7mge compression test

[dopeassjackson]

i bought a JDM 7mge engine last week and did a compression test. the pressure is between 226 and 236psi. this is a long block with no belts on it and only a auto trans flex plate. is the lack of draw from the accessories why its reading so high?
i have the head off now and dont see alot of carbon build up or any thing major. the engine is preaty clean on the inside and outside.

 

[Doward]

That's fine.

 

[Tanya]

That's a ridiculous amount of psi in those cylinders, I would assume the head and/or block has been decked....

Mine is 230psi and is a 10:1 compression engine so yeah lol

 

[jdub]

The TSRM spec's 156 psi or higher for the 7M-GE, with no more than a 14 psi defference between cylinders.

That said, this is the wrong section for this post. Moved to 7M-GE Tech section.

Please pay attention where you post.

 

[dopeassjackson]

sorry for post in the wrong section. i have another blown 7M and that piston looks a little more concave. is there a high and a low compression 7mge?
the pistons look factory as well as it having a toyota timing belt.

 

[jdub]

You could always look in the TRSM:
http://www.cygnusx1.net/supra/Library/TSRM/MK3/manual.aspx?Section=EM&P=20

(What a novel idea)

 

[IJ.]

That's a ridiculous amount of psi in those cylinders, I would assume the head and/or block has been decked....

Mine is 230psi and is a 10:1 compression engine so yeah lol

 

[Doward]

Orange > apple!

 

[IJ.]

You have a well known Orange bias though

 

[Tanya]

... how the fuck is that apples and oranges? 12 valve head, 24 valve head, well I am well aware of that. But I have NEVER heard of a 7MGE running around with 210+ psi unless it was modified in some way, 170-190psi seems to be the norm. It's probably BHG'd 5 times in it's life and been milled every time.


Try to be a little more educational in your posting if you're just going to critisize what I say. Learn this dumb yank as to why this 230psi 7MGE is normal.... thanks.

 

[IJ.]

... how the fuck is that apples and oranges? 12 valve head, 24 valve head, well I am well aware of that. But I have NEVER heard of a 7MGE running around with 210+ psi unless it was modified in some way, 170-190psi seems to be the norm. It's probably BHG'd 5 times in it's life and been milled every time.


Try to be a little more educational in your posting if you're just going to critisize what I say. Learn this dumb yank as to why this 230psi 7MGE is normal.... thanks.

Settle down.....

What's the CC of the Head?

Cylinder swept volume?

I bet they're not even close so YES Apples to Oranges.

 

[Tanya]

I give up in this thread... it's like talking to a wall. Good luck OP!

 

[IJ.]

Might be an idea if you went and washed the sand out....

I never for a second said 230 psi was in anyway normal.

What I said was comparing a 6M to a 7M is Apples to Oranges for the reasons I listed above, if you knew how to calculate Compression ratio's you'd understand this and NOT take it as a personal attack.

 

[Tanya]

Nope, I don't know a damn thing about calculating compresison ratios. I picked the 10:1 number for my engine out of my ass

I don't need to wash the sand out, I was merely stating #1 the cylinder pressures are NOT normal, which no one seems to have agreed with me until just now and #2 it would be helpful if a senior member of this forum would be educational in his posts instead of just throwing up goofball pictures like this was off topic.

I damn well know that a 5M/6Mand 7M are all apples, oranges, grapefruits, but the basic principle is the compression number he posted up is not what these engines should spec out as, and I would be highly wary of how much has been taken off both head and/or block or what pistons it has in it, especially if this guy wants to go turbo.

But, again, I will see myself out of this thread and let the "master" have at it.

 

[dopeassjackson]

i read more on the service manual and they are #2 pistons. by the look of the other piston the JDM piston would raise compression.

not sure on the head dome size.
head dome size is .630 on the JDM head in the flat spot in cyl #6 and .637 in the US head. the difference could be from carbon though.

looking closer at this head the EGR is removed and cooling block on the back of the head is not there and looks like it hasnt ever been there, that could be just a jap spec thing i guess.

 

[IJ.]

Never heard of an alternate compression ratio for NA's, from memory they have a 14cc dish piston (19cc for GTE's) and use the same 40cc combustion chamber volume.

This is not to say your engine may have had after market pistons fitted and this is the reason the comp test is so high.

 

[dopeassjackson]

Never heard of an alternate compression ratio for NA's, from memory they have a 14cc dish piston (19cc for GTE's) and use the same 40cc combustion chamber volume.

This is not to say your engine may have had after market pistons fitted and this is the reason the comp test is so high.

i can see a difference between the US piston and JDM piston tops. they both have two #2s on them the JDM one having larger numbers.
would a aftermarket piston usualy have different markings on the top of it?

 

[dopeassjackson]

JDM piston is around .082 dome and US is .113 dome.

just measured both blocks and there within .0010 of each other. i guess i will be pulling the oil pan tomorrow and taking a look around inside.

 

[IJ.]

If you get a chance measure the Deck to Valve cover seal surface

HG

and the block from the Main bearing saddle to the Deck surface, as I said I wasn't aware of different pistons in the Japanese/USDM engines as we got the Jap spec engines here.

But having said that the change in dish volume still wouldn't account for your 230+psi readings.

 

[dopeassjackson]

yes i measured the head dome depth, piston dome depth and block deck to oil pan sealing surface.

theres got to be somthing going on with this engine. the throttle body is not on the intake if it matters. i pulled all the plugs, bolted up a trans bell housing and starter. i used a small battery that i had sitting around for about a month and jumped 2x cars with it.