JaniH

​​​​​wider 112 Lsa compared to 110 of the zz502 cam. 731 has more lift and more duration. I am going to use the zz502 cam, stainless Marine exhaust with slightly extended 3" Taller risers.

kvogt

I would stay away from the 110 lobe separation if I were you.

Baja Rooster

iTrader: (1)

I had about 50 hours of run time on the ZZ502 cam. This was what my valve seats looked like. Definitely some reversion even with dry to the tip headers. Someone else here had roasted two engines with that cam.

JaniH

good info! Just dont understand how it is possible with small duration cam like this, there is many cams that guys are using here with more overlap. What I know is that in zz502 crate engine the cam is only 2 degrees advanced 108 degree icl. Hp500 cam is almost identical but has more lift, 110lsa, 6 degree advanced, 104 degree icl.

Baja Rooster

iTrader: (1)

A quick search of HP500 cam and reversion shows that it was quite an issue, especially with stock risers.

MILD THUNDER

iTrader: (3)

Something else that can play a role is ignition timing. Modern oem vehicles retard the chit out of the timing on cold starts, because it heats up the catalytic converters in a hurry. Having too much timing advance at idle, takes away alot of heat from the exhaust, as well as pressure.

Back in the day, a common cause for an engine running hot at idle, was timing was retarded. It would make the headers/manifolds really hot while idling.

Next time youre playing around setting timing, make a mental note of the exhaust sound while retarding or advancing the timing at idle. Youll find retarding it say to 10* btdc , the exhaust has more "bang" to it, and advancing it to say 30*, it gets a little quieter, and a little smoother. Its simple. The later you fire the plug, the closer the explosion happens relative to exhaust valve opening. This helps put pressure into the exhaust, helps heat the exhaust valve, and helps burn off condensation dripping in the pipes. Alot of guys run alot of base timing to acheive a smooth idle, but sometimes that may cause a reversion issue. Less timing will also require you to have the throttle blades opened more to achieve the same idle speed, which in turn lessons intake manifold vacuum, and in turn results in less reverse "suction" during idle overlap.

MikeSXT25

Ok we’re getting a lil side tracked maybe. I agree with my original compression figures being way off. I’ll have to get some small dome pistons. Prolly -12cc domes, ish. But my compression goal will be in the 9.5:1 range to stay on pump gas. Still need to figure out which heads I got for CC. 110/118 chambers. Not sure yet. But

Back to good cam selections. Preferably with some dyno proof of power output.

MILD THUNDER

iTrader: (3)

These wiseco pistons are a good deal. Ive used them in a 540ci, and a 516ci. Usually you can find them around 500 for a set and they come with a file fit plasma moly ring set.

https://www.summitracing.com/parts/wis-pts514a6

Baja Rooster

iTrader: (1)

As I said earlier, the ZZ502 dynos at your target of 500hp at 9.5cr and your same heads. The Crane 731 is just slightly bigger with a 112° degree lsa that’s far more marine friendly. Or you can go with the Crane 741 if you want to move the power up a little.

MikeSXT25

Baja rooster. Thanks. Target RPM is 5000-5500 ish. And be able to shift in and out of gear without beating my outdrive up. So needs to idle. At a reasonable rpm