Porting a U20 is Such a Waste of Time

[Alvin]

Anyone read ROADSTER magazine lately?




Popcorn at the ready. Microwave check.
ENJOY

[spyder]

I'll be the first to disagree.

[Alvin]

I'll be the first to disagree.

excellent. Where is your dyno result?

[Datsun.David]

This should be interesting...

Cue Greg....

[garth]

The forum's been a little tame of late, so trust Alvin to generate a provocative topic

An interesting subject but does it need recent fresh evidence? The U20 is nearly 50 years old. A lot of motivated racers and their technicians have studied, explored and documented the engine's power limits. This is an assignment for an archivist.

As Alvin suggests: produce before and after dyno results with description of modifications from stock. Pass the popcorn!

[fj20spl311]

Porting, valve stem size, and cam design all need to work together.

I have not read the article, but they are talking about applying "L" series theory to the U20 not working.

I think Wil might disagree with "its not worth the effort"

I am pretty sure you can easily make the port TOO big.

My buddy had an FIA head back in the day and the ports were much too big for an engine with a carburetor.

[GeoffM]

I don't even have a U20 nor do I have any experience in porting a head but I am enraged...enraged I say!!

[spyder]

I don't have a dyno results.
I port matched the manifold and head to the carbs (50mm) to take advantage of their flow potential. In the early days when I acquired these carbs I didn't realize they weren't stock. This is the old saw I get from some vendors, "You can't drive that on the road."
I tried 41mm venturies instead of the original 43mm ones but I didn't like the reduction at the top end so I went back with the 43's.
I notice in the part of the article that I can read it states "It is very difficult to get any more cylinder head flow without affecting drive-ability because it is so good." As far as my drive-ability goes, it is very tame until you hammer the gas. Without knowing how the engine is set up, SU's, 44's, what cam/ignition and/or drive train I find that statement useless.
Perhaps someone could post the full article for better elucidation.
Did anyone burn their popcorn?

[tjp]

Best I can do with a small crappy scanner. Hopefully these pages are legible.

http://s1316.photobucket.com/user/tputl ... t=2&page=1" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;

[mikeb]

Thanks, Tim - it reads just fine. A very good article...

Can't wait for next month: "In next months magazine, real world engine dyno figures will be shown comparing power figures of short four-into-one extractors versus long, tuned length systems on a modern-built U20"

Mike

[Gregs672000]

Sorry guys, I just don't have time to dig into this... Bought a house.. Soooo much to do. As
Phil said, it's part of a system, one I'm still working to adjust and achieve fully. I have not had time to put the Roadster on the dyno again with the Isky cam, let alone work on checking cam timing. What all U20 owners can take away from all of this is they have one of the best flowing production heads of the era. Steve has always jokingly said that a Roadster is "a cylinder head looking for a car." That said, there is always room for improvement. Cost effectiveness is a question to ask. If everything were perfect from the factory, then Steve wouldn't be modifying Ferarri heads for Dennison... Ya know, the guys who just won Pebble Beach...

[mitch_04]

I can't imagine any cylinder head not benefiting from a little port matching and smoothing of the intake and exhaust chamber. Sure, you could over-polish the intake and cause fuel droplets to form and fall out of the charge, but having a highly polished exhaust can generally do nothing but improve flow. As long as you aren't reducing port velocity, I wouldn't believe that increasing the air/fuel charge's ability to enter the chamber without being disrupted could hurt. I would believe it would help.

Then again, I have no dyno results to prove anything either. It takes me long enough to just work on it, much less investigate and test!

[Gregs672000]

Was able to read the article... laughed at the title... what did I say!!! As I, Phil and clearly Lou would agree, it is all about making the parts work as a system. Maintaining velocity is extremely important, and has always been central to our modifications. It may very well be that the cost of extensive head mods are not cost effective for what you gain, but I still think that is yet to be seen. I do believe that a major limiter on my engine is the header and likely cam timing, both of which I hope to address over the winter if I can get through the house buying and renting of our current houses without going insane. After that, you can be assured I will be re-visiting this topic!
So, put up your popcorn... and please, no microwave crap!

[mitch_04]

But the microwave is sooooo easy!

[fj20spl311]

Hot air works for me!