[Unknown User]

I Threw a rod in my 73 240, and I am planning to drop my 280zx block in it with either my E31 head or my E88. I've been told by some muscle car guys that running 11.0 to 11.5 compression (an educated guess) is to high for premium gas. I figured I'd get some advice from guys with some knowledge about real cars before I went back to the drawing board, though. Any info would be much apreciated!!

 

[Unknown User]

Re: zx bottom end + e31 or e88 head streetable or

I've heard that 10:1 is the limit to the street gasoline, after that special gas is needed, as far as any applicable advice: i don't know, get a 280zx motor(P79) keep it all and shave the head '080 tha t should give you 9.5:1 comp.? but double check that go to this site:

 

[Coop260]

Re: zx bottom end + e31 or e88 head streetable or

> I've heard that 10:1 is the limit to the
> street gasoline, after that special gas is
> needed, as far as any applicable advice: i
> don't know, get a 280zx motor(P79) keep it
> all and shave the head '080 tha t should
> give you 9.5:1 comp.? but double check that
> go to this site:

I am thinking about buying a P79 motor instead of rebuilding my L26 motor, but using my E88 head, essentially the same thing you are doing. According to the Datsun Z Garage info., an E88 on top of a P79 motor will give you 10.5/1. However, if you bore the motor .020 or .040 over when you rebuild it, that will drop the compression some. I am interested in hearing about what you decide is the best way to go after you speak to everyone. Note: The Datsun Z Garage site seems to feel the P79 flows better than the E88, so he recommends using the P79 head and motor, but shaving the head to get the compression up. You end up with the same compression as the E88 unshaven head, but the flow is supposed to be better, thus more H.P.!

 

[jeff]

Re: zx bottom end + e31 or e88 head streetable or

> I Threw a rod in my 73 240, and I am
> planning to drop my 280zx block in it with
> either my E31 head or my E88. I've been told
> by some muscle car guys that running 11.0 to
> 11.5 compression (an educated guess) is to
> high for premium gas. I figured I'd get some
> advice from guys with some knowledge about
> real cars before I went back to the drawing
> board, though. Any info would be much
> apreciated!!
Anything over 10:1 is too much.
As for the head swap, I'd stick to the P series. The P-series will flow way better then the E-series with the least amount of mods.

 

[Bob H]

Re: p series not always the best...

> Anything over 10:1 is too much.
> As for the head swap, I'd stick to the P
> series. The P-series will flow way better
> then the E-series with the least amount of
> mods.

be careful saying the p series will flow better than the e series.
for the P-90 and P-90A, that is an accurate statement, to an extent.
The N-42 has the same valve size, intake and exhaust runner size, so
it flows close to the same figures stock as the P-90's. Where the difference
comes in is the chamber design. The squish area of the P series head offers
significant benefits that can outweigh,(in the case of the P-79), the poor intake/exhaust
flow ratio. With the exhaust liners in the N-47 and P-79, the exhaust flow is severely hampered and there is a corresponding drop in performance, which the P-79 can make up for by its chamber design. On Bryan's page,(the Datusn garage), where he talks about shaving it 80 thousands, magnifies the benefit of the squish area, for it puts more of it to work. That is why he has such excellent performance from it. For a 280 motor, the N-42 is generally the best bet for the least outlay of money. The P-79 is good as well, but only if it is shaved as indicated on the web page,(involved process, but well worth it). the p-90 heads are best left to large displacement motors or forced induction. I am running the P-90A on a 3.1 with 10:1, but my head was shaved about 5-10 thou. The P series on a 280 motor without shaving yields about 7.5-8 comp ratio. too low for non forced induction performance use.
remember, there is a lot to consider.
-bob hanvey
ps-on my web page, i have started to outline some of the benefits of the p-90 heads. i still have a lot to add, but a lot is there, especially on the hydraulic p-90a heads.

 

[jeff]

Re: p series not always the best...

First off your right about the P90A. Anything with hydraulic valve adjustments isn't the best for high performance high rpm motors.
There is one important difference you mentioned but didn't really look at. Combustion chamber shape. The P-series unshrouded the valves and spark plug for better flow and combustion. A person can put 46mm intake and 38mm exhaust valves into a P-series head with minimum mods, try this in a E31 or E88 and you'll run into problems (trust me I know, thats the valves I'm running in my E88). The N-series isn't as bad.
I have a Nissan Motorsports catalog that lists all of the heads that can be used on the L-series 6cyl and they list a early E88 (44.7cc) and late E88 (47.4cc I think). The late E88 was used in '73 240Z's and all 260Z's. To make up for the larger combustion chamber the '73 240's have a raised dome piston (the high performance cast pistons Motorsports sells is the stock '73 240Z piston), the 260Z went back to the early pre'73 style piston because of the increased displaced it didn't need the increased compression height make up for the larger combustion chamber.
I read your article on heads at your web page and I have a couple questions.
The N47 Maxima head you mention. That looked like the head of choice to me, small combustion chamber (smaller than the E31 in fact) with a with a P-series design. Are the valves really small or what? I would almost have to say that someone modified the head that you looked at (if all the Maxima heads that you've seen, and I assume that would be 3 or more, are all the same design then I stand corrected), its a lot more common then people think. Anyone that knows OHC motors knows to increase compression you either change pistons (most likely to a dome top) or more perferably have the head welded up and reshaped. Dome top pistons (large domes that is) decrease the amount of HP a motor can make at high rpm (the dome interfers with the air flow in and out of the head reduces the swirl in the combustion chamber and all sorts of nasty stuff). I'm not trying to insult anyone, just get a couple things straight.

 

[Bob H]

Re: p series not always the best...

> First off your right about the P90A.
> Anything with hydraulic valve adjustments
> isn't the best for high performance high rpm
> motors.

I have to disagree here. Done correctly, they most certainly can. I use it on mine and reguarly drive up to and over 7k,(rev limiter at 7300). But for the average joe, it is much simpler and eaiser to use the P-90. But if you are refering to race type motors, yes, what you say is correct.

> There is one important difference you
> mentioned but didn't really look at.
> Combustion chamber shape. The P-series
> unshrouded the valves and spark plug for
> better flow and combustion. A person can put
> 46mm intake and 38mm exhaust valves into a
> P-series head with minimum mods, try this in
> a E31 or E88 and you'll run into problems
> (trust me I know, thats the valves I'm
> running in my E88).

Yes, it is much harder to put the larger valves in the early heads and see the benefit of them without some involved chamber work to unshroud them. The P series head solves some of that by the deeper chamber, they had more room to play with. The valves you are talking about putting in the early heads are huge for that head, 4mm and 5mm respectivly bigger. That is no small change. So I wouldn't say minimum of mods. Even on the later heads, that still requires redrilling the seat, etc... And I would say is only noticably effective if you are running high rpms.

> To make up for the larger combustion
> chamber the '73 240's have a raised dome
> piston (the high performance cast pistons
> Motorsports sells is the stock '73 240Z
> piston), the 260Z went back to the early
> pre'73 style piston because of the increased
> displaced it didn't need the increased
> compression height make up for the larger
> combustion chamber.

Be careful about calling it a dome of any kind, that implies a raised portion of the top. What you are refering to is a piston whose pin height is lower, which puts more of the piston up in the cylinder, reducing the final volume.

> I read your article on heads at your web
> page and I have a couple questions.
> The N47 Maxima head you mention. That looked
> like the head of choice to me, small
> combustion chamber (smaller than the E31 in
> fact) with a with a P-series design. Are the
> valves really small or what?

One of the valves,(would have to check old records), was the later larger size,(later Z heads), and the other was smaller. It was not identical to the P-series. It was a smaller version of it. But more pronounced than the N-42, etc... It still has the exhaust liners, so that limits you, but it offers excellent potential. I can give you the e-mail of the guy who found them and is working on a project budget L28 with that head.

>I would almost have to say that someone modified the head
> that you looked at (if all the Maxima heads
> that you've seen, and I assume that would be
> 3 or more, are all the same design then I
> stand corrected), its a lot more common then
> people think.

It is common like you say, but the design is more sublte than the p series, so some people may not recognize it. again, my friend has a lot more knowledge on it. it was stock, not modified. we were surprised that it has the n47 casting on it, not some other number. so it is possible that there are some Z style n47 heads on maximas. but it was a smaller motor, so the n47 from a z would make the compression low,(it was a L24). lots of posibilities.

>Anyone that knows OHC motors
> knows to increase compression you either
> change pistons (most likely to a dome top)
> or more perferably have the head welded up
> and reshaped. Dome top pistons (large domes
> that is) decrease the amount of HP a motor
> can make at high rpm (the dome interfers
> with the air flow in and out of the head
> reduces the swirl in the combustion chamber
> and all sorts of nasty stuff).

pistons are an expensive way to get hp. so is welding up the well thought out combustion chamber of nissans. you really need someone who REALLY knows what they are doing when you start modifying the combustion chamber. the eaisest and cheapest way to gain hp/ or compression ratio is by shaving the head. it usually produces a better chamber by reducing some of the excess space, emphasizing the better parts, etc... You just need be careful about the slack in the timing chain.
-Bob Hanvey

 

[larry]

Re: p series not always the best...

> I have to disagree here. Done correctly,
> they most certainly can. I use it on mine
> and reguarly drive up to and over 7k,(rev
> limiter at 7300). But for the average joe,
> it is much simpler and eaiser to use the
> P-90. But if you are refering to race type
> motors, yes, what you say is correct.

> Yes, it is much harder to put the larger
> valves in the early heads and see the
> benefit of them without some involved
> chamber work to unshroud them. The P series
> head solves some of that by the deeper
> chamber, they had more room to play with.
> The valves you are talking about putting in
> the early heads are huge for that head, 4mm
> and 5mm respectivly bigger. That is no small
> change. So I wouldn't say minimum of mods.
> Even on the later heads, that still requires
> redrilling the seat, etc... And I would say
> is only noticably effective if you are
> running high rpms.

> Be careful about calling it a dome of any
> kind, that implies a raised portion of the
> top. What you are refering to is a piston
> whose pin height is lower, which puts more
> of the piston up in the cylinder, reducing
> the final volume.

> One of the valves,(would have to check old
> records), was the later larger size,(later Z
> heads), and the other was smaller. It was
> not identical to the P-series. It was a
> smaller version of it. But more pronounced
> than the N-42, etc... It still has the
> exhaust liners, so that limits you, but it
> offers excellent potential. I can give you
> the e-mail of the guy who found them and is
> working on a project budget L28 with that
> head.

> It is common like you say, but the design is
> more sublte than the p series, so some
> people may not recognize it. again, my
> friend has a lot more knowledge on it. it
> was stock, not modified. we were surprised
> that it has the n47 casting on it, not some
> other number. so it is possible that there
> are some Z style n47 heads on maximas. but
> it was a smaller motor, so the n47 from a z
> would make the compression low,(it was a
> L24). lots of posibilities.

> pistons are an expensive way to get hp. so
> is welding up the well thought out
> combustion chamber of nissans. you really
> need someone who REALLY knows what they are
> doing when you start modifying the
> combustion chamber. the eaisest and cheapest
> way to gain hp/ or compression ratio is by
> shaving the head. it usually produces a
> better chamber by reducing some of the
> excess space, emphasizing the better parts,
> etc... You just need be careful about the
> slack in the timing chain.
> -Bob Hanvey
FOR BOB HANVEY,
LOTS OF GOOD INFORMATION. THANKS.....
MY QUESTION IS: HOW MUCH CAN I MILL THE HEAD BEFORE THE TIMING CHAIN SLACK WOULD BECOME A PROBLEM?
I HAVE BEEN THINKING ABOUT .050 TO RAISE C/R APPROX. .8 POINTS.
WHAT DO YOU THINK OR, HAVE YOU ALREADY BEEN THAT ROUTE?
LARRY

 

[Bob H]

Re:shaving heads for compresion ratio

> MY QUESTION IS: HOW MUCH CAN I MILL THE HEAD
> BEFORE THE TIMING CHAIN SLACK WOULD BECOME A
> PROBLEM?
> I HAVE BEEN THINKING ABOUT .050 TO RAISE C/R
> APPROX. .8 POINTS.
> WHAT DO YOU THINK OR, HAVE YOU ALREADY BEEN
> THAT ROUTE?
> LARRY

Yes, I have been that route. My head is shaved just a little, like 10-15 thousands. It is hard to say how much you can shave. It is not so much the slack that is the problem, for the tensioner takes care of that, but the way it retards the timing. There are two holes that will advance the cam timing 3 and 6 degrees,(i think, that is memory), anyways, that helps take up some slack from the chain slack. You can also look into tower spacers, which raise the cam back to the original height, but that involves playing with the lash pad heights, etc... not fun stuff. for profesionals only. what you are looking at is definatly a viable option. what head are you running right now? you might look at some other head that would lower your compresion without having to shave it. the chamber size of the z heads varies from about 44 cc's to 54cc's. That makes a huge difference in compression ratios. just some food for thought.
-bob hanvey

 

[norm]

Re:shaving heads for compresion ratio

>There is no big deal to getting head shims and using different pads.I shaved my N-42 head .070 to give me acompression of 9.7 w/dishtop pistons.I then ordered .015 shims from GOODSON.I used four shims and replaced my lash pads with .170 pads(stock lash pads are .120).I used a Crane cam with 272/282 duration and .450 lift. My wipe pattern was just slighty off center on the rocker arm towards the rocker pivot but left a good safety magin.I have 40,000 miles on head now and both the cam and rockers look great.IF YOU WILL BE USING A SIMILIAR CAM LIFT SPEC WITH A .050 HEADSHAVE I WOULD RECOMEND THREE .015 HEAD SHIMS WITH .160 LASH PADS.ASSUMING YOUR VALVES ARE NOT SUNK BADLY IN THE SEATS THIS SHOULD WORK WELL.JUST BE SURE THAT YOUR WIPE PATTERN IS NOT TO CLOSE (.1OO)TO EITHER END OF ROCKER ARM.YOU CAN CHECK WIPE PATTERN BY COATING ROCKER ARM WITH MACHINISTS BLUE AND ROTATING CAM WITH VALVES ADJUSTED PROPERLY.HOPE THIS INFO HELPS!