Cam selection for boost/high rpm
#1
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Cam selection for boost/high rpm
hey there guys... wrong wheel drive BPT guy here looking for some cam advice
this past fall my car put down 320whp/325wtq at 23psi. This is with a 323 GTR motor, completely stock from throttle body to turbine housing. My torque drops off fast at high rpm's, and i'm thinking it is most likely cam related. my boost level holds strong all the way to 7k, my intercooler is plenty big enough, and my exhaust is 3" all the way back...
here's my dyno plot:
Some details on the motor:
IHI ballbearing turbo, 65mm compressor wheel, supposedly fairly efficient to nearly 30psi
8.2:1 compression ratio
Intake cam duration 233° @ 0.003"
Intake cam opening 2° BTDC
Intake cam closing 51° ABDC
Intake cam lobe height 44.094mm (1.7360")
Intake cam base circle 35.941mm (1.415")
Intake valve lift 8.1534mm (0.321")
Exhaust cam duration 247° @ 0.003"
Exhaust cam opening 59° BBDC
Exhaust cam closing 8° ATDC
Exhaust cam lobe height 44.600mm (1.7560")
Exhaust cam base circle 35.941mm (1.415")
Exhaust valve lift 8.6614mm (0.341")
Valve overlap 10°
any suggestions on a suitable off-the-shelf cam grind that might open up my top end a bit? would adjustable cam gears alone be able to yield some decent results? i cant go too extreme, this thing still needs to be able to pass a tailpipe test... and it is driven daily on occasion. i found a good deal on a pair of "web cams 505+2.5" but i'm worried they might be a bit too aggressive.
this past fall my car put down 320whp/325wtq at 23psi. This is with a 323 GTR motor, completely stock from throttle body to turbine housing. My torque drops off fast at high rpm's, and i'm thinking it is most likely cam related. my boost level holds strong all the way to 7k, my intercooler is plenty big enough, and my exhaust is 3" all the way back...
here's my dyno plot:
Some details on the motor:
IHI ballbearing turbo, 65mm compressor wheel, supposedly fairly efficient to nearly 30psi
8.2:1 compression ratio
Intake cam duration 233° @ 0.003"
Intake cam opening 2° BTDC
Intake cam closing 51° ABDC
Intake cam lobe height 44.094mm (1.7360")
Intake cam base circle 35.941mm (1.415")
Intake valve lift 8.1534mm (0.321")
Exhaust cam duration 247° @ 0.003"
Exhaust cam opening 59° BBDC
Exhaust cam closing 8° ATDC
Exhaust cam lobe height 44.600mm (1.7560")
Exhaust cam base circle 35.941mm (1.415")
Exhaust valve lift 8.6614mm (0.341")
Valve overlap 10°
any suggestions on a suitable off-the-shelf cam grind that might open up my top end a bit? would adjustable cam gears alone be able to yield some decent results? i cant go too extreme, this thing still needs to be able to pass a tailpipe test... and it is driven daily on occasion. i found a good deal on a pair of "web cams 505+2.5" but i'm worried they might be a bit too aggressive.
#2
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1. search "intake manifold"
2. read all the threads you get
3. order an intake manifold from BEGi or make your own
4. ???
5. profit
Aftermarket IM is probably worth 40tq on your car at redline.
2. read all the threads you get
3. order an intake manifold from BEGi or make your own
4. ???
5. profit
Aftermarket IM is probably worth 40tq on your car at redline.
#4
I'd still put a set of rods in that motor. I know, I know, but at those power levels, I would.
Also +1 to new intake manifold. Also try retarding the intake cam ~6 degrees. That will take 6 degrees out of the overlap and put your intake valve closing at 57*ABDC. Youd probably retard it more and see larger gains after 5K+.
Also +1 to new intake manifold. Also try retarding the intake cam ~6 degrees. That will take 6 degrees out of the overlap and put your intake valve closing at 57*ABDC. Youd probably retard it more and see larger gains after 5K+.
#5
You guys are suggesting retarding his intake cam, when his BPT intake cam is already way retarded compared to a BP motor.
therealdeal, note that your motor makes the same power at 4500 RPM as at 7000 RPM. If you don't raise your revlimit, that's actually pretty good.
Now I have to ask, what is your objective? If you increase your power at 7000 RPM but reduce it at 4500 RPM, the car may end up being slower instead of faster, in day to day driving. Do you drag race? If so, what does RPM drop to after say, a 2-3 shift?
If you want to raise your revlimit, then I would suggest increasing your intake cam duration by 10*. The guy who can design and regrind your cams given your specs and requirements is Dema Elgin at www.elgincams.com .
therealdeal, note that your motor makes the same power at 4500 RPM as at 7000 RPM. If you don't raise your revlimit, that's actually pretty good.
Now I have to ask, what is your objective? If you increase your power at 7000 RPM but reduce it at 4500 RPM, the car may end up being slower instead of faster, in day to day driving. Do you drag race? If so, what does RPM drop to after say, a 2-3 shift?
If you want to raise your revlimit, then I would suggest increasing your intake cam duration by 10*. The guy who can design and regrind your cams given your specs and requirements is Dema Elgin at www.elgincams.com .
#10
Goto integral cams. Your situation is paticularly difficult because of the high exhaust manifold and intake manifold pressures. My advice would be to get a cam that has 15 degrees more duration and .38 inches or so of lift. Then dial it in with a cam gear. The idea would not be to have more overlap, but to keep the valve open longer while the piston is coming up the cylinder because your intake manifold pressure will be higher then your cylinder pressure for much longer in your case.
Your developing a kind of miller cycle engine in a way. Expect power to drop off boost, but increase every where boost of a reasonable amount exists (more then 10 psi or so) Your intake cam centerline should be a much later opening then stock. Other then that professionals should steer you in.
Your developing a kind of miller cycle engine in a way. Expect power to drop off boost, but increase every where boost of a reasonable amount exists (more then 10 psi or so) Your intake cam centerline should be a much later opening then stock. Other then that professionals should steer you in.
#12
Goto integral cams. Your situation is paticularly difficult because of the high exhaust manifold and intake manifold pressures. My advice would be to get a cam that has 15 degrees more duration and .38 inches or so of lift. Then dial it in with a cam gear. The idea would not be to have more overlap, but to keep the valve open longer while the piston is coming up the cylinder because your intake manifold pressure will be higher then your cylinder pressure for much longer in your case.
Your developing a kind of miller cycle engine in a way. Expect power to drop off boost, but increase every where boost of a reasonable amount exists (more then 10 psi or so) Your intake cam centerline should be a much later opening then stock. Other then that professionals should steer you in.
Your developing a kind of miller cycle engine in a way. Expect power to drop off boost, but increase every where boost of a reasonable amount exists (more then 10 psi or so) Your intake cam centerline should be a much later opening then stock. Other then that professionals should steer you in.
#13
The pressure gradient and the velocity gradient are synomous. You can continue filling the cylinder until the spring in the cylinder is fully compressed, and begins a reversion flow into the intake tract. Force on the spring is dictated by pressure in the valve area. So when the pressure in the cylinder becomes higher then the pressure in the intake tract the spring begins to unwind and the velocity vector value becomes negative (assuming cylinder filling direction is positive.)
You are right and I'm right, we're just talking about it in two different ways.
You are right and I'm right, we're just talking about it in two different ways.
#14
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i shouldnt need rods... these motors are built up pretty well from the factory. its basically a motor straight out of a WRC car...
GTR---------------------------------n/a BP----------------------------------B6T (BF GTX)
heres some info on the motor: GT-R Engine
i'm not sure the intake manifold is an issue, but theres no way to know for sure without putting a custom one on it. the begi one won't work without severe modifications.... FWD bp's breathe from the opposite end :(
i never realized that the miata intake cams had more lift than the fwd intake cams, thats interesting! in theory if i put a miata intake cam in there and retarded it 3 degrees, i'd gain a little lift but leave the rest of the specs essentially unchanged. of course i could always then play with intake cam timing from there...
so the 505+2.5... would they be a good choice or no? i found a set brand new for about $300 but the deal isn't going to last too long...
yes i do drag race, but i also drive the car around town, to work, etc (in the summer). i cant remember my rpm drop off hand... and it looks like the gear ratio calculator i usually use on an f-body site is now blocked by firefox (wtf?)
GTR---------------------------------n/a BP----------------------------------B6T (BF GTX)
heres some info on the motor: GT-R Engine
i'm not sure the intake manifold is an issue, but theres no way to know for sure without putting a custom one on it. the begi one won't work without severe modifications.... FWD bp's breathe from the opposite end :(
i never realized that the miata intake cams had more lift than the fwd intake cams, thats interesting! in theory if i put a miata intake cam in there and retarded it 3 degrees, i'd gain a little lift but leave the rest of the specs essentially unchanged. of course i could always then play with intake cam timing from there...
so the 505+2.5... would they be a good choice or no? i found a set brand new for about $300 but the deal isn't going to last too long...
yes i do drag race, but i also drive the car around town, to work, etc (in the summer). i cant remember my rpm drop off hand... and it looks like the gear ratio calculator i usually use on an f-body site is now blocked by firefox (wtf?)
#18
The pressure gradient and the velocity gradient are synomous. You can continue filling the cylinder until the spring in the cylinder is fully compressed, and begins a reversion flow into the intake tract. Force on the spring is dictated by pressure in the valve area. So when the pressure in the cylinder becomes higher then the pressure in the intake tract the spring begins to unwind and the velocity vector value becomes negative (assuming cylinder filling direction is positive.)
You are right and I'm right, we're just talking about it in two different ways.
You are right and I'm right, we're just talking about it in two different ways.
#19
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i know about the exhintake mod... but i really dont like how annoying it is to set up. X number of teeth off plus Y degrees... screw that lol.
i'll contact integrated to see what they think.
i have never heard of a GTR rod failing up near the wrist pin... ive seen a few that bent with around 400whp+detonation but i've never seen or heard of one that actually broke. do you have any pics, links to a thread?
gtx rods on the other hand have a much higher failure rate. mostly they seem to crack in the thin spots at the top corners of the big end.
i'll contact integrated to see what they think.
i have never heard of a GTR rod failing up near the wrist pin... ive seen a few that bent with around 400whp+detonation but i've never seen or heard of one that actually broke. do you have any pics, links to a thread?
gtx rods on the other hand have a much higher failure rate. mostly they seem to crack in the thin spots at the top corners of the big end.