# Lowering Compression.....



## OriginalGinger (Apr 19, 2011)

So I have an 87 NA 300zx and bought the turbo manifold and turbo off of an 88. I have the engine taken apart to where its just the block/tranny in the engine bay with the crank and pistons still in it. Is there a way to lower my compression from I think its 9:1 to where the turbo can safely function without detonation? I noticed the bottom of the heads right above where the pistons come up to isnt as big as the head of the pistons and was wondering if boring that out would help at all.


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## Shadao (Aug 14, 2007)

the only way you can lower the compression 'safely' is to get the cams out of a turbo engine... you should have just bought a complete turbo engine and swap it in... much easier less of a hassle, takes less time and costs about the same...

boring parts out can cause serious defects, you can cause walls to become to thin and things like water and oil galleries can rupture...

how much did you pay for your current turbo set-up... i hope it was very little


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## AZ-ZBum (Nov 21, 2004)

OriginalGinger said:


> So I have an 87 NA 300zx and bought the turbo manifold and turbo off of an 88.


The T25 is a dinky turbo and I don't know why people would want to use it. Should have gone for the 84-87's T3.


OriginalGinger said:


> I have the engine taken apart to where its just the block/tranny in the engine bay with the crank and pistons still in it.


Why? Was there something wrong with your motor?


OriginalGinger said:


> Is there a way to lower my compression from I think its 9:1 to where the turbo can safely function without detonation?


There are so many people running big turbos on the NA's 9:1 compression motors it's not even funny. You don't need to lower the compression.


OriginalGinger said:


> I noticed the bottom of the heads right above where the pistons come up to isnt as big as the head of the pistons and was wondering if boring that out would help at all.


NO! Don't do that. The heads were designed that way for a reason.



Shadao said:


> the only way you can lower the compression 'safely' is to get the cams out of a turbo engine.


WOW! Just... WOW! So much is wrong with this statement.
1. There is no difference between turbo and NA cams.
2. Cams don't affect compression at all.


Shadao said:


> you should have just bought a complete turbo engine and swap it in.


No. That would have been just as much of a waste as what he's already done.


Shadao said:


> much easier less of a hassle, takes less time and costs about the same.


You can get whole VG30 motors for less than the cost of a full gasket kit if you look hard enough.


Shadao said:


> boring parts out can cause serious defects, you can cause walls to become to thin and things like water and oil galleries can rupture...


True. But he was talking about boring out the heads. Which is stupid in itself.


Shadao said:


> how much did you pay for your current turbo set-up... i hope it was very little


Doesn't matter. He's already wasted a lot of time on stuff he didn't need to do.

Both of you guys should read this:
TURBO TURBO TURBO

OriginalGinger: Unless your motor had a blown head gasket, you've just wasted a lot of time on doing something you didn't need to do. You don't need to lower compression and you don't want to try to reshape the heads. If you really want to, you can buy thicker head gaskets to lower compression.

Shadao: I don't know where you got your information, but I suggest you forget all you thought you knew before giving advice on motors again.


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## jdg (Aug 27, 2009)

AZ-ZBum said:


> Shadao: I don't know where you got your information, but I suggest you forget all you thought you knew before giving advice on motors again.


+1
Still Winning!
(that makes 2 for the day...on a roll)


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## OriginalGinger (Apr 19, 2011)

I havnt shaved down anythign in the head yet or bought new pistons or anything i just bought the car from a junkyard and drove it home and took it apart to make sure piston walls/pistons were alright which they are all fine. I though without lowering the compression it would cause engine detonation or something. I bought the turbo manifold/turbo off an 88 for $250. So since the engine is already this far apart should i just keep the stock pistons and just replace the rings? My goal is to safly run about 15 psi intercooled.


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## AZ-ZBum (Nov 21, 2004)

The T25 won't flow 15psi on the VG30 without serious heat issues. Don't even try it.

I wouldn't take the bottom end apart at all unless there is scoring on the cylinder walls. But you've already got it that far apart, so I guess a few more hours of labor aren't going to kill you.


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## OriginalGinger (Apr 19, 2011)

But new piston rings in and stock compression....would that mean that I would just need more fuel to stop detonation or what? I dont want to spend the money put it back together and have it blow up. I know I have to get aftermarket injectors... I was thinking 550cc or so. Anyone know how much boost that would be good for and if the stock fuel system is a high or low impedence system???


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## AZ-ZBum (Nov 21, 2004)

You haven't read the link I posted, have you? You should go do that.


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## OriginalGinger (Apr 19, 2011)

Whenever you changed the timing in your 9:1 turbo motor did you have the variable cam gears or did you just turn the distributor?


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## AZ-ZBum (Nov 21, 2004)

You change the timing via the distributor.


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