What is too big of a cam for a turbo?
03-23-2003, 06:19 PM
#1
What is too big of a cam for a turbo? I was having a conversation with a couple of my friends and they all have different opinions on what is too big for a turbo setup with 6.0L heads at 9.1:1 compression with a forged bottom end 346ci car.. The cam sizes we talked about were all above 230 intake and 236 on the exhaust with a 114 or 115 lsa.. Do you guys think too much overlap is in play here? We were talking about running 10lbs of boost to get 600rwhp plus.. My opinion is the 230/236 cam would be more for a SC'd setup.. They were saying because turbos use exhaust to spool up it would be best to push more exhaust through..
03-23-2003, 07:00 PM
#2
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Re: What is too big of a cam for a turbo? </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by VINCE:
<strong> I was having a conversation with a couple of my friends and they all have different opinions on what is too big for a turbo setup with 6.0L heads at 9.1:1 compression with a forged bottom end 346ci car.. The cam sizes we talked about were all above 230 intake and 236 on the exhaust with a 114 or 115 lsa.. Do you guys think too much overlap is in play here? We were talking about running 10lbs of boost to get 600rwhp plus.. My opinion is the 230/236 cam would be more for a SC'd setup.. They were saying because turbos use exhaust to spool up it would be best to push more exhaust through.. </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">A lot of people seem to lean on crutching the exhaust in just about every application. I think that mostly stems from the old chevy exhaust port design. Most don't (yet) seem comfortable with trusting the new ex port, but I think they will soon enough. After all, when such eye-popping examples of excellent results are occurring with an intake biased bump-stick, it's hard to defend staying with the outdated theory of crutching the exhaust. The facts just don't support it.
That said, there's nothing wrong with high-lift, long-duration cams in a turbo car. It just tends to move the hp/tq up the graph. More duration = peak in higher rpms. It certainly softens the hit on the hydes, and it adds hp up top when the dynamic compression overcomes the bleed-off from the long durations (and overlaps). I would argue that a single pattern is by far the better way to go, however, as the exhaust backpressure is roughly 1.5x to 2x the intake pressure. This alone would argue against allowing the exhaust to hang open, especially in concert with excessive overlap.
More power to ya, but I think that with the enormous advantage that the stock cam brings, by way of driveablity, mileage, low-end torque, and how much easier it is on the valve train, it's hard to imagine giving it up for a more aggressive grind. Then again, I'm all about the street and highway, not so much the strip.
JM2c
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<small>[ March 23, 2003, 07:06 PM: Message edited by: SS00Blue ]</small>
<strong> I was having a conversation with a couple of my friends and they all have different opinions on what is too big for a turbo setup with 6.0L heads at 9.1:1 compression with a forged bottom end 346ci car.. The cam sizes we talked about were all above 230 intake and 236 on the exhaust with a 114 or 115 lsa.. Do you guys think too much overlap is in play here? We were talking about running 10lbs of boost to get 600rwhp plus.. My opinion is the 230/236 cam would be more for a SC'd setup.. They were saying because turbos use exhaust to spool up it would be best to push more exhaust through.. </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">A lot of people seem to lean on crutching the exhaust in just about every application. I think that mostly stems from the old chevy exhaust port design. Most don't (yet) seem comfortable with trusting the new ex port, but I think they will soon enough. After all, when such eye-popping examples of excellent results are occurring with an intake biased bump-stick, it's hard to defend staying with the outdated theory of crutching the exhaust. The facts just don't support it.
That said, there's nothing wrong with high-lift, long-duration cams in a turbo car. It just tends to move the hp/tq up the graph. More duration = peak in higher rpms. It certainly softens the hit on the hydes, and it adds hp up top when the dynamic compression overcomes the bleed-off from the long durations (and overlaps). I would argue that a single pattern is by far the better way to go, however, as the exhaust backpressure is roughly 1.5x to 2x the intake pressure. This alone would argue against allowing the exhaust to hang open, especially in concert with excessive overlap.
More power to ya, but I think that with the enormous advantage that the stock cam brings, by way of driveablity, mileage, low-end torque, and how much easier it is on the valve train, it's hard to imagine giving it up for a more aggressive grind. Then again, I'm all about the street and highway, not so much the strip.
JM2c
SC-
<small>[ March 23, 2003, 07:06 PM: Message edited by: SS00Blue ]</small>
03-23-2003, 07:57 PM
#3
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Re: What is too big of a cam for a turbo? I was talking to the designer of the XE-R families of cams at Comp Cams, and he said that turbo cars should run more intake duration and that if run too much exhaust duration it might scavenge too aggressively...
HP goals and shiftpoints dictate duration more than anything else IMO.
I am going to run a 23_/23_/11_ cam to make 700rwhp somewhere between 6600-7000... I plan to shift it around 7200. If I had upped the duration to the 24_/24_ range the car would have needed to be shifted in the 7500-7700 range to make the cam worthwhil on the LSA that we are using.
For 600rwhp and a turbo car I'd run something like 230/224/115/+2, and I think it will peak around 6600, and have nice topend, and hopefull sweet midrange but not the kind that makes the car useless on a radial tire...
HP goals and shiftpoints dictate duration more than anything else IMO.
I am going to run a 23_/23_/11_ cam to make 700rwhp somewhere between 6600-7000... I plan to shift it around 7200. If I had upped the duration to the 24_/24_ range the car would have needed to be shifted in the 7500-7700 range to make the cam worthwhil on the LSA that we are using.
For 600rwhp and a turbo car I'd run something like 230/224/115/+2, and I think it will peak around 6600, and have nice topend, and hopefull sweet midrange but not the kind that makes the car useless on a radial tire...
03-24-2003, 01:24 AM
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Re: What is too big of a cam for a turbo? I had duttweiler do my turbo cam....i told him i wanted something that pulled hard and high and matched my well flowing brodix heads and had a redline of 6500-6700rpm
he came back with a 232/232 on a 114lsa/114ic
just as a reference, you will usually find 2 types of turbo cams out there:
1) longer durations and some overlap
2) shorter durations and negative overlap
he came back with a 232/232 on a 114lsa/114ic
just as a reference, you will usually find 2 types of turbo cams out there:
1) longer durations and some overlap
2) shorter durations and negative overlap
03-24-2003, 10:14 AM
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Re: What is too big of a cam for a turbo? </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by VINCE:
<strong> So I am getting the impression that a 230/236 cam is not for turbo, but what about for supercharger? </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Fantastic cam for an S/C! It gives the added time to the exhaust event to completely purge the cylinder, and since there is no greater pressure trying to force it's way back into the cylinder (ala - turbo) it's all useful. I've seen bigger splits than that, but mostly on big roots units.
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<strong> So I am getting the impression that a 230/236 cam is not for turbo, but what about for supercharger? </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Fantastic cam for an S/C! It gives the added time to the exhaust event to completely purge the cylinder, and since there is no greater pressure trying to force it's way back into the cylinder (ala - turbo) it's all useful. I've seen bigger splits than that, but mostly on big roots units.
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