Engine master, Rocker arms
Burning Brakes
Joined: Nov 2012
Posts: 788
Likes: 100
From: Indianapolis IN
Pretty informative , thanks for the link. The end result was more than expected for 1,6's. I have an NOS set of Erson sbc billet rockers that are 1.6 and 1.7. The 1.7's will take dedication to be able to use properly, likely using a custom cam among all else to look into.
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
It is kinda sad that they didn't install higher valve spring pressure before they started to ensure valve control issues didn't come up!
it also shows you how difficult it is to make over 500 hp in engine like 372 -383 CI class motors
it also shows you how difficult it is to make over 500 hp in engine like 372 -383 CI class motors
Race Director
Joined: Jul 2015
Posts: 13,082
Likes: 3,399
From: SW Florida.
it didn't even answer the question they asked. they used 1.6 roller rockers. so the added power came fron the added lift. almost the eqiuvalent of changing cams. you would have to do same test with same ratio rollers to have comparison be fair.
Race Director
Joined: Jan 2000
Posts: 13,017
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From: Corsicana, Tx
2020 C2 of the Year - Modified Winner
2020 Corvette of the Year (performance mods)
C2 of Year Winner (performance mods) 2019
2017 C2 of Year Finalist
Did I miss it? What was the cam? If it was way too small...it would certainly love the added lift/duration of the 1.6's.
JIM
JIM
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Melting Slicks
Joined: Jul 2010
Posts: 3,176
Likes: 633
From: perth western australia
Melting Slicks
Joined: Jun 2016
Posts: 2,979
Likes: 332
From: Woodinville WA
Adam
Melting Slicks
Joined: Jun 2016
Posts: 2,979
Likes: 332
From: Woodinville WA
I calculated the added duration with my cam from switching from 1.5 to 1.6 RRs and my durations change from roughly 227 / 228 @0.050" to 230 / 232 (explains why the torque and hp peak RPMs moved upwards slightly with the ratio change). -I estimated using a simple calculation assuming a simple linear acceleration from the valve open event until the valve hitting max lift, though so it's off by a slight bit; I've rounded down.
Agree they didn't test whether roller rockers at the same ratio would increase power.
Adam
Last edited by NewbVetteGuy; Jan 9, 2018 at 03:13 PM.
Melting Slicks
Joined: Jun 2016
Posts: 2,979
Likes: 332
From: Woodinville WA
Here's the airflow chart for the AFR 195cc:
.200 .300 .400 .500 .550
Int 146 201 247 275 280
Exh 119 166 197 213 218
Definitely plenty of power to be made by increasing the lift (especially if you're not into the REALLY good air at 0.500").
If you had an intake lift of 0.450" with a 1.5:1 rocker and let's say your airflow is 261 CFM at that lift moving to a 1.65:1 RR gets you to 0.495" of valve lift (let's say 273 CFM) that's +12 CFM or +24 HP gain excluding the totally guestimated +2 deg extra duration @ 0.050", spending more time in higher lifts and a small torque gain from flowing that 12 CFM extra through the same size min CSA (more air velocity @ same RPM). Their +15 HP wasn't even a best-case scenario with that head; the jump in flow from 0.400" to 0.500" is pretty freakish.
Now to compare to a smaller head at a few lifts, here's the 185cc Profiler flow #s:
Lift Intake CFM Exh CFM % Exh/Int
0.200 135 110 81%
0.300 201 145 72%
0.400 245 180 73%
0.500 265 206 78%
0.600 270 213 79%
0.700 272 216 79%
Using the 2 HP per HP guideline and some HUGE lifts, you wouldn't expect to see much benefit going from 0.600 to 0.700 (4 HP) just based upon lift increases.
Adam
.200 .300 .400 .500 .550
Int 146 201 247 275 280
Exh 119 166 197 213 218
Definitely plenty of power to be made by increasing the lift (especially if you're not into the REALLY good air at 0.500").
If you had an intake lift of 0.450" with a 1.5:1 rocker and let's say your airflow is 261 CFM at that lift moving to a 1.65:1 RR gets you to 0.495" of valve lift (let's say 273 CFM) that's +12 CFM or +24 HP gain excluding the totally guestimated +2 deg extra duration @ 0.050", spending more time in higher lifts and a small torque gain from flowing that 12 CFM extra through the same size min CSA (more air velocity @ same RPM). Their +15 HP wasn't even a best-case scenario with that head; the jump in flow from 0.400" to 0.500" is pretty freakish.
Now to compare to a smaller head at a few lifts, here's the 185cc Profiler flow #s:
Lift Intake CFM Exh CFM % Exh/Int
0.200 135 110 81%
0.300 201 145 72%
0.400 245 180 73%
0.500 265 206 78%
0.600 270 213 79%
0.700 272 216 79%
Using the 2 HP per HP guideline and some HUGE lifts, you wouldn't expect to see much benefit going from 0.600 to 0.700 (4 HP) just based upon lift increases.
Adam
Last edited by NewbVetteGuy; Jan 9, 2018 at 06:13 PM.
Melting Slicks
Joined: Jun 2016
Posts: 2,979
Likes: 332
From: Woodinville WA
The Flow #'s of the 882 heads on my L82 tell a funny similar story but at normal valve lifts:
No real benefit above 0.400" in terms of flow, so switching rocker ratios to get more lift would gain nothing and just cost more $$ and longevity / reliability in the valve train.
0.100" 70CFM
0.200" 125CFM
0.300" 175CFM
0.400" 204CFM
0.500" 205CFM
0.600" 206CFM
Vortec L31's and GMPP's -intake flow DECREASES above 0.500"; so a higher ratio rocker there would REALLY be a bad idea.
IMHO, you need to weigh the benefits of the extra lift of the extra rocker ratio by looking at your head flow to determine if you'll get any benefits and if so, possibly how much. (If you plug your head airflow #'s into something like DesktopDyno it will do this for you, but it actually doesn't account for the slight increase in lift at 0.050" from the higher ratio.)
Adam
No real benefit above 0.400" in terms of flow, so switching rocker ratios to get more lift would gain nothing and just cost more $$ and longevity / reliability in the valve train.
0.100" 70CFM
0.200" 125CFM
0.300" 175CFM
0.400" 204CFM
0.500" 205CFM
0.600" 206CFM
Vortec L31's and GMPP's -intake flow DECREASES above 0.500"; so a higher ratio rocker there would REALLY be a bad idea.
IMHO, you need to weigh the benefits of the extra lift of the extra rocker ratio by looking at your head flow to determine if you'll get any benefits and if so, possibly how much. (If you plug your head airflow #'s into something like DesktopDyno it will do this for you, but it actually doesn't account for the slight increase in lift at 0.050" from the higher ratio.)
Adam
Last edited by NewbVetteGuy; Jan 9, 2018 at 03:32 PM.
Thread Starter
Safety Car
Joined: Jan 2008
Posts: 3,795
Likes: 434
From: Aarhus, Denmark
Anyone catch which AFR head they were using?
For 7,000 RPM, I'm going to guess the 220cc head; if so here's the airflow chart:
.200 .300 .400 .500 .550 .600 .650
Int 155 210 260 295 304 312 318
Exh 116 162 204 220 225 229
Definitely plenty of power to be made by increasing the lift.
Now to compare to a smaller head at a few lifts, here's the 185cc Profiler flow #s:
Lift Intake CFM Exh CFM % Exh/Int
0.200 135 110 81%
0.300 201 145 72%
0.400 245 180 73%
0.500 265 206 78%
0.600 270 213 79%
0.700 272 216 79%
Using the 2 HP per HP guideline and some HUGE lifts, you wouldn't expect to see much benefit going from 0.600 to 0.700 (4 HP) just based upon lift increases.
Adam
For 7,000 RPM, I'm going to guess the 220cc head; if so here's the airflow chart:
.200 .300 .400 .500 .550 .600 .650
Int 155 210 260 295 304 312 318
Exh 116 162 204 220 225 229
Definitely plenty of power to be made by increasing the lift.
Now to compare to a smaller head at a few lifts, here's the 185cc Profiler flow #s:
Lift Intake CFM Exh CFM % Exh/Int
0.200 135 110 81%
0.300 201 145 72%
0.400 245 180 73%
0.500 265 206 78%
0.600 270 213 79%
0.700 272 216 79%
Using the 2 HP per HP guideline and some HUGE lifts, you wouldn't expect to see much benefit going from 0.600 to 0.700 (4 HP) just based upon lift increases.
Adam
L98
195
65cc heads.
Look @ 3.12
Melting Slicks
Joined: Mar 2008
Posts: 2,666
Likes: 289
From: Spring Park MN
There is one thing that could have contributed to the gain of the 1.6 over the 1.5 roller rockers. The higher ratio rocker gives the valve spring more leverage over the lifter and pushrod weight. Given the valve springs look to be suspect in the 1.5 roller test, it is possible the extra mechanical advantage helped. It would have been nice if they would have had stronger springs. The 1.5 full rollers may have tested better and they would have had a better answer to which rocker worked best instead of more questions.
Mike
Mike
Race Director
Joined: Jan 2000
Posts: 12,399
Likes: 247
From: San Jose CA
The Flow #'s of the 882 heads on my L82 tell a funny similar story but at normal valve lifts:
No real benefit above 0.400" in terms of flow, so switching rocker ratios to get more lift would gain nothing and just cost more $$ and longevity / reliability in the valve train.
0.100" 70CFM
0.200" 125CFM
0.300" 175CFM
0.400" 204CFM
0.500" 205CFM
0.600" 206CFM
Vortec L31's and GMPP's -intake flow DECREASES above 0.500"; so a higher ratio rocker there would REALLY be a bad idea.
IMHO, you need to weigh the benefits of the extra lift of the extra rocker ratio by looking at your head flow to determine if you'll get any benefits and if so, possibly how much. (If you plug your head airflow #'s into something like DesktopDyno it will do this for you, but it actually doesn't account for the slight increase in lift at 0.050" from the higher ratio.)
Adam
No real benefit above 0.400" in terms of flow, so switching rocker ratios to get more lift would gain nothing and just cost more $$ and longevity / reliability in the valve train.
0.100" 70CFM
0.200" 125CFM
0.300" 175CFM
0.400" 204CFM
0.500" 205CFM
0.600" 206CFM
Vortec L31's and GMPP's -intake flow DECREASES above 0.500"; so a higher ratio rocker there would REALLY be a bad idea.
IMHO, you need to weigh the benefits of the extra lift of the extra rocker ratio by looking at your head flow to determine if you'll get any benefits and if so, possibly how much. (If you plug your head airflow #'s into something like DesktopDyno it will do this for you, but it actually doesn't account for the slight increase in lift at 0.050" from the higher ratio.)
Adam
But I do agree with the basic premise - it's likely not worth it. I watched the video and thought about it. The big boost they saw was at 6700 RPM - my engine revs to 6100. I might pick up 10hp. For $300 and a chunk of my time. If I was picking rocker arms to replace a broken set or upgrade from OE rockers, it'd be an easy decision for me. However, I've already sunk that $300 into a set of full-roller 1.52s that I've had since ~2004.
Does make me wish I went with the 1.6s during the last engine build, though... maybe if I go up in cam and intake after moving out of CA. We'll see.
Melting Slicks
Joined: Jun 2016
Posts: 2,979
Likes: 332
From: Woodinville WA
Remember that duration is a metric of how long a valve is open. CFM is "Cubic feet per minute". More valve open time = more air flowing through and filling the cylinder. So there would be more HP potential even if the CFM was the same. So getting the extra lift doesn't help but the duration that came with it would.
The GMPP head's flow FALLS from 243 CFM @ 0.500" to 238 CFM @ 0.600"; the Vortec L31 head's flow FALLS from 239 CFM @ 0.500" to 229 CFM @ 0.600"
The Vortec head would lose 20 hp worth of power at 0.600" vs. 0.500" at the same duration. ---Agree that you should increase duration but not lift with that head if your valve lift is already at 0.500 or thereabouts and you want more power without porting.
My point was simply that there are circumstances where the extra valve lift from a high ratio rocker won't really get you much extra power; the 882's above 0.400", for example. Tangent Alert: Which highlights again how @#$@#% the L82 cam was for L82 engines. That extra 0.050" of lift beyond 0.400"; not that useful.
Adam
Last edited by NewbVetteGuy; Jan 9, 2018 at 07:16 PM.