Big Camshfats And The V-cam System

[blk180]

i would think when it comes on boost you could keep it on if you wanted to 5200 full boost 10200 limiter you wouldnt be droping out of the power range?

[Sydneykid]

i have the 0.81 housing

OK, with that size housing you should be able to get decent boost at 4,750 rpm or so. You don’t need a dyno to tune the cam timing if you have a stop watch and your seat of the pants feel is tuned. You can try a few settings yourself and “feel” the results, look at the boost gauge or better still measure them with your stop watch.

Most times I find around 2 degrees advanced on the inlet camshaft and 4 degrees retarded on the exhaust camshaft works out pretty good for early boost build, without compromising top end power too much. So for a starter give that a try. Remember every car is different, so don’t be afraid to experiment around those numbers.

Keep in mind that you will be able to advance the ignition timing (not just the 4 degrees to make up for retarding the camshaft 4 degrees). My experience has been that you can get quite a bit more advance which helps again some more with the earlier boost build. I basically just keep advancing the timing until I see some knock on the PFC Commander or knock amp (whatever brand). If no knock readings available, then I use a set of chassis ears and listen for some pre-ignition. You will be surprised how much more responsive you can make it with a bit of fiddling on the ignition advance.

Warnings;

1. Be careful how much exhaust camshaft timing you test at they will hit the pistons. Remember on the exhaust stroke the exhaust valve is opening at the same time as the piston is travelling upwards. So make sure that you measure the piston to valve clearance if you want to try more than 3-5 degrees.

2. You will have to add some fuel (lots) as the boost build earlier, so keep an eye on the A/F ratios.

3. Pre-ignition at your power and rpm levels is BAD news, so make sure you listen carefully.

Hopefully that has been of some use, any questions, just ask.

cheers

[Faid]

hey thanks gary. Ill have a crack at the valve timing when i get to work in a couple of hours. if i could loose 400-500rpm off the full boost time, it would be a start. i use a HKS knock AMP for my knock detection, but on the job i have some chassis ears, as they have to be used when working on diesel engines (high comp mofo's). but so far on the PFC, my knock has not exeeded 7. My tune is a tad lean for my taste, on full boost i get a 11.8-11.9 ratio @ 79% duty cycle. but i have the timing expert collegue look over the timing, he does this sorta thing all day. for now i am happy with the on boost response of the car, it is just pushing constantly when you reach boost.

[Sydneykid]

hey thanks gary. Ill have a crack at the valve timing when i get to work in a couple of hours. if i could loose 400-500rpm off the full boost time, it would be a start. i use a HKS knock AMP for my knock detection, but on the job i have some chassis ears, as they have to be used when working on diesel engines (high comp mofo's). but so far on the PFC, my knock has not exeeded 7. My tune is a tad lean for my taste, on full boost i get a 11.8-11.9 ratio @ 79% duty cycle. but i have the timing expert collegue look over the timing, he does this sorta thing all day. for now i am happy with the on boost response of the car, it is just pushing constantly when you reach boost.

11.8 - 11.9 is fine, perfectly safe, just watch the knock, stay under 20.

You will get a bit out of the cam tiiming, but the resulting ignition timing that you can run is the big winner.

Don't be afraid to throw plenty of degrees at it, 5 - 10 degrees is common. On the R33GTST, I moved the off boost up 18 degrees in some places.

cheers

Edited October 10, 2006 by Sydneykid

[Faid]

well thanks gary, with the fiddling on the cam gears i now hit my full boost around the 4800ish. my advice to people with RB26 and cam gears, fiddle around with them, they help you alot. and also gary, while working on the ign map i was able to iron out some flat spots, so when moving to boost it feels way more responsive, and also the stopwatch trick prooved it to me with measurable numbers. i build my ful boos a full 0.8 secs earlier, the car pulls quite constantly towards boost, not like before when i would move like a donkey, and then run like a cheetah.

[Sydneykid]

well thanks gary, with the fiddling on the cam gears i now hit my full boost around the 4800ish. my advice to people with RB26 and cam gears, fiddle around with them, they help you alot. and also gary, while working on the ign map i was able to iron out some flat spots, so when moving to boost it feels way more responsive, and also the stopwatch trick prooved it to me with measurable numbers. i build my ful boos a full 0.8 secs earlier, the car pulls quite constantly towards boost, not like before when i would move like a donkey, and then run like a cheetah.

Glad to see you got the results Faid, just shows what is possible if you are prepared to go though the processes. A ~400 rpm improvement in boost build is always worth spending some time on.

cheers

PS; I like that "move like a donkey, then run like a cheetah" I am gunna use that for sure.