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Old 04-11-2006, 01:11 AM
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Port CFM vs. Valve Size vs. Port Velocity...Data WANTED!

Hello fellow gearheads, after searching the depths of the knowledge base I have gathered enough info to answer many questions without have to post...cool. So now I need to as a question; can someone point me to a basic guide for choosing a port cc volume or a port CFM aim point based on my specifics?
I'll list my hardware just in case someone might have an eduacated reccomendation but a resource for furhter research would be much appreciated!
Goal: 500 streetable HP
Chevy 383, Hooker 2112 super comps, 3" exhaust, tunnel RAM, dual 500 CFM Eddelbrocks, forged flatops, 11.6:1 CR...balanced, blueprinted, full floaters blah, blah, blah....57 Chevy, Tremec KO, 3.73 gears, 4-link etc.
Yes and the missing goods:
L-98 GM Aluminum vett heads 1.94/1.50, 163 CC intakes that flow around 196 CFM at .500 lift..and those wonderful 58 cc chambers that give me that CR with flatops.
Bump stick to be announced....currently .498 lift, forgotten duration and definately lacking.
Specifcially, I will look at installing the 2.00 intake/1.56 or 1.60 exhaust valves (you tell me) and then having them ported to what CC/CFM?
Right now too much low end and mid and not enough top end. Obviously the cam and heads are the cause. But I don't want to kill intake port velocity for the sake of huge CFM at .550 (intended cam range) lift. It still needs to get out of the hole and cruise down the highway. I'm guessing with all the cubes and high CR that this combo will absorb some decent port volume.
For the sake of argument, lets not get off on other head casting suggestions....I have a few bucks into the heads and want to keep the CR/flatop combo.
Thanks!

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Old 04-11-2006, 01:19 AM
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Sorry, forgot this nugget; these heads are limited to the 2.00 intake valve as the max size....where does that come into play on choosing a final flow CFM aimpoint? (will 1.6 rockers make up for some of the small valve limitations...currently 1.5 rollers)
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Old 04-11-2006, 11:18 AM
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Quote:
Originally Posted by Elevinpointsixtoone
...L-98 GM Aluminum vett heads 1.94/1.50, 163 CC intakes that flow around 196 CFM at .500 lift..and those wonderful 58 cc chambers that give me that CR with flatops.... Thanks!
These heads are OK, the down side is the poor short turn. A good port job will wake it up. Personally I'd stick with the stock valves. Open up the pinch point at the pushrod, smooth out the short turn removing as little material as possible. Concentrate most of the porting in the area 1" before and after the valve. Shoot for 235 SCFM on the intake side.

Camshaft selection will be critical.

Last edited by automotive breath; 04-11-2006 at 11:27 AM.
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Old 04-11-2006, 12:15 PM
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I would personally skip these heads. The money you will spend to get them ported could cost more than a set that flows this well already. Just my opinion. There are plenty of 58cc heads that flow much better than the old-school L98s.

I agree that 235 cfm is a good target flow. If you go with newer heads, I might bump that up to 250 or so. Many newer heads take advantage of port profiles that give more flow with less sacrifice to velocity. That means you can make more power in the heads with less cam and not sacrifice low RPM velocity.

Here's what I do:
-I find what my target intake flow should be at sites like this. flow calculator I like to use 28 inches of water as my test data in that calculator since that's how most heads are measured. Some trial and error there will get you a target flow. Keep in mind that those numbers are theoretical. Thats the power you COULD produce if the engine ingests all of that air. On an actual engine, 235 CFMs would require 6500 rpm to produce 500 hp and a whopper cam to get there. If you bumped it up to say 250 cfm, you could probably make that power at 6000 with a milder cam. It sounds backwards I know, but its the benefit of modern head design.
-Then I visit sites like this... head flow numbers and find chevy heads that flow those numbers (or close enough that I can port them to get it.) Disregard valve size for now. They can be an effective tool to boost flow if you need it, but putting 2" valves in a stock L98 head won't do much because its not the limiting factor. Once you find a group of acceptable heads with the right range of flow at about .500" lift, start comparing intake port volume, E/I ratio, and chamber volume. The smaller ports almost always win. If they flow the same with smaller ports, its a winner. Since this is an 11.6:1 motor, I doubt its as big a deal for you. You'll be burning a steady diet of 110 fuel, so I don't picture it as a cross-country cruiser. E/I ratio should be on the order of 75-80%. Chamber volume can be increased or decreased with milling, valve jobs, and chamber grinding, but the closer the better.
-Talk to a cam manufacturer and tell them everything you know so far. They'll help you pick a cam.
-Then I plug all my stuff into Desktop Dyno. Its not perfect, but what a wonderfully informative program. It at least helps to identify mismatches and little things. On DD you can "match" things up. Play with net valve lifts to see what rocker arm ratio you need, play with port flows, valve sizes, etc.
-Then I visit forums like this one and ask questions like, "how much can I mill off a set of xxx heads?" or "should I use 2" or 1.96" valves?"
-Then I bloody build it.

Have fun.
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Old 04-11-2006, 12:52 PM
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You should not have to pay more than $400 to $500 for the porting. I agree with what A/B mentioned. That's where your going to pick up the flow on that head. There and in the combustion chamber.

It would not be my first choice of a head especially with all the high RPM parts your matching with them. The runners are just too small.
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Old 04-11-2006, 03:44 PM
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Really good stuff guys. Thats what I'm looking for. When I put this motor together it was 1990 and the L-98 was an excellent buy compared to whatever other new castings were available which were few. Old decent castings were getting harder and harder to find and I wanted to go with a high CR so the aluminum made sense, and still does. I had started with a 283 and the 1.94 valves were the biggest you could make work in the 3 7/8" bore. I blew that one up and moved the heads to a 4 bolt 010 350 block. Ramped up the project to make use of the new 383 technology that was just hitting the aftermarket (cranks, pistons etc) and here I am attempting to fine tune the mill. I only have about 4 thousand miles on this engine.
The heads have been helicoiled, have had traditional valve cover mounting points weleded in (to accoodate my roller rockers), have hard guide plates and 7/16ths threaded studs installed. They have been port matched to both my intake and exhaust along with a good 3 angle grind including a back cut. Something was done to the valve guides...maybe opend up a bit? and the PC seals were ditched for something that allowed more oil to pass through...this was all done at Gromm Racing heads in San Jose CA. A good friend of mine worked there and I had all this done for free...or rather I took professional pics of his 65 351 stuffed stang dragster indoors in our studio at work as trade for all the head work.
Also, I have fully polished the exterior of the heads. So....I have a few things into them as they sit. I would rather use them but am open to making a swap if it just don't make sense. You folks are helping me to find the upside and downside of all my options....just what I was hoping for!
I would need to send these out for porting (if it goes that way). Can anyone reccomend someone who would know what to do to these heads? For a fair price? $400-$500 would be fine...
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Old 04-11-2006, 04:32 PM
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If you can't find someone local I can get them done for you, no problem. They would be flowed before and after.
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Old 04-11-2006, 06:28 PM
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Quote:
Originally Posted by Elevinpointsixtoone
... I would rather use them but am open to making a swap if it just don't make sense. You folks are helping me to find the upside and downside of all my options....just what I was hoping for!
I would need to send these out for porting (if it goes that way). Can anyone reccomend someone who would know what to do to these heads? For a fair price? $400-$500 would be fine...
Personally I'd follow curtis73 recommendations, spend your money on a set of heads with a better approach to the valve. The extra cubic inches of the 383 will love the increased flow potential.

If you’re really determined to stick with these heads go for it. Plenty people still run them. Your desired 500 HP will be more difficult to find but still with in reach. If you decide to spend the bucks on porting make sure you go with some one that knows what they are doing, plenty can go wrong when dealing with the wrong person.
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Old 04-11-2006, 07:19 PM
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i have seen many 383 running the e-tec 170 head with air gaps making 470hp and 490 torque.

if higher rpm then look at the e-tec 200's

high cfm and high air speeds is what you want.

on my drag quad i have stock sized valves and ultra high velocity porting and its the best head that i have had done. so i am a firm believer in the high speed and cfm stuff
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Old 04-11-2006, 11:08 PM
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For comparisons sake, at $500 it sounds like my heads would flow somewhere around 235 CFM. At what velocity I don't know. I would be pretty much done with these heads at that point unless someone thinks a 2.00 valve would have some value....I would think the bigger the valve the greater the potential velocity by nature of communicating a stronger signal to the port....just theorizing here.
Anyway, what could I buy for $500? Nothin really...so really how much would I need to spend to buy a head that will flow 235 CFM or better out of the box? Out of the box should be less money than buying new heads and porting them. Upside would be greater flow potential, bigger valves to start and some modern technology working its magic.
To offset this I would sell my L-98's....how much are they worth? Like new, fully polished with some nice machine work included. I would keep my rockers, guide plates, big studs and just move them to the new heads. Maybe $600?
So, can I buy my desired aluminum heads, 58cc chambers, 235 or better CFM, high velocity runners (gotta include at low lift here too), 2.02 or bigger intake valves, stainless seats etc. for $1100 ($600 + $500 from the porting I would have done)? Am I in the ball park? Of course I give up the pretty exterior polishing......whatever on that one. Damn, those L-98's made sense 16 years ago! I can't believe its been that long and I'm still dinking with this thing!
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Old 04-12-2006, 07:13 PM
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Quote:
Originally Posted by Elevinpointsixtoone
...Damn, those L-98's made sense 16 years ago! I can't believe its been that long and I'm still dinking with this thing!...
When comparing your heads to newer designs make sure you understand the differences. Focus your attention to the intake port floor shape and the approach to the valve. Also compare the combustion chambers.

It's imposable to "port" your heads to the current designs with out adding material. The port floor is too close to the valve seat and the chamber shape is wrong.

Here are a few pictures of a more desirable intake port and combustion chamber.




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Old 04-12-2006, 08:46 PM
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Quote:
Originally Posted by Elevinpointsixtoone
Hello fellow gearheads, after searching the depths of the knowledge base I have gathered enough info to answer many questions without have to post...cool. So now I need to as a question; can someone point me to a basic guide for choosing a port cc volume or a port CFM aim point based on my specifics?
I'll list my hardware just in case someone might have an eduacated reccomendation but a resource for furhter research would be much appreciated!
Goal: 500 streetable HP
Chevy 383, Hooker 2112 super comps, 3" exhaust, tunnel RAM, dual 500 CFM Eddelbrocks, forged flatops, 11.6:1 CR...balanced, blueprinted, full floaters blah, blah, blah....57 Chevy, Tremec KO, 3.73 gears, 4-link etc.
Yes and the missing goods:
L-98 GM Aluminum vett heads 1.94/1.50, 163 CC intakes that flow around 196 CFM at .500 lift..and those wonderful 58 cc chambers that give me that CR with flatops.
Bump stick to be announced....currently .498 lift, forgotten duration and definately lacking.
Specifcially, I will look at installing the 2.00 intake/1.56 or 1.60 exhaust valves (you tell me) and then having them ported to what CC/CFM?
Right now too much low end and mid and not enough top end. Obviously the cam and heads are the cause. But I don't want to kill intake port velocity for the sake of huge CFM at .550 (intended cam range) lift. It still needs to get out of the hole and cruise down the highway. I'm guessing with all the cubes and high CR that this combo will absorb some decent port volume.
For the sake of argument, lets not get off on other head casting suggestions....I have a few bucks into the heads and want to keep the CR/flatop combo.
Thanks!

Your cylinder head selection is illogical. L-98 aluminum heads are poor flowing heads. They can be made to be a fair performer, but are more suited to low end torque production.

Don't lie to yourself and think that you can on a budget, get them to produce race car like power. I know that you probably like the look of them, but by the time you actually pay someone to port them EFFECTIVELY. You could have went out and purchased a brand new set of aluminum heads from Brodix or Dart or RHS, and saved yourself a bunch of time, and also the disappointment that your goals aren't met.

Large cubic inch small blocks like 383's or 400's are under-valved no matter what you do, so why further hinder it by putting a restrictive, albeit aluminum head on there?

You want a daily driver and you are shooting for an 11.6:1 compression ratio? You should re-think that.

There are tons of good, new, affordable heads out there, why not use them?
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Old 04-12-2006, 10:54 PM
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Originally Posted by NAIRB
Don't lie to yourself and think that you can on a budget, get them to produce race car like power. I know that you probably like the look of them, but by the time you actually pay someone to port them EFFECTIVELY............You could have went out and purchased a brand new set of aluminum heads from Brodix or Dart or RHS, and saved yourself a bunch of time, and also the disappointment that your goals aren't met.
You want a daily driver and you are shooting for an 11.6:1 compression ratio? You should re-think that.
Wow! I think you may have missed my point of bringing up the subject to begin with. I'm looking for both the upside and downside of working on these heads, which I didn't have flow numbers for when purchased in 89. They were touted as being something pretty special and they were used on my 283 which still makes sense as "mid range torque heads" you yourself stated. They ended up on the 383 built in 92 since they were virtually new and had a few bucks put into them. All my cash went into a full balance and forged bottom end goodies. The polishing will not be a deciding factor..it just took me about 40 hours of hand labor to complete.
Another individual stated 400-500 would cover a good port, not me....if I can sell the L-98's for about $600 (was asking if that is reasonable or not) plus the $500 I would have spent I could go shopping for around $1100 and be spending the same amount of cash. Didn't say that was my budget...just finding an even level trade off for where I could be at....and I did find that $1100 would get me into some fast burns or Edelbrock heads. I was pleasantly surprised!
But where did a daily driver come from? Not this thread! And where did I state that the L-98's would produce the HP I was looking for? I was looking to you folks to illustrate the difficulties and options....never did I say something to the contrary....hmmmm...I do see a comment by me that states "if it just don't make sense, new heads are not out of the question". I also have ran this setup at the stated 11.6:1 CR for about 4000 miles and find it to be satisfying. I live at 5000 feet of elevation and can run 91 with octane boost on the street, if its not too hot outside, and not pre-ignite. But I do thank you for your comment no matter how misguieded and I am looking into new heads as the most likely choice.
Automotive Breath, thanks for the pics....I wish I could see what I'm comparing those too...I do see that the chambers look smaller, more contoured and deeper with a lot of quench... increased turbulence?
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Old 04-13-2006, 01:15 AM
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Rule of thumb says = normally aspirated you can get 2 h.p. per each cfm of intake flow on the flowbench, if the exhaust flow is 70% or better.

Using that...... you can't reasonably get 500 hp with those heads.....

of course, horsepower IS based on RPM.

Last edited by xntrik; 04-13-2006 at 01:27 AM.
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Old 04-13-2006, 06:30 AM
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Check this site out for what I believe are excellent prices for Brodix al. heads as well as intake and head gaskets.

tonybarkerracingengines.com

Last edited by ztoy; 04-13-2006 at 06:36 AM.
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