I'm shopping around for parts to wrap up a fresh motor for the turbo car. While looking for a set of main bearings I came across a selection of reasonably priced Schrick cams.
The case for the stock cam is thats its gentle on the valvetrain and it runs efficiently during normal driving. I've also got it tuned to within a "gnats ass" of where I want it, and I hate to mess with a good thing:
On the other hand, the 272 would presumably help tame the giant slug of torque that comes on when it spools up and move some of it up towards the top end. I expect that the 272 is mild enough that I wouldn't have to rev the motor to the moon to appreciate the gains. I would like to see peak power in the range of 5800-6000 RPM. The chart plotted above shakily manages peak power around 6400 RPM but thats after a perceptible drop off after 5500.
A buddy of mine has put the Schrick cam in his M20 but he had to also install stiffer springs so there was no valve float. I test drove his e28 and was considering buying it as he also had done the e to i head swap. But yeah I guess the deal is stiffer springs from what I've heard. On test drive, it sounded very lumpy, like it had a small block V6 in it very tasty.
i had an ireland 272 regrind with my first turbo. remember the 2860RS butt plug? the idle vac was so low i couldn't get two consecutive assisted brakes uses. first one was good, 2nd one was a brick wall. i had to cut my BOV spring so the BOV would stay closed at idle. i think it was like 13 or 14 inches of vac or something.
also i believe i did have some valve float. i blew up that cyl head and now have a the stock 325cam with metric mechanic beehive springs and a bullseye s256. honestly, i can't tell a whole lot of difference in the way it drives off boost. i don't know a lot about turbo cam profiles other than how to quote the specs so not sure how helpful this is. i will say this...the upgraded springs are pretty cool. they actually quiet down the valve train a good bit at high RPM and seem to control it better all around. i should have added those with my very first head build.
you'd probably agree, but i think the slug of torque you are talking about is just the nature of this motor/head. you can definitely still see it, even with the bigger cam. smoothing effect was very limited.
Here is a stock graph, low boost non intercooled and intercooled. Running on WG spring only which is a little lazy and with some creep so the hit is softer. T4 .58 housing on both.
You could try progressive boost control. That would certainly make up for a lack of torque, but I think a retune would be in order. Methanol injection that cuts in where you need more torque? The cam would probably work, but I've never had a turbo m20, so what do I know?
What you're seeing on the dyno is spoolup. Boost control does no good if the engine is running below the boost threshold. This motor and turbo just happen to spool up right into the beginning of the powerband.
I don't want more torque. Easy way to get that would be to run more boost. I'd like to trade some torque for some top end. The easy way to do that would be to run a 666 Fab short runner intake, but this comes at the expense of a lot of area under the curve. I have been thinking about one of those for a while. It'd make the car run like a two stroke, which actually might be fun.
Wait, trade some torque for some top end? What exactly do you mean. When I hear top end what I think is power at the upper end of the rev range. Power is directly proportional to rpm and torque at said RPM. You want more power, you need more torque, or get it revving higher.
Hence my suggestion of upping boost at the upper end of the rev range.
I think he means less mid range torque and abit more at the top end. Changing the cam as far as understand maybe a way but changing intake runner length and area is another. Shorter should move peak power up. However can't you also change the exhooassed manifold primary pipe length as well to achieve the same thing. Maybe do both along with a cam to get everything working in harmony.
Correct. Problem with intake manifold tuning is that its complicated and expensive. A cam would be a less radical departure from the current configuration, whereas a short runner intake would completely reshape the powerband. Exhaust manifold tuning isn't worth much on a turbo motor. Most of what you do there is negated by the turbine. Not enough there to make the difference for me.
If I had lots of money I would have done the intake by now just to see how I liked it. I've seen some dyno sheets with the 666Fab intake and they make a pretty radical powerband. Problem would be that torque peaks so late you miss out on a lot of area under the curve. It doesn't make sense to me to try to put together an M20 that wants to rev to 8500 RPM either. I definitely don't have the kind of money for something like that.
I hate to sound dense, here but wouldn't it be easier to use a different turbo that came on earlier and gentler then built up in a more manageable manner? Same power just more manageable. I'd think a turbo wouldn't cost much more $ than a Shrick.
That would help reduce the brutality of the power delivery, but it wouldn't do anything to increase top end power. I can deal with a brutal amount of power, I would just like to have a little more on tap for the top end. Since this motor has torque to spare I figure I could trade off some of that from the middle of the powerband for a little more on top.
The schrick would cost around $450, BTW. Attractively priced.
I purchased the GT3582R for an M52B28 I had in the garage. I ended up selling that since the old M20 was running so well I couldn't justify the cost and work to swap in the 24v motor. It was never intended for the old 12 valve motor, but it works. If I were to pick one just for this engine it'd be a GT3076R with the 1.06 AR turbine. That would be the bees knees. Its another thing I would like to do at some point, since I'm more or less committed to the M20. I could probably get one for a few hundred bucks depending on what I could get for the GT3582R.
Cams: we increase top end mass air flow (power) at a given boost level. I mess with drivability, stress the valvetrain, and induce overlap. Also, a pain to install.
Boost: Just turn up until the power you're making is too much.
HP/lb boost is just as silly and meaningless a metric as HP/Liter. Competent electronic boost control is far better. The only reasons I can think to do cams is if you are up against the 21.5psi limit on the stock MS MAP sensor, or you want your turbo's efficiency islands to reside in a different place.
Cams: we increase top end mass air flow (power) at a given boost level. I mess with drivability, stress the valvetrain, and induce overlap. Also, a pain to install.
Boost: Just turn up until the power you're making is too much.
HP/lb boost is just as silly and meaningless a metric as HP/Liter. Competent electronic boost control is far better. The only reasons I can think to do cams is if you are up against the 21.5psi limit on the stock MS MAP sensor, or you want your turbo's efficiency islands to reside in a different place.
Increased airflow at a given psi is always advantageous. Running as low as boost pressure as possible will always increase reliability.
Cams: we increase top end mass air flow (power) at a given boost level. I mess with drivability, stress the valvetrain, and induce overlap. Also, a pain to install.
Boost: Just turn up until the power you're making is too much.
HP/lb boost is just as silly and meaningless a metric as HP/Liter. Competent electronic boost control is far better. The only reasons I can think to do cams is if you are up against the 21.5psi limit on the stock MS MAP sensor, or you want your turbo's efficiency islands to reside in a different place.
The 272 is a mild cam. I would expect stock like driveability, good valvetrain life and a modest increase in top end power. Just enough to help tip the curve upward on the high end. Since I've got the block and head sitting on the workbench at the moment it causes me no additional trouble to use either one.
All I'm going to use for boost control are the springs in the wastegate. No need to complicate things just to work around the VE curve of this engine.
Aren't you using MS? Making a RPM dependent boost curve and an electronic boost controller is like, a couple hours worth of work, tops? I know BMW guys, generally, are hesitant about using the closed loop targets in MS because the code used to suck, but it's been fixed for a long time now. Just look at turbobricks.
It will definitely help in terms of hp per boost, at the high end (increased cylinder pressures, obviously). I just question the value of that metric
Yep. Still don't care for the prospect of additional hardware and tuning and more stuff to break down the road. Seems like a cheesy solution to me in any case. Increasing the high RPM efficiency of the engine is more appealing than simply jacking the boost up in an attempt to counteract the VE dropping off. Jacking up the boost also increases thermal loads and the risk of detonation.
Who said anything about HP per psi? I dont recall mentioning that. I don't plan on running any more boost, I would however like to make some more power out of it. Its not because I want a better "hp per boost" ratio specifically. I would just like to adjust the nature of the powerband. I have midrange torque that I would like to trade off for top end power. Simple as that.
Sounds like you just need to buy the cam, then. It would likely make your wall torque come on a little later, and will give you more power at higher revs. I believe the stock duration is around 260 degrees, so you're actually going to see a change. The intake manifold is already more of a hindrance at higher revs than low ones. Like TCD said, it should shift your torque curve to the right.
With a street turbo car, I wouldn't sacrifice area under the curve for a higher number at the end, but that's just me. So far as I can tell, this cam sounds exactly like what you're asking for.
turbodan wrote:
On the other hand, the 272 would presumably help tame the giant slug of torque that comes on when it spools up and move some of it up towards the top end.
Don´t you have electronic boost control to handle that?
Using EBC you can tailor the boost onset and non creep/creep to your taste,
More boost will do the same as a cam. I´d go with that rather then a cam.
