Rx1 headshim affects on the bottom end, how bad?

[Ski-Dooin' it]

For those who dont know what my sled is, 03 rx1 motor with a powderlites shim in it running on homebrew turbo system and it runs on propane, in a doo chassis.

My question is, now that I have octane to spare, and then some. I dont need the headshim for the boost levels im running, I have been running 12# lately and that gets me around quite fast, im just feeling like the bottom end is not what it could be, BUT< is it worth my time to take the giant turd apart and take the shim out? I doubt I will ever go over 15-16# of boost, and with propane on a stock motor, thats safe.

Just for those who have had a shimme vs non shimmed motor, how much more noticable is it?? mine is just sort of mushy out of the hole, wanting more snap to it.

 

[dirk_03]

Taking the head shim out should be a major difference, imo. I am contemplating taking mine out this summer and going back to stock and keeping the boost low.

 

[TurboTime]

For those who dont know what my sled is, 03 rx1 motor with a powderlites shim in it running on homebrew turbo system and it runs on propane, in a doo chassis.

My question is, now that I have octane to spare, and then some. I dont need the headshim for the boost levels im running, I have been running 12# lately and that gets me around quite fast, im just feeling like the bottom end is not what it could be, BUT< is it worth my time to take the giant turd apart and take the shim out? I doubt I will ever go over 15-16# of boost, and with propane on a stock motor, thats safe.

Just for those who have had a shimme vs non shimmed motor, how much more noticable is it?? mine is just sort of mushy out of the hole, wanting more snap to it.

Just an FYI, by taking the the headshim off and increasing the comp, you will be able to decrease the boost levels by a couple pounds and still run the same hp while incresing your response on the low end..

 

[kinger]

Take advantage of the shim and add more boost. Probably wont add a ton of response till you remove it but I would think you would be safe at 17-20 psi on propane.

 

[Wildman]

When you shimmed the head did you re-do the cam timing or leave it alone? If you have a decompressed motor with stock cam timing and go back to a stock motor it will be a huge difference. If you run to much octance for a motor it can hurt the performance too. I would go back to stock as I would think it would really help with the boondocking.

 

[Ski-Dooin' it]

as far as leavin the shim and cranking the boost. i dont need to, on 12# for the riding I like to do, its more then enough on the top end already, just the bottom end suffers for no reason now. I boondock this thing in places you woundnt ever take a yamaha, its still heavy, but now I am working with a buddy on a chromoly tube chassis,with some other stuff, so down about 100# for next year. so its gonna be a LOT lighter, and 12# is quite a bit in something thats not a total tank.

I did slot the cam gears on the exhaust side.. methinks.
I also forgot that it does make more power at lower boost on the same comp... wahoo. more power, just what i need, now just WHEN I need it..

I think I will order a new head gasket ant take the thing apart sometime when it gets warmer out.

 

[dirk_03]

So here is the next question? So if a guy was to remove the shim would there still be benefits changing cam timing to 114 degree lobe centers like PL does?

 

[tapex_07]

I believe you ment to say the intake cam gear..

 

[thamax]

there isn't a place i wouldn't take a yamaha the propane sleds never are fast off the line from what i've seen just take a few seconds for them to wind up. also did this problem get worse after the switched to propane?

 

[Ski-Dooin' it]

Hmm.. interesting on the propane, i ahve never been around one so its hard to say what brads setups run like. i think its in part due to a lack of accelerator pump style feature with the propane system, so it cant feed the demand as well as a gas system could.. and due to the lower energy per volume, when your not in boost, its not gonna make the same power gas would, especially with a low comp motor, so its gonna be extra laggy then.


also, when i swapped to propane i TOTALLY redid my turbo system, I think my charge tubing is really not helping me its 2.5" and its a impulse style header but the intercooler is way up in front of the motor, so it takes a while for boost to get where its headed to.. I am working on redesigning my turbo system to shorten up some stuff.. you ride an impulse, so you know how it works.

 

[thamax]

are u running a dual scroll turbo with a titanium turbine wheel cause i hear thats how they get rid of the lag.

 

[Ski-Dooin' it]

nah, just regular old turbo... I am workin on redoing the turbo system to dramaticaly decrease charge system volume, and also taking the headshim back out for the boost levels I want, also gonna play with the clutching.. so it is good to hear they arent wild out of the hole, i just know mine could be better.

I appreciate the input.

 

[thamax]

i know the propane sleds need alot more air i know the chargers that hp3 uses is about the size of 3071 they also have the gtx series out now u should try one and tell use how it works.

 

[kinger]

That is what I am saying add more boost and try it. I dont know why your limiting yourself to 12 lbs when you can probably handle 20 on propane maybe more. That way at part throttle you may have 12-16psi depnding on flipper positon and it may make the lag less noticable. Right now your fighting a COLD intake charge that is trying to light plus too little boost. Otherwise advance the timing a bit with the key in the stator.

If your stuck at 12 then removing the shim is the best way to get some response back even then I think you should be on 17psi to take advantage of the octane and burn out the charge inside teh cylinder when your at WOT.

 

[dirk_03]

I would imagine that you could ditch the intercooler as well. Especially if you can handle 18lbs of boost without the head shim with propane. It would be good at 12lbs and your response would go up. And as we both know your Ic is probally not the best flowing out there.