Determining Cam Centreline from duration figures??

Al Weyman · 8 Mar 2009, 12:00 (Ref:2411545)

Is this possible I don't see how it is but I have a cam duration at .50" is inlet 275 and exhaust 296, max lift with 1.5 rockers .69 inlet and .715 exhaust and thats all the info I have and want to time in the cam so is it possible with just these figures?

**Tim Falce** · 8 Mar 2009, 20:12 (Ref:2411594)

Assuming the .50 is max lift in inches and the 275/296 is the duration what does the .69 and .715 relate to?
You need to know/decide where you want max opening to be.

jerryk · 8 Mar 2009, 20:24 (Ref:2411603)

Quote:

Originally Posted by Al Weyman

Is this possible I don't see how it is but I have a cam duration at .50" is inlet 275 and exhaust 296, max lift with 1.5 rockers .69 inlet and .715 exhaust and thats all the info I have and want to time in the cam so is it possible with just these figures?

ok Al but these have nothing to do with it!
DTI gauge on the camshaft lobe , degree disc on the camshaft, turn camshaft till max deflection and set zero on gauge , turn camshaft till 10 thou deflection in one direction and then 10 thou in other direction and then halve the turn on the camshaft and that is max lift for timing .
easy peasy lemon thingy.

**Tim Falce** · 8 Mar 2009, 21:27 (Ref:2411651)

Jerry don't you mean put the degree disc on the crankshaft and not camshaft or am I missing something plus you still need to know what degree atdc you want max lift.

jerryk · 8 Mar 2009, 22:19 (Ref:2411679)

Quote:

Originally Posted by falcemob

Jerry don't you mean put the degree disc on the crankshaft and not camshaft or am I missing something plus you still need to know what degree atdc you want max lift.

does he say the camshaft is in the engine ? no .
if it is yes put disc on crankshaft then same story

as to what degrees to set it depends on profile,
the header read how to determine centreline .
thats what i have explained .
setting might not be atdc could be btdc or bbdc or abdc depending on which cam it is (inlet or exhaust ) and tuners whim of the day.
I am sure Al will understand all this if not best give it back to his engine man.

Al Weyman · 9 Mar 2009, 00:01 (Ref:2411728)

No I mislead you slightly with a typo that should have been duration at .05" not .5". The max lift is .690" inlet and .715 exhausts with 1.5 ratio rockers. I needed to know the centreline of the the camshaft lobe at full lift so I can determine the cam timing for example 108 degrees on the crankshaft.

Anyhow I don't think its possible to determine without the cam manufacturers figures or at least I could'nt figure it and as I wanted to button this engine up today (I am the engine man sadly Jerry!) so I have decided to stuck the cam out my other engine (also in bits) in this one as I have the details here for that and its more of a road race cam and have now timed it all in also I think with the lift and duration of this cam its a tad too wild for a road race car.

phoenix · 9 Mar 2009, 12:15 (Ref:2412088)

Quote:

Originally Posted by Al Weyman

No I mislead you slightly with a typo that should have been duration at .05" not .5". The max lift is .690" inlet and .715 exhausts with 1.5 ratio rockers. I needed to know the centreline of the the camshaft lobe at full lift so I can determine the cam timing for example 108 degrees on the crankshaft.

Anyhow I don't think its possible to determine without the cam manufacturers figures or at least I could'nt figure it and as I wanted to button this engine up today (I am the engine man sadly Jerry!) so I have decided to stuck the cam out my other engine (also in bits) in this one as I have the details here for that and its more of a road race cam and have now timed it all in also I think with the lift and duration of this cam its a tad too wild for a road race car.

In that case, without knowing the manfacturers lift at TDC figure, the only way to time the cam is at peak lift at 108 degrees atdc.

You need a 360 degree protractor on the crank pulley, a pointer for it, and a dial gauge to measure lift on the valve.

Setting the engine at 108 degrees atdc, swing the cam shaft until you get peak lift reading on the dial gauge. There will be some dwell at peak lift, so you need to find the middle of the dwell period. Say it is 10 degrees at peak lift, you need to set the cam so that at 5 degrees advance the valve stats to close and at 5 degrees retarded the valve begins to close. I am sure you understand the principle anyway. In truth, if you have an a-symetric cam profile (and some are) this is probably a better way of setting cam timing than using the lift at TDC method.

If you don't trust the TDC marking on the crank pully to set the protractor up, then you can find true TDC by measuring piston movement with the dial gauge, through the spark plug hole, to the top of the piston. Again there will be a dwell period of a few degrees while the piston is at TDC. You need to find the middle of that period to mark true TDC on the crank pulley.

Martin

phoenix · 9 Mar 2009, 12:37 (Ref:2412101)

Further to the above, with maximum lift at 108 degrees atdc, I would project the following:

Timing at .05" valve lift: 29.5 65.5 76 40 Lift @ TDC: Inlet: 4.758mm Exhaust: 5.835mm (both with tappet clearance set at 0.01")

Timing at 0 degrees cam lift (i.e. including opening and closing ramps):

41 81 87 51 Lift @ TDC: Inlet 4.759mm Exhaust: 5.825mm (both with tappet clearance set at 0.0" if measuring at the valve)

However, I would still suggest you use the peak lift method to set the cam timing.

Martin

Al Weyman · 9 Mar 2009, 13:12 (Ref:2412145)

Thanks Pheonix but I know how to set up camshafts and have all the correct gear including a massive 19" timing wheel I made up which allows for very accurate measurements. It was the 108 ATDC figure I was trying to determine, the above was just an example. As it is the timing for the other cam I have now used is 108 degrees and in fact I ended up with 109 but thats near enough for a 5.7 litre V8. ;-)

BTW if anyone is interested how I made up the 19 inch (to suit chevy v8) timing wheel, I downloaded a graphic, printed it on vinyl and laid this up on a piece of Dibond composite aluminuim sheet and cut round it with a jigsaw. It worked great. A similar moroso one would cost about £50 back here!

phoenix · 9 Mar 2009, 13:24 (Ref:2412158)

I have seen maximum lift recommendations, from people like Crane and Lunati, in the range 102 - 110 degrees ATDC. I think you will only find out on a dyno what works best with the cams you have.

Martin

**Tim Falce** · 9 Mar 2009, 17:52 (Ref:2412349)

Quote:

Originally Posted by jerryk

does he say the camshaft is in the engine ? no .
if it is yes put disc on crankshaft then same story

as to what degrees to set it depends on profile,
the header read how to determine centreline .
thats what i have explained .
setting might not be atdc could be btdc or bbdc or abdc depending on which cam it is (inlet or exhaust ) and tuners whim of the day.
I am sure Al will understand all this if not best give it back to his engine man.

Well I consider myself well and truly told.

Al Weyman · 9 Mar 2009, 22:23 (Ref:2412579)

Quote:

Originally Posted by phoenix

I have seen maximum lift recommendations, from people like Crane and Lunati, in the range 102 - 110 degrees ATDC. I think you will only find out on a dyno what works best with the cams you have.

Martin

Impractical on a Small block Chevy, its not like setting timing on a Pinto or a TC engine and I don't have the budgets for dynometers. No I would need to set it up to the cam makers spec if I had them! Incidently as I never had the specs before and bought the cam off eBay for a tenner (not bad for a steel billet roller cam brand virtually brand new) so took a flyer with it and fitted it straight up on the standard marks however I suspected the cam was timed incorrectly (too advanced) as it had a fair bit downstairs and when I finally found the spec from the maker he told me it should be flat as a pan cake low down as it was in fact a drag race cam.

phoenix · 9 Mar 2009, 22:53 (Ref:2412602)

Quote:

Originally Posted by Al Weyman

when I finally found the spec from the maker he told me it should be flat as a pan cake low down as it was in fact a drag race cam.

Forgive me, but if you have the spec from the manufacturer, what are you hoping to gain from asking us here? The manufacturers spec surely tells you where peak lift should be (on the inlet cam) even if it doesn't give a lift at TDC figure?

Out of interest, what make of cam is it? I have searched really hard (for you!) on the internet for a cam with those timings and lifts. The closest I came was also a drag-racing cam - but for a 7 litre engine!

Al Weyman · 10 Mar 2009, 08:09 (Ref:2412785)

I did'nt have the ATDC spec though all I had was the info I gave you and was hoping if any one would know how to caluclate the ATDC position from those details, as I said i needed to gett he thing buttoned up Sunday and this is a small manufacturer in the States so not like contactig Burton Engineering or someone.

Al Weyman · 10 Mar 2009, 09:13 (Ref:2412814)

BTW Pheonix I did appreciate you trying to help me, I probably phrased it all incorrectly to start with, thanks again. BTW I am waiting for the guy in the US to get back to me his initial response was set it at 0????? what ever that means, confused I will be!!!

zefarelly · 10 Mar 2009, 12:28 (Ref:2412916)

108-110 atdc seems very late, like a shopping/FF cam . . .maybe its a v8 thing . . .my latest engine hits peak at 98 atdc ( A8 advanced 2 degrees, 123 lb/ft & 138 bhp

)

never retard it . . .unless you have too much power, which I guess is possible these days

Chris Wilson · 10 Mar 2009, 12:41 (Ref:2412929)

Quote:

Originally Posted by Al Weyman

BTW if anyone is interested how I made up the 19 inch (to suit chevy v8) timing wheel, I downloaded a graphic, printed it on vinyl and laid this up on a piece of Dibond composite aluminuim sheet and cut round it with a jigsaw. It worked great. A similar moroso one would cost about £50 back here!

I don't suppose you'd be willing to share this graphic, would you? I have been after a big timing disc for a while.

ian_w · 10 Mar 2009, 12:55 (Ref:2412938)

Is there no manufactures marks on the cam from which you can trace some info? Failing that can you compare cams of similar duration from other manufactures and see what they recommend?

I don't see that you would be too far wrong using somewhere in the range 105-108 deg, in my experience thats where most race engines seem to end up. Production cars are normally in the 112-114 deg range.

Zefarelly - the A8 is a hugely long duration cam, to give you a sensible inlet valve closing point you probably end up having to run it very advanced as you have found with your 98 deg figure.

zefarelly · 10 Mar 2009, 13:29 (Ref:2412950)

108 seems a fairly average figure . . . . probably a good starting point

FF GT cam is 109, all kent cams for Fords are 103

A8 is 100, I didn't want it screaming too much, in the end the torque is there from 4-7k and peak power is just under 7000 from std 1500 precrossflow geometry, that suprised me. I was expecting it to be higher up the rev range

Al Weyman · 10 Mar 2009, 16:55 (Ref:2413068)

Quote:

Originally Posted by Chris Wilson

I don't suppose you'd be willing to share this graphic, would you? I have been after a big timing disc for a while.

Of course I can or I can print you out one onto vinyl if you want but would have to charge for that obviously.

Al Weyman · 11 Mar 2009, 01:35 (Ref:2413340)

I got the data at last, it should be at 101 to 102 ATDC at max lift.

phoenix · 11 Mar 2009, 16:46 (Ref:2413737)

Quote:

Originally Posted by zefarelly

A8 is 100, I didn't want it screaming too much, in the end the torque is there from 4-7k and peak power is just under 7000 from std 1500 precrossflow geometry, that suprised me. I was expecting it to be higher up the rev range

Hi Zef

I don't think the A8 is as wild as many people think; although it is quoted as a 306 degree duration cam, I believe that is at zero lift - so includes the ramp timing. What does your dial gauge say?

Martin

Al Weyman · 12 Mar 2009, 08:06 (Ref:2414120)

When i used to hotrod race many years ago I could not get on with the A8 I just found it too much cam and that was with a 1760 unit, more can be less sometimes.

Al Weyman · 12 Mar 2009, 08:43 (Ref:2414136)

Looking again at an incar video again when I was using this cam I recon I may have been overevving the old thing as the rev counter seems to play up at about 5500 and I thought in the heat of the moment it was missfiring but in fact it does keep building up revs although not shown on the tacho and I have no rev cut out so in fact it was making the power way up the rev band, could explain the latest engine problem i.e. too much cam!

aa/fd · 11 Apr 2009, 13:33 (Ref:2438572)

Try page 9 or so on this pdf file link at Comp Cams it will show you how to ascertain intake lobe center
http://www.compcams.com/Technical/In.../Files/145.pdf
You can also send it to any reputable cam grinder and have it plotted on a Cam Doctor.

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