Ditched the rebuilt P90 idea. How about this one?

[pjo046]

Well, found out that cam was wrong for a turbo application, and besides, if I am aiming at maximum 400hp, the stock head will do fine.

 

I have been thinking about installing a 1mm HKS headgasket though. This would raise the compression from 7.38:1 to 7.52:1. I was thinking this might help on the low end power and off boost characteristics of the engine? Will this be noticeable? Will it make much of a difference as to how much boost I can make? I know it will be less bost, more off boost power. Do you think it would be a good trade of for a street car?

 

Also, if I install a 1mm headgasket, will this cause a retardation of the timing, as the timing chain then would be a bit slacker? Noticeable? Bad?

[getZ]

I have a similar situation, a 1mm headgasket, but with custom forged pistons that were supposed to give me a final compression of 8.0:1.

 

The timing chain I put in was brand new and seemed a little tight. I'll let you know how it goes. I'm almost ready to break my new motor in. Hopefully this weekend. I had the same concerns about the head gasket thickness affecting the timing. I think spec for shaving a head was something like .2mm and a stock gasket compressed was at 1.2mm so you should be just on the edge of what my book specs (How to Rebuild Nissans).

 

Off the top of my head a full point of compression is worth somthing like 10% more horsepower so you are looking at something like 1.5% increase in power. You will probably see greater horsepower changes with a change in the weather.

[Guest znow white]

WOuldnt adding a thicker head gasket lower compression..? or am I off here cause thats what i have been reading for the longest time. for example a 2mm head gasket would increase the deck height but all of that new space would lower the compression? thats why the use it right? to run more boost..

[pjo046]

Yep, you are right! By installing a thicker headgasket you decrease the compression, thus enable the use of more boost without detonation.

[getZ]

A 2mm head gasket would increase the head volume and lower the final compression ratio. A simpler way of thinking of this would be to imagine the volume of the cylinder at the bottom of the stroke divided by the cylinder at the top of the stroke. Increasing the gasket thickness changes the volume of both, but because it is a much greater percentage of the volume of the cylinder at the top of the stroke the compression ratio goes down.

 

Not sure if that was any easier to understand or not.

 

Anyhow, the lower compression allows you to get away with more boost, which is why a lot of people run it. Apparently this change does not adversly change the valve train geometry. I only say that because I have heard of a lot of people have done it with no problems. It adds .8mm to the original deck height, like making the head thicker instead of shaving it. I know there are shims for the cam tower, but I haven't heard of anybody shaving down the cam tower after adding a thicker head gasket. That's just my 2 cents.

[jeffp]

 

So my question to you is what is the advantage of lower static compression and higher boost aside from the boost gauge reading a higher boost level?

 

The lower compression will enable you to run higher boost, but off boost the engine will have less power with the lower compression.

Correct me if I am wrong, but dont you want increased power off boost, lower boost pressure to get to the same hp? Seems to me the L engine ( sepecially the zxt engine ) is doggy to be kind just off idle up to about 2K then when it starts building boost it then get some power.

Have you been talking to steve? I still cant understand WHY running more boost is better then less boost. What is it in your mind that thinks higher boost is better, the higher the better mentality?

The CORRECT way to build the turbo engine is to increase the static compression to 8.5:1-9.0:1 at the extreme with the quality of pump fuel now days. Thus increasing off boost power off the line. Decreasing the amount of boost to get to the same power level as compared to the lower compression engine. This will in effect increase the efficency of the turbo as it will not be pumping, or compressing as much air, thereby decreasing the heat produced by compressing the air, and keep the boost levels in the most efficient part of the turbo boost map. The higher compression level will also enable you to run a smaller turbo to get the same power, and thus will enable you to acheive a better spool of the turbo due to the smaller size. Make since?

[spork]

Generally speaking, you'll get more hp by keeping the static compression low and running more boost than you will by upping the compression and running less boost. Boost will ake more Hp than the increase in static compression will get you. That said, a little increase in compression isn't a bad idea as the stock levels are awfully low. I prefer someting around the 8:1 range. It gives you plenty of "pep" on the street and off boost response as well as allowing you to build bigger boost levels to get the big power. I guess it all depends on the exact use of the car. (and what kind of fuel you're running)

 

As far as Pjo046, hes doing the right thing about wanting to raise the compression, just don't go too high, or you'll be resorting to high octane fuels not generally found at the pump

[pjo046]

Spork(James) have you received the e-mails I sent you? Haven't heard anything from you regarding that. If you could set me up with a ported head, then you could perhaps also alter it so that the compression would be raised to 8.0:1 with a stock headgasket.

 

Isn't it true that it would be better to have a stock headgasket than a 1mm steel unit? (IF detonation, god forbid, should occur?) Because then it would be more likely that the gasket is the thing getting blown, not my stock pistons. Right? Also, people have more trouble getting the metal gaskets to seal properly than the stock gasket.

 

If you could get back to me today regarding the questions etc in my e-mails, that would be great, as I need to know wether or not I shall tell a Z friend of mine that he can buy my P90 head if he wants to.

[pjo046]

Oh, and James, you do realise that here in Norway we have 98 octane at the pumps? Hehe. 8) That lets me run higher compression without fear of detonation. What compression would you recommend when my car is basicly going to be a streetcar, and I want the best possible respons of the line etc withoug having to rev the car to 3500 or more on launches.

[JMortensen]

Are you sure you have THE SAME 98 octane as we would have here right at the pump? There are 2 scales for rating octane, RON and MON. US uses the formula RON + MON / 2 = octane rating. Europe uses RON only IIRC. The same car that says "requires 92 octane" in the US says "requires 98 octane" (or something like that) in EU.

 

It wouldn't surprise me if you had better gas than us here especially those of us who suffer from oxygenated fuels at the pump, but I wouldn't go cranking up the boost because of the number on the pump in EU, because it doesn't translate to our number here.

 

Here's a link:

http://www.ozebook.com/compendium/suzi/octane.pdf

 

And the important bit:

Nowadays, in Europe, the results on the pump are the R(esearch) O(ctane) N(umber) and everyone thinks they've suddenly got really great fuel. In reality, the European fuel is the same old stuff, or worse, that we've always been used to.

[pjo046]

Hmmm.. Okay. Never thought of that. But, looking at that link you gave me, if I use what is called 98 octane here in Norway, that would be the same as 93.5 octane in the US. So that is a bit higher then what you guys normally have available at the pumps. Or? Because Norway, is one of very few countries in Europe that has 98 octane. Most other countries only have 95 octane and downwards. At gas stations in Norway, you find 98 and 95 octane unleaded, but in for example Germany, Holland, Denmark etc you find 95 and 92 octane at the pumps.

 

So, isn't 93.5 octane a bit higher than what you have available most places in the states?

[JMortensen]

Yes it is. Most of the states I've been to have 92, CA has 91, and I think a lot of the East coast has 93. Higher elevations tend to have less octane just because you don't need it there. The oxygenation of the fuel to reduce emissions cuts power too, and I imagine it would reduce the amount of boost you could run. So CA is about the worst with 91 and oxygenated gas.

[Tony D]

Here in Venezuela the Sin Plomb gas is 77 octane and costs about 20 cents per gallon......

 

There are lost of Impalas, Torinos, and Dodge Darts here...

 

But I digress. There is the argument of "low compression" versus "high compression"...

 

Most people use the argument that lower compression allows you to "run more boost" to make horsepower. This is true.

 

But to what extremes are we going to take the argument. An 8 or 8.5:1 compression engine will easily take 20psi of boost. And what are we making by that point? 350, 400HP? E'motive in 1983 with stone age electronics made 580HP at 7500rpm, on 20.6 pounds of boost, using racing gas, and a compression ratio ABOVE the stock ZXT of the day (considerably more if you talk with the people involved).

 

So the question becomes, in my mind at least, "How much money do you want to spend?" If you spend the money on head work and a cam, 580HP is waiting at 20-psi, but ASSUREDLY NOT at 7.4:1 compression ratio! You can get decent performance from a stock compression turbo, but for the money the drivability and spooling capabilities of a higher compression engine seem to win out when you weigh it. There really should be no trade-off in the octane scare between 7.4 and 8.5. I would personally waste my time with anything below 8.0!

 

The naysayers about "higher boost levels" might want to do a reality check and actually ask "how much boost do I terminally want to run?" For someoen going with 45psi, then yeah, I might say 7's would be in order. For someone with an inefficient intercooler? Maybe no more than 8:1. But for someone pushing a hybrid turbo and a decent intercooler on even 90 octane, I would shoot for the stock N/A drivability that 8.5:1 offers off-boost. Nothing is more discouraging to hear than some idiot with a well-tuned stocker say "I got him out of the hole till the boost come on!" Lets' not let those N.A. guys ever have the ability to say that!

 

In a roundabout way what I am trying to say isn't really about boost. It's about total mass flow through the engine. The power is, and always will be, in the HEAD of the L-Engine. A properly ported L-Head running 17# of boost will make more power than an unported engine running 20+. I have an acquaintance that did a before and after dyno test (headwork only). After retuning the TEC2 for the new flowing configuration, the SAME engine using the SAME turbo, and basically the SAME everything save for the portwork and runners in the intake manifold made more HP at 17# than he did at 21# before! (BTW, this was on an engine with 8:5:1 Slugs) So the "More Boost means more power" line of thinking is a bit corrupted. My training has (since I work in Compressed Air and Gasses for a living) always been that "pressure is the resistance to flow! The less resistance you have to flow, the more efficiently you transport air... So in some cases, LESS boost means MORE power! On the test vehicle, it assuredly did!

[randy 77zt]

the reason a l28 wont run like a 4 valve toyota supra motor-its the head.some guys run a n42 head on turbo engine with stock pistons.or get rid of dished pistons.if the hybrid z guys could order about 5 or 10 thousand cylinder heads maybe edelbrock or afr would make us a dohc head.

[pjo046]

Tony D, I really agree with what you're saying.

I am going to buy a P90 head, and have Spork port and polish it for me, and install a upgraded turbo-cam. But I also want to raise my compression, and much more than what I get by just installing a 1mm gasket. I see from my Lengine calculator that by swapping to flat top pistons instead of the dished turbo-pistons that come stock, I get a compression of 8.52:1. The only problem with this is that forged turbo pistons are expensive, and that I don't know if I am able to do the swap myself. What I was thinking doing instead is let Spork shave enough of the P90 to get me to a compression of about 8.5:1. What do you think about this? Doable? Or would it perhaps be better to go with a E88 head and a 1mm gasket? That would give me a compression of 8.46:1. But this head isn't as good as the P90. Would it be possible to make it as good by heavy porting, installing a aftermarket turbocam and perhaps bigger SS valves? What do you all say? All input on this appreciated.

 

And furthermore, if going with a compression around 8.5:1, how much boost will I be able to use when I have a good intercooler, 3" exhaust, am getting a custom intake manifold, ported exhaust manifold, and have a T3/T04B hybrid?

I have TEC3 engine management, so the timing etc can be tuned optimally.

You see, I'd rather have a engine that is really responsive and have a broad powerband, than having a low compression slug that needs high RPM's and much lag to wake up. This is going to be a streetcar, not a quartermile-runner. Can I still achieve my goal of 350-400RWHP? Will the turbo I have be to big(Since I will be using lower boost with this higher compression?)

Remember, I have 93.5 octane available at the pumps.