Thread: Track Times
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Old 08-29-2002   #19
f-crazy
GTA Member
 
Join Date: Oct 2001
Location: michigan/New york
Posts: 404


part #2

To start with I had a plan but it got changed around a bit. First I decided to hold off on the valve job. I also decided to do some porting first, get the numbers, then cut for the 2.02's, to see if they really make a difference, instead of cutting them first like I was going to.
So I did step 3 of my plan first, and part of step 4. This amounts to removing all the wierd bumps in the passages, a little bit of widening of the port at the pushrod pinch, some light pocket work, and a light radiusing of the short turn and valve guides. I also deburred the rest of the head, and radiused the oil drain back holes since I was going. I just left the ports rough cut and did absolutely no polishing. So here are the numbers, all taken on our superflow 300 at 28" of water.

Stock Stage One Port
Lift Intake Exhaust Intake Exhaust
.1 53.9 41.6 63.5 41.2
.2 111.2 95.2 115.2 87.7
.3 157.3 112.4 163.2 122.7
.4 182.0 116.6 198.2 151.6
.5 192.0 116.9 224.8 161.3
.6 193.6 117.6 228.6 170.7

As you can see, with just a little bit of work (about 2-2 1/2 hours for a complete set of heads, if you've got good tools, longer if your gonna use a dremel) we picked up 35 CFM on the intake, and a great gain of 53.1 on the exhaust, which takes our intake exhaust ratio to a much better 74%, instead of the stock 60%. And this is without touching the factory single angle valve job (which really sucks on these heads).

So far we've seen an 18% improvement on the intake and 45% on the exhaust with just basic work that anyone can do. Just take it easy with the grinder and don't remove too much metal. Air flow velocity is also up as well.

My posted goals were 254 on the intake and 180 on the exhaust. As you can see we're well on our way there, especially on the exhaust side.

Coming up I'll do some bowl work, get a little more serious in the pocket, and at the pushrod pinch. I've got a lot more meat to smooth out the short turn radius and do some more profiling of the valve guides. Also a valve job, which will really improve low lift flow especially. Match to the intake ports (I'm doing the LT1 intake conversion). And finally cutting for 2.02/1.6 valves and unshrouding them. Also if you look down the ports you'll see a bad area where the rocker studs come down. It's a pretty big dip and I'm sure is hurting flow, dunno what, if anything I'm going to do about that yet.

Theoretically our stock heads will support up to 400 hp with the right matched components. Our lightly ported heads will support up to 470 hp, now on a 350 you'd have to spin it to between 6200 and 6800 rpm to get that kind of power (once again theoretically). On a 400 it would be between 5500 and 6000. Desktop dyno shows an increase vs. stock l98 heads of 20 hp on a stock tpi with small tube headers. More than 40 on a 383 with lt4 hot cam and intake mods.

Couple of notes here:
All theoretical math is done with accepted formulas provide by superflow.
All flow numbers are corrected to standard atmospheric conditions. Not much of a difference (about 1%).
A valve job would help these numbers a lot, the reason I'm not doing it til later is 'cause most of you wouldn't be able to do one at home, and I don't want to have to do it twice, so I'm waiting til I get the heads cut for the bigger valves.
This level of porting would cost you around 150-200.
In part one I mentioned blocking or restricting the exhaust cross over port to make sure you got accurate flow #'s. I tested the difference on this so you could see it. My numbers are with it blocked, WITHOUT it blocked the exhaust flow at .6 on the stock heads was 150.6, a substantial difference that you wouldn't see on a running engine.
My damn camera still isn't working, soon as I can I'll get some pics up for ya.
A variable speed of some kind is imperative, a fixed speed setup just doesn't give you enough control. Car craft had a neat trick where they just hooked there single speed unit up to a dimmer switch if you don't have a variable speed unit.
Think that covers it for this installment. I'll keep you posted.
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