for my new engine i want to kinda go undercover. build a 406 with iron heads , stock valve covers, 327 stickers etc... was wondering what it would cost me power wise going with a set of ported cleaned up rams horns. I run chambered sidepipes on my 65 vette and have been told the backpressure pretty much negates the headers better flow anyhow. anyone have any dyno experiance with this?

 

(This is a copy of an answer to a post on Chevelle forum, Gary)

Too bad this question "popped" up this soon. We've begun testing stock cast exhaust manifolds brought about by the new classs of racing on the east coast here. We've only tested a handful so far, but the results were a little surprising. Two units left here to date with factory pipes.

The first was a true 350/300HP SB. Came off the dyno at 360 HP and 390 Torque. The unit was tested with the stock pipes AND a set of headers. Made no difference up or down in power.

The second was 496" BB stroker, cast intake (factory LS-5), Q-jet, Comp Hyd.Roller-retro, 9:1 C.R., and stock "oval" ports with small valves. I don't have the paperwork here, it may have had 2.190" intakes only, I don't recall. This came off the dyno at 410 HP and 485 Torque. Again, tested with both stock exhaust AND headers, same results, absolutely no difference.

Both are now in "100% stock" appearing vehicles. This was the reason for both tests.

As I type this we are waiting for some cast exhaust's to come back from "Extrude-Hone" in Pa. for some future tests. Some of these units are destined for "class" racing in Englishtown. Thanks, Gary in N.Y.

P.S. What we've seen from these particular tests is there's no loss/gain in certain applications. It ALL depends on the overall design of each individual unit as it come up for testing. There's less chance of gaining power unless the headers are "uncorked". I will add this however, it's somewhat on the expensive side getting a pair of stock cast pipes opened up, somewhere in the neighborhood of $700.00 per pair plus freight!

 

Keep us posted on your project. I'm pretty much thinking about the same kind of project: 406 with stock valve covers, rams horns, etc... I'm planning to use Dart Pro 1 aluminum heads (maybe painted with engine paint) and an LT-1 cam.

 

Someone just posted Dyno results of their 383 engine with the 2 1/2" manifolds, outstanding results. i think it was in the C2 section and not the engine section. Also, I think it is A1 auto or automotive who sells knock off 2 1/2" replacement manifolds for less than $100 each.

 

I picked up a set of 1A Auto's (made in China) BB exhaust manifolds a couple years ago. For $149 each I was very impressed with the quality and fit. I did however have a custom set of pipes installed so I can't say for sure how a stock set would bolt up.

They don't make the LH for 66-69, I don't remember but I think the LH on 66-69 huged the bolck closer. I had a 69 BB and used the 70-74 LH they sale and it worked fine.

 

I am really interested in this topic. I posted something like this in the C4 performance section.

I have to remove my longtube headers from my vette due to California stupidity and was wondering if extrude honing the stock manifolds would produce a worthwhile gain or if it was a waste of time and money.

Anyway, could you give me a link to the post/thread you got this info from? Or even better, the person's email address so I can talk with them. Thanks.

 

I would like to keep ALL things clear here, about this subject. We are not saying that "stock manifolds will make the same power as headers".
You have to read the line above (quote) "It ALL depends on the overall design of each individual unit as it come up for testing." (end quote)
We don't see any HP losses on many units we've tested so far because there are other "limiting" items on each unit. For example, the '72 LS-5 we did recently would show no loss/gain one way or the other with/without headers. The "stock" cast iron intake manifold was the "choke" point. If we were "allowed" to change that piece then the headers would have been a "positive". These are all "factory-appearing" units to this point. Class "rules"!

Now, as for opening the stock exh. manifolds, we know this will "add" to the numbers we're looking for, BUT, and this issue is very important, by merely opening the manifolds with the "Extrude-Hone" process is not the real answer. Many of these are already being "hand-ported" first, as much as possible, and THEN sent to the "honer". Much like porting heads, we "move & shape" the ports in the heads by hand. "Extrude-Hone" WILL NOT redesign a manifold, it will merely make it larger inside. By doing this process alone some manifolds respond well, BUT there are some we want exhaust "redirected". For this reason we will be doing some hand grinding first, on many, but not all. Thanks, Gary in N.Y.

P.S. Keep in mind, many of these units we do are destined to shows, and MUST appear "110%" original. However, our customers still want the maximum power available ! I mentioned the LS-5 above, it was a "test-mule" for us in relation to being all stock. It was run with a few outside components changed, for testing only, but delivered "original". Without
an intake manifold change on this particular unit, any add'l time spent in the dyno room would have been wasted! The intake is very poor design in order to maintain "under-the-hood" clearances. This is a 1972 LS-5. I believe the original HP was some where around the 275 number. It does move the 4000# vehicle "respectably" with 485 ft lbs. torque and only a 9:1 c.r. and a Q-jet carb. AND no power brake issues running 15+ inches vacuum.

 

I put together a 383 for my '67 convertible with rams horn exhaust manifolds and made 375.19 rwhp on my DynoJet. I started with a ZZ383 short block and cam then added iron heads.

Most people are shocked when I pop the hood and they see exhaust manifolds. I just wanted to do something a little different this time. I run a full undercar exhaust.

Steve

 

hi steve, i'd really like to hear some more details onyour engine. what type of cam, where you setpeak power, tyour shift points. the usual
thanks
greg
PS
your PM is full

 

nice

 

Here are two links that will give you all the info you need:
http://forums.corvetteforum.com/show....php?t=1283055
http://forums.corvetteforum.com/show....php?t=1341674

comp: Thanks!

Steve