V-4 Yamaha Comp.

[Dingie 2]

On a V-4 Yamaha what kind of compression numbers are you guys running on the V-4's that have been modified but still use 93 octaine gas ? Seems like the old 130's had a head from the factory with 20 more lbs than the stock 115 had .I know that 150 is approx the magic number on a Merc.Whats the magic number on these Yamaha's ? Thanks for any help Joe R

[Markus]

Dingie, since no-one has answered your question, I´ll give it a try:

V6 Yamahas have the geometry as V4s. On the V6, depending on whom you ask, people will either say "about same as Merc", "160 psi", or "160 psi, are you crazy? You will go through lots of pistons, that´s for sure". I guess the answer depends on what timing they run, as you will get very different answers for max. timing as well.

So, I would say that the magic number with 93 octane fuel is approximately the same as on a 2.5 liter Mercury.

[Dingie 2]

Markus thanks for a shot. I asked Nathan at Hydro Tech(being he has answered every question that I asked ) he said that all of there testing was done with 89 oct. gas with the HT8300 heads that I have.I think that I am just going to keep using 93 oct. gas because it worked well with this set up in the past. It may run better with 89 but IM afraid to lower the oct. just in case I get some olds or bad gas it wouldn't be worth it to me to take that chance.Some say that I may get a increase in performance lowering the oct.from 93-89 but IM just not sure if its worth it to me. It will be a long time before I pay this power head off and I want it to last. Joe Raimondo