RKT head jetting?

[BackCountryBob]

04 REV-X, 7,000-10,000' altitude. I recently installed a used RKT head 'cause I trashed my stock head when I lost a piston:

1) is there a way to find out the compress ratio?
2) doo you go richer, leaner, or stay the same?
3) any power gains?

Thanks.

BCB

 

[sledsrock]

You don't know what CR head you bought? You need to call Kelsey and get his input, after all it's his head.

 

[Danzick]

i bought the same head used and it came with 2 dome kits. look on the back of it, and there is some numbers. one of my domes have 8040 1402. that means its a 14:1 compression dome. the other kit has 800 1462. these are 14.6:1 compression domes. its most likely a 14 to 1 compression head.

 

[BackCountryBob]

What sled are you running and what jetting did you go to, what's your average elevation? What octane gas works best for you? I am always concerned about mid range as I seem to run 6,500/7,000 rpm most of the time.

Thanks,

BCB

 

[Danzick]

i havent ran this new head set up yet. i got it when my motor blew a week ago, but this head will be going on an 04 800. ive been doing some homework on it. kelsey told me i need to run 7500 ft plus for the 14.6 to 1 compression to be safely ran. anything lower than that for awhile will detonante and screw things up and id have to run race fuel. as for jetting, his head is supposed to cool a lot better than stock so i would start with 390s or 380s to be safe. some people are going all the way down to 360s with his set up. and my elevations fluctuate a lot. the places i go start at like 5000 ft, and the bowls up top are like 11 thousand ft. if you find out your compression is 14 to 1 compression, you should be safe if your over 5000 ft most of the ride.

 

[Danzick]

oh and did you put his pistons in, or stock ones? kelsey told me his head wont work with stock pistons at all. the guy i bought my head from ran the 14.6 compression domes with stock pistons and he said that thing ran really strong. pulling the head is like 20 mins. i do that and get the numbers engraved on the back side of the domes. its pretty important to know what compression your running.

 

[Vailguy]

Did you goto kelsey's site? his install instructions I have found to be spot on for several of the heads I have purchased. I always excersized caution and ran fat jets, and slowly leaned them out reading plug and EGT's, but ended up landing on his suggestions.

 

[BackCountryBob]

I went to Kelsey's site. He recommends 340mj for 04 and up REV models. No reference to altitude. 92 octane pump--does not recommend convenience store fuels.

His jetting seems way too lean to me. I just got off the Flattops for 3 days--8-10,000' with the same 390mj I had with a bone stock engine--new DOO OEM pistons--sled ran great and averaged 11 mpg 89 octane breaking in--no high marking with too much avy danger.

Plugs looked good. Kelsey writes that "no wash" (black pistons) "does not suggest a lean condition". How can you check jetting if piston wash does not matter?

I am, only RKT pistons with his head, 340mj piston wash not applicable---what am I missing here?

I'll be on the Grand Mesa for a 3 day Club ride and will Doo a compression test and plug checks on 87 pump.

BCB

 

[Danzick]

89 octane? man ive never not ran 91 premium in my sled no matter if it was stock or modded.

 

[PJ-Hunter]

89 octane? man ive never not ran 91 premium in my sled no matter if it was stock or modded.

No kidding. With the ethanol BS we in Colorado have to deal with paired with an aftermarket head that is increasing compression, no way in Hell would I go less than 91.

I'm running the 14.8 RKT head. 500 mains, needle shimmed up one. I could probably go down to a 480 main, but will have to wait and see what happen when temps drop again. Hard to jet when it's 35+ degrees out.

 

[BackCountryBob]

I just ran a compression test in my drive at 5,500', cold with throttle WO--125

According to the techs at Vickery, that is normal for a stock 800 DOO so I think it is safe to assume the RKT I have is less than 14:1. I have had numerous high compression modded sleds that had engine issues so I am happy to know that I will not have to worry about detonation or spot on jetting or getting crappy gas. I will use 91 from now on--thanks for the advice.