BB Exhaust manifold testing revisted

Hi guys,

We recently had a discussion on the effectiveness of ported manifolds, and I can only recall doing the testing years ago, and just some general numbers..

I recently had a 70 455 STG 1 motor sent to me by a board member from Ohio, to evaluate it's performance. It came with ported 1970 exhaust manifolds. Since I always start with my dyno headers, which allow EGT readings on each cylinder, and I happen to have a set of nice stock 70 455 manifolds on the shelf, doing a header vs ported vs stock manifolds test was not difficult.

So I did it.

The motor is your basic warmed up 455.. lots of deck clearance (unmilled matching number block) ported heads, ported intake, small performance camshaft and Q-jet.

Headers are TA 2012 CH 1-7/8 Primarys, 3 1/2 collectors

Stock manifolds are just that.. and the manifold entry is bigger than the head exhaust port exit. 2.00 inch exit

Ported manifolds- Unknown origin, have tag that says "PHS" riveted to them.. they look like the typical ported manifold, with 2.4" exits

Graphs are the best way to look at the numbers, so I did make a few.


First, we see a the HP comparison.



Headers in blue Stock manifolds in Red, ported manifolds in green.

And the Torque comparison:



Again, headers in blue, stock manifolds in Red, Ported manifolds in Green.

Ignore the 2500 rpm and below numbers, those are produced before the tests actually starts and are known as "steady state" numbers.

The results are pretty much exactly as I recalled from the last time I did the testing.

On a 450 HP engine, headers are 15 to 20 numbers better, torque and HP, and ported and unported manifolds are very similar.

I will be re-running the manifold test again when this motor is finished, this time I will up the size of the down pipes, that connect the manifolds to the 8" dyno exhaust system. This test was done with a 2.25" down pipe, which may not be ideal for the ported manifolds.

JW

 

Nice to see the difference in real world numbers. :TU:



Nelson

 

I'll look forward to seeing the ported manifolds test run again with the larger down pipes as well. My motor was dyno'd with headers vs ported manifolds with the T/A 2 1/2" down pipes and the difference was 18 HP (450 vs 468).

 

Good stuff Jim.
Thanks for posting.:TU:

 

Good stuff Jim, thanks for posting.

 

dats dat:gp:

 

Great comparison Jim, thanks for taking the time to do it!

 

I would think that like all port work, the end result would be dependent on who did the work and how much time they spent flow testing along the way. This is no different than any other port work, except perhaps that there isn't as much to be gained and there aren't as many people doing it.

 

Actually pretty simple Bob..

Without slicing open the manifolds to do complete port work to them, your pretty much just limited to squaring up and smoothing out the entry's and enlarging the outlet.

Although I did just get an offer to test a set that had been extrude hone ported, which would be intesting.

As far as the "know how" aspect.. the first time I did this test, I had both the street strip as well as the full competition manifolds from Greg Gessler.

Results were similar to what we see here.

JW

 

Thanks for taking the time to do this. Headers are such a pain it is good to see evidence they are worth it.

 

I asked about the extrude honing in the other thread. My guess is it will be worth a few extra ponies over ported manifolds but nothing like even shorty headers.

Basically, utterly not worth the cost unless otherwise restricted to manifolds and every last pony must be extracted to be competitive.

 

Nothing new in this test. Similar numbers have been reported many times. Some guys choose manifolds and some choose headers. Those that choose manifolds often choose ported if good performance is wanted. Besides, necking down from 2.400 to 2.250 isnt giving the ported manifolds a chance.

In the end dyno numbers mean very little, they vary from pull to pull, dyno to dyno, location to location, day to day and operator to operator not to mention many others. The dyno is a tuning tool. This coming from arguably the best dyno operator in the country with the very best equipment. Way too many variables. The only thing that matters is how the engine performs in the car.

 

I did find it interesting that at the lower RPMs the ported manifolds were below the stock manifolds. As Mr. Rodgers noted, this could just be normal variance. But I also think it is interesting to note that the ported manifolds after the cross over provide more horsepower at every other single point.

I'm going to slip into analogy mode, but I think what some are arguing is that headers are an Ace versus the Jack you are dealt with ported manifolds. No argument there. But that Jack beats the 10 of stock factory manifolds everywhere (once you get past that 2500 rpm or so). All else being equal ported > stock. It is up to the individual to determine whether the expense is worthwhile. For those of us that don't like the header look, it just may be.

 

Thank you for your testing! What is the overlap of the camshaft and the LSA?

 

Rob, didn't you and Norm Diehl do similar testing some years ago? And the results very similar. If I remember correctly,found that on the iron manifolds that the inlet cleanup and exhaust outlet were the biggest advantage, and that full inside porting produced some but little gain.
Gary

 

We did, I recall the ported manifolds were ~12 or 14 hp. The results are on George Nenadovich's site but I can't get to it at work. And yes, the biggest gain seemed to be opening the outlet and I think we only ran 2.25" outlets also.

 

I am going to do that test again, considering the outlet pipe size. I want to remove that variable. Do you have a recommendation on 2.5" vs 3"? Optimum length?

JW

 

My suggestion would be to use 2.5 as most of the ported exhaust manifolds would go on basically stock appearing cars. And, F.A.S.T. limits head and tail pipes to 2.5 in. in both of their racing classes anyway.:TU:

 

I believe it is a TA 212.. but that motor dis-assembly and inspection is the first thing in my list to do today.

I will get back to you with the specifics.

As I recall, when I did this years ago, it was on a 462 with one of the very first sets of TA STG 1 SE heads.. That was an extensive 2 day test, over 30 pulls as I recall.

We did try both the TA 288-92H and the 288-94H cam, which at that time were identical, save for the 110 vs 114 lob sep. I don't recall the manifolds caring which cam was in it, the test results were the same Manifolds vs headers, with each cam.

I did like the wider lobe center version, while it didn't make quite the power at the peaks, it idled so much better, and produced more usable power over the entire rpm range tested.

I would be open to suggestion from those of you who have done this, my customer is open to changes in cam, within reason.. and this motor will in fact have the ported manifolds on it, when it goes back in the car.

His main focus is low rpm grunt with this one, not what happens after 5000..

Thanks


JW

 

For exhaust manifolds, I think wider LSA is better although I can't really prove it. hahaha My thinking is less overlap should reduce back pressure which should help the exhaust manifold.