hottest cam with CIS pistons

[bruboy]

My 3.0 CIS engine is about to start a rebuild following a head stud failure. I am considering going to carbs and a hotter cam.

Ideally I would like to keep my original 9.8:1 P & C's so valve clearance will be an issue with the hotter cam.

Are there any recommendations for what cam will fit?

thanks

[jluetjen]

The guy that you want to talk to is "Camgrinder". In the mean time, you can read up on the subject on this thread.

[jpnovak]

Its the exhaust side that has little clearance due to the dome shape of a CIS piston. There are some possibilities and Camgrinder is the one to talk with. If the budget allows you may want to consider some pistons to match to you can really get that extra performance.

[john walker's workshop]

webcam 20/21 grind adds some pep, while not compromising driveability. even passes emissions, in washington at least.

[tctnd]

If you are interested, I have a brand new pair of billet Webcam 20-21's for sale. From Webcam they are $834, these are $600 + shipping.
regards,
Phil

[Henry Schmidt]

CD 20 and DC 22 for cam grinder compare very well to the Web 20-21. I have used all 3 and there is very little difference in the seat of the pants.
For that matter 964, DC20, DC22 and Web 20-21 have very little difference in practical use.
I would love to see an actual engine development using these cams and a dyno that isolates changes to just the cam. My feeling is that the dyno would show very little difference when CIS injection is concerned. With EFI an a programmable chip the differences might be a little more evident.
My experience on the big dyno (highway 15) is that you can't really tell the difference.

[bruboy]

Originally posted by Henry Schmidt
CD 20 and DC 22 for cam grinder compare very well to the Web 20-21. I have used all 3 and there is very little difference in the seat of the pants.
For that matter 964, DC20, DC22 and Web 20-21 have very little difference in practical use.

Henry was this on CIS engines?

I need to lift the max rpm on my engine for DE work, its currently a standard 204bhp euro with SSI's that produced peak power on tha last dyno test at 6230RPM and max torque at 5440RPM.

One, possibly two head studs have now failed and the motor needs rebuilding, will the cams you mention lift the peak power RPM significantly over my standard engine with CIS?

I had assumed that peak power at much more than 6200RPM would require more overlap and hence carbs to make work (within my budget anyway!) If I can get the revs on CIS I will be more than happy not to invest in a set of carbs!

thanks

[Henry Schmidt]

Carbs, pistons and cams to get peak power much highter than stock.

[jluetjen]

Originally posted by bruboy

I need to lift the max rpm on my engine for DE work, its currently a standard 204bhp euro with SSI's that produced peak power on tha last dyno test at 6230RPM and max torque at 5440RPM.

I had assumed that peak power at much more than 6200RPM would require more overlap and hence carbs to make work (within my budget anyway!) If I can get the revs on CIS I will be more than happy not to invest in a set of carbs!

Let me condense my earlier thread down to the essentials for this discussion:

Selecting the Appropriate Cam for Your Engine.

• What is the desired rev range? The lower number of your range will be close to your peak torque engine speed and will define roughly the duration that you will need.
o Ball-park Intake Duration (in degrees) = (Peak Torque engine speed – 3151)/32.53
o You can further refine this by looking at the top of your desired rev range. This number should be close to your peak HP engine speed. You can use the following formula to get a rough idea of how much exhaust duration you should shoot for:
o Ballpark Exhaust duration (in degrees) = (Peak HP engine speed + 9083 )/ 66.62
• Where are you going to use it? On the street? Track? Race? Are emissions important? What sort of induction system are you planning on using? Carbs? MFI? CIS? EFI or Individual Throttle Bodies? Here are some starting points
o For engines that will be emissions tested, keep overlap less then 10 degrees. Also if you are using any sort of intake system that uses a common plenum such as CIS or EFI, you’ll want to keep the overlap to less then 10 degrees since more then that will hurt both your part throttle drivability and potentially your peak HP.
o For Autocross and DE use on an engine with carbs, MFI or individual throttle bodies, target an overlap of 60 degrees or less.
o For Full Race use on an engine with carbs, MFI or individual throttle bodies, you’ll want to target overlaps ranging from 40 degrees up to over 80 degrees.

Originally posted by Henry Schmidt
Carbs, pistons and cams to get peak power mauch highter than stock.

Also to add to Henry's very pithy remarks, he's right (as usual) -- Carbs, Cams and Pistons will allow you to make bigger HP at higher RPMs -- for a while. But if you want your engine to hold together, you're also looking at valve springs, crank modifications, further balancing, higher spec rod bolts and many other mods to give your engine enough of a life time for you to enjoy it.