Porting a U20 is Such a Waste of Time

[Daryl Smith]

Parallels what I've been saying about the R16, and the reason I started the header thread for it. At a lower power level, obviously.

What I've been hearing when looking into the head porting is that port matching, a quick cleanup of the casting flash, smooth ridges at the valve seat inside the port, and a good valve job will account for most of the gains in flow, and as Lou said in the article, should not be more than a few hours work.
It will also increase flow at all rpms/valve lift, increasing low end torque as well as high end horsepower.

Watching for the header article.

[Datsun.David]

Old School. Canola oil, electric frying pan... and tirelessly shaking so it doesn't end up like carbon... Childhood before Orville Redenbacher...

[SLOroadster]

The first and only time my car has been on the dyno, 141 hp 132 pound feet of torque at the wheels, with a 60K mile bottom end and a Rebello built head and cam. Intake ports were 212 cfm, exhaust 174 (I think). Those hp numbers were with a 2 inch exhaust and 37mm venturis, it was a different car with the 40 mm venturis and the 2.25 inch exhaust. I'd love to get a BRE style header for it and see what it can do with that.

I trust Lou's opinion, but this one has me scratching my head.

Will

[Mike Unger]

Hmmmmm, maybe you should ask my competitors if I'm wasting my time porting my heads.

[Datsun.David]

Mike -

Are you running 50 mm Mikunis?

Lou said the porting makes the most sense with them... I think the article title is a little bit journalistically inflammatory. Overall, it is a pretty good article I thought. Makes some good sense. Next issue promises some real world dyno results on some different set ups...

Just curious - practically - I know nothing on the flow characteristics side of the equation...

dw

[Mike Unger]

I use tapered bore 44mm carbs. Overall flow is one thing but how the air flows to enhance combustion is what is really important and can be enhanced by porting, camshaft and exhaust design. For a race car there are gains to be made by careful porting.

[Datsun.David]

Seldom is anything perfect. There is always room for improvement. It is pretty cool to see some of the stuff they are doing in other parts of the world... In this month's magazine, there are two different references to multiple fuel pumps with a surge tank in between... Cool.

[spyder]

I finally got around to reading the article. My take is there is not much benefit to porting the head with a 44PHH carb because the head flows enough to run out of carb. It also states, "You can now see why the factory race U20's ran Mikuni 50PHH with 43 mm chokes." This is my setup and and why I noticed better performance with port matching the manifold and head.

[SLOroadster]

I'd love to try a set of 50s on my car. The 44s with 40s work pretty well, but if there is more to be had, I'd be thrilled to see what its like.

Will

[Gregs672000]

I ran 40mm chokes and recently switched back to 37s on 45mm Dellortos. While I probably lost a tad on the top end, I gained a lot in overall street driving and throttle response. All of my transition problems from the low speed system to the mains went away. I have yet to time my cam, which I feel is likely to benefit the engine, perhaps a lot. I also plan on a custom header given Lou's results and comments. The head definitely outflows the intake overall, but the bigger chokes apparently did not give a good enough signal to the mains to get them to respond fast enough to not cause transition problems. Once it was on the mains it was great, but not fun to drive in general. This may change some with a better flowing exhaust, as an engine is an air pump and (in general) if there is a restriction then the pump can't pump as efficiently/effectively. Currently, for my engine and street driving, the 37s are the way to go. I hope to have the time and money to do a header and time my cam over the winter, then back to the dyno to see what that does...

[jamesw]

Since 50mm Solex Kyogos are unobtanium - has anyone tried 50mm Webers?

Cheers
James

[Alvin]

Does anyone have a copy of this article? Can you please post it here?

[spyder]

Didn't you originally post it?
It must have had a link because I at some point read it.

[Alvin]

Didn't you originally post it?
It must have had a link because I at some point read it.

No. Unfortunately all I had was a photo someone sent me…can’t recall who. Yes, someone subscribed and posted a link but that’s gone.

[iloveredmeat]

Didn't you originally post it?
It must have had a link because I at some point read it.

No. Unfortunately all I had was a photo someone sent me…can’t recall who. Yes, someone subscribed and posted a link but that’s gone.

@ tjp posted it, has anyone reached out?