I read in the new 4-wheel action that the Trinity 680 can run on pump gas
So let me know what you guys think the highest comp ratio that can ruin good on pump gas 93 octane. Later

 

cannondale runs 12.5:1 on their quads and dirt bikes. i seriously doubt you could go any higher than that without race gas.



laterz

 

Hey Joey9, This Jersey gas is the worst. I wouldn't go over 11:1
Don't forget to go with a colder spark plug too.

 

A stock Mojave is 11:1 and the manual says you can run 87, but I run 92-93.

 

Joey9,

Was hoping Raptor720 or RapTech would respond to your inquiry with a lengthy explanation. Hopefully they will. Anyhow my short version of what they might say is not to go past 10.5:1 compression on an unmodified Raptor head. If you do, you will need race gas. The down side is that you won't get any better performance than a 10.5:1 setup running 93 octane. The head has to be reworked to take advantage of any compression higher than 10.5:1. Personally, I would play it safe and stay around 10:1.

I saw an ad for an 11:1 Raptor piston that stated it needed race gas. The problem is that 11:1 will not produce more HP than 10.5:1 without doing other mods to the head. You can get a good piston from JE or Ross.

Love my NEW Raptor (no not the 2002, just my plain old 2001 with new Elka Suspension)

 

Checkout Powroll's website:

http://www.powroll.com/yamaha_raptor.htm

They specifically state what I mentioned in the previous post.

Have you checked out Rausch Creek in PA yet? www.rauschcreekracing.com. They have an ATV track, MX tracks, 2 7 mile hare scrambles, and 700+ acres. It is about 30 minutes north of Harrisburg on 81. Not sure how far this is from your house. Planning to check it out this weekend.

Later...

 

Joey,

I also read that article in the mag and have been somewhat concerned to the statement that "the 680 kit can run on 93 octane".

I have the Trinity 680 kit and was specifically told by Harry to run 103 octane. I have been running 103 and haven't had any problems with pinging or over heating. To me, it's not that big deal to have to run 103, as I am so used to having to mix for my old zilla. It would be nice to run 93 if I could get away with it though.

I too, would love to hear from Raptor720 on this topic.

Where ya at Raptor720?

 

I know you shouldn't listen to mags, but that's kinda basic. If the 680 runs WELL on pump gas I would do it now. If not I'll wait till I move out near the dunes and do it. That's when I'll really need it. Stupid question, but where and/or how do you buy race fuel. I know I could buy it at the drag strip, but that's about 2 hrs away from me. Thanks guys. Later

 

Ok, here is my 2.5 cents.

First off, you must understand that the advertised compression ratio of a piston means little to an engine builder. It is very easy to run 12:1 compression ratio pistions on "pump" gas without pings. This is how it works:

First, you must understand that the cam's valve timing events really controls your final compression ratio (cylinder pressures). For example, a late closing exhaust and early closing intake with substanitally limit the amount of fuel/air being compressed. (I could go into great detail on this issue but the example will do the job. Ford Motors SVO division actually ran 13.5:1 compression ratio pistons in a modified 4.6 litre engine that ran on the cheap pump gas without problems. They did it using a special roller cam and careful adjustment of the ignition and fuel delivery systems.)

Next, we look at the shape of the piston dome and shape of the chamber. Unfortunately, this is where the Raptor is hurting. When you step up the compression with a large dome piston, because of the poor design of the 5 valve chamber, flame front (the travel of the lit fuel) is very rough. This is where a true hemi head or even the (yes I will say it, the DS -- yuck) has an advantage. However, with some work to the chamber and some fine tuning to the top of the piston dome coupled with the proper cam and ignition timing, you will be fine.

Here is the other deal, the higher the octane (resistance to ping), the harder the fuel is to light and the slower it may burn. Also, if you are using one of the cheaper leaded race fuels, you might even experience lead fouling when the lead does not get hot enough to properly vaporize and melts to the spark plug. I prefer the unleaded MS103 from VP fuels at a 50/50 ratio with pump gas for the Raptor especially if you plan on a sustained hard run.

Understand that I have no problem running just pump gas even in a 105mm -- there is no problem. I can also verify that a 102mm with the 11:1 advertised c/r piston will run fine on pump gas with the stock cam or most other cams that do not require major piston and head mods. I have never seen a problem.

If you do experience pinging, I would seriously consider removing the 660 head and checking to see if oil is being sucked past the intake valve seals and guides. I have seen this problem on a few Raptors and the difference on the hill between a leaker and a clean burner is about 6 bikes period.

Finally, on the spark plug issue, I noted some recommendations to use colder plugs with the higher compression. That is generally good advice; however, start with the stock heat range properly gapped and see how it goes. Try a cold chop and check the plug. If everything is to your liking don't go colder. A colder plug can easily foul with carbon or lead especially if you went down on the range without a proper plug read. If you are running really high cylinder pressures, you may want to even close the plug gap down slightly if you use stock ignitions. The higher the cylinder pressure, the harder it is for the spark to jump the gap. I have seen a .003" change in gap make a 5 hp difference on a Banshee.