Need Help On Cam For STS Turbo!!!!!
01-26-2011, 03:49 AM
#1
Staging Lane
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Need Help On Cam For STS Turbo!!!!! I ve got a 1999 Camaro Z28, Built Auto. all suspension work done on it,
ive recently purchased a sts turbo kit with intercooler. I wanna keep the stock bottom end in it. Plans are to pick up a set of Patroit stage 3 heads CNC'd. Also planned on going a ms4 camshaft?? was recently told that patroit heads arent good because of the 1.60 intake valve. 1.55 makes more power??? and that a MS4 camshaft wouldnt do me anygood on stock displacement ls1. I was also told that a 230's cam would better suit that STS i want a good healthy cam sound yet make power? i guess im lost on what cam would work best and also heads but not looking to spend more than 1600 or so on heads!! ANY HELP WOULD BE AWESOME
ive recently purchased a sts turbo kit with intercooler. I wanna keep the stock bottom end in it. Plans are to pick up a set of Patroit stage 3 heads CNC'd. Also planned on going a ms4 camshaft?? was recently told that patroit heads arent good because of the 1.60 intake valve. 1.55 makes more power??? and that a MS4 camshaft wouldnt do me anygood on stock displacement ls1. I was also told that a 230's cam would better suit that STS i want a good healthy cam sound yet make power? i guess im lost on what cam would work best and also heads but not looking to spend more than 1600 or so on heads!! ANY HELP WOULD BE AWESOME
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01-26-2011, 10:22 AM
#8
When you are looking for a turbo cam you want something small to get you in to boost quickly and something that doesn't have a lot of overlap. Overlap will cause boost to be bled off and thats never good for making power. Something like what predator-z suggested earlier would work really well for an STS kit. A cam like the MS4 with a similar LSA would have a lot of overlap, which wouldn't work well with the turbo.
01-26-2011, 03:11 PM
#9
TECH Senior Member
It is not that overlap will not work with turbo, it is just there is a point where the need to compensate the bleed with more boost is innevitable. That requires a built motor.
01-26-2011, 03:39 PM
#10
That is exactly what I said. Overlap bleeds off boost so you can either get a cam that has low overlap or run more boost. If you get a properly specced cam you won't need to build a motor depending on what kind if power level you are looking for. Thanks for correcting me.
Last edited by Sales4@Texas-Speed; 01-26-2011 at 03:55 PM.
01-26-2011, 03:57 PM
#11
TECH Senior Member
That is exactly what I said. Overlap bleeds off boost so you can either get a cam that has low overlap or run more boost. If you get a properly specced cam you won't need to build a motor depending on what kind if power level you are looking for. You know tech was pretty nice for those 6-8 months I didn't see you posting.
"Overlap will cause boost to be bled off and thats never good for making power"
Yeap, you are right, kinda kept me from reading stupidities like the above quote.
01-27-2011, 03:01 AM
#12
Staging Lane
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Awesome! thanks guys i really appriciate it. See i called texas speed today. they told me run a 233/239 cam on a sts with a 113 lobe separation but im gonna def. look into that comp cam. i just really want the loopy idle/ yet be smart with it and make power. Now what kind of rpms would be smart to run for shift points and stall converter?
02-13-2013, 11:47 AM
#13
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ive been wondering about this as well for awhile. been getting alot of different recommendations across the board about which cam for rear mounts. id like to see if anything has develpoed in the past few years.
I know that Ive talked to a rep at hawksthirdgen and they have a f-body with the 228R cam in it and said it drives great. now they also have the car on E85 so im sure that helps power production too lol
I know that Ive talked to a rep at hawksthirdgen and they have a f-body with the 228R cam in it and said it drives great. now they also have the car on E85 so im sure that helps power production too lol
02-14-2013, 11:21 AM
#14
TECH Senior Member
The cam I gave in a previous post 228/228 114LSA is a 228R but on 114 lobe separation instead of 112 of TSP. TSP can do the exact specs I gave and you'll be satisfied.
02-14-2013, 12:02 PM
#15
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ive actually gotten an interesting recommendation from Tick that i think i might go with. I was initially gonna go 228R 114, but then tick made a turbo cam, and then i was gonna go with the 226 turbo cam, but then i talk to Martin lol and he gave me what at first seemed like the strangest sized cam to me, 226/235, but then explained it to me and said it would operate almost like the 228R but give more exhaust pulsing to help spool the rear t76. im gonna give that one a shot and see how it goes. I was almost dead set on the 228r but then the trubo specific cam caught my attention, lol and then i made the mistake of asking martin lol and i got schooled in the arts of turbo camshafts lol but it should be interesting.
02-14-2013, 04:41 PM
#16
How in the hell does overlap bleed off boost when overlap occurs at TDC when the piston hasn't even barely even started it's intake stroke yet? The intake valve has just begun to open for a miniscule amount of time before the exhaust valve shuts. How is that bleeding off boost and losing power? Overlap=power, balancing that amount of overlap is what is critical and putting a blanket statement on it that overlap is bad for forced induction isn't correct IMO. You still have the rest of the intake stroke and compression stroke to allow that boost to build cylinder pressure the whole time this is happening the exhaust valve is shut. I don't see how that bleeds boost.
02-15-2013, 01:17 AM
#17
TECH Senior Member
Yes Martin you're correct. Overlap equal power. The action you spoke of above is theoretically correct under normal pressures, but under raised pressures, just cracking that intake while exhaust is not shut yet does let pressure out.
Of course we both know that where overlap occurs as well as if the cam is intake or exhaust biased from TDC makes a difference in the amount of pressure lost.
What happens is that you end up compensating lost pressure with extra amount to make up for that amount lost.
On street, I experienced that roughly up to 6* overlap is tolerable at relatively low boost levels without very noticeable side effects. After that you star seeing less returns for amount of boost injected.
Of course we both know that where overlap occurs as well as if the cam is intake or exhaust biased from TDC makes a difference in the amount of pressure lost.
What happens is that you end up compensating lost pressure with extra amount to make up for that amount lost.
On street, I experienced that roughly up to 6* overlap is tolerable at relatively low boost levels without very noticeable side effects. After that you star seeing less returns for amount of boost injected.
02-15-2013, 05:16 AM
#18
Yes Martin you're correct. Overlap equal power. The action you spoke of above is theoretically correct under normal pressures, but under raised pressures, just cracking that intake while exhaust is not shut yet does let pressure out.
Of course we both know that where overlap occurs as well as if the cam is intake or exhaust biased from TDC makes a difference in the amount of pressure lost.
What happens is that you end up compensating lost pressure with extra amount to make up for that amount lost.
On street, I experienced that roughly up to 6* overlap is tolerable at relatively low boost levels without very noticeable side effects. After that you star seeing less returns for amount of boost injected.
Of course we both know that where overlap occurs as well as if the cam is intake or exhaust biased from TDC makes a difference in the amount of pressure lost.
What happens is that you end up compensating lost pressure with extra amount to make up for that amount lost.
On street, I experienced that roughly up to 6* overlap is tolerable at relatively low boost levels without very noticeable side effects. After that you star seeing less returns for amount of boost injected.
I felt I needed to say something about this because I've also found that overlap can add exhaust volume to the exhaust volume that is already present and can actually aid in spool time and not hurt it. I've also found that opening the exhaust valve earlier to allow the pressure wave that is normally used to continue driving the piston downwards on the power stroke, can be used to spool the turbine and "overdrive" it. If you go too far though on the EVO you just end up losing torque that could of been used to propel the vehicle forwards under heavy acceleration.
This is just my opinion on it, and I'm sure you have your own as John@TSP has his. This is what I've found to work best in my cam grinds.
02-15-2013, 06:37 AM
#19
TECH Senior Member
I'm glad I'm not the only one that saw a small flaw in that statement. I agree that when operating above atmospeheric pressures, air mass moves and operates in ways that can't be compared to operating below atmospheric pressure. I still have a hard time seeing how for such a miniscule amount of crank degrees that the exhaust valve would be open during overlap that boost would be lost and could never be compensated for and returned. It's not magic and it doens't just dissapear. I also 100% agree with you about where the overlap is biased makes a HUGE difference in what is lost. On large turbine set-ups that won't choke sooner than a smaller turbine set-up I will allow the exhaust valve to close similarly to a N/A set-up where the exhaust valve closes ATDC. When I'm working with a small turbine set-up like a STS turbo kit, I close the exhaust valve before TDC so that the amount of crank degrees that the intake and exhaust valve are both open at low lifts is minimized. Unless I'm doing some solid roller profile for a very large turbine equipped combo, my EVC event occurs right at TDC or slightly before it every time.
I felt I needed to say something about this because I've also found that overlap can add exhaust volume to the exhaust volume that is already present and can actually aid in spool time and not hurt it. I've also found that opening the exhaust valve earlier to allow the pressure wave that is normally used to continue driving the piston downwards on the power stroke, can be used to spool the turbine and "overdrive" it. If you go too far though on the EVO you just end up losing torque that could of been used to propel the vehicle forwards under heavy acceleration.
This is just my opinion on it, and I'm sure you have your own as John@TSP has his. This is what I've found to work best in my cam grinds.
I felt I needed to say something about this because I've also found that overlap can add exhaust volume to the exhaust volume that is already present and can actually aid in spool time and not hurt it. I've also found that opening the exhaust valve earlier to allow the pressure wave that is normally used to continue driving the piston downwards on the power stroke, can be used to spool the turbine and "overdrive" it. If you go too far though on the EVO you just end up losing torque that could of been used to propel the vehicle forwards under heavy acceleration.
This is just my opinion on it, and I'm sure you have your own as John@TSP has his. This is what I've found to work best in my cam grinds.
IVO>0
IVC>48
EVO>48
EVC>0
ECL> 114
OVERLAP>0
02-15-2013, 07:16 AM
#20
I don't like XER lobes with boost as I've seen too many combinations have valve float N/A with XER lobes let alone using boost. More times than I can count I've seen this problem occur. The most aggressive lobe in the catalog is almost never needed for a hydraulic roller application that is anything less than a full out race engine. I use LXL and HUC lobes 90% of the time with boost, but I also use the less aggressive Extreme RPM High Lift lobes(not to be confused with XE-R lobes) and Extreme Marine High and Low Lift lobes too.
Here are my valve events for JoshuaGrooms rear mounted T76 turbo:
1
45
53.5
1.5
112ICL 114LSA 116ECL
2.5 degrees overlap
I feel that since the turbo is mounted in the rear, that the exhaust pulses once they reach the turbo will be much weaker than if it were front mounted. For this reason I like to add a little overlap to get some unburnt fuel/air mixture added to the already spent exhaust gases that make up the majority of the exhaust volume already present. With the cams that I do, I've found that using this method verses others spools the turbo quicker. Too much overlap though will choke the exhaust housing/turbine wheel and cause the engine to peak at a much earlier RPM than if less overlap was utilized.
I also have found that if you open the exhaust valve later, the pressure wave is used up more in driving the piston downward, and the resulting pulse that leaves the exhaust port is weaker than if you opened it sooner. I've found that this helps "overdrive" the turbine wheel, but as I said earlier too much will result in loss of torque that could of been used to propel the vehicle forwards under acceleration. Too much can also cause excessive drive pressure issues.
I'm also closing the intake valve earlier with my profiles for rear mount turbo's in order to build more cylinder pressure which will add torque across the board which will help accelerate the car faster and help combat the lag that rear mount set-ups are known for.
Camshaft profiles are all a giant compromise and about balance. We're just trying to find that happy medium that performs the best.
Here are my valve events for JoshuaGrooms rear mounted T76 turbo:
1
45
53.5
1.5
112ICL 114LSA 116ECL
2.5 degrees overlap
I feel that since the turbo is mounted in the rear, that the exhaust pulses once they reach the turbo will be much weaker than if it were front mounted. For this reason I like to add a little overlap to get some unburnt fuel/air mixture added to the already spent exhaust gases that make up the majority of the exhaust volume already present. With the cams that I do, I've found that using this method verses others spools the turbo quicker. Too much overlap though will choke the exhaust housing/turbine wheel and cause the engine to peak at a much earlier RPM than if less overlap was utilized.
I also have found that if you open the exhaust valve later, the pressure wave is used up more in driving the piston downward, and the resulting pulse that leaves the exhaust port is weaker than if you opened it sooner. I've found that this helps "overdrive" the turbine wheel, but as I said earlier too much will result in loss of torque that could of been used to propel the vehicle forwards under acceleration. Too much can also cause excessive drive pressure issues.
I'm also closing the intake valve earlier with my profiles for rear mount turbo's in order to build more cylinder pressure which will add torque across the board which will help accelerate the car faster and help combat the lag that rear mount set-ups are known for.
Camshaft profiles are all a giant compromise and about balance. We're just trying to find that happy medium that performs the best.
Last edited by Sales@Tick; 02-15-2013 at 07:31 AM.
