Firewalker

Well, they have the motor on the dyno right now after changing the oiling system and bearings. The motor made 489hp at 5000 rpm and 568 ft/lbs at 3500 rpm. This is a stock ZZ 502 with an 800 Holley carb.
They are now going to change the Intake, cam, springs, and move to roller rockers. The cam is an HP 500 cam. So it will be interesting to see if there are any changes.

RT

Firewalker

Soooooooooo, anyone guess at how much the accessories will rob and how much less power Imco Powerflows make than dyno headers. I think I am trying to compare this to a real HP500 merc on the hp front in my head.
The HP 500 with Rec head, and this motor with Aluminum Ovals, but with more compression.
I was hoping to see 500 at the prop, but it sure doesn't look like it.

RT

Pat McPherson

If you're going from a ZZ502 cam to a Merc HP500 carb cam, you are not changing that much.
A single plane intake will likely give you a little more up top.
I thought a ZZ502 has roller rockers from GM.
The HP500 was rated 470 at the prop and I think they dyno at around 520HP, so you're not far off...

Firewalker

I think there is .10 more lift in the new cam and a few other things. We are also looking for reliability.

RT

ROTAX454

Pat, Stamped steel rockers on the crate motor. My info from Merc has the HP500 rated at 500 HP at the crank, and 470 HP rated at the prop. Interesting, the crate motor comes with an 850 cfm vac sec carb. My experiences with GM and their crate motors are that the published HP/TQ numbers are very conservative. Hmmmm. May do a search on HOT ROD mag to see if they have ever dynoed a ZZ502 crate motor.

Pat McPherson

Yup you're right, stamped rockers, and 850cfm carb...

GM rates the ZZ502 502HP @ 5200rpm.

I checked Hot Rod magazine for a Dyno test. The only one I could find was a ZZ502 with an after-market fuel injection system. The tests showed between 508 and 528HP at 5400rpm.

So ROTAX, are you saying that Firewalker should be seeing more out of his ZZ502 stock?

Firewalker

Mine came without the carb or ignition.
I would also think that every dyno is different. I will get a HP 500 chart from them also to see the difference.

RT

Do any of you think it would be worth changing the SS exhaust valves to Inconel?, and the head gaskets while that is being done?

RT

Airpacker

Rob, waynes dyno is notoriously stingy on numbers. He likes it that way Under promise, over deliver!!!!

Firewalker

Thanks Packer

Picking up the new sled on Sat...... you getting pumped up yet?


RT

Airpacker

Geez, not another polarass I hope

Yep, the cats gone beddy bye for the winter, sleds will come out this weekend I guess.