Solving the HKS 272 Cam Timing Mystery
Sorry to bring an old thread back from the grave ... but I've been researching and reading up on cam timing, since in about 1 1/2 weeks it will be time for me to dial in the HKS 280s that are now on my car.
To summarize my situation: I am in the process of breaking in an AMS GT3071R turbo kit on a built 2.0 liter engine that will support a 9000 rpm redline. I want a setup that will work well for circuit racing, meaning that I want a fairly wide powerband and will take power in the higher rpms over torque in the lower rpms.
Now, if I have read and understood all the bits of info floating around in here, the HKS 280 cams have a LSA of 110 and, per the link Ted provided, increasing the LSA should net me some topend along with a slew of other benefits (better idle, decrease in cylinder pressure, decreased chance of knock) at the expense of low-end torque. With that in mind, I am thinking of taking this approach to dialing in my cams:
- test for a good "straight up" setting (i.e. 0/0, -1/-1, -3/-3)
- then take the best of those and re-run it with a slightly advanced exhaust cam (i.e. -3/-2, -3/-1, etc.)
Based on BadazzCR's testing it doesn't look like the 280s respond well to the -4/-1 setting of the 272s, BUT IIRC that was with a stock turbo, which runs out of steam in the upper rpms ranges to begin with. I'm thinking a 3071 might do better.
Any thoughts?
l8r)
To summarize my situation: I am in the process of breaking in an AMS GT3071R turbo kit on a built 2.0 liter engine that will support a 9000 rpm redline. I want a setup that will work well for circuit racing, meaning that I want a fairly wide powerband and will take power in the higher rpms over torque in the lower rpms.
Now, if I have read and understood all the bits of info floating around in here, the HKS 280 cams have a LSA of 110 and, per the link Ted provided, increasing the LSA should net me some topend along with a slew of other benefits (better idle, decrease in cylinder pressure, decreased chance of knock) at the expense of low-end torque. With that in mind, I am thinking of taking this approach to dialing in my cams:
- test for a good "straight up" setting (i.e. 0/0, -1/-1, -3/-3)
- then take the best of those and re-run it with a slightly advanced exhaust cam (i.e. -3/-2, -3/-1, etc.)
Based on BadazzCR's testing it doesn't look like the 280s respond well to the -4/-1 setting of the 272s, BUT IIRC that was with a stock turbo, which runs out of steam in the upper rpms ranges to begin with. I'm thinking a 3071 might do better.
Any thoughts?
l8r)
ludikraut
you have the specs for the cams. if you can pass me the numbers for the open and close events at 0 and 1mm .. i can plug this into my calc and get an estimate..
3971 definitely did not like -4/-1 with 272s..
you have the specs for the cams. if you can pass me the numbers for the open and close events at 0 and 1mm .. i can plug this into my calc and get an estimate..
3971 definitely did not like -4/-1 with 272s..
Ludikraut,
I know when you run - cam timing you can add timing up top witch will produce more power.
But with your turbo set up I think you need to try all the settings and see witch setting would allow you to run the most amount of safe timing.
IMHO
Eric
I know when you run - cam timing you can add timing up top witch will produce more power.
But with your turbo set up I think you need to try all the settings and see witch setting would allow you to run the most amount of safe timing.
IMHO
Eric
just thought Id add for anyone who cares that I just installed a new GSC 272 intake to match my 272 hks exhaust and w/ the +2/0 setting, my car goes knock crazy. At 33% throttle and cruising ~2500-3300RPM I get serious knock. This tune worked well on the 264/272 I had so the tune is good... I even compared it to stock and it is MORE CONSERVATIVE in that load/rpm range than the stock maps in both timing and fuel. Gonna try -3/-3 and -2/-2 etc. anyone w/ GSC cams and the crazy 280 advertised duration of them w/ good settings for torque, lemme know.
This is easily explained by the fact that the GSC 272s are ground on 107/112 deg lobe centerlines, while the HKS are ground on 110/110 deg lobe centerlines. You wouldn't want to set the GSCs to +2/0 anyway, because there is a difference in duration @1mm as compared to the HKS.
Set your GSCs to -0.5/-2 and try that. I think that will be about the best you can do for what you want.
Set your GSCs to -0.5/-2 and try that. I think that will be about the best you can do for what you want.
I'll try that. Today I set them to -3/-2 and there was much less knock. I still get odd knock at ~32%-40% throttle ~2500-3300 RPM (85-105 load range) just cruising. However, where it used to be 2,3, and sometimes 4 counts, it's a sporadic treo of 1s. So you think that setting the exhaust more negative (giving more overlap) is a good idea? I figured I needed to get rid of a bit of that excessive overlap from the 280 advertised duration of the GSC inake cam by making the intake more retarded than the exhaust.
One other note perhaps you can help with... I tried many many combinations today and was not able to get more than 5-6 inHg of vaccuum at idle. No matter what I did I couldn't improve it. Before the swap (w/ hks 264 intake) I had ~15 in. but I cannot get it back. The only thing I can think is that it's the reduced lift of the GSC intake cam that causes it. I even went so far as -3/+2 to see if I could get rid of the overlap...
The only other thing I figure is that I'm a total idiot and don't comprehend which way is advancing and which way is retarding. (advancing the cam is to turn the cam in a clockwise motion if you are looking at the gears, correct?)
One other note perhaps you can help with... I tried many many combinations today and was not able to get more than 5-6 inHg of vaccuum at idle. No matter what I did I couldn't improve it. Before the swap (w/ hks 264 intake) I had ~15 in. but I cannot get it back. The only thing I can think is that it's the reduced lift of the GSC intake cam that causes it. I even went so far as -3/+2 to see if I could get rid of the overlap...
The only other thing I figure is that I'm a total idiot and don't comprehend which way is advancing and which way is retarding. (advancing the cam is to turn the cam in a clockwise motion if you are looking at the gears, correct?)
Last edited by honki24; Mar 17, 2007 at 06:38 PM.
So you think that setting the exhaust more negative (giving more overlap) is a good idea? I figured I needed to get rid of a bit of that excessive overlap from the 280 advertised duration of the GSC inake cam by making the intake more retarded than the exhaust.
Before the swap (w/ hks 264 intake) I had ~15 in. but I cannot get it back. The only thing I can think is that it's the reduced lift of the GSC intake cam that causes it. I even went so far as -3/+2 to see if I could get rid of the overlap...
The only other thing I figure is that I'm a total idiot and don't comprehend which way is advancing and which way is retarding. (advancing the cam is to turn the cam in a clockwise motion if you are looking at the gears, correct?)
Before the swap (w/ hks 264 intake) I had ~15 in. but I cannot get it back. The only thing I can think is that it's the reduced lift of the GSC intake cam that causes it. I even went so far as -3/+2 to see if I could get rid of the overlap...
The only other thing I figure is that I'm a total idiot and don't comprehend which way is advancing and which way is retarding. (advancing the cam is to turn the cam in a clockwise motion if you are looking at the gears, correct?)
Greater overlap reduces vacuum at idle. Greater overlap decreases the knock threshold. Greater overlap also makes the motor very mechanically efficient at midrange rpm (if big torque is one's goal). If you experience a high incidence of knock, remove some overlap (with the exhaust cam) and try again.
very good post, thank you. Any idea on why I can't make more vaccuum than a miserable 5in? Like I said, I used -3/+2, which should have reduced overlap a good deal but no increase in vaccuum. I noticed much bigger changes in vaccum w/ cam gear settings when using the HKS cam.
Ok, maybe this will clear the muddy water...
As installed straight up, the HKS 272 cams are ground on 110deg LC and have a LSA of 110deg.
If a -4/-1 setting is desired, we look at our cam gear marks and adjust the Intake cam to 4 deg retard and retard the exhaust cam 1 deg.
The -4/-1 setting is represented in cam gears, let's see what this does to our cam specs:
The intake cam has a LC of 110 deg. If we retard the intake cam 4 cam degrees, this equals 8 crank degrees. The new setting gives the intake cam an LC of 118 deg because retarding the intake cam INCREASES its LC.
The exhaust cam has a LC of 110 deg. If we retard the intake cam 1 cam degrees, this equals 2 crank degrees. The new setting gives the intake cam an LC of 108 deg because retarding the exhaust cam REDUCES its LC.
Since LSA = (Intake LC + Exhaust LC)/2, the new LSA = 117deg.
Notes:
- Remember, the EXHAUST lobe comes around just before the INTAKE lobe, not the other way around. As the exhaust lobe comes around, the exhaust gases are vented, then you have overlap when the intake valve opens immediately afterward, followed by the long blank section between the lobes is where the cam is turning during the compression stroke, when no valves are open.
- LSA is always expressed in CAM degrees because it tells you the angle of separation between the intake and exhaust LOBES on the cam itself.
- Lobe centers are always expressed in CRANK degrees because they tell you the position of the crankshaft with respect to the cam lobes.
As installed straight up, the HKS 272 cams are ground on 110deg LC and have a LSA of 110deg.
If a -4/-1 setting is desired, we look at our cam gear marks and adjust the Intake cam to 4 deg retard and retard the exhaust cam 1 deg.
The -4/-1 setting is represented in cam gears, let's see what this does to our cam specs:
The intake cam has a LC of 110 deg. If we retard the intake cam 4 cam degrees, this equals 8 crank degrees. The new setting gives the intake cam an LC of 118 deg because retarding the intake cam INCREASES its LC.
The exhaust cam has a LC of 110 deg. If we retard the intake cam 1 cam degrees, this equals 2 crank degrees. The new setting gives the intake cam an LC of 108 deg because retarding the exhaust cam REDUCES its LC.
Since LSA = (Intake LC + Exhaust LC)/2, the new LSA = 117deg.
Notes:
- Remember, the EXHAUST lobe comes around just before the INTAKE lobe, not the other way around. As the exhaust lobe comes around, the exhaust gases are vented, then you have overlap when the intake valve opens immediately afterward, followed by the long blank section between the lobes is where the cam is turning during the compression stroke, when no valves are open.
- LSA is always expressed in CAM degrees because it tells you the angle of separation between the intake and exhaust LOBES on the cam itself.
- Lobe centers are always expressed in CRANK degrees because they tell you the position of the crankshaft with respect to the cam lobes.
Two part question:
#1 - I got a set of 272 Comp Cams on the way and from my understanding these have the same grounds/specs as the HKS 272's which means I could use the -4/-1settings correct?
#2 - I'm still waiting on my Xede & a custom tune, but until then would I be safe to install and run these cams with no problems? Also could I see any benefits or power gains with these cams installed and adjusted on a stock 8 w/basic bolt-ons prior to a tune? Thanks
Comp Cams 272s are ground on 104/112 LCs, which are significantly different than HKS cams. Comp Cams will not give best power numbers without cam gears.
To set Comp Cams like HKS at -4/1, they would have to be set at -7/-2.
Got cam gears coming also, no need for cams unless i can fine tune them right? And did u mean to say -4/-1 instead of -4/1? Would this setting (-7/-2) be best if i wanted more power & torque in my upper rpms and have a better idle?Also my #2 question?? Do i need a tune w/cams right away or is it safe to run until tuned properly?
Last edited by Tha Shocker!; Mar 19, 2007 at 04:15 PM.
I meant to say "-4/-1", correct.
The Comp Cams setting I quoted would be best suited toward best peak hp and best average hp for drag racing. The tradeoff is a little spool time.
You can drive it around untuned with cams, but I wouldn't beat up on it, simply because the cams WILL affect the AFR.
The Comp Cams setting I quoted would be best suited toward best peak hp and best average hp for drag racing. The tradeoff is a little spool time.
You can drive it around untuned with cams, but I wouldn't beat up on it, simply because the cams WILL affect the AFR.
I meant to say "-4/-1", correct.
The Comp Cams setting I quoted would be best suited toward best peak hp and best average hp for drag racing. The tradeoff is a little spool time.
You can drive it around untuned with cams, but I wouldn't beat up on it, simply because the cams WILL affect the AFR.
The Comp Cams setting I quoted would be best suited toward best peak hp and best average hp for drag racing. The tradeoff is a little spool time.
You can drive it around untuned with cams, but I wouldn't beat up on it, simply because the cams WILL affect the AFR.