PDA

View Full Version : SST120 low revs



ics
07-30-2007, 08:35 AM
Hi,
I have a standard 120 powerhead and I can only get 6500rpm out of her.
Does anyone have any advice on how to get the RPM's up?

Shaun Torrente
07-30-2007, 10:46 AM
how high into the tunnel is the bullet on your gearcase??

Shaun

ics
07-30-2007, 01:41 PM
The centre of the gear case is fractionally higher than the lowest point of the sponsons. Hydraulic up/down as well and still not much increase, just instability.

Shaun Torrente
07-30-2007, 03:09 PM
The reason i ask is because on our 120 stuff we run right around 2" above the sponsons... we turn them 92-9600 rpm

Shaun

spn#43
07-30-2007, 05:32 PM
About on the test wheel, what rpm you see there?
Or with smaller prop.

ics
07-31-2007, 02:10 AM
Water has been quite rough the last couple of races, hopefully next one will be calmer, maybe then I can raise engine more, failing that I will try a smaller pitch prop. Cheers
Ian

Zonkercraft
07-31-2007, 05:05 AM
In Europe, the F2 ( SST 120's ) are larger boats, the water is rougher, and they don't run sprint type races, so the setup would be very different. The stability of your boat would need to be the determining factor in your setup. The RPM level's that Shaun gave you are what a top level, SST 120 here, would be running to be competive. He should know, he's one of the best around. Your target RPM levels may be much different than that.
With that said, the fact that you have adjusted the height, with little to no change in RPM, except for stabilty, would lead me to believe that you have a problem with the motor, gearcase ( which one are you running, # 6 or #4 ) or prop ( how much pitch & dia. ). Did you just loose the RPM, or has it always been at this level? Have you tried another powerhead? What did it show on a test wheel? What have you changed, or tried to diagnois in the ignition or carbs? Do you have access to a dyno?
As you can guess, there are many things that can give you poor performance in an SST 120.
Information is the key. The more you have, the faster you can get it straightened out.
There is a wealth of knowledge on this site, and is a good source to tap into. Everyone here would be glad to help you, or at least, express an opinion.
Zonkercraft

ics
07-31-2007, 07:59 AM
The boat came as is, all included, as far as I know the power head has never had high rpm. gear case is a #6, the prop I have been using has some garbled numbers stamped in, I know it has been worked but unfortunatly I cannot tell. I will be trying a smaller dia prop at the weekend to see if that makes a difference. Would a small inline fuel filtre possibly cause the problem? It does seem small to me.

ics
09-05-2007, 08:20 AM
Thanks all for the advice all.
Tried a few different props, raised engine height and put a larger inline fuel filtre in. Revs now 7500 plus and I kept up with the big boys, just. So I'm happy with that. Anybody give me a nod as to how to strip a #6 gearbox down, I have a spare damaged one that I want to take a look into?

tabararacing
09-05-2007, 01:03 PM
Are you sure your tach is accurate? Rectifiers go all the time and don't read accurate, sometimes they only work half correct.
If you have a tiny tach laying there maybe just double check yourself before getting to far ahead.

BOATBUSTERS
11-28-2007, 10:42 AM
Contact Chris Fairchild at chis@fairchildracing.com he is the doctor on them