wowzers

Hi guys,

I heard that there was a comparison between a smaller runner (1.25") vs a larger runner (1.5") on an exhaust manifold for the 4G63.

The results indicated that there was only marginal gains up in the high RPMS only.

I am unable to locate any info or find the article/test other than that it may have been Burchur racing that did the test, not ETS as i had been told.

Thanks & regards,

michaelrc51

iTrader: (37)

I would say it depends on your engine/ head/ cams/ turbo if it would be worth it or not.

I am sure there are benefits up top but I would think the real question is how much low and mid range do you loose?
All going to depend on your setup and goals IMO

Ted B

iTrader: (6)

And you would be correct. IIRC, the test was conducted by Geoff of Full Race. The smaller primary tube delivered superior gas velocity and better spool characteristics without giving ground to the larger primary until 650whp or so. Again IIRC, the test was conducted pursuant to determining appropriate primary sizing recommendations for made-to-order Full Race manifolds.

EvoDan2004

iTrader: (94)

Hey ted. How are you. Miss talking to you

I find my results a bit strange.

Old setup T4 1.06 ATP housing HTA 86 small runner 1.25 sch40 2.5inch ICP

New setup T4 1.15 PTE 6466 1.50 sch5 with 3.0uicp. I picked up spool and carried HP longer. Maybe I had a restriction with the HTA turbo? I don't know. I love my new setup though.

Ted B

iTrader: (6)

Hi Dan! May have been an issue with the ATP housing among other things to explain results contradictory to Geoff's A/B testing. I disassembled my turbo to give that housing a thorough internal overhaul.

JohnBradley

iTrader: (30)

And it is at this point I throw in a stepped header with fairly straight exits out of the port would be the best option if it would fit in the engine bay.

wowzers

Yeah, thats what I've heard.

and now its either ETS, Burchur & Full face.

can anyone supply the article?

cheers

Ted B

iTrader: (6)

Perhaps you should PM Geoff Raicer and ask him to confirm/comment.

mrfred

iTrader: (50)

My own comparison: https://www.evolutionm.net/forums/ve...-toxicfab.html

Cliff notes is that they were very close to the same on the dyno, but the 1.5" manifold had better daily driving manners. Issue with the 1.25" primaries was that it felt a bit like it was being choked during off boost daily driving. It was nothing I could capture in a data log. Just seat of the pants difference in responsiveness.

michaelrc51

iTrader: (37)

Interesting read, Mychalo.

I would have thought there would be more differences between the 2 runner sizes.

Ted B

iTrader: (6)

Manifold design will influence the picture as well.

michaelrc51

iTrader: (37)

Sure, but to what degree?
The thing that surprises me on Mychalo's test is how the manifold pressure is similar.
I would be interested in seeing any data on that.


I originally had a full race OE replacement manifold when my car had a Buschur 2.3 and DBB green. I went with the TF V3 OE replacement w/ billet collector on this new build. I wish I had just swapped the manifolds so I would have had some data but I had to change motors and I changed just about everything else as well. I figured the header change would shift power to the right a bit, but how much is the question?

Ted B

iTrader: (6)

It's a difficult question to answer because these manifolds all contain various design compromises in order to physically fit. These waters run a bit muddy, and it's difficult to render them crystal clear unless one can eliminate a handful of changing variables. The only way to do that is with two manifolds of better design that are otherwise identical aside from primary diameter. And as soon as we switch to a different brand/design, those observations may vary to some extent.

mrfred

iTrader: (50)

The two key aspects that I see in header design are flow resistance and how well the collector lines up with the volutes in the hotside.

Here are my thoughts on factors affecting flow resistance.

1) Tubing diameter.

2) Number of bends.

3) The tubing transition where the manifold bolts to the head. The exhaust ports on the head are much larger in cross section than the ID of the 1.25" tubing header. I've not been impressed with most of the transitions I've seen on small diameter headers. Its typically a 45 deg cone reducer that takes place over the thickness of the header flange (1/2" at the most). This was the case for the FiD manifold. The ToxicFab I tried had the same transition method, but since it was 1.5" tubing, it was a more gentle transition. My personal opinion is that this transition is very important. I think a poor transition could be worth 10 bends. The good news is that many of the newer manifolds out there (ToxicFab V3, MAP) use a much smoother transition.

I think the bottom line though is that these aspects of header design have a relatively small effect on exhaust back pressure, probably in the range of 0-5 psi depending on exhaust flow rate. This would be important for a naturally aspirated motor, but for a turbo motor where exhaust manifold back pressure quickly rises above 10 psi under boost and typically matches the boost pressure at peak power (20+ psi for many Evo owners and probably 40+ psi for most stock turbo owners running E85), header design perhaps comes into play predominantly for people who are running relatively tame boost levels.

As far as the collector goes, a well aimed collector will efficiently shoot the exhaust pulses down the volute. A smaller diameter tubing at the collector will also result in a higher velocity pulse shooting down the volute. I think the FiD won here because of the smaller diameter tubing, the collector angle was tighter (better aiming), and it was pointed more accurately down the volutes.

I've love to see a header similar to what Aaron suggested - 1.5" primaries with a well-aimed 1.25" tubing collector. If there were room in the engine bay, I'd actually merge the tubing pairs before the turbo so that a single tube could be pointed down each volute for the most accurate targeting down the volutes. If only I knew how to weld, I could come up with the craziest stuff.

Ted B

iTrader: (6)

All else being equal, the primary diameter that preserves the maximum exhaust gas velocity without causing a significant backpressure penalty at peak mass airflow (peak hp) generates the quickest spool characteristics and most power under the curve. I emphasized all else being equal because exhaust backpressure represents an average reading that doesn't tell us the complete picture where primary gas velocity and pulse reflection are concerned, especially on an individual cylinder basis. Any disruption along the flow path (especially the tubing walls) tends to create some degree of pulse reflection, which results in an instantaneous pressure wave in the opposite direction. Where the engine speed results in the reflected wave returning to the exhaust valve at the same instant that valve opens, VE is reduced at that rpm. This is disadvantageous in a turbo engine, just as it is an NA engine, and is one big reason why a good FF manifold presents the potential for better power. One advantageous design feature mentioned by 'John Bradley' (above) is a length of straight tubing at the exhaust port exit, before the first bend. Better designs employ at least 4" (100mm) before the first bend. This feature of manifold design reduces the effect of a significant source of pulse reflection.

IF the primary orifice is smaller than the exhaust port as you mentioned the case with one of the manifolds you tested, that is a source of velocity-reducing turbulence and pulse reflection, which again, accounts for the all else being equal caveat. Efficient designs often feature a low angle adjustment from the port orifice into the closest tubing size, but that isn't something we can expect to see in an OE fitment exhaust manifold.