Head shimed low end

[1CrazySledder]

Do these things really effect the low end off the line that much? As I'm researching this thing I'm finding that is sort of inbetween the lines a bit?

How much is really lost? For a guy that don't race pro, would I even notice?

My sled is tore completely down and about to pull the head, but I just want to be sure I'm doing the right thing. I want to run 12lbs on pump fuel, but not at a cost of losing the snap of the line.

 

[gunnerthesnowman]

Do these things really effect the low end off the line that much? As I'm researching this thing I'm finding that is sort of inbetween the lines a bit?

How much is really lost? For a guy that don't race pro, would I even notice?

My sled is tore completely down and about to pull the head, but I just want to be sure I'm doing the right thing. I want to run 12lbs on pump fuel, but not at a cost of losing the snap of the line.

What are you asking ,were you running the sled stock , no turbo , now you are installing a turbo with head shim?

 

[mbarryracing]

I've read and heard the same things. Unfortunately I never had the chance to ride my rear mount turbo Apex with stock compression. I went right to decompressed pistons out of the chute since I am also running 12 lbs on pump fuel, so I have nothing to gauge against. But comparing it now to before boosting, it has real good response from engagement on up. At least on mine, the off-idle could be improved as that is only where I notice a laziness, which I doubt is related to the lower compression ratio and has more to do with fueling that I haven't figured out yet. But in reality that is not a range that it's ever in when trail riding anyhow so I haven't felt the need to try to tinker there yet.
You didn't mention if your sled was carb'd or EFI... If you use an EFI programmer that also can control igntion timing, or a separate programmable ignition on a carb's sled, then increasing ignition timing on the low end wakes them up.
Also, clutching has a big influence on perceived response... I've discovered that when I run my heavier drag race clutching for 20+ lbs set-on-kill boost, my low end response goes to crap without changing anything else. Trying to accelerate a heavier rotating mass...

 

[kinger]

On a supercharged engine honestly 'losing low end' shouldn't even be brought up, I mean your at 4 psi when the clutch engages. On a turbo its more pronounced with no other changes but most kits optimize it for the shimmed engine and you wouldn't even notice then.

10:1 down from 11:1 is still high compression were not working on 350's going to 7:1 or something where it gets soft.

Good luck with the sled!

 

[1CrazySledder]

Thats all i really wanted to hear. Lol needed to be sure because it was on my mind. I went with a blower 4 years ago because of the low end....didnt want to lose any of it....especially since the boost is going up.

 

[jabber800]

Is anyone out there running the compression down at 8.5 to 1 on a supercharged engine? I am in the process of building a big bore 1100 and was thinking of trying it at 8.5 to 1 and cranking the boost up a few more pounds on pump gas. Was thinking I could probably run around 14 or 15 pounds boost with this compression ratio. Anyone have any experience with this?

 

[kinger]

I toyed with the same idea and posted the question, a lot of good builders reccomended against it because of the timing of the stock ecu is too light, you would need full control of the engine and no what your doing.

Possible but not for a amateur.

 

[FLYBYU]

You don't need to go that low for that amount. 9.5 to 1 is what i run at 14 lbs.

 

[TurboJamie]

I would say the decompressed engine is slightly slower to rev.