Engine master, Rocker arms
01-09-2018, 07:56 PM
#21
Race Director
This is flat tappet vs roller but similar theory. Actually if you raised the red line up and followed the same profile as the blue line you get why the power increases. The extra duration and lift is almost all above .200 where flow is best. A noticeably bigger duration @ .300 and even more @ .400
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NewbVetteGuy (01-09-2018)
01-09-2018, 08:07 PM
#22
Melting Slicks
This is flat tappet vs roller but similar theory. Actually if you raised the red line up and followed the same profile as the blue line you get why the power increases. The extra duration and lift is almost all above .200 where flow is best. A noticeably bigger duration @ .300 and even more @ .400
A 3D version that could include the CFM Air flow #'s for a particular head as the "Z" axis would be the best illustration; haven't seen that one yet, though. ;-)
If I understand correctly, a more aggressive lobe vs. a less aggressive lobe in general looks more like the roller cam red line in your diagram and the less aggressive lobes look more and more like the blue line. (but a smaller difference).
Same difference between a typical hydraulic roller lobe and an aggressive solid race roller lobe; faster valve action means spending more time in the "good airflow" with the top part of that curve getting wider and wider.
Adam
Last edited by NewbVetteGuy; 01-09-2018 at 08:13 PM.
01-10-2018, 01:51 AM
#24
Race Director
I'm confused on what you're arguing for / against.
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 @#$@#% the L82 cam was for L82 engines. That extra 0.050" of lift beyond 0.400"; not that useful.
Adam
The GMPP head's flow FALLS from 243 CFM @ 0.500" to 238 CFM @ 0.600"; the Vortec L31 head's flow FALLS from 239 CFM @ 0.500" to 229 CFM @ 0.600"
The Vortec head would lose 20 hp worth of power at 0.600" vs. 0.500" at the same duration. ---Agree that you should increase duration but not lift with that head if your valve lift is already at 0.500 or thereabouts and you want more power without porting.
My point was simply that there are circumstances where the extra valve lift from a high ratio rocker won't really get you much extra power; the 882's above 0.400", for example. Tangent Alert: Which highlights again how @#$@#% the L82 cam was for L82 engines. That extra 0.050" of lift beyond 0.400"; not that useful.
Adam
Not dealing with any of those castings at all is a better choice yet. I'm on my second set of AFRs (switched from the original AFR 195s to Eliminators with my second engine build).
Last edited by Shark Racer; 01-10-2018 at 01:52 AM.
01-10-2018, 10:42 AM
#25
Safety Car
Thread Starter
01-11-2018, 07:51 PM
#26
Race Director
Going with higher ratio rockers increases the duration of the cam - you'll hit that 0.050" lift number sooner and move your existing cam towards the more aggressive lobes in the charts that were posted. Going with different cam timing is probably the better choice.
Not dealing with any of those castings at all is a better choice yet. I'm on my second set of AFRs (switched from the original AFR 195s to Eliminators with my second engine build).
Not dealing with any of those castings at all is a better choice yet. I'm on my second set of AFRs (switched from the original AFR 195s to Eliminators with my second engine build).
01-12-2018, 03:32 AM
#27
Race Director
The numbers were good enough that a 2007 Corvette would have passed putting out the same numbers. Not bad for an old 'vette.
That said, it was tested once with the Q-Jet and a bad cat and passed. Those numbers were with brand new catalysts and TB-EFI (MSD Atomic EFI).
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63mako (01-13-2018)
01-13-2018, 03:54 PM
#28
Race Director
Yes you did - and you tell me.
The numbers were good enough that a 2007 Corvette would have passed putting out the same numbers. Not bad for an old 'vette.
That said, it was tested once with the Q-Jet and a bad cat and passed. Those numbers were with brand new catalysts and TB-EFI (MSD Atomic EFI).
The numbers were good enough that a 2007 Corvette would have passed putting out the same numbers. Not bad for an old 'vette.
That said, it was tested once with the Q-Jet and a bad cat and passed. Those numbers were with brand new catalysts and TB-EFI (MSD Atomic EFI).
Last edited by 63mako; 01-13-2018 at 04:11 PM.
01-13-2018, 11:22 PM
#29
Race Director
That is sweet. Efficiency, all the fuel is being converted to power. 427 SB, 475 Hp correct? That was a custom grind out of the comp lobe catalog and speced LSA, the engine was all CARB certified parts. The cam also needed to work with FI. Tough build. I had not talked to you since it was all 100% done and went in to test. Glad it turned out good.
400sb, 451hp. I just put a single plane on it, I'd bet it's closer to the 475 now than not but would have to dyno again.
01-14-2018, 12:04 AM
#30
Team Owner
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St. Jude Donor '22
Yeah hard to believe how long it's been at this point too. I went with the XFI lobes because they had some decent ramp rates and tighet LSA for smog.
400sb, 451hp. I just put a single plane on it, I'd bet it's closer to the 475 now than not but would have to dyno again.
400sb, 451hp. I just put a single plane on it, I'd bet it's closer to the 475 now than not but would have to dyno again.
could you share the particulars of your smog build?
compression ratio
lobe seperation
I have been searching for info so I won't fail the sniffer.
thank you
01-14-2018, 12:29 AM
#31
Race Director
* Comp Cams XFI cam (the off-the-shelf XFI268 is what I used as a baseline for the custom cam, slightly hotter) 113 LSA. The XFI 268 is 218/224 duration @0.050
* 10.24:1 compression
* Forged pistons, rods, crank
* ZZ4 intake manifold
* 1 5/8" headers (Hedmans, smog legal)
First time I ran it, it was running an MSD module/coil/cap in the 78 HEI housing with a 17058228 Q-Jet that I restored, modified and tuned.
Second time is an MSD billet ready-to-run distributor, 6AL, Blaster 2 coil, timing and fueling via MSD Atomic EFI ECM.
I'm also running a Tremec TKO 600. The manuals have slightly looser tolerances on smog IIRC.