Horse power limit with exhaust manifold 318

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Eworth

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How far can I realistically go with horsepower on a small block before stock exhaust manifolds start being a problem?

Or is the real question, what rpm? Can I get 6000 rpm on stock exhaust manifolds? This 318 is in my 64 Dart and I don't really want to deal with the header headache.

Just want to push this car a bit. 1/4 mile the 12s? 13?s. Will have 904 auto with 8 3/4 3:55 suregrip.

Thanks folks
 
Might look into magnum manifolds from the salvage yard. Flow better than the original manifolds with larger outlet. A 2.5" dual exhaust would let your motor breath well
 
Or 340 manifolds. They flow well also.
 
Not sure that'll work . Drivers side is super funky shaped due to the steering box. I need to make the best out of what I have.

For the sake of this post, let's say the best I can do with what I've got at present.
 
I just typed "manifolds" in the search box and checked the "title only" box. There's lots of threads about this here.
 
How large are the outlets to the manifolds you have? Can they be opened up a little? A 2"-2.25" dual would still let your motor rev provided the rest of the combination is set up for it. 12's in the 1/4 may not be realistic but 13's is still lots of fun and very respectable for a street car and would have good manners as well. Have you looked at shorty headers? I have seen early A's with them, do a search and I believe hedman makes them that will clear the power steering
 
If they are the stock 273 manifolds for the early As, not much you can do with them. Even the 273 hp engines got a big boost in the seat of the pants dyno by putting on headers. Best thing to do is to get over your phobia of headers and the sticker shock of the ones for the early As and put them on and let the horses run free.
 
I've got some homework to do. Due to tight quarters, I could only get 2" off the manifolds, and then open up to 2 1/2 (which I don't think makes any improvement, just what we had available. I would be absolutely thrilled with 13s. Any day and all day long
 
I guess I could keep my eyes out for headers but I really just want to see what the limit would be with what I've got a present.

19DART66 said:
If they are the stock 273 manifolds for the early As, not much you can do with them. Even the 273 hp engines got a big boost in the seat of the pants dyno by putting on headers. Best thing to do is to get over your phobia of headers and the sticker shock of the ones for the early As and put them on and let the horses run free.
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That's a really loaded question.
I bet in Neutral,you could hit any rpm you care to rev the little teener to, short of blowing it up. Whether or not it will hit the same rpm in third gear is another question.
Then there's the question of why do you want to hit this high rpm, and why do you want to keep manifolds.
If you are a streeter with 3.23s and an automatic, 6000 rpm is right about 60mph.Since the A-body is is putting a fairly light load on the engine at these slow speeds, I see no reason decent manifolds with a free-flowing exhaust, can't get you there in a reasonable time.But the 60 to 100 mph/ET will of course point out the short-comings of manifolds. If you have an Early A,of course, it will be less of an issue, cuz weight is the enemy of all engines. And wind resistance increases as the square of the speed, so it is an ever bigger enemy.Hope that helps
Have you seen the Hooker Super Comp 5208HKRs.
http://www.summitracing.com/int/parts/hok-5208hkr/overview/make/plymouth
Might be an option,IDK
 
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Look into headers for the early A's, they do exist and will compliment any improvements to your motor. Search for the 318 and 273 combos only thread in the small block thread forum. Lots of posts in that thread and quite a few members with early A's in that thread. Look at their posts for a possible combo and pm them for further info if need be.
 
I have a set of both 318 and 360 stock manifolds. The port size of the 318 are vastly smaller. If you're dead set on running stock manifolds, find a 360 or 340 set. Can get those cheap, usually. Other wise go headers.

The sheer small size is gonna limit your power greatly, especially if you're doing any type of compression bump. My guess is you'd be lucky to break 300 on stock manifolds
 
thanks folks for all the input. I do really just want to see what I can do with what I have at present like my OP.

There will always be bigger, better and more expensive options but there are limitations to my pocket book (especially after this engine swap already). Holy cow, I went way over budget (for my budget).
 
300 hp in an early a & 2600 lbs would be plenty fun for this 50 year old

dukeboy_318 said:
I have a set of both 318 and 360 stock manifolds. The port size of the 318 are vastly smaller. If you're dead set on running stock manifolds, find a 360 or 340 set. Can get those cheap, usually. Other wise go headers.

The sheer small size is gonna limit your power greatly, especially if you're doing any type of compression bump. My guess is you'd be lucky to break 300 on stock manifolds
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how about 10's with manifolds???? Not an early A, but.......
 
And expensive. Those competitors in that class have to sink quite a bit of money to run like that and have factory appearing equipment. Doable of course, but pricey
 
Eworth said:
300 hp in an early a & 2600 lbs would be plenty fun for this 50 year old
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Doesn't mean they'll support that, just probably the max under optimum conditions. Heck just find some 360 manifolds, they can be had extremely cheap.
 
When I built the 318 in my 69 Dart Swinger I had the exhaust manifolds extrude-honed to increase the flow. This worked well as with street-slicks and 3.55 gears I ran in the low 12's at Union Grove Drag-a-Way. This was back in the 80's so I'm not sure who does Extrude-honing anymore, you might Google it and see.
 
Hi, can anyone tell me whereexhaust manifolds can be extrude honed? I live in Wisconsin.
 
Have you personally put 360 manifolds on an early A with a stock manual steering box?

dukeboy_318 said:
Doesn't mean they'll support that, just probably the max under optimum conditions. Heck just find some 360 manifolds, they can be had extremely cheap.
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342.675831 HP @ 5,996.456331 RPM.


Eworth said:
How far can I realistically go with horsepower on a small block before stock exhaust manifolds start being a problem?

Or is the real question, what rpm? Can I get 6000 rpm on stock exhaust manifolds? This 318 is in my 64 Dart and I don't really want to deal with the header headache.

Just want to push this car a bit. 1/4 mile the 12s? 13?s. Will have 904 auto with 8 3/4 3:55 suregrip.

Thanks folks
Click to expand...
 
Eworth, think of the engine as a giant air pump.

It's a 3 inch pump with a 3 inch inlet and a 3 inch outlet.

If you do anything to increase the efficiency of the pump, ie.,improve flow or replace heads, cam, , compression etc. or just replace with larger pump (engine), say a 4 inch pump (360) you're still restricted by a 3 inch outlet.

If you increase you inlet to 4 inch, by replacing the intake manifold, carb, etc.

You are still running a 3 inch outlet.

Back in the day, the most cost efficient way to increase H/P was headers, cheap 10% hp for $125.

hope it helps..
 
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