01-31-2010, 06:59 PM #1
Super Jet project - what octane gas?
Putting the finishing touches on my '90 SJ SN restore project. The ski is a 701 62T conversion with a Factory B pipe. Not much else performance-wise.The engine compression is 190 in the front an 187 in the rear, which seems pretty high to me, but I don't have much experience with these engines or Yamaha in general. Can this engine be run on pump gas, I didn't want to have to run high octane fuel?
01-31-2010, 07:23 PM #2
- Join Date
- Jul 2005
- Central North Carolina
170-175 psi is high as you can go with 93 octain gas on these motors, You could get by with a 50/50 mix race gas 110 octain and 93 octain gas up to 190 psi over that you need 110 race gas only. Tommy Jordan
01-31-2010, 08:32 PM #3
- Join Date
- Apr 2006
- panama city beach 'fl
01-31-2010, 11:35 PM #4
195 in one of my 61X's and never a problem with 93 octane.
Cranking PSI is not an exact way to determine what octane to use. It is just a general "rule".
Just what is done to your engine that is has that high cranking PSI?
01-31-2010, 11:45 PM #5
02-01-2010, 12:16 AM #6
There's a very good chance the high compression is a result of all of the oil that was put into this engine before it was put into long-term storage. I forgot about that. I'll run it on the hose for a few minutes with 93 @ 40:1 & clean it out. I'll do another check after & see what it is.
The gauge is OK - calibrated to +/- 0.5% FS which is an error of 1 psi @ a reading of 200psi. Durned good Wika gauge.
02-01-2010, 08:43 PM #7
I've run with a few SJ's with compression just under 200 psi on pump gas.. But they are not WOT for any more than a few seconds at a time. Straight up freestyle skis.
I ran my kids 701 right at 150psi.
Also, I was under the impression that you could not effectively cut a stock 701 head due to the domes/squish area...
02-02-2010, 11:16 AM #8
more info on the domes/squish is a good idea to find out if they were cut etc..
I use 93 on my sj at 190 psi
02-02-2010, 01:24 PM #9
Honestly, I can't rely on my memory after 4-1/2 years! I could have been thinking of any number of engines, and have to admit I really don't know how the compression was achieved on this one. I'm just happy it has compression at all and it's that close cylinder to cylinder.
02-02-2010, 03:41 PM #10
Users Browsing this Thread
There are currently 1 users browsing this thread. (0 members and 1 guests)
By WATER WOODY in forum Yamaha Projects & Build ThreadsReplies: 44Last Post: 10-22-2007, 08:32 PM
By wishihad1 in forum Yamaha PWC Performance (2-stroke)Replies: 2Last Post: 06-28-2007, 08:04 AM
By spaceman in forum Yamaha PWC Performance (2-stroke)Replies: 4Last Post: 03-06-2007, 07:29 PM
By JFizzleJR in forum 4-Tec PerformanceReplies: 3Last Post: 08-08-2006, 04:17 PM
By GeoRXT in forum 4-Tec PerformanceReplies: 8Last Post: 03-06-2006, 05:10 PM