A
Anonymous
Guest
How many Thou needs to be taken of a standard XD250 Xflow head to bring it to 10 - 1 comp
Thanx Guys
Thanx Guys
READ THE WARNING BELOW!
Around 0.010 thou equals .16 of a point on a 3.9 OHC. Care of 32 pound smokin Joe, aka gm destrya! On an XD, its about 0.15 of a point per 10 thou. About 35 thou or so will give you 10:1 compression ratio.
The best way is to grab a stock XD head, which has a blueprint chamber cc of about 53 cc, and fill it with water and a small amount of detergent, grab a vetinarians drench measuring tube, and measure the distance of freeboard in thousandths of an inch when you hit a 48 cc target.
Try feeding the values into this, http://falconperformance.sundog.net/compcalculator.asp.
The stock gasket is about 30 to 40 thou compressed, the pistons stops short about 15 to 25 thou, and the stock piston is about 19 cc, I think. Replacement ones are always of a bigger volume unless you specify 3.3 or high compression pistons. The stock CR is about 9.35:1, but this progam doesn't go that accurate, probably a good thing!
Input data I used:-
Number Of Cylinders 6
Bore Diameter [inches] 3.68
Stroke Length [inches] 3.91
Combustion Chamber Volume [cubic centimeters] 53
Head Gasket Compressed Thickness [inches] 0.035
Head Gasket Bore Diameter [inches] 3.75
Piston To Deck Clearance [inches] 0.015
Select Piston Type Flat Top Dished (not Domed)
Dish/Valve Relief/Dome Volume [positive cubic centimeters] 19
Volumetric Efficiency: 80%
RPM: 4000
Planing the head 35 thou should give around a 48 cc chamber. Shove 48 cc in the formula, and you get about 10:1.
Make sure the edge of the combustion chamber has a 45 degree bevel which should be further blunted with emery paper beofre the vlaves are re-assembled. Detonation can result!
Note the potential power increase of from 140 hp (105 kW) to 148 hp (110 kW)@ 4000 RPM.
WARNING: Even with great ignition, a 10:1 compression is risky. Our fuel octane rating is poor, and the stock ignition may not be set correctly. Alloy heads are good with higer compression ratios, but if it detonates, your 5 kW power boost will result in a 1000 buck budget blowout.
Around 0.010 thou equals .16 of a point on a 3.9 OHC. Care of 32 pound smokin Joe, aka gm destrya! On an XD, its about 0.15 of a point per 10 thou. About 35 thou or so will give you 10:1 compression ratio.
The best way is to grab a stock XD head, which has a blueprint chamber cc of about 53 cc, and fill it with water and a small amount of detergent, grab a vetinarians drench measuring tube, and measure the distance of freeboard in thousandths of an inch when you hit a 48 cc target.
Try feeding the values into this, http://falconperformance.sundog.net/compcalculator.asp.
The stock gasket is about 30 to 40 thou compressed, the pistons stops short about 15 to 25 thou, and the stock piston is about 19 cc, I think. Replacement ones are always of a bigger volume unless you specify 3.3 or high compression pistons. The stock CR is about 9.35:1, but this progam doesn't go that accurate, probably a good thing!
Input data I used:-
Number Of Cylinders 6
Bore Diameter [inches] 3.68
Stroke Length [inches] 3.91
Combustion Chamber Volume [cubic centimeters] 53
Head Gasket Compressed Thickness [inches] 0.035
Head Gasket Bore Diameter [inches] 3.75
Piston To Deck Clearance [inches] 0.015
Select Piston Type Flat Top Dished (not Domed)
Dish/Valve Relief/Dome Volume [positive cubic centimeters] 19
Volumetric Efficiency: 80%
RPM: 4000
Planing the head 35 thou should give around a 48 cc chamber. Shove 48 cc in the formula, and you get about 10:1.
Make sure the edge of the combustion chamber has a 45 degree bevel which should be further blunted with emery paper beofre the vlaves are re-assembled. Detonation can result!
Note the potential power increase of from 140 hp (105 kW) to 148 hp (110 kW)@ 4000 RPM.
WARNING: Even with great ignition, a 10:1 compression is risky. Our fuel octane rating is poor, and the stock ignition may not be set correctly. Alloy heads are good with higer compression ratios, but if it detonates, your 5 kW power boost will result in a 1000 buck budget blowout.
A
Anonymous
Guest
we had the head on a 250 xd shaved and after that it forever had pre ignition trouble , it had around 10 or 10.5 comp on it.
thats my 2 pennies
thats my 2 pennies
