compression 200psi

[chunky]

i got my 97sj engine bored from 701 to760 and got the 701 riva domes machined to suit the 760
did a compression test on it, engine warm running 200psi in both cylinders
i am running 93 octane, would there be any issues with the compression this high, its just there doesnt seem to be to many here running that psi

 

[madoyster]

Yes you are going to have issues running 93, I think you need to get a little help from one of the builders on the board. LPW or Team scream know there Chiot.

 

[Tuttle]

there doesnt seem to be to many here running that psi

Yeah there is, They just use race fuel :sad:

 

[tor*p*do]

110 octane, baby!

 

[chunky]

oh ********
i quess then my next question is what psi can i go to with 93 octane

 

[Tuttle]

oh ********
i quess then my next question is what psi can i go to with 93 octane

185 psi = 93 Is what I hear.

Where in Ireland? Have friends in Donegal (spelling?) and spent a month over there when you all played Camaroon and Germany in the first rounds of the World Cup.

 

[eel]

:dunno:

 

[Matt_E]

185 psi = 93 Is what I hear.

Not on an 84mm bore. I would stick to 175psi for 92-93 octane. 200 is waaaaay to high for a 760 on pumpgas for rec use.

Also, since you are in Ireland, you must check how the pump gas octane is calculated.

Most countries in Europe us the RON only method (vs (RON+MON)/2 method in the US), which yields a very misleading higher-than-actual octane number.
In other words, you think you're using 93 octane gas, but in ADA's book, you're using 87 octane. Be very careful here!

 

[keefer]

Either have your domes recut to 38cc and the squish corrected for the 84mm piston size or just buy some new domes. This will give you about 180psi or so depending on your porting. Do yourself a favor and get with a reputable engine builder and go over your exact engine specs to make sure you are getting the best setup.. I know that octane is figured differently here in the states than it is in other countries. I forget the specifics but the numbers are different depending on whether you are talking MON or RON octane ratings. Maybe the guys at ATP in Britain can help you and possibly save on shipping costs..
http://www.queenford.8m.com/index.html

 

[keefer]

Oops, I guess Matt already covered the octane issue. Thats what I get for starting a post and walking away for 45 minutes before I finish it.:squareeyed:

 

[Speedfreak]

I had 215 psi running 93 octane with an msd enhancer. My motor is a ADA 5 mm stroker. I am having new domes cut to lower my compression to 200. And I am going to try 3 degrees static timing advance. Everybody agrees that you can run 220 psi compression on pump gas all day long if you have a TL system. Which has more timing advance down low. But none on top. So if you don't go WOT then why does everybody worry about the compression.


If you don't let noobs ride your ski and only a second at WOT when your popping off a wake then your fine. People are worried about the PSI when it is the timing. I ran 230 PSI on my 01 SJ for a season with 93 octane and stock timing never had a problem. Someone prove me wrong. I had 230 or 250 something stupid in an old 650 and we ran it for years trying to blow it up on 87 octane we even used old gas out of the lawn mower.

 

[Matt_E]

It is PSI AND Timing AND a whole sleuth of other factors.

A 5 mm stroker has absolutely no play into what gas to run.
What's your bore?

And who agrees you can run 220 psi on pumpgas? :dunno:

Even with a TL, that is pushing it very hard and very far.

Factors for octane requirements:
Compression ratio
Timing advance and curve
Squish
Dome shape
Piston shape
Pipe setup
Cooling setup
Bore diameter
Porting

Generally speaking, on a piped SJ 185psi is the limit for pumpgas for the average rec rider.

Bump that to a 760 SJ and the limit will be 175psi.

Yes, there are plenty of exceptions to this.
Are you really going to recommend to just anyone on the board here to go ahead and run 230PSI on 93 octane?

 

[keefer]

You are the exception to the general rule I would say. Many cannot exercise enough throttle control to not WOT and deto it to death. When I first built my 760 years ago I had a crappy comp guage and was running around 205psi on 93 octane when I thought I was at 185. I was breaking in the engine and had not done any WOT. The jetting was probably a little lean as I was still in the tuning and break in phase. I ended up overheating the front cyl piston and breaking off the exh edge of the piston. I know that it could have been avoided with better jetting and a TL timing but I was not as informed back then on such things. An experienced rider with a well tuned engine and a conservative timing curve can probably live on the edge and avoid failure. I don't want to have to worry about trashing an expensive engine while riding so I pony up for the 110 octane and just ride.

 

[chunky]

Where in Ireland? Have friends in Donegal (spelling?) and spent a month over there when you all played Camaroon and Germany in the first rounds of the World Cup.
live in carrickfergus, 10 miles north of belfast, is isnt that far from donegal about 1 & half hrs drive, unfortunatly we dont get the waves they get up there, its right on the north west coast at the atlantic we are on the north east coast, its more sheltered.

 

[eel]

I had 215 psi running 93 octane with an msd enhancer. My motor is a ADA 5 mm stroker. I am having new domes cut to lower my compression to 200. And I am going to try 3 degrees static timing advance. Everybody agrees that you can run 220 psi compression on pump gas all day long if you have a TL system. Which has more timing advance down low. But none on top. So if you don't go WOT then why does everybody worry about the compression.


If you don't let noobs ride your ski and only a second at WOT when your popping off a wake then your fine. People are worried about the PSI when it is the timing. I ran 230 PSI on my 01 SJ for a season with 93 octane and stock timing never had a problem. Someone prove me wrong. I had 230 or 250 something stupid in an old 650 and we ran it for years trying to blow it up on 87 octane we even used old gas out of the lawn mower.

Have you still got some lawnmower gas?

 

[chunky]

Also, since you are in Ireland, you must check how the pump gas octane is calculated.

Most countries in Europe us the RON only method (vs (RON+MON)/2 method in the US), which yields a very misleading higher-than-actual octane number.
In other words, you think you're using 93 octane gas, but in ADA's book, you're using 87 octane. Be very careful here!

the higher octane in are pumps here is called super unleaded, it says it is 97 octane. i know what your saying, i think that would work out about your 93 octane, would that be right?

 

[chunky]

I had 215 psi running 93 octane with an msd enhancer. My motor is a ADA 5 mm stroker. I am having new domes cut to lower my compression to 200. And I am going to try 3 degrees static timing advance. Everybody agrees that you can run 220 psi compression on pump gas all day long if you have a TL system. Which has more timing advance down low. But none on top. So if you don't go WOT then why does everybody worry about the compression.


If you don't let noobs ride your ski and only a second at WOT when your popping off a wake then your fine.

my ski at the minute has no porting just head, b-pipe and a few bits that dont come into this, although my next buy is reeds and an advent ignition.
i do not race but we set a coarse up sometimes and ride it has hard as i can.

 

[Matt_E]

the higher octane in are pumps here is called super unleaded, it says it is 97 octane. i know what your saying, i think that would work out about your 93 octane, would that be right?

Yes, that'd be right.

 

[chunky]

think i will go with the majority on this one
just spent nearly £1,000 getting this engine work done, dont want to take that chance.

 

[Speedfreak]

It is PSI AND Timing AND a whole sleuth of other factors.

My bore it at 86mm on my 5mm ADA. I will be running a 6 X 86mm with 200 psi with more aggressive porting next week when my crank comes in. Which will be run with 3 degrees of timing advance and 93 octane.

And my '01 with a stock block had the 230 PSI the first year with an R@D head and the rest of it's life it had a speedwerx freestyle pipe a speedwerx head with 200 PSI and an enhancer and would hold it WOT all day long. I rode it like that for 5 years.

I would agree that 185 is the norm but no one has ever blown a stock block motor with that timing/compression. IF it is tuned right. So there is more power to be had pushing it to the limit. It would be like installing a chip in your car but then a spacer on the floor so that you can't use the whole peddle.