flat tops, p90, and boost

[twogees]

I have been searching for quite some time. Found a few things that are similar , but nothing that pertains to my particular set-up. I have a basic idea but trying to figure out what i can get away with as far as comp ratios go.

First, a run down of my setup pertaining to this ?- n42 block w/flattops , p90a head, turbo, front mount, old ms1 for fuel only, msd btm,and i have a wideband that will be installed when running again . That being said, i have a certain level of control so that leaves me with a lil wiggle room for adjustments at the tuner if im correct. Why it was setup this way, i dont know( i ask myself that about half the stuff on this car) but im stuck with it now. So it is what it is. Just to give you an idea of power range, I saw past dyno sheets from it, and he car was making about 240 hp at one point. Whether it was making that when i got it i dont know. I'd like to be in that ballpark again if possible maybe 240-275 range,(haha) likely .

 

I had a metal head gasket on there. It is over 2mm, maybe 2.5 new not sure. It is reading lil over 2.25 mm now. Which was used to bring the comp down obviously.( i didn't build this). Well long story short(lol) i wont bore you with details, but the gasket i believe blew from an over boost error. Never mixed coolant /oil, but never ran quite the same after that either. Did a compressed air test in each cyl, and 4-5 both had air leaking to the each other when other cyl's didn't . since the cyl were next to each other i figured blown gasket. got the gasket off , and tell me if im missing some thing, but the gasket bore is 90mm and the block is 86mm. So that cant be right. Second the gasket doesn't seem to be matched to the block, it has passages the p90a has that the block doesn't. i feel they should be blocked at the head not the other way around..no? had the head taken to the machine shop said it was really flat so ok good there. not sure how much exactly the head has been cut since new, gonna try to get a # on the thickness of the head that i will post later . i need a head gasket either way.

 

I'm tapped for cash an forking over 300 or so just for another 2+mm gasket is hard to swallow right now, among the other things i need to get this car moving. I mean if i have to, i eventually will. Changing to dished pistons which is ideal i know, but is outta the question at this moment. So my ? is , with keeping my comp down as much as i can , can one of you gurus tell me whats the minimum gasket i can run. id like to buy a reg gasket,( for $$ reasons and to keep it my weak link) like a lot of you have but not sure if my set-up can handle it. My car's been sitting for a long time, and i just want to hear it run again. I've been racking my brain trying not to ask, but i need some help. If i missed anything, let me know and i will post back up. thanks a lot. I wanna hear this thing scream again!! -Ben

Edited September 17, 2010 by twogees

[sticky280zx]

i will say 12 second SU norm used to double stack regular headgaskets...just a thought.

 

 

I'm tapped for cash an forking over 300 or so just for another 2+mm gasket is hard to swallow right now, among the other things i need to get this car moving.

Edited September 17, 2010 by sticky280zx

[twogees]

i will say 12 second SU norm used to double stack regular headgaskets...just a thought.

I dont know who that is, but I had thought of that. I was told it was a big no no. The way they seat on the surface. i dont know im not an expert by no means. So it can be done? maybe, but do want to find out the hard way..lol. you say he used to..is anyone donig that anymore?

[sticky280zx]

yep pretty sure, but he did alot of weird things that were "no no's" but do you know anyone with an l28 with a dual su setup running 12's lol prolly not, search his name and you will find some interesting stuff

[twogees]

im wondering if maybe the gasket didn't blow, considering it was a metal one. I know they break too, but if some thing else happened, maybe the weak link was the stock bolts and they gave from overboost and was loosing comp because of that instead. Might be a dumb ? but, is there a way to tell if the gasket really is blown or not?

[twogees]

Basically in a nut shell what i want to know is , with the items and set-up i have, can a good re-tune get this thing working properly(not a band aid fix) w/a felpro gasket, or will i have to stick with the thicker head gasket to keep detonation from knockin at my door. I know i can run an additive like aces if i had to but id rather be on pump gas alone. http://www.americancleanenergysystems.com/products_gasoline_catalyst.php alot of guys i know run this in their performance boats with high comp heads. so i know it works.

 

If so, im buying that gasket tomorrow so i can get this thing purrin'

[BRAAP]

i will say 12 second SU norm used to double stack regular headgaskets...just a thought.

 

 

Dave Rebello, (Rebello Racing), also uses the double gasket on some of their N/A Flatop piston N42/47 combos with great success.

[twogees]

Dave Rebello, (Rebello Racing), also uses the double gasket on some of their N/A Flatop piston N42/47 combos with great success.

 

I'm guessing thers no difference if he's n/a and im boosting? any trick if i use two, or just put the two on top of each other and torque like normal? sorry never used two head gaskets before.

Edited September 18, 2010 by twogees

[softopz]

This is very interesting . I know I have heard of people running 2 headgaskets but every car buddy I mention it to is like "no no" And since you cant find 2mm Metal Headgasket this could be a good option>

Braap or any of you guys know what brand of Headgasket's Norm used? Cause I know the OEM HG is much better than the FEL PRO

 

Hussein

[Tony D]

"I know I have heard of people running 2 headgaskets but every car buddy I mention it to is like "no no" "

 

My suggestion: For every one of those guys who says it, ASK THEM WHY THEY SAY NO.

Then, when they explain it, ask them why they are saying that.

 

Repeat this four more times to every answer they give you.

 

They can not use 'I knew a guy who' or 'because' in ANY response, that invalidates it.

 

If they can't stand up to the "Five Whys Test" they don't know WTF they are talking about, and should be disregarded on the issue.

 

MANY self-proclaimed 'experts' fail this test. That means they're not experts.

 

It's a good test to give yourself before posting a response to anything as well...

[twogees]

ok so ive been searching all day off and on and all i can find for the n42 other than metal gaskets are the felpro, beck arnley and the nippon. i was hoping to find ishino but by the looks of it i can only find it for the f54...seeing from thread to thread gaskets /suppliers come and go all the time, does anyone know where i can currently get one? .. if not which out of those 3 those would you recommend? i haven't read much good about any of them. Is there away to tell for sure if my metal gasket truly is blown ?

 

i was still wondering about putting the two gaskets together though. do it just like normal? Do i really need to double it up? Considering the mods i have, can i get it to run right with one gasket on the flat-top/p90 combo.. . i plan on getting it tuned on the dyno after its running. After reading alot of guys running much higher comp #'s boosted i feel 1 gasket might be sufficient. Please any help is appreciated. thanks-B

[Pyro]

have you seen these?

 

http://www.autozone.com/autozone/parts/1976-Nissan-Datsun-280Z/Head-Spacer-Shim-Gasket/_/N-int6pZ8zq8p?filterByKeyWord=head+gasket&fromString=search

 

head shims to make up for too many head resurface jobs. works with a stock head gasket. nissan head gasket should be 1.25mm and this shim is 0.50mm which will make 1.75mm (very close to 2mm and much cheaper).

 

The issue you will have with a thick head gasket is it will advance the cam, which increases cylinder pressure. An adjustable cam gear sprocket is the fix for a thick head gasket but is expensive. If you are using the stock gear setup then install it on the 1st position and hopefully the chain is old and stretched a little.

 

another fix is to run a bigger cam. a bigger cam "bleeds" off cylinder pressure due to a later closing intake valve.

 

Send your stock cam for a regrind. Deltacams can do if for $60. For a turbo setup, just regrind the intake lobes for more lift and duration. go to 260 degrees of duration and 0.420" lift on the intake lobes and add 0.160" lashpads to make up for the regrind (courtesy nissan, 3.00/each). This will help reduce detonation and make more power.

[2eighTZ4me]

"over boost error" - "never ran right since"......hmmmmm " never mixed water and oil".......happened to me once. It was FAR from a head gasket. You have done your diagnosis though, and a leakdown test shows 4 and 5 leaking air? I lost 3 sets of ring lands when those last words were uttered.....

[twogees]

yea ive read about the shims, but as it was mentioned, I took it that the small gain wasn't worth the risk of having that thing flapping around if (and when) the gasket blew again. the car was already running and tuned with the thicker gasket. it was previously running at 12lbs. seemed like it had no lower end torque . 1-2 sucked but then 3-4 pulled real nice and strong when in boost. it is stock cam gear. i was gonna replace the timing kit cause there seems to be some groves worn on the guide. and everywhere it says to just put a new kit in. i think im just gonna put a single gasket on and have it re tuned on the dyno and see what happens. im figuring the compression for the p90- std bore p79 flat tops to be 8.5 /8.8 -1 .which is not all that high for boost, just not ideal for our cars ... some know better? and im guess my best bet for a gasket now days is the felpro permatorque? since ishino doesn't seem to have one that i can find for the n42.

 

i can just drop the boost a notch maybe run it at 10 psi (or lower) depending on the out come of the tune. and be good for some mild driving. no racing or anything crazy just to have my car mobile and drivable again. Just to mention all this is temporary . i have a few upgrades set aside for the future, along with a new shell w tops im throwing this motorset in. eventually.

 

as far as the ringlands im being optimistic in thinking since it was two joining cyls that were leaking (according to my findings) and there is no scoring on the two cylinder walls it was the head gasket. looking at the gasket in between cyls 4-5 there seems to be a clean wash so to say of the carbon ring . unlike the other cyls that have a solid ring indicating a good seal.i dont know that just my 1st theory. i could be wrong. The thought as crossed my mind of another scenario, ok so the metal gaskets are strong, the ringlands apear to be ok from that i can see so whats the weak link? the head bolts? they are known to be weak. maybe they stretched and caused a leak that way? what if i just bought arp's, and torqued everything down again. maybe it would be ok then? wouldn't be that strange of a theory i dont think...what do you guys think?

[Pyro]

you need the head gasket that matches the block (n42). if you put a F54 head gasket on a n42 block then it will over heat.

 

what kind of efi system are you using?

 

what does your ignition timing curve look like?

[twogees]

yea I read that in a thread somewhere match the gasket to the block. i just ordered a complete gasket set today.

 

as for efi i have ms 1 v2.2 , injectors 440cc walbro pump.

 

the timing is just being controlled by msd6 btm the knob is between 2-3. the distributor is non turbo 280zx with vacuum advance locked according to the receipt . running off a magnetic pickup plugged to the msd. as far as timing curve, if your talking about in the Megasquirt its not in there. actually i wish i knew. i only have a bunch of old MS setting pages from the previous owner.I'm not even sure what values (fuel)the board is set to now. im guessing what ever the table opens up to when you open mega tune would be whats currently on the board? im not sure. ill have to wait to get it hooked back up to tell.

[Brad-ManQ45]

At the power range you are looking at, I believe that you are doing yourself a disservice in getting a thicker head gasket.

 

You would have 10.5:1 with the 44.6cc N42 head.

 

With the larger combustion chamber of the P90/P79 head (53.6cc), your compression will be considerably lower.

 

You will have at most 9:1 compression ratio with flat tops and the P90 head.

 

Even at 9.5:1 you should be ok.

 

There are plenty of people that have run this combo with good fueling and ignition maps and made over 300 hp.

 

You say you only want 240-275 - problem solved.

 

Lowering compression will compromise much needed off boost torque that the people who use flat tops instead of the dished Turbo pistons enjoy. You'll even get better gas mileage with the higher compression.

 

Buy an intercooler and piping to keep the intake charge cool and cap boost at 12-15 psi and you're gold.

 

Now if you were gonna run HIGH boost, that is another story, but that would be in the 20+ psi range...

Edited September 22, 2010 by Brad-ManQ45

[jc052685]

Who says the oem Nissan head gasket is "better" than the felpro? Why?

 

And what gaskets are being stacked? MLS or composite?

[twogees]

brad- yea i was just trying to keep it how it was set up (w/ lower compression) yea i know it lost some torque by having it low. maybe the car will feel better when i get it up and running w/ the bump in comp.. i do currently have a spearco front mount and piping still have my stupid stock down pipe though, but 3" exhaust back from there. i double checked the last megasquirt settings and the car was dynoed at it was(according to this) 15lbs, not what i stated earlier.

 

 

I seemed to have read that many places in other threads..I decided im not gonna stack em.. just gonna stick with one. and go with new arp studs instead . its gonna be a stock type gasket. i had a metal one on there.

[Pyro]

I have tuned a 8.8:1 cr L28 turbo engine and it could only take 17 degrees of total ignition timing at 8 psi of boost with 93 octane.

 

I would use the vacuum advance, as it help gas milage. boost will shut it down.

 

sounds like the distributor mechanical advance is locked (this is the typical setup for a retro fit turbo setup).

 

you need to figure out your ignition system, as this is critical for the engine to live on boost. check to see if the mechanical advance is locked, what the initial timing is, total timing, and what the msd is doing on boost (how much retard)

 

I can run 27 degrees of ignition timing on my 7.4;1 cr engine with 13 psi of boost on 93 octane. 8.8:1 cr at that same boost could handle maybe 12 degrees. (big difference).

 

better to run less compression and more boost and timing.