Need help with 1.5jz build

[suprahero]

Why are you people trying to scare me again? Am I the only one that's ever went 1.5jz and had these problems? Does everyone else have to order custom made pistons? I don't get it. Now I don't know which direction I need to go............:dunno:


Maybe I should have bought the vette after all...........:cry:

 

[jdub]

Not trying to scare you Jay
All depends on how much $$$ you want to spend.

I wouldn't go over a 2mm MHG though for the reason stated.

Personally, I think IJ touched on it earlier with the way you had your cams degreed.

 

[suprahero]

Not trying to scare you Jay
All depends on how much $$$ you want to spend.

I wouldn't go over a 2mm MHG though for the reason stated.

Personally, I think IJ touched on it earlier with the way you had your cams degreed.

Lots of overlap = low cylinder pressures so you can get away with the timing/boost you were running

Less overlap ie: Your cam settings = High peak cylinder pressures and you either need to back the timing down or the boost or mechanical damge will happen.

Why did you open the cams up so wide?
(just curious)

What if I put them back at 0 when I install them? Would that help? It's hard to degree the cams with the motor in the car, but maybe I can degree them this time before I install it. I tried last time, but it didn't work out so well. I have a brand new degreeing wheel, but I don't really have the know how to use it. I watched the tricked out video like ten times and did it like they said, but it wasn't working out for me. I guess it won't hurt to try it again, but if anyone has any suggestions then bring them on.

 

[jdub]

It's not so much setting the cams to "zero" like an initial degree will, but what you did on the dyno with the adjustable cam gears. (You should BTW find your cams starting zero by degreeing them) Like IJ said, you took a lot of overlap out, raising your cc pressures as a result...if you do that, you need to back off timing/boost. Even if you run lean and your not in boost, it can cause problems with the cams set like that.

The quench area on these motors is not the best to begin with...the head is a Pent-Roof design that gives you relatively small chamber volume and surface area to volume ratio. This helps keep cc temps down, but is countered by the dish shape of the pistons giving you less quench area to start with. A thicker MHG makes it worse in this respect. If you think you need less CR than a 2mm MHG will give you, custom pistons or a 2J head are the options IMO.

 

[suprahero]

Would the stock 1jz cams be better for me? I don't have them any more since I gave them to BigZavz, but I'm just wondering if that will help with the overlap. I really like my crower cams, but I don't want to blow anything up again. Maybe the 2mm will get my cr to where I need it. Only time and some mathematics will tell. Thanks.

 

[jdub]

It's not the cams per say, it's this:

The cam are set as follows. Exhaust +8 degrees and the intake is -4degrees.

This is a lot. You need to back off those settings and increase your overlap.

Jay - one other thing you might want to do if you have access to a 2J head is measure the volume and compare to your 1J.

 

[p5150]

The quench on a 2jz ge vs gte is also determined by the head that is on the engine. The GTE head does not have a recessed combustion chamber but the GE does. With the GE block I think you will end up with a deck height near 0 or slightly over.

The only thing about using an uber thick MHG to lower compression is the effect on quench area...too thick a MHG decreases quench area and you increase the chance of detonation.

It would suck to blow the motor again.

I wouldn't go over a 2mm MHG though for the reason stated.

Well, you dont really know the quench area until you measure the deck height and compare it with the head, so dont you think its kind of premature to say that a 2mm head gasket is too thick?

Does anybody have a pic of a 1jz combustion chamber?

 

[jdub]

Like I said, the quench area on these motors is not that good to begin with due to the head chamber design combined with dish pistons. And I know for a fact increasing MHG thickness is going to reduce quench. Personally, I would want to minimize the effect to the max possible.

 

[p5150]

Like I said, the quench area on these motors is not that good to begin with due to the head chamber design combined with dish pistons. And I know for a fact increasing MHG thickness is going to reduce quench. Personally, I would want to minimize the effect to the max possible.

If you look at the GTE head and the GE heads the combustion chamber is actually recessed on the GE head to give a bit more quench area for the pistons on the GE block and thinner head gasket. So that is why I was wondering if somebody has a pic of the 1j head. My bet is that it looks like a 2jzgte head, without a recession.

If the 1j head does not have a recessed squish band like the 2jzGE head, then you would want a thicker head gasket to compensate for your loss of quench.....

The only way to know is if its measured....

 

[jdub]

The recessed band (I assume along the edge of the cumbustion chamber) is there to more closely match the outside edge of the piston. Increase the distance between the piston edge and the recessed edge on the head, and you reduce quench. That is exactly what a thicker MHG will do...all the measurements will tell you is how much you reduced the quench.

I do have a question...Jay's using a 2JZ-GE block and pistons correct? Isn't the CR on the GE pistions higher than the GTE like the one he blew?

 

[suprahero]

Yes, I think they are.

 

[jdub]

Why do you want to raise CR by using GE pistons?
With the boost you're running, do you really want to do that?

 

[suprahero]

I don't have any gte pistons. I'm using a ge block with stock ge pistons for now so I can get it running. I plan on building the gte block that I just took out of it with some new cp pistons when I get some money. If I had some stock gte pistons, I would use them. Hopefully I can get the cr's to run at a safe level with a thicker hg. I'm trying to remain positive, but it's sounding more and more like a problem is awaiting me.

 

[pbasil1]

Sounds scary to me Jay... Im now strongly reconsidering rebuilding my 1J bottom end as this problem was unforeseen when i was told to just buy GE block. To me running a massive HG seems unsafe and could cause problems down the road.... I think ill sit back and see where you go with this, and what has to be done before i make the final move on my rebuild.... I have everything i need for the rebuild except for the block (if i go 1.5jz), gaskets,and seals.

 

[p5150]

The recessed band (I assume along the edge of the cumbustion chamber) is there to more closely match the outside edge of the piston.

Yes, it is there on the GE head because the piston goes a bit closer to the head on the GE block.

Increase the distance between the piston edge and the recessed edge on the head, and you reduce quench. That is exactly what a thicker MHG will do...all the measurements will tell you is how much you reduced the quench.

The measurements will tell him how much quench he will have, not just how much he has reduced it.

Once again, we are back to square one; it simply needs to be measured before being assembled. Im confident that an acceptable quench height can be found with an appropriately sized head gasket selected to produce the correct c/r for his power goals.

There are already a couple of guys making tons of power with their headgasket-adjusted motors. Is it the ideal setup? No. Ideally I would want a 2jzgte balanced and blueprinted to drop in - but I have to look at the costs and benefits.

No, it wont be perfect, but for what Jay's goals are I think it will work out just fine and he will be more than happy with the results.

I do have a question...Jay's using a 2JZ-GE block and pistons correct? Isn't the CR on the GE pistions higher than the GTE like the one he blew?

But saying the above isnt really correct, I believe that the cause of Jay's detonation was the fact that he used a stock 1jz head gasket and it left the CR too high... The GE and GTE pistons really arent that much different which is why im still confident about using a head gasket to correct this.

Even if he had to go with a 2mm head gasket, with a deck height of .006 (that was mine but his may be a bit different) that will put him at .071" or so on the squish assuming that the 1j head is flat....

 

[p5150]

Jay, all we need to know is the deck height of your pistons and the CC volume of your head. Then we can figure out your quench height and you can figure out if you want to use it.

 

[p5150]

Why do you want to raise CR by using GE pistons?
With the boost you're running, do you really want to do that?

How is this any different than the guys running NAT GE engines? Its still a headgasket adjusted CR with less than ideal squish.....

http://www.supraforums.com/forum/forumdisplay.php?f=16 some guys in this thread are pumping out over 700 HP with their NAT setup!

 

[IJ.]

I "believe" the failure was caused by the Cam settings that had been adjusted for the 1jz on the dyno raising the dynamic compression after squeezing the extra cylinder volume into the smaller 1j CC's.

As for using a thicker HG to adjust comp ratio's while it's NOT ideal it works fine I did it for a year on a 7M with no side effects.
(what you lose to inefficient burn you more than make up in extra boost overhead)

 

[suprahero]

When the block gets here, I will get you the deck height. I'm ready to start making some definitive decisions on this build. The weather is way too pretty to have my car sitting on jack stands. I'm about ready to just drop a 22R in there and be done with it...........:biglaugh:

Thanks again for all of your help.............Lord knows I need it.

 

[jdub]

I "believe" the failure was caused by the Cam settings that had been adjusted for the 1jz on the dyno raising the dynamic compression after squeezing the extra cylinder volume into the smaller 1j CC's.

I too "think" the cam gear settings was the cause, for the same reason.

I'm not saying don't use a thicker MHG...I'm saying if you go over 2mm thick, you are having a significant effect on quench/squish. About 40 thou is about optium iirc.

If the CC chamber on the 1J head is smaller than a 2J (I have NFI), the use of GE pistons will increase CR (above what you would see on a 2J NA-T). A thicker HG will help, but could just as easily put the CR at where the motor that blew was or higher if you use a 2mm HG...it depends on what total CC volume there is.

P5150 - we are saying the same thing. The difference is I would still measure/compare the CC head volumes on the 1J vs a 2J to see what you have vs what was designed. Especially using these pistons...the combination of all of the above (with a bigger reduction in quench) is what I'm concerned about.