Shim or no shim on Nytro

[pelon]

This is just a feeler thread:

How many of you have not put in a head shim on your Nytro?

Provice some feedback on:
1) Boost levels run
2) elevation
3) octane

There are quite a few around my area not running them with years of success. They are running up to 12 psi and 91 octane @ 10000 to 12000 feet.

 

[TRUEBLUEMAX]

From what I hear the MCX 180 kit runs that kind of boost at that altitude. (hope to know first hand before too long.) Which means you are at about 180 horses up at high elevation.

 

[sledheadd]

Nytro with headshim 18psi @ 5000 - 10000 on av gas
15psi @ 1300- 4000 on av gas

 

[Sleds R Fun]

Head shim

I"m the same as above. Head shim from MCX 4500- 6500, 18 pounds with Av Gas mixed with Lucas oil. So I would think at your altitude with 12 that would be safe with no shim.

 

[snowmanx]

Haven't run it yet, but Nytro MCXpress at 17# with headshim, 91 octane 5000-8000 feet.

Not sure why you guys are running AV gas with your MCXpress kits? I spoke with Mark Leipheimer( who would know), and he says you can run that kit from sea level and up with 91 only?

Just saying.

 

[sled-fiend]

Not sure why you guys are running AV gas with your MCXpress kits? I spoke with Mark Leipheimer( who would know), and he says you can run that kit from sea level and up with 91 only?

Just saying.

Cheap insurance is why I run AV with my 270 kit, never know what the pumps gonna put out. Not to mention AV is close to the same price as premium anyway.

 

[Cookn]

I"m the same as above. Head shim from MCX 4500- 6500, 18 pounds with Av Gas mixed with Lucas oil. So I would think at your altitude with 12 that would be safe with no shim.

Why do you mix with Lucas oil?

 

[letsgetrad]

yea same. why do you run lucas oil?

And I ran my nytro 180kit at 11 lbs no head shim with a 50/50 mix C111 and pump 94 at 3500-7000 feet. ran great all year. put the 270 kit on last week and the motor was fine when we took it apart for the head shim. just lots of lead deposits. going with avgas now for the low lead like everyone else.

 

[Sleds R Fun]

I've been mixing Lucas Upper oil lubricant with av gas for 3400 Miles. just running the lubricant as insurance with the av gas as it's dry like all race fuels. No difference in av than 112, just some lead, but Av is a much better fuel in my opinion and I have tested them all.( high end flash point of av is 130)
This year I'm gona run 50/50 av and gas, will let you know how that works. The kit I have is first generation MCX and it recommended 98 octane, now if thats european #'s or canadian who knows! Happy MCX owner so far!
Will keep you posted on motor life!!!

 

[pelon]

Thanks for all your input.

 

[skidawg]

I've got a 08 hp3 simmons propane nytro.
Last year: 18-22# of boost shimmed .079
6500-9500 elev.
propane fuel

This year: 12-15# of boost no shim and ported
6500-9500
propane

Last year I raced a guy that was setup great and he beat me running 12# to my 18#. He is a friend of my and I am going to try his setup. If you can't beat um, join um.

 

[pelon]

So your saying that no headshim and 12-15 lbs did better than 18lbs with a head shim?

 

[skidawg]

Yes, 12# max is what he ran on pump gas with no head shim at 7500 elev. He has had his sled for six years now (rx 1 ton) and has got it dialed in, motor, suspension, clutching, etc... I am planning on running up to 15# with no head shim, but you have to remember, propane has a very high octane rating. We ride mostly in Cooke.

 

[skidawg]

One more thing, before I decided to not run a head shim, I talked to Gus Bohne about it and I asked him why do most people run a head shim? His answer was "to sell product"! We will find out this winter and I'll let you know in the spring.

 

[Polarisrocks]

if you dont have enough octain it will detonate and egg out your cylinders start leaking anti and then you are looking for a motor... so be more conservative then less just say...I am on my 2nd motor.

 

[mattymac]

no shim has its benifits, lower octane isnt one of em!

I rode a BD nytro @ 14 lbs around 10K feet (this was in 08, first year of the nytro) it was running straight c12 (going off of memory) it was very strong to say the least! ran very well!!!!

 

[AKRMK05]

6-10 lbs boost
no shim
450ft to 7000ft
50/50 av gas and prem pump
runs great so far