I have a '70 Lemans with a 350 2bbl and I'm thinking of pulling the 350 out to preserve it and meanwhile having some fun with a bigger mill while I'm driving this car daily.
It currently has the original log manifolds which I've been told are not bad for a Pontiac engine up to a point. I'm not sure what that point is though. NO HEADERS, I have those on two other cars. I want a low rpm torque engine, I have factory big valve high compression heads and a tri-power I want to use on a 400 or 428 (or 455 if I buy a crank and pistons). Will the log manifolds on the car now be 'ok' or is that out of the question? I've seen those D-ports ram-air manifolds for the gto's but I don't know what they cost or where to get them. Are they worth it over the log manifolds I have now or are they more of a novelty?

 

They'll work OK for what you're doing. A nice "upgrade" I've found is to have them Extrude Honed to open up the passages slightly and remove all the sharp edges and casing slag from inside. It's one of my favorite "stealth" tricks. Ponchos in stock or near-stock form really don't like being spun beyond about 5200-5500. Hogged out stock manifolds will work fine for this. Plus you don't have to wonder if they'll fit correctly.

 

Thanks Damon, whats it cost to have them extrude honed? I've heard of that process but don't know much about it. yeah I just found those RA/HO manifolds on the Pypes website, nice but pricey. For that much money I would get the "long branch" manifolds if they will fit, they're more like headers. i think the extrude honing is probably the best cost effective way to go, but I gotta find out where and how much.

 

When I switched to headers, from manifolds I noticed a very significant gain in power... deffinetly can be felt. Probably somewhere around 30hp that you'd be giving up.... but I did have mid 70's smogger manifolds, and I noticed the earlier manifolds atleast look like they would flow better.

The D-port ram-air style manifolds are probably your best compromise.

 

I imagine that a set of Ram Air III or IV manifolds would be about your best bet if you want to avoid Headers.

 

It will cost you more to have stock manifolds extrude honed than a set of headers will cost. I only did it for a "stealth" kinda street performance motor. It is NOT a bang-for-the-buck modification. Headers are cheaper and will make more power than modified stock exh. manifolds. I thought I'd throw it out there if you felt like doing something a little "different."

Even without porting them out they will STILL work quite well for what you are doing. Pontiac exhaust manifolds are a little better out of the box than a typical small block Chevy exhaust manfiold, which was designed for low cost and not much else.

 

I remember seeing an article in Musclecar review magazine a couplw years back. They Dyno tested a 400 R/A III with the 3 different factory manifolds Log, Dport Ram Air, Long branch R/A.

The Long branch manifolds showed the most gain followed by the Dports. But the Dport R/A manifolds were only marginally better than the Log manifolds. The difference was less than 10 HP.

 

Still siding against headers, the RA manifolds are clearly my first choice now. I found them new for about $300 - $360. Thats the least expensive I coud find and the later is for slightly opened up version. There are NO longbranch manifolds that will fit the A-bodies so unfortunately those are not an option.
I think the best scenario at this point would be to find some used RA manifolds. Otherwise the dollar for horsepower scale is getting a little outa wack for this particular project but I'm not gonna rule new ones out until I'm ready to install the engine. Alright then, thanks for the replys.

 

the ram air iv will NOT work...the two center ports are night and day different on the RA III and RAIV manifolds....nothing will beat the value of headers for the performance. headers will keep you cost down....the ra manifolds will keep costs up and you will have less perf. AND my car gains 25 horse from raiv manifolds to headers. That may just be a product of the ram air iv heads flowing tons better. I have a 69 400 RA IV Firebird. good luck.

 

Right, the RAIV uses a round port. Only talking about the d-port RA manifolds.

 

Hmmm, so there I was doing a search on previous posts I've made, and came across this. Bad grammer, 69 Firebird, Ram Air IV heads....yup, that's my roomate under my screen name. In case anyone thinks I own a classic (not that I wouldn't mind, I love his car).

 

Keep us posted on what you do for your exhaust. I have a 71 Lemans and am also looking for that upgrade. I would be interested to see how it turns out.