Fun with Camshafts
Thread Starter
Drifting
Joined: Jun 2008
Posts: 1,565
Likes: 111
You could probably get a good custom grind from Straub and take some of the guessing out of it for you.
I think a custom cam would get the most out of your combo, however I do like a proven product, mine is certainly proven...lolBut for reference,
On my 496 with probably a tad less head flow then you'll have, I peak at 5750 rpms, shift at 6000-6100.... That's with an Isky hyd roller 238/248*@.050", .578/.608", 110 LSA. I do have 1.75 rockers on the intake side tho....so its probably close to .600"I.
I would think this cam in a 468" would peak a couple hundred later....It has mild lobes, easy on valve springs(kind of) and great driveability. (12" vacuum in mine).
Good luck on the new build Neil....
I think a custom cam would get the most out of your combo, however I do like a proven product, mine is certainly proven...lolBut for reference,
On my 496 with probably a tad less head flow then you'll have, I peak at 5750 rpms, shift at 6000-6100.... That's with an Isky hyd roller 238/248*@.050", .578/.608", 110 LSA. I do have 1.75 rockers on the intake side tho....so its probably close to .600"I.
I would think this cam in a 468" would peak a couple hundred later....It has mild lobes, easy on valve springs(kind of) and great driveability. (12" vacuum in mine).
Good luck on the new build Neil....
Last edited by Neil B; Aug 31, 2017 at 08:18 PM.
Thread Starter
Drifting
Joined: Jun 2008
Posts: 1,565
Likes: 111
I have never really understood the dynamic compression ratio measurement. Wouldn't it vary with rpm. I have seen people pick a cam based on a certain dynamic compression ratio number at low rpms to keep it from detonating. But at high rpm, when those cylinders start filling, in some cases it would rattle. Maybe I am understanding it wrong. Love your car!
Bill
Bill
Le Mans Master
Joined: May 2006
Posts: 9,993
Likes: 1,136
From: League City Tx
Thanks! I've ordered from Chris before and certainly will again. But the fun in these projects for me is learning why certain things work and other things don't. Having a custom cam shipped to my door (with no input or thought on my part) kind of takes the fun out of it for me. Your hp peak of 5,750 rpm with 238/248 cam gives me some validation that I'm in the right duration range for my 468 with a 6,000 rpm peak. My current 461ci engine with big valve 781 heads peaks at around 5,400 with a 282/230 intake lobe and it's DONE at 5,800. It pulls hard but I need the party to continue up higher in the rpm range with my gearing.
I'd probably do a solid roller and shoot for a 6500 peak, 7000 max..... Should be good to make 625hp with your heads and a good intake...and be hella fun to boot...
Thread Starter
Drifting
Joined: Jun 2008
Posts: 1,565
Likes: 111
I'd do a solid roller in a heartbeat on the Corvette, but I've got a set of Morel 4603's sitting on the shelf that are begging to be used.
Le Mans Master
Joined: May 2006
Posts: 9,993
Likes: 1,136
From: League City Tx
This is a COMPLETELY different combo, but in the name of conversation and comparison...
I had Straub do a hyd roller for a 396 (408") we built for my dad's '65 vert.... It was a stock appearing build that we wanted to replicate the SFT cam performance but without the maintenance.
Stock rect port, closed chamber heads, stock aluminum square bore intake (not the good 963 intake like the 427s had), stock vette manifolds. 10.0-1 compression.
He spec'd a 237/245*, .620/.556", 109lsa. It peaked at 6300 rpms and pulled clean to 6600 rpms but was nosing over by 6500 ish. I was chasing a slight misfire problem at around 6100 but it would clean up after that. (Factory TI ignition box).
Ofcourse it didn't make much power due to the stock manifolds and too small of a carb (650 cfm) but....it did show what a 237 cam would peak at in 408" with a bunch of restrictions on it.
Last edited by ajrothm; Aug 31, 2017 at 08:58 PM.
Melting Slicks
Joined: Mar 2008
Posts: 2,666
Likes: 289
From: Spring Park MN
Maybe it'll run better with more exhaust flow, maybe not.
Darin Morgan has made some pretty bold statements about air bench flow numbers on exhaust ports and just how little correlation there is between how an exhaust port flows at room temperature and 1 PSI when in an operating engine it's operating at 500+ PSI and 1,300F or more...
Direct quote:
Personally, I care very little about how much the exhaust port flows. It’s at the very bottom of my list of importance. I don’t try and make the exhaust port flow as much as possible, because I have been down that path hundreds of times and it’s a dead end street! The pressures the exhaust port has to deal with in the running engine are hundreds of times greater than the flow bench could possibly simulate. Ask yourself this: why would you design a port using 1 PSI test pressure at 70°F, when it’s actually flowing at 500PSI+ and 1300°F?
http://darinmorgan.net/frank-talk-about-flow-numbers/
I find this subject particularly interesting when comparing CFM #s for intake and exhaust ports between AFR and other top-tier SBC 23 degree heads. (Many of them have caught or slightly surpassed AFR on the intake ports, but not the exhaust ports on the flow bench, BUT if the exhaust CFM #s aren't actually what matters then what does the extra $300-$400 get you on a running engine.....?!?...)
Adam
Darin Morgan has made some pretty bold statements about air bench flow numbers on exhaust ports and just how little correlation there is between how an exhaust port flows at room temperature and 1 PSI when in an operating engine it's operating at 500+ PSI and 1,300F or more...
Direct quote:
Personally, I care very little about how much the exhaust port flows. It’s at the very bottom of my list of importance. I don’t try and make the exhaust port flow as much as possible, because I have been down that path hundreds of times and it’s a dead end street! The pressures the exhaust port has to deal with in the running engine are hundreds of times greater than the flow bench could possibly simulate. Ask yourself this: why would you design a port using 1 PSI test pressure at 70°F, when it’s actually flowing at 500PSI+ and 1300°F?
http://darinmorgan.net/frank-talk-about-flow-numbers/
I find this subject particularly interesting when comparing CFM #s for intake and exhaust ports between AFR and other top-tier SBC 23 degree heads. (Many of them have caught or slightly surpassed AFR on the intake ports, but not the exhaust ports on the flow bench, BUT if the exhaust CFM #s aren't actually what matters then what does the extra $300-$400 get you on a running engine.....?!?...)
Adam
I've spent many years on the flow bench, dyno and race track. I have many world records under my belt on the drag strip and land speed racing, small classes and large classes, gas and nitromethane. I can tell you absolutely that poorer flowing exhaust ports require more duration and better flowing ports require less duration.
Running a lot of duration with a very good flowing exhaust will kill power, especially in the bottom and mid range. Running too little duration with a poor flowing exhaust port will kill top end power. I have tested this in great detail.
Mike
Melting Slicks
Joined: Jun 2016
Posts: 2,979
Likes: 332
From: Woodinville WA
Keep in mind that Pro Stock engine and head builders are some of the most secretive people on earth. I have stood next to racers and engine builders that lied straight faced to people who asked them questions. Just because Morgan said this, does not mean he practices it.
Mike
Mike
Profiler SBC 23 Deg: 185cc Runner
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%
0.800 275 218 79%
Profiler 210cc Runner
Lift Intake CFM Exh CFM % Exh/Int
0.200 145 110 76%
0.300 207 145 70%
0.400 258 180 70%
0.500 283 206 73%
0.600 285 213 75%
0.700 291 216 74%
0.800 297 218 73%
The entire Profiler 23Deg SBC head lineup uses the same exhaust port and produce great power mostly because the average velocity is just fantastic with great CFM for the CSA.
The guy said that exhaust CFM is the last thing on his list and a lineup of heads that he had complete reign over shows just that.
Adam
Last edited by NewbVetteGuy; Aug 31, 2017 at 10:57 PM.
Melting Slicks
Joined: Mar 2008
Posts: 2,666
Likes: 289
From: Spring Park MN
Sure, but in this case we have actual Darin Morgan-designed heads that clearly show that he's not BSing in this case; this secretive head designer spent 2-3 years working for a very non-secretive, mass market after market SBC-focused company with all of his work out in full view in the public space.
Profiler SBC 23 Deg: 185cc Runner
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%
0.800 275 218 79%
Profiler 210cc Runner
Lift Intake CFM Exh CFM % Exh/Int
0.200 145 110 76%
0.300 207 145 70%
0.400 258 180 70%
0.500 283 206 73%
0.600 285 213 75%
0.700 291 216 74%
0.800 297 218 73%
The entire Profiler 23Deg SBC head lineup uses the same exhaust port and produce great power mostly because the average velocity is just fantastic with great CFM for the CSA.
The guy said that exhaust CFM is the last thing on his list and a lineup of heads that he had complete reign over shows just that.
Adam
Profiler SBC 23 Deg: 185cc Runner
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%
0.800 275 218 79%
Profiler 210cc Runner
Lift Intake CFM Exh CFM % Exh/Int
0.200 145 110 76%
0.300 207 145 70%
0.400 258 180 70%
0.500 283 206 73%
0.600 285 213 75%
0.700 291 216 74%
0.800 297 218 73%
The entire Profiler 23Deg SBC head lineup uses the same exhaust port and produce great power mostly because the average velocity is just fantastic with great CFM for the CSA.
The guy said that exhaust CFM is the last thing on his list and a lineup of heads that he had complete reign over shows just that.
Adam
It doesn't change what I am saying about duration of exhaust lobe and exhaust port flow. As I said, I've done the testing and proved it both on the dyno and on the track.
Mike
Last edited by v2racing; Sep 1, 2017 at 09:45 AM.
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Melting Slicks
Joined: Jun 2016
Posts: 2,979
Likes: 332
From: Woodinville WA
And yet the exhaust to intake ratio is right in the range that head builders have been using for decades, 70% to 80%.
It doesn't change what I am saying about duration of exhaust lobe and exhaust port flow. As I said, I've done the testing and proved it both on the dyno and on the track.
Mike
It doesn't change what I am saying about duration of exhaust lobe and exhaust port flow. As I said, I've done the testing and proved it both on the dyno and on the track.
Mike
I think I finally understand what you're saying and I think it makes sense.
Darin's perspective that there are definitely bigger issues to making power and that essentially "good enough is good enough" when it comes to exhaust ports and focusing on how the port is going to flow at high temps and high pressure, coupled with your perspective on 70% - 80% being the historical intake to exhaust ratio range where best power is made are totally compatible with each other and provide a more complete picture, IMHO.
That 65% of the Brodix head does seem low. Brodix has such a good reputation I'm honestly surprised at the 65% #.
Adam
Le Mans Master
Joined: Oct 2010
Posts: 6,900
Likes: 833
From: melbourne florida
2023 C3 of the Year Finalist - Modified
I agree with V2 100% on exhaust port flow. And totally agree about pro class racers . I ran a pro stock car in the late 70's and that was my experience. Bruce Crower helped me get on track. The term genius gets thrown around lightly these days but that man was.