SBC 12 to 1 4.060 x 3.625 x 6.00" with ported TFS Double Hump heads, Factory GM Holley Intake and Holley Carb. Vintage Road Race....Factory NOS manifolds with port work, Dyno sheet the lighter set of lines is the 1 5/8" headers and the darker is the ported manifolds. 18HP between difference. Pretty impressive for 58 year old manifolds...

 

Thank you for sharing the data.

 

Impressive!!

JIM

 

Nice info. How did the tfs heads do out of the box then after porting ?

 

not bad for a manifold but add an 18 inch header extension to the headers and do it again, they will gain another 20 across the board

 

I guess that dyno test shoots holes in all the "rams horn" are horrible story. I am installing stock Corvette manifolds on the big block,.....probably even less loss due to the better design of the big block manifold. I know that headers do make a difference,....I spent lots of money on them, but my point is......its not really that significant in REALITY with street driving the way most of us drive. It makes a difference on a track when you are competing with others....but on the street.....its just more stuff we do because it makes us feel good.

 

put the full exhaust behind it an you lose atleast another 50 hp. those would definitely benefit with some cutouts at the end of that tube

 

Then, attach a full dual exhaust system with mufflers and see what happens
Scotty

 

thats what the cutouts would solve, best of both worlds

 

How much port work went into the manifolds? If you were billing someone for this work, how much money would they be out?

Can you post pictures of the header ports? How do the manifolds compare to a 1 3/4 or 1 7/8"?

What cam was run on this engine? Was it designed to take advantage of the exhaust manifolds?

Also, looks like 20 hp at peak, not 18. 18 looks like the torque figure. 2 hp is well within rounding error of course. Do you have figures for average HP/TQ? It looks like the headers are making more power everywhere, judging from the chart.

 

Its a vintage road race engine that will be using the manifolds. I can go into cam specs in detail. Cam is 600 lift and in the 250 range for .050" Duration and was designed for competition in road racing for a broad range of torque. BAsed on the piston speed a little larger header would have helped on the top end for this combo. 1 5/8" headers were used only as a comparison.

Dyno Sheet...Headers...

 

I went from 2" RHs to the 2.5" RHs.
The 2.25 ex was replaced w/ 2.5 x pipe ex.
I gained 20 hp and 15 tq.
My engine would be about 400 hp.

 

This thread has been great!

If you have a compelling need to retain Rams Horns on your C3, be it for fashion or race-class rules, a viable option is ported and polished 2 1/2" RHs.

 

I only seen 8 hp gain with headers, compared to 2” Berzenski ported manifolds on a stock 1970 L46 build.

 

I agree. The ported manifolds did a commendable job. I would not use this as a basis for argument in a "should I do stock manifolds or headers", though - we are not comparing apples and apples here. And a key point is that the undersized headers still did better throughout the powerband.

And thank you, Straub, for the info.

I will try to get a picture of a stock Ram's Horn port later.

 

What I find surprising about this comparison is that you always hear that a mild engine won't get very much out of full length headers vs the stock manifolds, but a really souped up engine will incur a drastic improvement from full length headers. The engine in question is fairly souped up, (1.4 horsepower per cubic inch is pretty healthy) and the headers don't seem to make a drastic difference here.

Scotty

 

I disagree. 20 peak horsepower more on a set of undersized headers vs a set of custom-ported manifolds, plus the average power differences across the entire curve. If the engine were equipped with 1 3/4" or 1 7/8" headers, we may have seen a power gap of 30 or 40 peak hp. At this point, with this motor, would you chase a little more cam to get a little bit more power and shift the RPM range up, or go with long-tube headers and make more power everywhere in the curve? Not to mention, if you had started with stock ram's horns, the work to replicate this may be equivalent to, if not more expensive than just buying a set of headers. I'd also be very curious how the stock ram's horn setup compares to the ported setup. (@StraubTech - that port work is beautiful, by the way.)

I think the takeaway here is if your build is constrained to manifolds, you can do work to them to minimize the amount of power you're losing not going to a full length header. Straub's point is excellent - there's plenty of race classes that require manifolds. If your car doesn't have header fitment, you don't like them for packaging reasons (spark plug access, ground clearance, heat management) or you can't do it for smog reasons, this shows that ported manifolds are a very viable alternative.

But I wouldn't herald this data point as "the guys who have been championing long-tube headers are wrong", which a lot of people in this thread seem to be doing.

This may be the last time I join in on one of these threads, but I will continue to cite that my personal experience has proven without a doubt (to me, anyway), that even a puny little L-48 can get a nice performance wakeup going from stock manifolds to headers.

 

So 20-40 HP more at peak RPM, driven on the street, is something an average driver is going to notice, and make a difference in the way car feels, when driven at 20-55 mph? Its a question.

I already know it makes a difference on a race car, in competition.

 

If you car has less than 200 to start with, yes. I'm certainly not going to use anything but long-tube headers in my cars. But if you HAVE to use stock-looking logs for some reason, 2 1/2" ported, polished rams horns seem to be a good option. The OP did a great job on them, and posting actual test data like this should be commended and encouraged.

 

I'm sorry, but you clearly didn't read my post.


Look at the dyno chart. 20HP at peak. 20+lb-ft EVERYWHERE in the displayed curve. It's not just a near peak-to-peak difference with long tube headers. That chart actually dispels your post entirely, along with a wide held belief that long-tube headers only increase power at peaks. Not true. They increase power across the entire curve, and that's what I've seen in my personal experience and numerous other dyno tests.