24 replies to this topic

[fessie]

Thinking of doing a big bore this summer just wondering what you guys think pros cons between the two still want to run 87 octane and reliability is number one

[XXROBBOBXX]

you wanna run 87 in a big bore?

[watchthis907]

you wanna run 87 in a big bore?

i know right, E10 is where its at

[XXROBBOBXX]

i know right, E10 is where its at

lol

[TT670]

Whats wrong with building a motor for 87 octane? I prefer it that way, I never know what kind of fuel I'll run into in my travels.

[XXROBBOBXX]

Whats wrong with building a motor for 87 octane? I prefer it that way, I never know what kind of fuel I'll run into in my travels.

i suppose...i guess you can run what you want

[one_fast_x]

The 640 kit will be cheaper(and can be made into a 660 with a .040 over 670 piston), as it uses a 670 piston and a shim plate, the 662 is a Kawi 650 watercraft piston without shimming, both dual ring pistons....
basically it comes down to who has better porting and supporting mods as there is really only 1-2 HP gain in going to a 662 vs a 640....
If I had the option to go back in time I would have Left it a ported 600 and put a head, pipe, and reeds on it vs just the bigbore.

[TT670]

If I could fill up with a gas can every time Id build it for a race fuel mix but since I might have saddlebags and buying whatever fuel is offered I need to be conservative, and see no sense in dumping $$$ into an engine package that I have to worry about every time I pull up to a pump. The difference for my engine build when choosing between average pump gas and known good 92-93 octane was .005 more squish clearance. Most people probably wouldn notice the power difference.

[XXROBBOBXX]

If I could fill up with a gas can every time Id build it for a race fuel mix but since I might have saddlebags and buying whatever fuel is offered I need to be conservative, and see no sense in dumping $$$ into an engine package that I have to worry about every time I pull up to a pump. The difference for my engine build when choosing between average pump gas and known good 92-93 octane was .005 more squish clearance. Most people probably wouldn notice the power difference.

understandable i guess i dont really think about that sort of thing since i dont really have to worry about running questionable gas around my area. atleast for right now. im sure it will change very soon

[one_fast_x]

understandable i guess i dont really think about that sort of thing since i dont really have to worry about running questionable gas around my area. atleast for right now. im sure it will change very soon

U blow ur sled up on bad gas once and it will always be on your mind, I wont buy gas from a station without premium(I always run premium if at all possible) simply because 90% of the stations only have premium and 87, to obtain mid grade they take from each tank and mix while filling... if a station only has mid grade, most likely it is just 87 in a tank that isnt used much....

[XXROBBOBXX]

U blow ur sled up on bad gas once and it will always be on your mind, I wont buy gas from a station without premium(I always run premium if at all possible) simply because 90% of the stations only have premium and 87, to obtain mid grade they take from each tank and mix while filling... if a station only has mid grade, most likely it is just 87 in a tank that isnt used much....

no i agree with you...thats why i said what i did in the first place.

i only run premium in my sleds.

[djm]

The only trouble with running premium only is that not a lot of cars use premium any more... and so some of the premium sitting in tanks is old..and of questionable Octane. In the expose done by TV in Californian, they found 75 Octane in one Exxon Station's premium tank.
Set
One of the reasons I ride cross country and mix my own gas. Have most of my engines set up for 91 Octane. If I do go trail riding, I will put almost 100% 110 race gas, then will fill up on the trail while I still have 3 gallons or so left in the tank. The race gas is purely for fuel security in my case and to guarantee that I don't get it trouble. Have been doing it for the last 8 years or so.... knock on wood, no pistons have been added to the piston pile in that time period.

[watchthis907]

The only trouble with running premium only is that not a lot of cars use premium any more... and so some of the premium sitting in tanks is old..and of questionable Octane. In the expose done by TV in Californian, they found 75 Octane in one Exxon Station's premium tank.
Set
One of the reasons I ride cross country and mix my own gas. Have most of my engines set up for 91 Octane. If I do go trail riding, I will put almost 100% 110 race gas, then will fill up on the trail while I still have 3 gallons or so left in the tank. The race gas is purely for fuel security in my case and to guarantee that I don't get it trouble. Have been doing it for the last 8 years or so.... knock on wood, no pistons have been added to the piston pile in that time period.

thnx djm,you saved me some typing

[marc_brown98]

Building a big bore to run on 87 is doable, however, you need to contend with a few things. First, most big bores are performance oriented and want to extract max hp / torque as possible. Starting with 87 puts you at a deficit. It's not unreasonable to run a looser squish and run premium in it anyway and maybe a 12.5 CR. I don't know about the 640, but my 662 was reliable in the stock RPM range with a loose squish. When I tightened up the squish, increased rpm and had a custom pipe made it was a bit more finicky on fuel and I lost a piston. Understand that motor was set to 13.25:1 CR, very tight squish and would make peak power @ 8700 rpms then fall slightly until 9000 rpms, peak torque was around 8400. So, a very different motor than a stock rpm big bore. It was a hoot to ride, but fuel had to be good. I don't have any experience with a 640 other than some help on the boards trying to help dial them in.

[2001mxzlongtrack]

has anyone scourced their own pistons and did their own big bore instead of paying out all the cash? If you can get buy with 670 pistons at .040 overbore or 650 kawi pistons, wouldnt all thats needed is a bore to fit them correctly? then put on a custom head, and for the die hards a diy port job. i guess this question could be for marc, would the race logic sport port kit for the 500ss work on one of the above overbores, added with a head and be ok? if we could figure out a way to do our own bigbores, we could cut cost and have the satisfaction of doing it ourselves. just thinking i guess, thats all...