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Discussion Starter #1
In the process of my turbo build, I was planning on using the Cosworth 1.2mm head gasket to reduce the compression ratio, mainly because Radium tested it on their turbo kit and it "safely allowed another ~50whp to be had on pump gas fuel"

Untill recently I always told it would be good to add. I've now heard it might be worse due to the affects on quench on the motor, though I still cannot seem to get a definitive answer... Are the negative affects on "quench" enough to outweigh the benefit to reduction in CR on the 2ZZ?
 

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This is an old trick. It can and has been done on many Toyota engines. Look at what the 3S-GTE guys have been up to (try the MR2OC ). There are reasons not to use a thicker gasket including surface compliance, increased clamping force requirements etc..

PM me if you would like some details on best practices for this type of modification. BTW I can point you to some great engine builders up in Asheville NC who have LONG resumes and do high quality work.
 

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To lower it a *little* its okay. But overall not the right way to do it (which is by piston/rod choice).
 

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Discussion Starter #4
I guess the question is at what point does it become a bad thing to have? I would think for an extra 50whp to be had, going with a 25whp increase and leaving the other half just to be easier on the motor would end up outweighing the negatives.

Sort of a pros vs cons type balance;
Pros:
-Lower compression aka easier on the motor resulting in less chance of detonation and other internal component failure (safer motor)
-Allows more horsepower to be had (up to 50whp depending on how safe you want it to be)

Cons:
-Negative affect on quench (though just how negative I have yet to get a solid answer on)
-Higher weakness at head gasket

seeing as how a little thicker wouldn't do all that much to reduce the cr, I would think you would want something on the higher end
 

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Discussion Starter #6
That's what I ended up buying, but now I don't know if I should even install it now :confused:
Most of the people I've talked to suggest it, but when members like Phil advise otherwise, it leaves me with no idea what to think.

When I asked him to explain, he only answered with questions that didn't really answer to the actual affects of a thicker gasket. Pretty much raised question of why one would want to lower the compression in the first place? Now that seems to go against everything I've known since people even doing a full build put lower compression pistons in. Why would everybody be lowering the compression ratio (using pistons, gaskets, ect) if it's a bad thing?

Google is going to give you just as many mixed answers, and there doesn't seem to be any interest in discussion over it on here which is quite suprising considering the number of people running FI and the high CR of the 2ZZ.
 

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That's what I ended up buying, but now I don't know if I should even install it now :confused:
Most of the people I've talked to suggest it, but when members like Phil advise otherwise, it leaves me with no idea what to think.

When I asked him to explain, he only answered with questions that didn't really answer to the actual affects of a thicker gasket. Pretty much raised question of why one would want to lower the compression in the first place? Now that seems to go against everything I've known since people even doing a full build put lower compression pistons in. Why would everybody be lowering the compression ratio (using pistons, gaskets, ect) if it's a bad thing?

Google is going to give you just as many mixed answers, and there doesn't seem to be any interest in discussion over it on here which is quite suprising considering the number of people running FI and the high CR of the 2ZZ.
:D

It's one of those, "if you have to ask" type of deals. I think the thread you and I started that dialogue was evidence of what happens when a fella jumps into a project making big changes without a thought-out plan... and a fella sorta has to understand the subject matter to develop a plan that makes sense. Just being able to wield a wrench successfully without understanding the build plan is usually a recipe for things like plumbing coolant lines into the PCV or similar ;) Fortunately for the fella mentioned, he has a good attitude about it and is eager to learn:up:

Without teaching a class on engines, a few points.

1) As else equal, lowering the compression isn't "safer". Running the compression/boost combination that your tune is designed for is the *safest* and most powerful route (assuming tune and original configuration is good/proven)

2) All else equal, lowering the compression will reduce power

3) A non-intercooled MP62 such as that found on Katana, BWR, and BOE REV250 is already creating a lot of intake temperature (over 250F). This IS SAFE since the tune is designed for it. If you lower the compression, you will have to increase the boost to try and recover the power lost from less compression. This is not very productive on the aforementioned setups because the blower is quickly loosing efficiency at the stock Katana/BWR/REV250 blower RPMs, let alone spinning it faster yet. Losing efficiency essentially means that the blower is starting to create more heat relative to the amount of air it moves.

4) Hotter air is less dense, which means you cannot properly mix as much fuel with it. Less properly mixed fuel makes a smaller boom (burn actually), which means it makes less power.

5) Hotter hair is not necessarily more dangerous as long as the tune is designed for it (within reason of course).

6) Since spinning the M62 tighter isn't super productive unless you have copious amounts of intercooling to make up for the efficiency issues, your best bet is to run a high compression/low boost setup (read, stock compression). With good intercooling, you can get away with lowering compression a bit and stepping up the boost, but again the M62 was never designed for high boost (high pressure ratios), so you'll be fighting an uphill battle with that blower...

7) Before heading down a build path which deviates from what was provided by the kit supplier (lotus or otherwise), you need to make sure you can tune the thing. The 2ZZ (or any car with variable camshafts) is not the worlds easiest car to tune, so tread smartly...


Hope that helps,

Phil
 

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Discussion Starter #8
and a fella sorta has to understand the subject matter to develop a plan that makes sense.
Which is what I've been working on since day 1 :D Definitely eager to learn, but I would much rather trust a discussion on LT, especially since half the info on the internet tends to be wrong.

3) A non-intercooled MP62 such as that found on Katana, BWR, and BOE REV250 is already creating a lot of intake temperature (over 250F). This IS SAFE since the tune is designed for it. If you lower the compression, you will have to increase the boost to try and recover the power lost from less compression. This is not very productive on the aforementioned setups because the blower is quickly loosing efficiency at the stock Katana/BWR/REV250 blower RPMs, let alone spinning it faster yet. Losing efficiency essentially means that the blower is starting to create more heat relative to the amount of air it moves.
6) Since spinning the M62 tighter isn't super productive unless you have copious amounts of intercooling to make up for the efficiency issues, your best bet is to run a high compression/low boost setup (read, stock compression). With good intercooling, you can get away with lowering compression a bit and stepping up the boost, but again the M62 was never designed for high boost (high pressure ratios), so you'll be fighting an uphill battle with that blower...
Thanks, Phil! A great explanation of why it wouldn't be the best thing on the supercharger :clap:. But how does that balance of efficiency compare to turning up the boost on a turbocharger?
 

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Since I have not taken this engine apart yet, I don't know how the valve timing is adjusted. With the thicker head gasket, is there a way to compensate for the change in timing? That would be your biggest loss if it is not.
 

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Since I have not taken this engine apart yet, I don't know how the valve timing is adjusted. With the thicker head gasket, is there a way to compensate for the change in timing? That would be your biggest loss if it is not.
Centerline on the exhaust cam would change and is one of the reasons lowering static CR with a thick headgasket is not the "right" way to do it. The intake centerline is also changed however the car has dynamic (electronic) adjustability on the intake side so a good tuner can tune around it.

Wek in general the reason you are not getting a straight answer about the lowering of compression being good or bad is because it is application dependent. I agree with everything Phil said, he is spot on. With any build you need to big picture and the interaction between all the parts and what exactly you are trying to accomplish. We would really need to know what you are trying to accomplish. What is the car being built for , power goals, budget etc.
 

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There are other ways to lower the compression which are better choices than a thicker head gasket.
1. Lower compression pistons (One of the better choices)
2. Shorter rods (perhaps not available)
3. Increasing the volume of the combustion chamber (The choice I made on a different performance build)
As Phil pointed out, with stock compression on the 2zz engine, you are already slightly beyond the sweet spot of the MP62 supercharger. Going with a smaller pulley only makes matters tougher.
A TVS1320 is a better choice for bigger power at lower compression. You are closer to it's sweet spot with higher boost. This supercharger will produce more boost at a lower intake air temperature (IAT) than the MP62. The lower your IAT, the easier the tuning is (less compensation required in the tune to deal with high IAT)
 

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Discussion Starter #12
We would really need to know what you are trying to accomplish. What is the car being built for, power goals, budget etc.
I am actually planning on starting out on a stock motor with enough boost to get a nice kick, but low enough to keep the chances of blowing the stock motor very low. I currently daily drive mine, so I need something more toward the reliable end.
(Next summer after I get a chance to learn more about building a motor and formulate a good build plan, I plan on building the motor up to stop around 350-400hp. That way I will have time to try out the basic turbo setup, and learn everything I can in the meantime. It would be mainly a street car, with 3-5 track events a year.)

But until then, since I will be on a stock motor, I would like to keep it as safe as I can, while getting the most out of it. And from what I'd gathered about turbo setups so far, I had heard lowering the CR on the 2ZZ was a good idea to not only make things "safer" but allow more hp to be had on pump gas. Sounded like the smart thing to do in the meantime until I can get a good build plan in place. Now I'm not so sure... :shrug:
 

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If you do the Head Gasket then get some ARP studs for it. That will overcome any difficulties with clamping force as they're a good percentage higher than stock. I wouldn't go with custom pistons and custom length rods as the RS ratio on that engine is pretty good from the factory.

Personally I'd drop the CR to 10.5 using pistons. By keeping the quench you keep the burn speed up and by picking a middle of the road compression ratio you still get decent scavage. Don't forget the high lift cam has a lot of overlap so dropping the CR will give you signifiant losses. I've seen hondas lose 15whp NA because of this, yet with a small overlap cam, a 2 number increase in CR only nets 5whp.

Like everything in engines there is a balancing act with tradeoffs.
 

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Discussion Starter #14
I wouldn't go with custom pistons ...
Personally I'd drop the CR to 10.5 using pistons.
:confused: wait what??

Like everything in engines there is a balancing act with tradeoffs.
Which boils down to the real question; is the balance of adding JUST the gasket in a turbo 2ZZ enough of a tradeoff to prove beneficial overall (at least until motor can be built up correctly)
 

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Discussion Starter #15
Bump. Is this something, given a choice between gasket or no gasket only, it would be worth installing on a turbo application (stock motor)?
 

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My opinion is no, its not worth it.

Given the labor involved with putting a new headgasket in the car you might as well do it the right way and put aftermarket lower compression pistons in it.

Remember even with a larger head gasket you are still running the stock pistons are which are physically weak items. The lowering of compression just helps keep the knock threshold back but does not make the pistons any stronger.

If I were in your shoes I would get everything together on a stock engine and spend all the time money and effort you were going to put into a head gasket swap into a good tune. If you really want/need more power later on then pull the motor build it and then turn up the wick.
 

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What he said ^^

Also, since you have to remove the head to install the gasket, you can upgrade it with better valves/springs.
 

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I thought the problem with the 2ZZ engine was with the valve stems and not the valve springs. Replace the valves too! Springs are needed for higher RPMs too.
 

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Mostly agreed with the others.

The way I see it, you're doing a large amount of labor for a head gasket install. It's almost the same job (plus a couple of hours max) to do a piston install. It costs slightly more ($569 pistons + $50 OEM gasket) vs $179 for thick gasket but that is pretty minimal.

One other consideration is piston material. If you have a questionable tune, a tank of bad fuel, overboost, engine overheat etc and you do get detonation then Mahle 10.5:1 pistons will take a heck of a lot more of it before failure compared to fragile stock cast pistons with a thicker head gasket and similar compression.
 
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