Turbo with performance cam question.and a quick smt-6 ques

[nitro325is]

Ok Ive started to tear down a super eta block I have in preparation for a 2.8 turbo similiar to Matts setup.No custom pistoms just a stock supereta rebuild with a TD crank replacing the eta crank.I understand slapping any "i" head will result in a 8.5 ratio.So thats perfect.Since this is a spare engine I have plenty of time to work on it on the side with no down time.

However I would like to use the head from my current engine since it is a completely new head with BMP HD valve springs and a BMP 282/272 cam.Is this cam too much for a 2.8l turbo.As it is it comes on at about 3800 rpm.Or should I go back to a stock "i" cam or something more mild than mine.

Im also gonna send gunni some cash for the smt-6.Should I get that installed on my current setup even though Ill have to redo the settings later this summer when i drop the rebuilt engine in and turbo.Or should I just wait and slap everything in at the same time.

[E30godz]

i dont think you would want to go with that performance NA cam, as its about the exact opposite of what a turbo cam should be.

[diegom6]

i dont think you would want to go with that performance NA cam, as its about the exact opposite of what a turbo cam should be.

I second that!

Jim (BimmerJim) had a 290 cam I think he finished taking it out and replacing for the stock one in his turbo setup...looks like hot cam+Turbo= doesn't match well.

if you get the SMT6 just install in your currently setup it wont' affect when you put the turbo since it has different "save" tunable settings, that measn that when you get the turbo runing you will need to modify the settings to suit the turbo.

[rwh11385]

i dont think you would want to go with that performance NA cam, as its about the exact opposite of what a turbo cam should be.

WORD.

I first read about this in a Honda magazine back in the day. Basically a NA motor is helped by longer duration and lift by being able to get more air in. With FI, you're pushing it in there enough, so the cam doesn't help!

And for some reason, it reduces power, with a hot cam on a turbo. No clue why? I think stock would be fine, or perhaps a mild cam......like 274 max. Not sure.

[808BMW]

What about cams designed for turbo's? None made yet for e30's?

[rwh11385]

Just searched a little, seems very short overlap makes for a good turbo cam. Only last time I checked, there is a single cam...... :P So that theory seems irrelevant.

Also, something mentioned high lift is good. Lets air in. Much high duration is still bad.

I'm guessing no M20 Turbo cams were made. But if needed, maybe have Racetep make some for you. Make a high lift "I" cam. Or easier, could you get oversized eccentrics and use those to up the lift?

EDIT: Crane Cams: Honda 1.6L SOHC Camshafts

HON-261-2SR-10 Honda CamshaftCam Spec Card
This cam profile features our unique "Split Duration" lobe profile design (exhaust duration is less than intake duration). "Spools" turbo faster for quicker boost and response. Reduces turbo "lag-time". Strong upper mid-range and top-end HP when turbo boost is applied. For max HP and RPM, use low-restriction aftermarket exhaust and air intake system. Use new stock valve springs. RPM range: 1,500-7,500

251-0014$371.72

I think Racetep could do dual pattern as well.....but not sure. Ask Jordan, he's gotten his cam from them.

[M3 Ryan]

Just searched a little, seems very short overlap makes for a good turbo cam. Only last time I checked, there is a single cam...... :P So that theory seems irrelevant.

It doesn't matter that it is a single cam, it STILL has overlap because of the exhaust and intake open at the same time...
Use a stock cam, it will do just fine.

[E30godz]

yea, in Bell's book he says something to the like of "you cant get a better performance turbo cam that the stock item" in referring that most stock cams are geared torwards economy somewhat and would not have the high overlap etc etc prevailent in a hi-po NA car.

[nitro325is]

Well the cam Ive got is a dual profile cam. Its a 282/272 it is also very high lift 11.5 on the intake and 11.0 on the exhaust.Because of the lift I was hoping it would be beneficial in a FI setup.The duration is not too high when compared to other popular cams such as 288/288 or 290/290 Those are just ridiculous on any m20 that is not going to see track use.But i guess you guys might be right...it still might be a bit much for FI.

Just trying to use all the goodies I already have.

[Stuart B]

i guess with high over lap the turbo will just blow in one valve and out the othertaking fuel and air with it.

isn't overlap on an na car yo use the inertia of the exhaust gasses to pull more fuel/air into the cylinder??? Which i guess isn't required when the turbo is pusing the nixture in.

you could sell your head if its good to offset costs anyway.

Stu

[STS]

You want to stick with the stock cam unless you can find/have made a cam with higher lift but no more overlap. Overlap on an NA engine is designed so that the low pressure wave from another cylinder's exhaust helps to "pull" the intake charge into the cylinder that's next in line to fire. This is what tuned headers do... they time the arrival of the low pressure wave to coincide with the overlap of the valves on another cylinder. As was mentioned, when using FI, lots of overlap simply allows the charge air to "blow through" the cylinder, dimminishing the effect of FI.