Discussion about turbo cams, overlap, boost and reversion
06-11-2009, 06:54 PM
#21
I thought about describing it in percentage as well, but it doesn't seem right to me since it's a dynamic system measured in CFM and has a time unit. Dealing in percentage makes me think of a static situation (which it is when based off of the 360 degrees the cam has). The flow through the valves is constantly varying due to the amount of back pressure present in the exhaust and the amount of pressure coming in through the intake, VE varying with rpm, etc.
Maybe someone could clarify which would be the better way to look at this.
Maybe someone could clarify which would be the better way to look at this.
By presenting it in percentage form, it looks more significant, which it is IMO. Either way you look at it, it's the same thoguh. As ms, it still doesn't account for how open or at what lift the valves are at any point within that .XXms.
06-11-2009, 07:12 PM
#23
Like Zombie said, it's not that easy to figure out based on spring and pressure supplied. You have to know all the internal geometry of the WG as well as the exhaust pressure, which defeats the purpose of doing the calcs.
It is pretty easy to measure backpressure, though.
Mike
It is pretty easy to measure backpressure, though.
Mike
06-11-2009, 07:19 PM
#24
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I've never seen an auto drag car with a 1-1 pressure ratio.they are way to lazy to spool.even my 436 with twin 88's didn't have a 1-1 ratio.Either way the cam in Fireball's engine in no way shape or form resembles an n/a cam
06-11-2009, 07:56 PM
#27
Apparently, they don't resemble traditional turbo OR NA cam specs, which leaves...um...nothing, since both of those run the entire gamut of split, reverse split, single pattern, long duration, short duration, high LSA, and low LSA.
06-11-2009, 07:58 PM
#28
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Probably not... There's some crazy stuff coming out of Shawn's shop.
I'd keep it close-hold too, that's what's going to earn him the money and time he spent on R&D back!
I'd keep it close-hold too, that's what's going to earn him the money and time he spent on R&D back!
06-11-2009, 08:01 PM
#29
Well, my 388 on a little T76 GTS is at 2/1. Any smaller displacement or larger turbo can only improve on this, and you have both. Even if you were at 1.5/1, you're getting into the NA E-I pressure differential area.
06-11-2009, 08:10 PM
#30
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yeah..but consider that I'm also running close to 30 psi and making probably close to twice the power (airflow) that your 388 is consuming...that air has to go thru the housing...is it bigger? yes...but that flow backs up in a hurry. I bet I'm approx 2:1 also...
06-11-2009, 09:04 PM
#31
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you forgot to add in rpm and intake pressure in your equation.as both rise ex backpressure also rises.what rpm and intake pressure are you 2-1 at?Fireball is at 8000rpm and 30 psi,this makes a big difference
06-11-2009, 09:47 PM
#32
Just for giggles I called Comp Cams today to see what they recommend for my build. 370ci, 9.3:1, twin 61mm T3 turbos with 76mm turbine wheel .82AR, 15-20+lbs of boost, heavy as heck 4100lb GTO, TH400 trans, 3400 rpm stall, 3.46 gears. I want to hit 1000+ at the crank.
They recommended this:
228/230 .588/.592 on a 115 +3 with xer lobes.
Other folks are telling me this is a small baby cam.
Shawn at Va Speed is working on a cam for me right now. I just have to pay him, lol. Then of course sign my name in my own blood to not spill the beans on the cam specs. Just kidding, lol.
Edit: How would this work guys?
Magic Stick V.3 237/242 .603/.609 on a 114
They recommended this:
228/230 .588/.592 on a 115 +3 with xer lobes.
Other folks are telling me this is a small baby cam.
Shawn at Va Speed is working on a cam for me right now. I just have to pay him, lol. Then of course sign my name in my own blood to not spill the beans on the cam specs. Just kidding, lol.
Edit: How would this work guys?
Magic Stick V.3 237/242 .603/.609 on a 114
Last edited by TurboAv; 06-12-2009 at 07:00 AM.
06-12-2009, 08:15 AM
#33
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On my previous setup, this is what I had.....
370ci, 9.5:1, GT47-88 turbo, ported L92 heads, GMPP single plane, elbow and a FAST 78mm TB. I used a Comp 238-242 .605-.610 115 LSA on XER lobes. I shifted at 7000 rpm, it probably would have peaked a little higher, I just didn't feel the need to spin it more. It was a N/A type cam that worked great in a 88mm turbo application for me.
It made over 1000 hp, and took me well into the 8's. It spooled well, and ran pretty damn good. It was someting I shot in the dark with, since at the time, there was not any data of a 370 turbo and ported L92's. I consulted with several cam/engine guys, like Patrick G, Kurt Urban, Louis G, Ed Hutchins, they all told me to just try the cam I had and see how it performed. Nobody really knew how well it would do for sure.
That being said, on the new setup, I had Shawn spec me a custom cam for the new heads, and it does not look like my old one! The whole combination has to be taken into consideration.
370ci, 9.5:1, GT47-88 turbo, ported L92 heads, GMPP single plane, elbow and a FAST 78mm TB. I used a Comp 238-242 .605-.610 115 LSA on XER lobes. I shifted at 7000 rpm, it probably would have peaked a little higher, I just didn't feel the need to spin it more. It was a N/A type cam that worked great in a 88mm turbo application for me.
It made over 1000 hp, and took me well into the 8's. It spooled well, and ran pretty damn good. It was someting I shot in the dark with, since at the time, there was not any data of a 370 turbo and ported L92's. I consulted with several cam/engine guys, like Patrick G, Kurt Urban, Louis G, Ed Hutchins, they all told me to just try the cam I had and see how it performed. Nobody really knew how well it would do for sure.
That being said, on the new setup, I had Shawn spec me a custom cam for the new heads, and it does not look like my old one! The whole combination has to be taken into consideration.
06-12-2009, 08:42 AM
#34
Just for giggles I called Comp Cams today to see what they recommend for my build. 370ci, 9.3:1, twin 61mm T3 turbos with 76mm turbine wheel .82AR, 15-20+lbs of boost, heavy as heck 4100lb GTO, TH400 trans, 3400 rpm stall, 3.46 gears. I want to hit 1000+ at the crank.
They recommended this:
228/230 .588/.592 on a 115 +3 with xer lobes.
Other folks are telling me this is a small baby cam.
Shawn at Va Speed is working on a cam for me right now. I just have to pay him, lol. Then of course sign my name in my own blood to not spill the beans on the cam specs. Just kidding, lol.
Edit: How would this work guys?
Magic Stick V.3 237/242 .603/.609 on a 114
They recommended this:
228/230 .588/.592 on a 115 +3 with xer lobes.
Other folks are telling me this is a small baby cam.
Shawn at Va Speed is working on a cam for me right now. I just have to pay him, lol. Then of course sign my name in my own blood to not spill the beans on the cam specs. Just kidding, lol.
Edit: How would this work guys?
Magic Stick V.3 237/242 .603/.609 on a 114
Last edited by 98Z28CobraKiller; 06-12-2009 at 09:00 AM.
