Stroked SBC

I've got a question for the guys who port on the LS based heads alot. What kinda of air speed in FPS are some of you guys seeing over the short turn. I've had a 243 casting laying around the shop for over a year and finally got around to picking it up and playing with it the other day. Cut it for 2.02, ground the snot out of it and it went 297@.580 and held there till .620 before it backed up. Backed it back down to .575 and probed it with the pitot and spent the next 20 minutes trying to figure out what was wrong with my pitot as the airspeed I was getting I thought was WAY to high.

So I was wondering what you guys are seeing for airspeed on these heads after porting?

Stroked SBC

Holy smokes Batman, there doesnt appear to be anyone on this site that actually does their own head porting. Or atleast someone who measures airspeed. Can this be possible?

Adrenaline_Z

I would search or PM users:

airflowdevelop
nighttrain66

If you can't get a hold of them, there are others I can direct you to (not on
this site however).

airflowdevelop

How fast...and yes...this is a major problem with most of the cathedral port heads...you have to change your porting technique a little.

I assume it was over 330fps. I also assume that you had to bolt the bench down to the floor.

Can you send me a straight on pic of the SSR? What is the taper %?

What for valvejob, and any back-cuts if made. What is the throat diameter.

Where is current limiting factor (MCSA)? What is the CSA over the SSR?

Dennis

Stroked SBC

Hey Dennis,

Actually current airspeed is as high as 408 over the apex. I haven't really messed with it a whole lot as of yet. Knocked out the bolt boss and widened the whole port out some, but could have gone further, but I did take quite a bit out of the hook wall, and raised the roof some on that side as well. I didn't even take out all of the airdam on the guide, only about 85-90% of it. I laid the short turn back some and increased the bias some, but nothing major. I pretty much just roughed it in and hit it with a 60 really quick to smooth some of the real rough parts. I haven't even taken any measurements yet.
Currently it has a 38/45/60/75 vj but was thinking of going to a 65 bottom just to see what it does. I was actually kinda surprised that it didn't explode when it backed up, just started skipping at about .580 till .620, and at .700 was still only down about 10-15 and didn't run you out of the room by any means. Next time I get to it I'm going move over the strait wall some more and start massaging the short turn and bowl bit by bit. The one head I have is just kinda a learning tool, as the LS stuff still hasnt caught on up here in MT yet.

airflowdevelop

I would concentrate on the SSR design. What is the distance from the deck to apex? if it has enough CSA in theory (which I am betting it doesn't at that kind of air speed) you can start probing the transition on the pinch wall. A super soft SSR is about the only way I can get these things to calm down with my style of porting.

I never really seen too much out of the airdam, short of some localized velocity problems. If you match both sides of the guide equal to the seat on a 243, you will most likely hit water...so watch for that.

Have you tried pooring on some depression? I would think from what you are telling me, that before 36" these things will be backing up at .500". Eventhough 90% of all cathedral ports do this...don't think it is right by any means. Fix this problem, and you will be rewarded!

I would stop playing with the bowl, until you get the SSR under control, it is your limiting factor currently. Your valvejob should work pretty nice. Make sure you blend the venturi on SSR and bias side into the 75.

Dennis

Stroked SBC

Thanks for the tips Dennis.

I'm should be able to pick it up again this week as I'm getting caught up a little right now. I'll let you know how it all works out.

Thanks again.