More Lift = Less HP?
Thread Starter
Melting Slicks
Joined: Sep 2004
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More Lift = Less HP?
I used Desktop Dyno 2000 when I first decided to go with 1.5 rockers but I thought that with my new intake and carb things might have changed, guess not. How accurate do you guys think this is? I input all the head flow numbers into the program. And I realize that my engine won't make this much hp, but I think that power increases will still relate.
If you don't agree with this how much power do you suppose that I'll make by going from 1.5 - 1.6 rockers on a my AFR195 383? Lift .520 .540 corrected lift .555 .576... I think.
1.5 Rockers
1.6 Rockers
If you don't agree with this how much power do you suppose that I'll make by going from 1.5 - 1.6 rockers on a my AFR195 383? Lift .520 .540 corrected lift .555 .576... I think.
1.5 Rockers
1.6 Rockers
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
THose AFR heads max out CFM wise at .500" lift therefore it dosen't matter if you open the valve another inch you are at max flow that is why there is no HP gain
Thread Starter
Melting Slicks
Joined: Sep 2004
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Originally Posted by MotorHead
THose AFR heads max out CFM wise at .500" lift therefore it dosen't matter if you open the valve another inch you are at max flow that is why there is no HP gain
Safety Car
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From: Youngstown Ohio
Originally Posted by torqvette
Awesome, thanks for saving me some money Motor Head.
I have DynoSim software also, and I get slightly higher HP numbers when adding higher rocker ratios to the mix.....in the Cylinder Heads section, click "airflow data" and enter the actual cfm flow numbers for your AFRs at each lift point. The numbers go higher to .650 lift or so; enter this info and you should your numbers change. (If you don't have your numbers, they are posted on AFR's website).
Thread Starter
Melting Slicks
Joined: Sep 2004
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Originally Posted by VETDRMS
Are those the street ported 195's, or the competition ported?
Didn't have 2k+ in my budget for heads.
Last edited by enkeivette; Mar 19, 2006 at 05:18 PM.
Thread Starter
Melting Slicks
Joined: Sep 2004
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Originally Posted by C3 Stroker
Torqvette;
I have DynoSim software also, and I get slightly higher HP numbers when adding higher rocker ratios to the mix.....in the Cylinder Heads section, click "airflow data" and enter the actual cfm flow numbers for your AFRs at each lift point. The numbers go higher to .650 lift or so; enter this info and you should your numbers change. (If you don't have your numbers, they are posted on AFR's website).
I have DynoSim software also, and I get slightly higher HP numbers when adding higher rocker ratios to the mix.....in the Cylinder Heads section, click "airflow data" and enter the actual cfm flow numbers for your AFRs at each lift point. The numbers go higher to .650 lift or so; enter this info and you should your numbers change. (If you don't have your numbers, they are posted on AFR's website).
And if you look closely, I do actually gain hp with the 1.6 rockers, but only 6hp after 6.5k, I'll be shifting before then anyways. And at that point I've lost some torque with the 1.6s. The 1.5s offer more hp across the band.
Last edited by enkeivette; Mar 19, 2006 at 05:23 PM.
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Safety Car
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From: Youngstown Ohio
Originally Posted by torqvette
I did enter the actual numbers for each lift, from .1 - .65
And if you look closely, I do actually gain hp with the 1.6 rockers, but only 6hp after 6.5k, I'll be shifting before then anyways. And at that point I've lost some torque with the 1.6s. The 1.5s offer more hp across the band.
And if you look closely, I do actually gain hp with the 1.6 rockers, but only 6hp after 6.5k, I'll be shifting before then anyways. And at that point I've lost some torque with the 1.6s. The 1.5s offer more hp across the band.
I see your point. Seems odd,though, that more lift could make less HP under 6500 rpm but I've seen tests done by David Vizard in his books showing the same results with some cams.BTW, I popped the extra money for the competition ported AFR 195's and judging by the increased HP over the Trick Flow 195's I had previously, the flow numbers are quite accurate if not conservative.
Thread Starter
Melting Slicks
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Originally Posted by C3 Stroker
OK I see your point. Seems odd,though, that more lift could make less HP under 6500 rpm but I've seen tests done by David Vizard in his books showing the same results with some cams.
BTW, I popped the extra money for the competition ported AFR 195's and judging by the increased HP over the Trick Flow 195's I had previously, the flow numbers are quite accurate if not conservative.
I see your point. Seems odd,though, that more lift could make less HP under 6500 rpm but I've seen tests done by David Vizard in his books showing the same results with some cams.BTW, I popped the extra money for the competition ported AFR 195's and judging by the increased HP over the Trick Flow 195's I had previously, the flow numbers are quite accurate if not conservative.
Team Owner
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From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Originally Posted by MotorHead
THose AFR heads max out CFM wise at .500" lift therefore it dosen't matter if you open the valve another inch you are at max flow that is why there is no HP gain
What does matter is: You want to lift the valve to max CFM and keep it there for the longest time. So if max CFM is at .500 and you lift the valve to .600. You will be keeping the valve at max cfm for allot more degrees.
I use 1.65 intake rockers. It would actually be better in your case of relatively low compression of 10.2 to go with 4 or so less degrees of cam and use 1.7 or 1.75 rockers. I have that cam ground on 112 lc in my 383 and it probably makes max power at 7000 rpm. It's way to peaky.
Pro
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St. Jude Donor '09, '24
With a high lift cam at a shorter duration you will make more tourque then HP in the bottom to mid range in the powerband. The heads should flow more then enough air for the street. You will lose some top end HP but you will make up for it with more bottom and mid range tourque just as your graphs show. I run a short duration (230) and high lift (560) roller cam on the street just for that reason. If you're not running the straightaways at Daytona I wouldn't worry to much about the difference in rocker arm ratio either. 10 to 15 HP gain when you motor is close to 500 HP to start with is very hard to actually see and feel, especially on the street. If it is a track car I might tweek it but for the street don't worry about it, houstonvett
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
Originally Posted by gkull
What does matter is: You want to lift the valve to max CFM and keep it there for the longest time. So if max CFM is at .500 and you lift the valve to .600. You will be keeping the valve at max cfm for allot more degrees.
I use 1.65 intake rockers. It would actually be better in your case of relatively low compression of 10.2 to go with 4 or so less degrees of cam and use 1.7 or 1.75 rockers. I have that cam ground on 112 lc in my 383 and it probably makes max power at 7000 rpm. It's way to peaky.
I use 1.65 intake rockers. It would actually be better in your case of relatively low compression of 10.2 to go with 4 or so less degrees of cam and use 1.7 or 1.75 rockers. I have that cam ground on 112 lc in my 383 and it probably makes max power at 7000 rpm. It's way to peaky.
Now if you have selected a cam that opens to say .570" with 1.5 rockers then the 1.6 rockers will open the valve to over .600" lift which allows it to take advantage of the extra CFM @ .600" lift vs. .570" lift.
So as I stated I don't think they are worth it on his motor because from the flow difference between .500" and .600" is minimal
Team Owner
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From: Reno Nevada
2024 C3 of the Year Finalist- Modified
True cylinder and HP potential is the average of the CFM at all valve lift points. That's all those discussions about the value of heads with ports that have higher CFM of flow on the mid lifts ranges.
The AFR 195 street head has
.200 lift = 132 CFM
.300 = 198
.400 = 240
.500 = 260
.600 = 262
Total cfm at all lifts = 1092 / 5 lift points = roughly 218 average cfm if you lift it to .600 What skews the average lift is how steep the cams ramps are.
That is why i've always installed extreeme ramps with over .600 lift. My 383 was .635/.644 lift and now i'm running .620/.620 net lift after solid valve lash. You gain higher average power throughout the entire rpm range of the motor. So you can't just look a single rpm value and say that you gained only 10 hp with higher ratio rockers.
I went out driving my Vette yesterday and got several comments on how it sounds.
The AFR 195 street head has
.200 lift = 132 CFM
.300 = 198
.400 = 240
.500 = 260
.600 = 262
Total cfm at all lifts = 1092 / 5 lift points = roughly 218 average cfm if you lift it to .600 What skews the average lift is how steep the cams ramps are.
That is why i've always installed extreeme ramps with over .600 lift. My 383 was .635/.644 lift and now i'm running .620/.620 net lift after solid valve lash. You gain higher average power throughout the entire rpm range of the motor. So you can't just look a single rpm value and say that you gained only 10 hp with higher ratio rockers.
I went out driving my Vette yesterday and got several comments on how it sounds.
Team Owner
Joined: Apr 1999
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From: Reno Nevada
2024 C3 of the Year Finalist- Modified
The 750 cfm carb might be down on power at higher rpm. But 427 ci with 3 inch race mufflers and solid roller sounds like a real race car. I was manually shifting my 4 speed auto right at 7000 rpm
I've never heard it from outside my car, but everybody tells me that they have not heard anything like it out on the street.
It's just a joy to have it fire right up after three months because of snow and bad weather and go out a smoke the tires!
I've never heard it from outside my car, but everybody tells me that they have not heard anything like it out on the street.
It's just a joy to have it fire right up after three months because of snow and bad weather and go out a smoke the tires!