Turbo cam recomendation from Cam Motion
03-20-2007, 09:37 PM
#61
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Originally Posted by engineermike
Not sure if that's a smart-@ss remark or not, but I'll try and fill in the blanks for you.
03-20-2007, 09:39 PM
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Originally Posted by engineermike
With a combo like you are building, you've surely read up on turbine-induced backpressure, it's affects, and how the cid and turbo size affect it.
03-20-2007, 10:10 PM
#63
The problem with turbo cam theory and selection is this:
Everyone knows that the pressures are different in a turbo engine than an NA engine. In David Vizard's SBC camshaft book, he goes into detail about turbo cams. He says, "forget about the dynamics and look just at the pressures." Using this theory, he designed a cam for a 2/1 backpressure/boost engine. The cam turned out to be something like 200/234 - 122 LSA, 5 deg retarded. The motor made okay power, but recent combo's have made much more. Plus, one of the turbo GN guys tried a similar cam and was unhappy with it.
Folks like INTMD8, in particular, have been using cams closer and closer to NA cams and are making great power with them. This would imply that maybe we should "forget about the pressures and look just at the dynamics." In this case, we could cam a turbo engine just like we cam an NA engine. A 262/268 - 106 LSA, +4 would make the most power possible with a turbo. I don't think this is the right answer either.
Others still, say that the turbocharger and cid dictate the rpm range of the engine and you should cam it to match the turbo's optimum rpm range. I, for one, have tried 363, 383, and 388 cid with the cam installed at 0 and +4 and didn't see more than 100 rpm difference in peak power. This, to me, indicates there is some truth to that theory also.
So, which way is the correct way to do it? Most likely, all 3 will affect turbo cam selection.
How much do you weigh each method? I have no idea. However, most agree that if boost matches backpressure, then you can cam it like NA.
Who out there considers all 3, weighs each one appropriately, and specs a cam that's best for you? Probably no one.
That's why I say to choose a cam that meets your power goals in a similar combination.
Mike
Everyone knows that the pressures are different in a turbo engine than an NA engine. In David Vizard's SBC camshaft book, he goes into detail about turbo cams. He says, "forget about the dynamics and look just at the pressures." Using this theory, he designed a cam for a 2/1 backpressure/boost engine. The cam turned out to be something like 200/234 - 122 LSA, 5 deg retarded. The motor made okay power, but recent combo's have made much more. Plus, one of the turbo GN guys tried a similar cam and was unhappy with it.
Folks like INTMD8, in particular, have been using cams closer and closer to NA cams and are making great power with them. This would imply that maybe we should "forget about the pressures and look just at the dynamics." In this case, we could cam a turbo engine just like we cam an NA engine. A 262/268 - 106 LSA, +4 would make the most power possible with a turbo. I don't think this is the right answer either.
Others still, say that the turbocharger and cid dictate the rpm range of the engine and you should cam it to match the turbo's optimum rpm range. I, for one, have tried 363, 383, and 388 cid with the cam installed at 0 and +4 and didn't see more than 100 rpm difference in peak power. This, to me, indicates there is some truth to that theory also.
So, which way is the correct way to do it? Most likely, all 3 will affect turbo cam selection.
How much do you weigh each method? I have no idea. However, most agree that if boost matches backpressure, then you can cam it like NA.
Who out there considers all 3, weighs each one appropriately, and specs a cam that's best for you? Probably no one.
That's why I say to choose a cam that meets your power goals in a similar combination.
Mike
03-20-2007, 10:14 PM
#64
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Originally Posted by engineermike
I say "yay" on the Comp cam, or if you want more power get a clone of the Speed Inc 370/T88 cam that's dyno-proven to make ridiculous power in a very similar combo.
Mike
Mike
03-20-2007, 10:19 PM
#65
Originally Posted by Pro Stock John
Why not splurge and spend the extra $25 and order the cam right from Speed Inc. Since you are an LT1 guy you should order the cam from Jim @ Speed Inc. (Intmd8) while being clear about your goals, max rpm, and the fuel you will run.
I'm not the one looking for a cam, though. It's dhdenney, who has an LS1. If I swap cams, it'll be from my 224/236-114 to something more like 230/236-114 or 115. I can't increase my rpm range much because the T76GTS limits the rpm of my 388.
Mike
03-21-2007, 12:39 PM
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Originally Posted by dhdenney
What sort of times are you running with that? What converter? What rear gear?
03-21-2007, 12:44 PM
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Originally Posted by Mr_president
10.2 th400 3:55 gears 3600 fuddle cheapest stall converter still holding up yeay
03-21-2007, 07:37 PM
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Originally Posted by engineermike
Look at valve events NOT LSA. Heck, the stock turbo GN cam is on a 106 LSA.
Speed Inc 236/242-112, +4
EVO: 57 BBDC
EVC: 5 ATDC
IVO: 10 BTDC
IVC: 46 ABDC
Comp 232/234-115, +4
EVO: 58 BBDC
EVC: 0 ATDC
IVO: 7 BTDC
IVC: 49 ABDC
IVC and EVO are very close, so you can expect the rpm range to be very similar. The biggest difference between these two is in the overlap area, where the Comp cam has 7 deg and the Speed cam has 15 deg overlap. We can be sure that if your backpressure is <5 psi higher than boost, then more overlap will only help power by better filling the cylinder. We can also be sure that the Speed cam will have a rougher idle. The unknown here is how high is your backpressure in relation to boost, and how will that affect the benefits of added overlap.
Mike
Speed Inc 236/242-112, +4
EVO: 57 BBDC
EVC: 5 ATDC
IVO: 10 BTDC
IVC: 46 ABDC
Comp 232/234-115, +4
EVO: 58 BBDC
EVC: 0 ATDC
IVO: 7 BTDC
IVC: 49 ABDC
IVC and EVO are very close, so you can expect the rpm range to be very similar. The biggest difference between these two is in the overlap area, where the Comp cam has 7 deg and the Speed cam has 15 deg overlap. We can be sure that if your backpressure is <5 psi higher than boost, then more overlap will only help power by better filling the cylinder. We can also be sure that the Speed cam will have a rougher idle. The unknown here is how high is your backpressure in relation to boost, and how will that affect the benefits of added overlap.
Mike
03-23-2007, 07:06 PM
#73
Originally Posted by dhdenney
> >ported 853's, approx 210cc intake ports, 2.00" 1.55" valves, 67cc chamber
> >intake flow numbers are:
> >3.900" bore
> >
> >0.05 39.1
> >0.1 70.6
> >0.15 104
> >0.2 142
> >0.25 177
> >0.3 209
> >0.35 226
> >0.4 246
> >0.45 261
> >0.5 266
> >0.55 272
> >0.6 279
> >0.65 285
> >0.7 289
> >0.75 295
> >
> >
> >
> >intake flow numbers are:
> >3.900" bore
> >
> >0.05 39.1
> >0.1 70.6
> >0.15 104
> >0.2 142
> >0.25 177
> >0.3 209
> >0.35 226
> >0.4 246
> >0.45 261
> >0.5 266
> >0.55 272
> >0.6 279
> >0.65 285
> >0.7 289
> >0.75 295
> >
> >
> >
Mike
03-23-2007, 07:54 PM
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Originally Posted by engineermike
Hey, we just put 2 and 2 together today. My good friend ported your heads. In fact, he lives 1 mile from me.
Mike
Mike
03-23-2007, 08:07 PM
#75
Originally Posted by dhdenney
. . . I shot him a PM a few days ago to check on the status but I haven't heard back from him yet.
Originally Posted by dhdenney
I think the flow is amazing for stock valves on these heads. I had kinda been looking for oversize valved heads but being a turbo motor, I didn't think it would be as important and these would be fresh.
Mike
03-23-2007, 08:25 PM
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We didn't talk a whole lot but I wound up with a set of bogus heads on Ebay (which I ended up getting my money back on). I had a thread going about the port work and he got in there and indicated what was wrong with them. He then PM'ed me about a set of 853's he was doing and priced them to me. I ran a search on some of his posts and his trader rating and it all looked good so I took him up on them.
