L98 Iron Head Project Part 2. Long but informative
 

Ok back to the L98 Iron head project. For those of you who might have missed part one here's the link.
https://www.thirdgen.org/techbb2/sho...threadid=96065

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.

Interesting read, thanks for sharing. Anychance of you posting some pics of your handywork?

Yeah, check the notes at the end, soon as I get the camera working, or get a new one.
John

Interesting... Keep it Up.

Great read. Makes me wanna keep the stock heads.

Hey, where can I get the desktop dyno?
Sounds like something worth having.

BTW For comparison here are the flow #'s on the L98 Aluminum heads.

Corvette Aluminum # 113
Lift/Intake/Exhaust
.100 62 49
.200 116 98
.300 161 130
.400 185 152
.500 195 155
.600 199 159

2 hours work and you now have a set of heads that will outflow the corvette heads throughout the lift range? Nice work :) How hard is it? Do you have to have any special knowledge? How much does the equipment cost? And you expect to get better? Please post some pics when you get your camera up. Thanks.

Thanks, it's not that hard, It was about the same level of porting as in CHP's most recent home head porting article, which is minimal. Have to admit I was pretty dissapointed in their gains. No real special knowledge, the only thing that's counterintuitive is the fact that removing more metal is not always good. Some reading would help, good article in car craft a couple months ago, and check www.mondellotwister.com, there are some good articles there. Equipment is a couple hundred bucks. Yes I figure I can get at least another 30 cfm on the intake, 20 on the exhaust, conservatively. Should have some pictures this week.

Excellent! I'm going to try this on an old set of heads I have lying around. Looking forward to the pics.

I'm currently in the middle of a porting project that has taken 2 weeks spending 2+ hours every night after work. It brings a whole new angle on the cast vs alum head debate. I went with cast becaues of the thermal advantages, heat = power. However having seemingly dumped half my life into one porting job i can say that cast iron doesn't "Cast" and never will as well as aluminum. Aluminum cuts 1/2 the porting time off the job.
1.) the ports start off cleaner
2.) the material is 10x easier to work with, almost TO easy.

However like fram knows so well, there's nothing like the feeling of a job well done. Im almost scared that i'm going to get more flow than I want :p

I have another thread with some pics after removing all the flash but you can still see some cast seam, not to mention you have to do all your worth within the limitation of your tools. Its nearly impossible to find a stone longer than 1" and the burrs that are longer can hit $40 for carbide.

There's not enough credit given to port work so here's rhuarc30's credit, GOOD JOB MAN!!!

:D

Yes, bringing up an old post:)
 

Rhuarc...couple of questions for you regarding Stage 1 porting..

Did you radius and blend the seats to the runners? I notice some severe sharp edges there.

Did you tear drop the guides in stage 1?


Reason I'm asking is your Stage 1 numbers for flow pretty much match posted numbers for my Accel base and runner setup.

Thanks

Also, did you radius the quench and CC lines on the heads for detonation?

I guess you know what I'm doing today;)