How much will this help airflow??

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How much will this help airflow??

Postby type85 » Sun Jan 08, 2017 12:47 am

What's the limiting factor on the intake tract for a N/A 10v engine (I'm already running EFI, so the intake is just a 3" pipe to a cone filter)?
I have the largest throttle body I could find 34mm x 52mm.
I just did a huge amount of work blending the outlet of the TB to the intake man. flange, I then ground down the throttle shafts to increase flow around them. I also cleaned up the manifold runners and match ported it with the heads intake ports.
All the transitions are super smooth, I probably took of 5lbs. of aluminum from the manifold and throttle body!
The cyl. head itself has had a ton of work done to it including flow porting and big valves, it's mated to a 2.6L. The problem is, it doesn't breath, it has massive midrange punch but runs out of breath by 5,750, I'm hoping the throttle body was one of the limiting factors and all the work I did will help flow....


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Re: How much will this help airflow??

Postby FFF » Sun Jan 08, 2017 10:54 am

Be interesting to see the differences from a flow bench but it certainly looks like it will make a difference, looks good.
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Re: How much will this help airflow??

Postby Noisy Cricket » Sun Jan 08, 2017 1:26 pm

Camshaft is probably limiting airflow a good deal too, and the ports in the head are tiiiiny.... Measure the vacuum in the plenum, if it stays within 1in-Hg of atmospheric on a WOT pull, your throttle body's not the problem.
Pete, that rallycross guy

'84 RX-7 (bridge ported, fuel injected, way modified dirt buggy)
'86 QSW (MC2 goes here. Eventually.)
'83 GTI (accidental ownership, now what?)
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Re: How much will this help airflow??

Postby type85 » Sun Jan 08, 2017 2:06 pm

Noisy Cricket wrote:Camshaft is probably limiting airflow a good deal too, and the ports in the head are tiiiiny.... Measure the vacuum in the plenum, if it stays within 1in-Hg of atmospheric on a WOT pull, your throttle body's not the problem.


So even with the flow porting and big vavles, you think the ports are the limiting factor?

According to the Schrick catalog: I/O56 I/C16 E/O16 E/C56deg 11.5mm lift, I'm running an adjustable cam pulley with about 6deg. of advance as well.. so that means the intake valve is opening 62deg. before TDC???
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Re: How much will this help airflow??

Postby Noisy Cricket » Sun Jan 08, 2017 8:21 pm

I think the numbers got mixed up! Usually the intake closes 1/3rd-1/2way through the compression stroke, those numbers have it closing right away. Yeah that isn't right sounding at all.

Are those numbers at .050" lift or are they "seat to seat"? Reversing the numbers so they make sense, that is 254 degrees, which is really kinda small I think for seat-seat, but decently big if it's at 1mm lift or .050" or something like that.

Not that you'd want a huge cam anyway.

What are you considering "big valves"? IIRC you can't really get any bigger than 42-43mm intakes in the VW 2v cylinder head geometry without major work.
Pete, that rallycross guy

'84 RX-7 (bridge ported, fuel injected, way modified dirt buggy)
'86 QSW (MC2 goes here. Eventually.)
'83 GTI (accidental ownership, now what?)
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Re: How much will this help airflow??

Postby type85 » Sun Jan 08, 2017 9:54 pm

Closing is 16deg after bottom dead center.
I do belive it's measured at 1mm, I'll have to check...
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Re: How much will this help airflow??

Postby GTJeff » Mon Jan 09, 2017 8:45 pm

Have you tried retarding the cam?
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Re: How much will this help airflow??

Postby type85 » Mon Jan 09, 2017 10:09 pm

GTJeff wrote:Have you tried retarding the cam?


been there, done that, I lose all the midrange torque for a small increase on the top end, this engine REALLY needs the intake valves to open REALLY early! This is in a 2.6L 82.5 x 95.5, the huge stroke makes it a torque monster!


Sorry! I got the timing wrong somehow, Schrick catalog says: I/O28 I/C68 E/O68 E/C28deg 11.5mm lift, 110deg lobe center. "Since engines with hydraulic lifters have no valve lash, the stated valve lift is also the actual valve lift."
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Re: How much will this help airflow??

Postby carl » Tue Jan 10, 2017 4:36 pm

Looks like it will help for sure, if you haven't already, shorter valve guides help too, any problems with exhaust? Maybe a diff monoblade throttle with custom adapter would help, something like a vette AS&M Mono Blade, a bit crazy but flows plenty lol. Maybe go to wreckers and cut off/weld a new flange to manifold. Biggest problem on 10v heads is they're counterflow though.
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