PG Turbo compression - 95 lbs?

[specialk6r]

My 10' M8 was built by Rexburg Motorsports with an 11' BDPG kit. It runs awesome but the bottom end is fairly soft, so out of curiosity I did a compression check. It blew a perfect 95 lbs on both sides (at 6500 ft.) With the same gauge my M7 with a 14.1 domes' blows 130 lbs. So my question is, what's your guess of whats been done to it? Pistons? Cut domes?

I don't think it's a problem because my pistons look good and it's even on both sides, but I'm wondering if I can get a little more bottom end if I go back to stock compression somehow.

 

[WyoBoy1000]

One those you have to pull real hard and like 10 times, but my 09 was over 120psi on both sides. Pull until the gauge quits climbing.

 

[specialk6r]

Yeah, I've found that to be true with my M1000s too so I pull until the gauge stops moving, then a few more times to make sure.

They had no record of what had been done to the sled, other than the turbo install. They welded in EGTs, so I know their records are incomplete.

 

[backcountryislife]

I would assume they loosened the head on that sled, Cutler does the same on his kits as well.

On a stock 07-09 type head around here (about 8-8500' at the shops) we pull around 105 if I recall. I'd guess you're lower than us, but still getting less psi, seems a bit soft to me. I've never tested my 11 that was cut for boost... you've got me wondering what that one pulls now.

 

[WyoBoy1000]

my 09, 126/128psi at 5000ft. But thats pulling hard

 

[specialk6r]

I was guessing the heat was cut a bit, but I know that VOHK often runs BD PG kits with stock heads for tree riders. Since boondocking is all I do, maybe I'll try to get a stock head? What year head should I aim for?

 

[Wheel House Motorsports]

because the m7 with 14:1 is only pushing out 130 on your gauge, i wouldnt be nearly as worried, thats a bit low for such a high comp motor..

 

[backcountryislife]

I was guessing the heat was cut a bit, but I know that VOHK often runs BD PG kits with stock heads for tree riders. Since boondocking is all I do, maybe I'll try to get a stock head? What year head should I aim for?

10,11,12 are the same.

 

[tcat boy]

for a true comp reading pull all the spark plugs hold the throttle wot and give her three pulls of the rope any other way is wrong period.

 

[RACINSTATION]

95 is way too low.

You should be pulling around 120 with 2007-2009 head at 6000 to 7000 foot elevation and about 128 with the 2010-2012 head. Give or take a few for gauge flaw.

The important thing is that they are even, but 95 is too low know matter how you cut it unless your gauge is just reading low. Try another gauge just to be sure.

You could also drop a piece of solder in the spark plug hole and run it to the edge and spin the clutch over slowly, then pull it out and measure you squish clearance to see what is going on.

 

[knzee]

for a true comp reading pull all the spark plugs hold the throttle wot and give her three pulls of the rope any other way is wrong period.

I might be wrong here but if you pull both spark plugs on the same jug, stick the tester back in one of the holes and try to get a reading on that side you are going to get no air pressure in that gauge, period...Well maybe 5-10 psi that can't escape out the huge hole you have where the other plug used to be.

 

[specialk6r]

Well I got a new gauge and tried again, but this time with the throttle roped to the bar and got 120 on both sides. I tried my gauge again with the same technique and got the same thing, so apparently holding the throttle open made the difference. Ya learn something new everyday... if you're born dumb eough.

As a sidenote, it made no difference whether or not the plug in the cylinder not being tested was in or out.

 

[RACINSTATION]

I think Knzee meant removing both plugs from one side and then putting the gauge in one hole, the compression would all escape out the other hole.

120 sounds more like it!