Cam Timing

[dapiper]

Anyone have experience with L28 cam timing; advance and retard impact on peak power/torque @ RPM?

[spork]

are you talking turbo cam or n/a? If N/a, check outhis link to zcar.com Where norm12secdualsudude did a write-up.

 

http://www.zcar.com/forums/read.php?f=1&i=155935&t=155906

If you're looking for info on your turbo car...this may not apply.

[dapiper]

Thanks for the link.

 

My app is N42 custom turbo with old Racer Brown turbo grind. 236°I/246°E @ 0.025" lift on 110° lobe ctrs and 20° overlap. Lift is 0.485". Also using ArizonaZ adj cam sprocket.

 

Thought maybe installed one tooth (9°) advanced, but cannot see notch with ArizonaZ sprocket. Might try replacing with stock sprocket to check, but hassle removing cam trigger.

 

Retarded cam 5° crank and seems to pull better, but getting knock while developing boost. OK once at boost. Boost limited to 15 psig. Will check on dyno Monday.

 

Anyone know max retard without piston clearance problems? Using 8:1 CR and 11cc dish. Might try another 5° retard if improved.

[AK-Z]

It might be better if you advance it 5 degrees (asuming normal) and retard the timing on the spark end. That will help with knocking.

[dapiper]

Finally pulled cam sprocket to check timing and found short chain; during engine assy, had advanced one tooth to allow cam dowel to index with crank at TDC. Same head, same cam tower shims, same block. If anything, head may be thinner a few thou. Did replace chain and sprockets with MSA parts, but used ArizonaZ adj cam sprocket, which was fine, except way it's made could not check alignment of notch with groove.

 

With crank at TDC and cam indexed to sprocket on #1 hole and notch centered on oblong groove, I could not install sprocket with chain onto cam nose. Had to advance cam considerably, later determined to be 10°. If I retarded cam one tooth, cam was excessively retarded; notch aligned off left end of oblong groove.

 

Finally had to retard one tooth (-18°) and use #3 hole on cam sprocket (+8°) for total retard of 10°. The only explanation is the chain is too short.

Watch out, take care, beware of certain aftermarket parts.

 

The L28 will run with 18° adv, but power down 20% at 5300 - 6000 RPM. Nice wide power curve, just too low. Lift is 0.485" at valve with 11cc dished pistons at zero deck. Try dyno again tomorrow.