Build Predator Hemi 212cc Higher Compression On Pump Gas

cpu77

cpu77

Member
#1
#1
I am building a another Hemi engine and this time would like to add a little more compression. I want to still run pump gas (91 octane). Its for my Original Doodlebug.

Here is my setup.....
ARC flywheel
Black mamba Jr cam
26lb springs
gx140 emulsion tube w/Jets
Intake
Under Seat Header with RLV Muffler
Stainless Stock sized valves
Colder Plug
No porting or polishing head
Governor Removed
TAV2 w/11t/60t

To get more compression would I....
Mill the head if so how much?
.010 head gasket
ARC .020 over rod (Assuming there is room)
 
Prowler08

Prowler08

New Member
#4
#4
If running the Hemi head you would have to mill off .080 or more before you had to worry about higher than 91 octane...
Do they not sell plain 94 octane at the pump? Sunoco ultra94?

You can mix Xylene in the gas to bump it up a couple points...
But at that point it would be easier and cheaper to run Methanol...
 
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cpu77

cpu77

Member
#6
#6
OND said:
Yep ...just ethanol free pump gas and it runs fine.
Click to expand...
Thanks for getting back to me! I really appreciate it!

This is the setup you ended up running correct.....
Milled .030
Headgasket .041 thick (Where did you buy)
Stock predator fire ring gasket.
+.020 Rod
 
Prowler08

Prowler08

New Member
#8
#8
I believe I answered a few posts up...
The .040 gasket is the stock gasket...

BM Karting sells a stock one... If not they sell a bunch on eBay...
If you want the .045 gasket search 212cc gasket. A lot of generator motors take these parts...
 
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OND

OND

#9
#9
The reason I used the .040 stock head gasket is because the .020 rod put me even at the hole...not .005 down in the hole ..but even. My predator engine was new so I used the stock fire ring gasket.
 
Prowler08

Prowler08

New Member
#10
#10
Wow... How do you get away with a .020 Rod and flush deck?

Any Hemi I have built I used the .040 Rod and either was .005-.010 pop up...
Still perfect for a .045 gasket...

And the Non Hemi I put a Honda crank in with a Hemi flat top... Puts me .090 in the hole and use a Honda .100 Rod to give me .010 pop up and still use a .045 gasket...
 
OND

OND

#11
#11
Well It was my first hemi engine and I measured it at .020 in the hole before I ordered the rod...and sure enough it put me at .000 with the .020 longer rod.

 
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OND

OND

#12
#12
I would pull the head and see where your piston is at TDC if its .040 in the hole like some of prowlers engines then get a .020 rod and use a .009 head gasket instead of the .041 gasket. jmo
 
Prowler08

Prowler08

New Member
#13
#13
Yes defiantly check what piton depth you have...
Most of the Hemis I had were .025-.030 in the hole good for a .040 Rod and thick gasket... and most Non Hemis were .040-.050 in the hole... Perfect candidate for a Honda crank and Honda .080-.100 Rod... Or a .040 Rod and thin gasket...
So many different combos to play with!!!

Heck the couple Champion 208cc motors were .110 in the hole... Because of the piston pin height...
Easily fixed with a .020 Rod and a Hemi piston to bring it to ..020 in the hole... Or throw a Predator crank and a .020 Rod for flush deck...
 
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