Comp ratio compensation for low comp pistons

[77srxdude]

Seeing as I have to replace my pistons - want to go with low comps - can I and if so how do I adjust the boost calc for 10:1 pistons?

Are the heavier studs necesary if I am plannin to max at 15 bs of boost with low comp pistons? If so, where can I find them?

I am planning on running low comp pistons and the headgasket that comes with the Wisecos - or - should I get the head shim and where can I get a head shim? Obviously this depends on how the calc works witht he low comp pistons.

Would like to run 10-12 lbs on 93 and 15 lbs on 50/50.

Thanks in advance for help.

I have searched through many many threads and can not find more info on the studs or head shim as to where to buy.

 

[rxwarrior]

Head Shim

I have a new RX head shim in stock if you are looking for one. Cost would be $75.00 plus shipping.

 

[rxrider]

The Wisecos 10:1 pistons together with the Wiseco gasket that comes with the kit (0.27"), will put your motor at 10:1 compression ratio.

In the Boostcalculator replace 11.8 CR with 10.0, you will notice a drop in octane requirements going with low comp pistons.

 

[77srxdude]

Thanks RX Rider and RX Warrior - exactly what I was looking for - as for the shim - I assume you replace the gasket with that - or do you use it in conjunction - and how thick is the shim compressed?

If I decide to go with the shim - how fast can ya ship it? I am in MN and plan to do the rebuild this weekend.

Thanks!

 

[Rx1M5]

When you shim you take a stock Yamaha head gasket (New, New, New) drill out the rivets and split it apart toss the center section and use the head shim instead of the center section. You need to spray high tack sealer on all surfaces then reassemble the motor. With a .080 head shim your cr if I remember correctly will be about 9.3 or somthing close to that. Dave at Powderlites stocks the head shims as I believe he actually makes them. When I did mine I did the cam gear timing mod as well. If you are doing it yourself buy Veedy's Alpine turbo install DVD as it all explained there on the vid.

Rx1M5

 

[rxrider]

77srxdude - If you use a shim go with Rx1M5 says and adjust the intake cam gear back to stock position.

With 10:1 pistons and Wiseco (0.27") or single stock gasket there is no change in head position, thus no need for a cam timing change.

Hardened head studs are not mandatory at 15 lbs, but they cost about $90USD, for your piece of mind install them. They will not stretch under load so head lift and blown gaskets would not be a problem if head is torked down correctly.

Good luck on your build

 

[77srxdude]

77srxdude - If you use a shim go with Rx1M5 says and adjust the intake cam gear back to stock position.

Hardened head studs are not mandatory at 15 lbs, but they cost about $90USD, for your piece of mind install them. They will not stretch under load so head lift and blown gaskets would not be a problem if head is torked down correctly.

Good luck on your build

Thanks RX - I have never adjusted my intake cam from stock on my rx - that wasn't a requirement with the bender II rear mount - didn't touch the engine at all.

Does anyone know where to get the hardened stdus - I did a search and no luck.

 

[rxrider]

Hardened head studs ask

Ted at Jannetty Racing Enterprice
Jeff at Simons CPR
Freddie at Easter Cycle Performance or
American Performance Engineering

Depending on the thickness of the headshim and gasket combo you put in the intake and exhaust cams moves and timing changes a bit. On the exhaust cam it is ok because it makes the exhaust timing better for turbo. On the intake cam this movement does lower the HP output, putting the intake cam timing back to stock makes more power. The amount one have to move the intake cam depends on the thickness of the head gaskets and shim combo, like I said above. The boostcalculator spread sheet in the sticky has the formulas to do the calculations on how much you need to change the intake cam timing.