155 psi compression, What piston is in it? Sparks 6* key ok?

[Hult250R]

So I bought my 2nd 400EX a month or so ago.
Bone stock but it was "rebuilt about a year ago"

I ordered a sparks 6* key last week, got it and the gasket in but I figured I'd do a compression test prior to make sure it wasn't way too high.
I got 155 psi compression with the throttle wide open.

Anyone have comparable numbers? If so what piston are you running?
Is the sparks key going to be ok with 91 pump gas?

[CJM]

Ive got an 11:1 piston and it is about the same.

[WoodTRD]

Stock compression is around 120-128 if everything is in good shape so you're definitely running higher compression than stock...I've heard the +6 is ok with a 10:1 on 93 but not 11:1, but I don't have any personal experience. I'm still waiting on my stock piston to go south and thinking about leaving my +6 in and going with a 10:1 rather than take it out and run 11:1...gotta love the instant throttle response with the sparks key

[Hult250R]

Update:
So I got a Stage 2 Hot Cam this last week and decided to put it in today.
Come to find out it already had a Stage 1 in it.

Without the decompression on the stage 1 cam, what piston would give the 155psi compression reading?
Im trying to decide if I want to put the 6* Sparks key in or if Im going to machine my own 3* key for it.

Ive got no problems making my own key, Just trying to decide if I can run the 6* with 155ps compression on 91 octane.
Im not going to run race gas, too expensive and a pain to get.

[Pipeless416]

Originally posted by WoodTRD
Stock compression is around 120-128 if everything is in good shape so you're definitely running higher compression than stock...I've heard the +6 is ok with a 10:1 on 93 but not 11:1, but I don't have any personal experience. I'm still waiting on my stock piston to go south and thinking about leaving my +6 in and going with a 10:1 rather than take it out and run 11:1...gotta love the instant throttle response with the sparks key

You will gain much more from the higher compression than you will the key.

FWIW, I ran the sparks key with 11:1 cr for a couple years now, and just recently took it out for peace of mind.. that's not saying I ever had a problem with it.

[CJM]

Stage 2 will work better than a stage 1 will if you have a hi-comp piston.

Id be willing to bet you have a 10;1 or 11:1 with 155psi.

[Hult250R]

I guess im looking for real world compression test numbers from motors with an aftermarket cam to eliminate the stock decompression, and for sure what exact compression piston was in them.

Im thinking it shouldnt be much higher than stock or possibly stock, as stock compression WITH the decompression on the stock cam is 100-128
Thats lower than what a stock piston would be with the decompression removed.
Stock piston with no decompression could be 150-155psi Im assuming?

[CJM]

Yep, thats about what 416 11:1, stage 2 hotcam reads. I think i had like 165psi to be exact last time I checked it.

[Hult250R]

I thought the 11:1 was closer to 200psi compression?

[CJM]

Originally posted by Hult250R
I thought the 11:1 was closer to 200psi compression?

Not on mine, 200psi would be insane.

Think of it like this,stock is about 100-128, stock comp is 9:1 too.