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I have been watching the S4 cam developments since day dot and one thing that puzzled me was the centerline's on these cams. They are quite different to N1's, kelfords etc. I Dont doubt Franklins ability one bit as i know theire various cams (not limited to ve's) are performing well down this neck of the woods. I just want do understand how they came at such different Cl's
What do you guys think the reasoning would be behind this?
I have been reading up and cam timing and tuning to try and understand better why this would be done and have come up with this. The book I have been reading is called "performance tuning in theory and practice" by A. Graham Bell it is an old book and it only really touches on twin cam's breifly so the info may be a bit out of date by now but i figure the basics must apply. So here goes....
In the book he talks about retarding the inlet to acheive more top end and advancing the exhaust to gain back some of the lost botttom/mid range. So if you were to take some cams with n1 CL's and retard the intake and advance the exhaust the centerlines would move closer to the s4's cl's. I realise we are talking somewhere in the vicinity of 8 deg but you get the idea. Therefore do you think this could be the reasoning behind the different Cl's and could it also explain why the S4's have such phenomonal top end?
Before selling my car I noticed that retarding the exhaust cam 2.5 degrees on the stock 2.0 cams the car ran better on the top side. I never dynoed it like this but I can tell you the car was faster than at stock settings.
the centerlines on the FS4 cams that i got were pretty far off from optimal in my book for making power.
typically, SR's and VE's like to see about 100 deg IN and about 105 EX C/L.
N1 cams are at 104 and 110 and work well drop in.
std VE are at 104 IN and 114 EX. you can gain a few WHP by retarding the EX cam on the std ve cams.
the N1's work best at about +4 -4 - +5 -5 give or take, that puts them to about 99-100 deg IN and 105-106 DEG EX.
the FS4 cams that I measured were 115 IN and 100 EX? i think off the top of my head or somewhere around there. almost like they got mixed up. The only way I'd run cams like this is on a very hihg RPM turbo motor with large displacement. but that tells me that the EX cam is too small and the intake is too big.
I would run the FS4 cams at straight up 0,0, then run the intake cam advanced 1 whole tooth, and from there retard it about 5-6 deg. the exhaust i'd advance about 6 to start with.
personally i think if they had so much RnD on these cams to start with they would have dyno tested them before selling them and found what lobe centers they work best with.
I talked to him very breifly about CL's when i talked to him the other day. From what i understand their de cams are using similar CL's. I know when the were developing the cams they brought a motor and measured the stock cams in the motor. i.e the specs at the valve.
What determines where your centerline should be? if thats not a really stupid question. To me what i know about Cam timing (albeit limited) it makes sense that they make so much power up top, why is it that an engine "likes" a certain range of CL's?
Johnathan Merkel and Kyle Davis were right about you Charles. You really know more than you post here on the forums. Way more than I can understand sometimes, but I don't plan on being lost for too long. As always, thank you for everything from your wisdom to your hard work in R&D for the SR faithful. Time to start the 1st homework reading for SR20Turbofreak 101 class....
Thanks Charles that is the exact answer i was looking for. Couldn't have been more clear. Cheers.
Do you have any books you can recommend on performance tuning. The one i am reading at the moment is good although it is a bit vague at times on explaining why you do something and is probably getting a bit out dated now.
Look forward to the next installment.
Interestingly I talked to Adrian from franklins today about the s4's and i asked how the CL's compared to standard amoung other things and he said that they had tightened them up a bit from standard. He didn't actually say what they were but to me that seems they should be about where you were saying earlier.
Perhaps it may be beneficial if you get in touch with him and tell him what you have measured them up at and perhaps find out what they actuall are/should be?
wow dude some good read right there.. what books have you read any titles you got that i can go pick up?
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The official Franklin centerline is the same as what Charles measured.
Since I've been running with the FS4 for awhile, I've already tried 11 different combination of centerlines with the cam gears and the engine definately runs better than leaving the cams at 0/0. The FS4 likes the lobe separation angle(LSA) in the neighborhood of 107, anymore or any less and the bottom end or top end will suffer.
On Ivan's car, we will install adjustable cam gears and you will see how important cam gears are to big cams.
ooOOOooooo, no one here has done any amount of tweaking with cam timing on the stage 4's. Will be interested in finding out how they run on what settings. It's a little harder for us to get access to dyno's here, the select few that are willing to hire out dyno time certainly know how to charge for it!
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the set that I tested were not tightened up, they were spread apart, maybe they were ground wrong, either way i'm not sure. maybe he changed the grind afterwards. I will test them on the built motor and share my few cents with them about the cams.
Yeah I realise they certainly weren't tightened thats why I thought there might have been something weird going on. Will be interesting to see how they perform in your built motor.
Hey 5 Speed Is that LSA of 107 for both the intake and the exhaust? When do you think you guys will be heading back to the dyno again?
Yes I know the difference between the LSA and lobe centerline.
LSA = intake centerline + exhaust centerline / 2
I have two dyno sheets with the centerline at 100 intake/110 exhaust and 108 in./108 ex. With the intake centerline at 100 I only had .050 piston to valve clearance. The peak power was at 7800. This is a big difference from Ivan and Clint power peak.
We will be heading back to the dyno with the cam gears for Ivan's car. Once testings are finish, we will release all the dyno graphs.
Those with sr16 pistons have plenty of leeway when it comes to pvc. My pvc was tight because I'm running with 20V pistons. At one point I was more worry about valve to valve clearance than pvc. I had the intake and exhaust centerline at 100.
The valve clearance is why i notched my 16ve pistons another .050". With my big lobe cams, i can run 10 deg adv IN and 10 deg ret on ex and still have .100" valve to piston clearance.
So by applying what you said earlier in the thread, that would be a good setup for a nice and broad power band that goes to about 8000-8500rpm, as exhaust gases might start to revert back with that much exhaust cam timing retard?
Great info, Charles. Do you have the centerline specs for SR16 cams?
And do you think it is worthwhile to use adjustable cam gears? If so, what settings do you recommend?
Quote:
Originally Posted by SR20Turbofreak
the centerlines on the FS4 cams that i got were pretty far off from optimal in my book for making power.
typically, SR's and VE's like to see about 100 deg IN and about 105 EX C/L.
N1 cams are at 104 and 110 and work well drop in.
std VE are at 104 IN and 114 EX. you can gain a few WHP by retarding the EX cam on the std ve cams.
the N1's work best at about +4 -4 - +5 -5 give or take, that puts them to about 99-100 deg IN and 105-106 DEG EX.
the FS4 cams that I measured were 115 IN and 100 EX? i think off the top of my head or somewhere around there. almost like they got mixed up. The only way I'd run cams like this is on a very hihg RPM turbo motor with large displacement. but that tells me that the EX cam is too small and the intake is too big.
I would run the FS4 cams at straight up 0,0, then run the intake cam advanced 1 whole tooth, and from there retard it about 5-6 deg. the exhaust i'd advance about 6 to start with.
personally i think if they had so much RnD on these cams to start with they would have dyno tested them before selling them and found what lobe centers they work best with.
