How Cam Timing affects compression pressure

Continuing our special Father’s Day, Jemal discusses how valve clearance affects cam timing and compression pressure.

[@jimciancio9005]

I'm a Briggs vanguard guy but I love how you braced the flywheel side of the block with aluminum plate. Gives me some good ideas, I'm in the middle of building a turbo 35 cube Rt now and have been playing around with all types of ideas now thanks to you tractor pulling guy's. But I definitely understand the frustration, no need for apologies after a long day at work to make a video. Thanks so very much for posting. I love one thing about them kohlers the vanguard can't compete with is using SBC valve train parts! Lucky! Back in the day when they were new we had a problem from kohler and valve train noise. #1 was non adjustable rockers and 2 all it takes is a piece of dirt to clog a hydraulic lifter check valve, so we were replacing the OEM kohler lifters with Chevy small block ones. No fancy rollers though lol. But always awesome to see how things progress again thank you for taking the time and sharing your knowledge. 👍

[@AGClassicCarTuning]

A very interesting video, and it raises a question for me regarding an engine that I recently overhauled, designed to be around at a CR of 10.8:1 and set cam timing to the makers spec but at quite an unusual figure and I'm finding that compression is a touch on the low side at 130psi per cylinder and quite even across all 4. I'd regard this as more of a used engine compression reading rather than a refresh/rebuild??? So the cam timing figure, as you'll know typical 'A' series cam timing is usually in the region or 102 ATDC to maybe 108ATDC.....with 106 ATDC being a typical and as recommended by such Kent for many of their cams. The particular maker that I used suggested that they had seen good torque and power figures obtained when cams were timed in at 99.5 to 100 ATDC. As far as I could work out by my averages I set this cam at 99.75 (doubtfully that accurate but...) I have adjustable duplex, so do you think the compression may increase to as much as 150 or 170 psi for example if I was to change the cam timing from 99.75 ATDC to a more typical 104 or 106 ATDC? Or is this far too much of a pressure gain to expect? Any advice would be much appreciated thanks.

[@bentonrodeheaver2596]

Profiles,lifts,duration all aside I just want to ask. I'm working (again) on a four cyl w/ double overhead chain driven cams. IF one cam is off say 2-3 teeth could this cause a false "misfire" up to 2500 rpm or so? Please email back when you have time.

[@pounsfos]

gosh yes, 3 teeth is alot!!!, I take it you have a non - interference head, because 3 teeth out is enough for the valves and pistons to high five each other, fix asap

[@MattBerrymotorsport]

Great video, i also subbed! I'm trying to understand cam timing a little better to try optimise top end power and torque on my built n/a engine... are you able to give a quick description on how advancing/ retarding intake/exhaust cams can improve power and torque. The engine i have is a toyota twin cam 5efe 1500cc engine. It is currently 11.8-1 comp, e85 fuel, 292/292 camshafts, itb manifold and a basic 4-2-1 exhaust manifold. Any info is much appreciated it is very hard to find anyone willing to share secrets lol

[@JemalCRM]

Aah a twin cam has more flexibility... and complexity! Obviously I cannot set intake and exhaust SEPARATELY with the single cam pushrod engine, so different rules apply. What you run into is that it's not possible to set to the best power AND torque because each ends up being at the expense of the other. With the A-series engines of the Classic Mini, advancing the cam makes a bit more HP, but torque suffers. So If racing, you want advance and race gas for sure.... I explain how compression PRESSURE is higher. For the street, where you have to deal with intersections, not so much. So you have to seek out the best compromise for your intended use. I've set up twin cam superbikes and my Lotus Twin Cam with specific timing, but without vast experience with these, I used the best recommendations and experience of others. I hope it doesn't sound like I'm hiding secrets! I don't think there is one. Anything you do affects everything else, so you just sneak up on it if you have the patience and a scientific approach. Or look at what others have done and the results.

[@FreeSwimmer]

@@JemalCRM Im working with a SBC and assembled compression is .8 less than all other parts were planned with. So, the heads are being milled .025" and cam is being moved back from 108-107, to solve this. It will change the cam timing event slightly for compression bump and make small % more torque and small % less Hp

[@ahitah1]

309° cam....very interesting,13@1....hps?

[@JemalCRM]

Yes this is a full race engine. We have dyno'd this at over 135 HP at the wheels so far. My goal is 100BHP per liter with reliability, so that would be 138 from 1380cc. Probably around 180 at the crank.

[@jareknowak8712]

@@JemalCRM I think that with 180hp @crank there will be ~150 @wheels. Quite impressive to get 180hp out of this old construction!

[@nizambashir2911]

Need to make more power by degreeing the camshaft

[@car852]

Doctor Evil??

[@fernandohood5542]

Did nor game much from the video. A lot of assumptions made about the user knowing about clearance.