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914World.com _ 914World Garage _ Obtaining CAM shaft specs without disassembling the engine?

Posted by: GGerg1186 Dec 27 2020, 05:21 PM

I purchased a used 1.7L engine out of an autocross 914 car. Seller said it had a "performance cam" in it which could mean anything. Planning to pop a valve cover off with a dial indicator and the degree wheel on the front of the engine "spec" my cam. Should be able to get open, close, lift, and calculate duration. Should I put the dial indicator on the push rod side or the valve side of the rocker? Anyone had any success with identifying their cam without engine disassembly?

Next question, any way to determine compression ratio without removing the cylinder head? I am leaning towards removing the cylinder head just to see if I have cast or forged pistons & connecting rods.

Ultimately, I want to know whether I can run regular pump gas, what max engine speed should be, and an appropriate carburation system to match the cam.

Let me know your thoughts.

Posted by: Mark Henry Dec 28 2020, 07:35 AM

Pop the oil pump off, most aftermarket cams are stamped with the grind number in the pump drive area. If the gear has rivets it's stock, if it has bolts it's aftermarket.

Posted by: mlindner Dec 28 2020, 07:54 AM

I like Marks idea. but if you want to measure like I did of the valve it tells the story. Mark

Posted by: barefoot Dec 28 2020, 08:36 AM

Cam makers specify valve lift, not lobe lift, so indicate on valve retainer.

Posted by: Mark Henry Dec 29 2020, 07:37 AM

QUOTE(barefoot @ Dec 28 2020, 09:36 AM)

Cam makers specify valve lift, not lobe lift, so indicate on valve retainer.

Or times by 1.3 the rocker ratio.

Posted by: bbrock Dec 29 2020, 09:13 AM

I don't want to hijack but I'm getting ready to do my valve geometry and have a related question, so thought it might fit here.

I have an Elgin 6408 cam and the spec he provides is CAM Lift and also lists intake rocker ratio as 1.3 and exhaust as 1.25. https://elgincams.com/porsche914/

Am I correct that I need to multiply the CAM Lift (in my case .296 for intake and exhaust) by those ratios to get valve lift of 0.385 intake, and 0.370 exhaust to get my reference valve lift for setting geometry? I'll be following Jake's procedure.

Posted by: GGerg1186 Dec 29 2020, 12:24 PM

QUOTE(bbrock @ Dec 29 2020, 09:13 AM)

Am I correct that I need to multiply the CAM Lift (in my case .296 for intake and exhaust) by those ratios to get valve lift of 0.385 intake, and 0.370 exhaust to get my reference valve lift for setting geometry?

If the spec is truly CAM lift, then the multiplication would be required to understand valve lift.