion dam, open up the outlets, and smooth & blend everything into the manifolds as far as you can. That & a free flowing dual exhaust with a balance tube ought to do.
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Old 01-07-2009, 12:21 AM
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All cast iron manifolds are junk. Stop trying to justify them. Move the motor to the passenger side of the car like you should have done in the first place and put some equal-length, long-tube, 1 3/4" headers on it. Keep the centerline of the crankshaft perpendicular to the rear axle and you'll be fine.
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Old 01-07-2009, 12:24 AM
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Yes! I was wondering when someone was going to say it!
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Old 01-07-2009, 01:00 AM
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Quote:
Originally Posted by techinspector1
All cast iron manifolds are junk. Stop trying to justify them. Move the motor to the passenger side of the car like you should have done in the first place and put some equal-length, long-tube, 1 3/4" headers on it. Keep the centerline of the crankshaft perpendicular to the rear axle and you'll be fine.
Somehow, I doubt the guy is going to want to go to the trouble. Probably because in his first post he mentioned that custom headers involved more work than he was willing to do.

If he asked about cast iron manifolds because he didn't want to make the effort, I'll take odds he doesn't want go to the trouble of altering the position of the engine so he can then deal with squeezing in a set of headers.

I agree that debating the relative merits of cast exhaust iron manifolds is sort of like arguing about virtue among prostitutes. Personally, I wouldn't use them unless some sort of rules/regs compelled me to. But the man wants to use them, and he asked which are best. Some are a little better than others even though none are great.
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Old 01-07-2009, 01:19 AM
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i agree with techinspector and double v23, all the stock manifolds are junk. with that being said if you want to go with stock manifolds look into the c2 corvette manifolds, they are the ram horn manifolds that came on the hi-perf engines. they have a 2.5 outlet as opposed to the 2 or 2 1/4 outlet of other chevies. someone mentioned offsetting the engine for exhaust clearance--the 63/67 corvettes all have their engines offset 1.5 inches to the passengers side--look closely at one some time--> . this was not done for exhaust clearance but was done to gain room for the added pedals on the 4-speed cars. (there are also other reasons, the offset of the block made up for the drivers weight (thanks zora). as you can tell i'm a vette guy. offset your engine for clearance and don't worry about it. keep all your angles correcct and you will be fine ...
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Old 01-07-2009, 07:24 AM
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Thank you all for your replies, perhaps a little more explanation is in order as to why I am looking for the best manifold. As I indicated, I tried headers first and considered offseting the engine (like the corvette) to allow use of headers however I wanted to use mechanical engine driven cooling since I am setting the truck up to tow 5000#. I also wanted the biggest fan that I could fit for cooling while towing and pulling the long hills. That drove me in the direction of centering the engine (and raising the centerline of the fan-used a Zips housing like "deuce") and I wanted to fabricate a decent looking shroud. I have attached a link with pictures of the stainless steel shroud that I fabricated. It was discussed in a previous thread on this forum.

http://www.ford-trucks.com/user_gall...&albumid=27774

I am fond of my shroud and want the engine driven cooling. High reving HP is not my goal but good grunt is.
Right or wrong that is where I am at and the reason for the question.

Last edited by 49willard; 01-07-2009 at 07:43 AM.
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Old 01-07-2009, 02:14 PM
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willard, that is as fine as I've ever seen for using a non-automotive item and adapting it to a better use. It takes a lot to impress me, but I'm impressed.

When I go to the grocery, I always go down the cooking aisle to eyeball the pots and pans. There are some stainless bowls there that would make excellent headlight buckets for an early rod and some stainless frying pans that would make nice splash shields for the front brakes if you just cut a notch out of them for the caliper to fit and made some mounting tabs.

Anyway, back to the subject at hand. I understand what you're trying to do at this point, but if you are this handy with cutting and dicing parts, certainly you could have cut and re-welded the core support to position the radiator to the passenger side. I'm not raggin' on you, I'm adding this for other engine swap wannabees.
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