Head Porting - How much flow is too much?
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Pro
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From: La Jolla California
Head Porting - How much flow is too much?
I'm in the progress of having my LT1 heads ported. My porter currently has them flowing the following:
Intake
.200 127
.300 188
.400 230
.500 258
.600 261
Exhaust
.600 190 (only one I know off-hand)
This seems to be about consistent with most "Stage II" LT1 porting jobs. However, my porter says he can get the intake up to about 270 cfm for $100 more.
Would this be worth it? Or would I have to rev my engine higher to take advantage of it? Does higher flow help performance at all RPMs or just allow the engine to breath at higher RPMs?
I'm going to be running either a 230/236/110 or 236/242/110 duration cam in my 383 LT1 with 11.5:1 compression if it matters. The rest of my setup is in my sig.
Thanks
Intake
.200 127
.300 188
.400 230
.500 258
.600 261
Exhaust
.600 190 (only one I know off-hand)
This seems to be about consistent with most "Stage II" LT1 porting jobs. However, my porter says he can get the intake up to about 270 cfm for $100 more.
Would this be worth it? Or would I have to rev my engine higher to take advantage of it? Does higher flow help performance at all RPMs or just allow the engine to breath at higher RPMs?
I'm going to be running either a 230/236/110 or 236/242/110 duration cam in my 383 LT1 with 11.5:1 compression if it matters. The rest of my setup is in my sig.
Thanks
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Re: Head Porting - How much flow is too much? (Langadorf)
The more flow you have the less cam it takes to make the same amount of power. Monty once posted and average flow rate equasion. So it's not total flow that counts unless you have solid lifter radical ramps which hold the valve at max. CFM for a period of time.
You flows are okay. IMO go with 112 LSA and steeper ramps. My heads are 304/230 CFM at .600
You flows are okay. IMO go with 112 LSA and steeper ramps. My heads are 304/230 CFM at .600
Burning Brakes
Joined: May 2000
Posts: 958
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From: Brisbane, Australia 1985 Coupe
Re: Head Porting - How much flow is too much? (Langadorf)
If you are not going to rev it a lot with high lift then I would think the .400 to .500 lift flows would be more important......... but then again George and others know far more than I.
:cheers:
:cheers:
Burning Brakes
Joined: Jul 2000
Posts: 963
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From: melbourne,Australia
Re: Head Porting - How much flow is too much? (Langadorf)
What goes in has to come out again or there is no point putting it in....that is a simple way of saying that you should start at the other end,what capacity can your exhaust system flow?.then look at what % your ex valves flow in comparison to the inlet side...look for +80%.....Chevy Hiperformance have done a long series on head flows and it is on their website.......good luck......john :chevy ;)
Le Mans Master
Joined: Aug 2000
Posts: 6,273
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From: Austin TX
Re: Head Porting - How much flow is too much? (Langadorf)
Fuel injection heads on street cars which operate at low and medium RPM need velocity and CFM to perform. This means smooth runners end to end and good bowl transition.
I've been told that torquey engines like the 383 do better with high velocity, lower cfm heads. Not sure what this means for cam selection.
I've been told that torquey engines like the 383 do better with high velocity, lower cfm heads. Not sure what this means for cam selection.
Race Director
Joined: Oct 2000
Posts: 15,017
Likes: 79
From: central FL, near the beach.
Re: Head Porting - How much flow is too much? (Langadorf)
it depends on what he is doing. if he is cutting the guide way down or going very close to a water jacket i would say no, otherwise things like a back cut on the valves are a no brainer.
Thread Starter
Pro
Joined: Jun 2002
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From: La Jolla California
Re: Head Porting - How much flow is too much? (Matt Gruber)
I'm not sure exactly what he's doing to get the extra 7, but I'll ask him (I'm sure it's not cutting down the guides or anything like that).
I've got the exhaust numbers also:
190 .600
185 .500
177 .400
141 .300
104 .200
My goal is to be in the 11s. Will these flow numbers support this much HP? Or would the 7 more CFM be worth it/needed?
I've got the exhaust numbers also:
190 .600
185 .500
177 .400
141 .300
104 .200
My goal is to be in the 11s. Will these flow numbers support this much HP? Or would the 7 more CFM be worth it/needed?
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Re: Head Porting - How much flow is too much? (Langadorf)
I made some guesses in DD2000 for you on intake type headers and cam event numbers. also valve size. I installed all the CFM's you gave me this is with the milder 230/236 cam. I really need the cam card even numbers to get it right on:)
Chevy 383
37
1 4.030000
1 3.750000
8
1 2.020000 intake
1 1.600000 exhaust valve size
1 11.700000 cr
1 750.000000 cfm
Tuned-Port Injection
Large-Tube Headers With Mufflers
Dual Purpose Street Roller
0.050-Lift
1 0.550000
1 0.600000
Cam event numbers
1 7.000000
1 43.000000
1 52.000000
1 4.000000
HP TQ
2000 201.150177 528.019226
2500 247.074982 518.857422
3000 301.112671 526.947144
3500 359.938873 539.908325
4000 411.296875 539.827148
4500 454.907440 530.725342
5000 490.813599 515.354309
5500 508.991516 485.855530
6000 511.236328 447.331787
6500 502.457764 405.831268
Give me the right stuff and I cam run both cams with the increase in CFM :cheers:
Chevy 383
37
1 4.030000
1 3.750000
8
1 2.020000 intake
1 1.600000 exhaust valve size
1 11.700000 cr
1 750.000000 cfm
Tuned-Port Injection
Large-Tube Headers With Mufflers
Dual Purpose Street Roller
0.050-Lift
1 0.550000
1 0.600000
Cam event numbers
1 7.000000
1 43.000000
1 52.000000
1 4.000000
HP TQ
2000 201.150177 528.019226
2500 247.074982 518.857422
3000 301.112671 526.947144
3500 359.938873 539.908325
4000 411.296875 539.827148
4500 454.907440 530.725342
5000 490.813599 515.354309
5500 508.991516 485.855530
6000 511.236328 447.331787
6500 502.457764 405.831268
Give me the right stuff and I cam run both cams with the increase in CFM :cheers:
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Thread Starter
Pro
Joined: Jun 2002
Posts: 544
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From: La Jolla California
Re: Head Porting - How much flow is too much? (gkull)
Here are the cam cards for those 2 cams:
http://www.compcams.com/information/...umber=08-432-8 http://www.compcams.com/information/...umber=08-433-8
I'm also running a carburetor, not tuned port injection.
Thanks alot!
http://www.compcams.com/information/...umber=08-432-8 http://www.compcams.com/information/...umber=08-433-8
I'm also running a carburetor, not tuned port injection.
Thanks alot!
Drifting
Joined: Jun 2002
Posts: 1,620
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From: Orlando Florida
Re: Head Porting - How much flow is too much? (Langadorf)
Hey, Im just a Florida Man with my .02 worth. I would spend the money and get those heads to flow at what Gkull has. If you want to go elevens in a C3 start removing weight. Remove the emergency brake tabs and get a big tire under there, but not sticking out. Why am I talking about tires? Because with the potential you have, traction is gonna be a big issue. Now back to your combination, I prefer Crane, but Comp also makes a good product. I like the profile of the 288, and if this is not a daily driver I would go with a 9" converter. Im sure folks would disagree, but these cars are so heavy that it takes a decent stall converter to pull the short times required to go mid 11's.
You should have no problem meeting your goal with that combination.
Good luck,
:cool: :chevy
You should have no problem meeting your goal with that combination.
Good luck,
:cool: :chevy
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Re: Head Porting - How much flow is too much? (Langadorf)
What carb and what intake? The numbers changes aren't drastic when you vary intake types. What size valves?
Tire smokin 427 is right about the weight. For tires on the strip plan on 10X28 slicks with about 10 pounds of air. With the 500 foot pounds of Tq higher stall isn't as important. I have a 3500 stall now. higher stalls can overpower even the best of tires.
I should have known not to bother looking at CC suckass wed site. I told them 5 years ago I wouldn't buy their products because the web sit is so pisspoor I need real .050 cam event numbers not some guess at what does .006 really mean
:rolleyes:
[Modified by gkull, 11:01 PM 8/20/2002]
Tire smokin 427 is right about the weight. For tires on the strip plan on 10X28 slicks with about 10 pounds of air. With the 500 foot pounds of Tq higher stall isn't as important. I have a 3500 stall now. higher stalls can overpower even the best of tires.
I should have known not to bother looking at CC suckass wed site. I told them 5 years ago I wouldn't buy their products because the web sit is so pisspoor I need real .050 cam event numbers not some guess at what does .006 really mean
:rolleyes:
[Modified by gkull, 11:01 PM 8/20/2002]
Thread Starter
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Joined: Jun 2002
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From: La Jolla California
Re: Head Porting - How much flow is too much? (gkull)
Carb - 750cfm Holley DP carb
Intake - Thinking of going with an Edelbrock Torker Original or GM's dual plane intake for LT1s.
Valves - 2.02/1.6
Cam- Those links do have .05 cam numbers. They are 230/236 and 236/242 respectively.
Intake - Thinking of going with an Edelbrock Torker Original or GM's dual plane intake for LT1s.
Valves - 2.02/1.6
Cam- Those links do have .05 cam numbers. They are 230/236 and 236/242 respectively.
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Re: Head Porting - How much flow is too much? (Langadorf)
You have me all confused. I was thinking that you had a modern Lt1 1990's motor with aluminum heads. Well maybe on second thought you do. Your intake choices have to match your heads ports and intended rpm range.
Cam event numbers are like this. duration numbers are a very ruff story of what a cam really is.
7 43 intake 52 4 exhaust
The 7 is when the valve opens before top dead center it closes 43 degrees after bottom dead center The exhaust opens at 52 degrees before BDC and closes at 4 degrees before TDC. Those events make for a 230/236 cam with 111 LSA or lobe center. That cam is just some numbers I picked out to get the power graph above. That cam would run into problems with 11.7 compression trying to run on pump gas the valve overlap is only 11 degrees
Cam event numbers are like this. duration numbers are a very ruff story of what a cam really is.
7 43 intake 52 4 exhaust
The 7 is when the valve opens before top dead center it closes 43 degrees after bottom dead center The exhaust opens at 52 degrees before BDC and closes at 4 degrees before TDC. Those events make for a 230/236 cam with 111 LSA or lobe center. That cam is just some numbers I picked out to get the power graph above. That cam would run into problems with 11.7 compression trying to run on pump gas the valve overlap is only 11 degrees
Thread Starter
Pro
Joined: Jun 2002
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From: La Jolla California
Re: Head Porting - How much flow is too much? (gkull)
Yeah it's a '90s LT1.
I gotcha - I misread "cam events" to mean duration. I'll talk to comp cams today and see if they can give me valve timing @.50.
I gotcha - I misread "cam events" to mean duration. I'll talk to comp cams today and see if they can give me valve timing @.50.
Race Director
Joined: Oct 2000
Posts: 15,017
Likes: 79
From: central FL, near the beach.
Re: Head Porting - How much flow is too much? (Langadorf)
rule of thumb:
each cfm equals about 2hp
so
7 cfm is ABOUT 14 hp
i think it is worth $100 if it does not compromise the strength of the casting
good luck :cheers:
each cfm equals about 2hp
so
7 cfm is ABOUT 14 hp
i think it is worth $100 if it does not compromise the strength of the casting
good luck :cheers:
Team Owner
Joined: Apr 1999
Posts: 21,953
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From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Re: Head Porting - How much flow is too much? (Matt Gruber)
Matt what is the equasion for CFM = number of total hp. Like Monty's small block with 358 cfm heads on his 427 small block reach just under 700 hp and 600 flbs on the dyno. My heads are 304 cfm at .600 lift.
My advice for anyone building your dream motor is to spend the $39.95 and get DD2000. Then play with all the figures. I haven't played much with the cam vs. static compression ratio section. But it would be very helpful to make decisions about having to use race gas or not.
Chuck harmond was explaining to me about how his L-88 with 12.5 pistons had less cranking pressure than some 9.5 cr motor because of his cam
As for your choices of cams you might need the hotter one to bleed off pressure from your high compression. But then your going to need a small single plane intake to feed it. Then the flip side is you H-roller cam has a 6500 or less rpm limit and your get max power at or near red line. Which is not good. BeachBum C-4 section has a very good 11.65 car with less power than your trying to attain.
My advice for anyone building your dream motor is to spend the $39.95 and get DD2000. Then play with all the figures. I haven't played much with the cam vs. static compression ratio section. But it would be very helpful to make decisions about having to use race gas or not.
Chuck harmond was explaining to me about how his L-88 with 12.5 pistons had less cranking pressure than some 9.5 cr motor because of his cam
As for your choices of cams you might need the hotter one to bleed off pressure from your high compression. But then your going to need a small single plane intake to feed it. Then the flip side is you H-roller cam has a 6500 or less rpm limit and your get max power at or near red line. Which is not good. BeachBum C-4 section has a very good 11.65 car with less power than your trying to attain.
Race Director
Joined: Oct 2000
Posts: 15,017
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From: central FL, near the beach.
Re: Head Porting - How much flow is too much? (gkull)
the rule of thumb for carb size is 1.6 cfm for each hp.
so 500 hp requires 800 cfm.
i always put a vacuum gauge on the windshield for a redline WOT test in 2nd gear. if it pulls 2" the carb is too small.
so 500 hp requires 800 cfm.
i always put a vacuum gauge on the windshield for a redline WOT test in 2nd gear. if it pulls 2" the carb is too small.
