Take the Whipple upgrade kit off of the 600, and restore it back to Merc factory specs.

The 710 ilmor is faster than the 600 merc. In fact all the testing we did at fountain the ilmor was within a few mph of the 700 merc.

it should be. In these boats with the same gear ratio and style of prop ....it is NOT!!!!!!

It is either the lighter engine in the rear causing the heavy deckboat bow to ride wet or it is the increased prop speed causing higher slip % or some combo of both.

Any constructive opinions?

Agreed! All the testing we did at Donzi, the ILMOR was ALWAYS FASTER.

I would say a prop change would make the difference. Maybe a labbed 28 with a little extra cup to get the slip down, or perhaps a completely different prop. Last theoretical possibility would be a slight spacer to get the prop a little deeper and decrease the slip.

First lets talk about prop speed.

the ilmor is turning 6300 rpm with a 1.5 gear ratio.....the prop rpm is 4200. 26 pitch

the merc is turning 5400 rpm with a 1.5 gear ratio....the prop rpm is 3600. 30 pitch

Theoretically these should be the same speed.... http://www.go-fast.com/sterndrive_gear_ratios.htm

is the prop speed a big deal? or is it the 200lbs less weight in the rear of the boat from the lighter engine.

The 700 should smoke the 600 on the top end.....it does not with the same drive height and same style props.

My 600 with whipple kit in a Howard Deck boat hull runs up to 95 mph with a 29 p5x. Don't know if this helps or not because of the whipple kit mod.

Prop speed has to have something to do with it... I know my REV 4 kicks my 3 blade props butt all over the place in performance and slip values except near the top end where the slip on the REV 4 spikes up (don't remember the exact values but if memory serves me correctly the slip number jumped about 10% higher from about 4500 engine RPMs to 5200 engine RPMs and this is through an Alpha SS with a 1.5 ratio). Brett at BBlades said he could fix that for me if I wanted to send the prop back and get it labbed. I am sure the same could be done with whatever prop they used in this test. I did not play with the numbers, but what would the speed be for the Ilmor if you could get that slip down to 13%.