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Author Topic:   World JR head porting?

Posts: 786
From: God's Country!... Port Alberni B.C. Canada
Registered: Jul 2001

posted 04-09-2002 12:54 AM     Click Here to See the Profile for stang106   Click Here to Email stang106     Edit/Delete Message   Reply w/Quote
For those who are familiar with the World Jr and their shortcomings, where are the weak areas? After reading David Vizard's head book on Chevys, I see possibly two problem areas, but lack the experience to be certain. The application is a street 351W 10:1, 569/585lift, 239/247 @.050 duration, RPM manifold, 750 holley, 6500 max rpm.
1) The guide area at the bottom of the port pocket is too narrow. The guide needs to be narrowed and the floor by the guide needs to be widend. Is this thinking correct?
2) About .125 and further below the exhaust valve seat the port is very narrow, especially the short side radius. How much wider than the seat face should the port be? I understand the importance of smooth transitions but it does seem excessive.
3) I was also going to carefully take a nail file to the machine faced angle points to smooth the valve angles- Vizard claims a six cfm low flow increase with this?
The machinist says to just bolt them on but he is a chevy guy, or doesn't want to spend the time looking and explaining it. I think I can do better.

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Posts: 935
From: Lakewood, CO, USA
Registered: Jun 2001

posted 04-09-2002 10:48 AM     Click Here to See the Profile for JCQuinn@work   Click Here to Email JCQuinn@work     Edit/Delete Message   Reply w/Quote
I am not familiar with the World Jr heads but I have done a lot of work with a flow bench. On production type heads 90% of the flow gains are made between the guide and the valve. Every head I have worked with (pre 1980) needs to have the guide boss narrowed. As to the narroeing of the port itself, there seems to be two schools of thought. One is that the port should be constant volume all the way through. The other theory is the port should be a venturii shape with the restriction at or very near the valve seat. I don't know which theory is best but my flow bench always showed the biggest gains from enlarging the valve size and opening up the area just below the seat.

In general the heads I worked with ( small block Chevy and Ford Windsor and Cleveland) liked th have the guide removed from the port, the bowl area below the valve opened up as far as possible, and the largest valve possible installed. Both the intake and exhaust liked the port raised, especially the exhaust. The exhaust also liked a rounded top.

On a street car I would not remove the guide completely. Just narrow it and maybe shorten it. When you are working on the guide remember the direction of flow and that the most efficient airflow shape is a teardrop.

Smoothing the sharp ridges will increase the smoothness of the flow but will it be worth the effort? A good machine shop should have a Serdi type head machine that will cut all the seat angles all at once with a cutter. There are cutters available that cut a radiused seat with no more effort or time that a stock valve job. If your machine shop does not have a seat cutter for this, offer to buy the cutter blade and bring it with you when you get your heads done.

Probably the most effective head work and some of the cheapest head work is what most shops call the stage one. they clean up the bowl area and sometimes install larger valves. If your machinist says just bolt them on I would seriously consider finding a machinist who has some understanding of what high performance is.

John Quinn

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Posts: 1341
From: Charlotte NC usa
Registered: Apr 2001

posted 04-09-2002 11:12 AM     Click Here to See the Profile for Mpcoluv   Click Here to Email Mpcoluv     Edit/Delete Message   Reply w/Quote
Why are you considering Windsor Jrs on a 351?
If you don't have them yet, buy Roush 200 heads. You will save a lot in port work.
FWIW Vizard has a set of Windsor Jr lites (aluminum) on his 5.0 mustang. He likes the Junoirs for 289-302 sized motors.

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Daniel Jones

Posts: 898
From: St. Louis, MO
Registered: Aug 99

posted 04-09-2002 12:48 PM     Click Here to See the Profile for Daniel Jones   Click Here to Email Daniel Jones     Edit/Delete Message   Reply w/Quote
Vizard also wrote a recent artice on porting the Windsor Jr.'s in one of the Mustang magazines. A very good article. I can't recal if it was 5.0 or MMFF but it was within the last 2 months.

Dan Jones

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Posts: 786
From: God's Country!... Port Alberni B.C. Canada
Registered: Jul 2001

posted 04-10-2002 12:34 AM     Click Here to See the Profile for stang106   Click Here to Email stang106     Edit/Delete Message   Reply w/Quote
Thanks guys,
Yes, I do have the heads. They are the Jr's as for a primary street car I wanted the velocity for bottom end street use; the few times a year it will see the track I can live to sacrifice a bit of top-end power. If anyone sees the Vizard article please let me know, after reading his work I really respect his knowledge and would like to hear about what he has to say about the World Jr's porting.

'70 ragtop Stang
"I live my life 16.090 seconds at a time"

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