E31 valve size

[zwrenchturner]

How you guys doin? This is my first post but I've been reading the forums for a couple of days to see if anyone had any information on E31 porting. Havnt found what I'm looking for but there are a lot of threads...

But the story is: I just bought a 1971 240Z in sorry shape from a lady for $500, and immediatly started tearing through the engine in hopes of my first all out rebuild. Long story short I'm starting out on the heads and already bought a cam (480 lift, 274 duration) next on my list was valves, I was wondering if anyone could recommend a good valve size that they used and any advice that they might be able to throw my way.

As far as the car goes, I was thinking street cruiser, weekend 1/4 mile or something, we'll see... but I would like to run off of pump gas (if possible) I was thinking 9.5:1 or maybe 10:1 but if I read right I could have my heads cc'd to that compression right?

I've heard you guys mention notching the cylindersfor vavle clearance, if I bore the L24 over 1mm will it still be necessary?

oh, and I was thinking of running those tripple miks "zvoiture" posted a while back.

I think thats about it for now. Thanks in advance.

[Ed]

Welcome, to the club.

Hmmm, not really sure of what your trying to do. But if your looking for more horsepower and don't really care about originality then forget boring the L24 and get a L28. Use the cam in it and you would have gained 15-20 hp easy.

[zwrenchturner]

I dont really mind origionality and I thought about doing an L28 but I'd really like to stick with the block I already have since I did pay for it. Seems like going to an L28 now would be taking a step back. Especially after all the time I spent cleaning the dang thing up, the lady before me let her sit in a field for 4 years and to say it had some corrosion would be a big understatement. Really I'm just looking for a bit more horsepower from every nook and cranney, and the bigger valves would be a big compliment to the cam I have and the tripple miks I want.

Like I said, this is my first all out rebuild and I'm really looking forward to dressing everything up as much as possible and having something awesome to show off when I'm done, and when people ask, I can say "Thats right, I did it all"

[Gav240z]

Ok first of all i understand that you want to be able to say I did it all myself which is great Im the same.

What you have to realise is that you can't do everything yourself at some stage a machinist is gonna have to do the work to the engine unless of course you have the tools.

Some good mods are:-

With your E31 put valves from a L28 head in it. Also change the valve stem seals so it can run on unleaded.

Of course if you want to race the car there can be some problems entering in a class where you are limited on valve size.

An L28 block i would imagine is very cheap to pick up from a junk yard and by the time you replace bearings, rings, and bore out the current block your better starting with an L28 just my opinion.

The big cam is a good start and the E31 is high compression so I think the L28 bottom end with need the dished pistons to be ~10:1 im not 100% sure on that.

You will need to change the SU's to accomodate the bigger bore and SM needles are good from www.ztherapy.com

You can get a 240z flywheel and have it lightened and then get a 240z front harmonic balancer the one with only the single pulley assembly this will let the motor rev quicker and I have done this on my L28 and it seems alot nicer than before.

I could go on for a while but i think the best thing to do is work out a budget and go from there.

i always like Brian littles information...

Car of the month a Zcar

http://www.zcar.com/month/2001/04/

his website at...

http://geocities.com/zgarage2001/

However i'm told you shouldn't take all the information as 100% correct.

[zwrenchturner]

thanks a million gav,

but I knew I'd need a machinest for the porting work and the block work I wanted done, but you knew what I meant.

but you got me thinking about that L28 block, I'll have to sleep on it for a night, I'm on a tight budget so I'll have to price a couple or save a few pennys. either way...

but say I did stick with the L24 I'm working with now, what do you think the compression ratio would be with them E31 heads? (11 or 12:1 maybe?) and if I used the valves you recommended (and did the 1mm bore over) would I still need to notch the cylinders? either way...

but now that I've looked into it a bit more I dont know how much racing I'll be doing, from what I hear some of the classes are pretty tight when it comes to certain mods, maybe I'll build another one after this with autocross in mind. we'll see, I dont want to get ahead of myself.

but you mentioned using valves from an L28... I'm confused did you mean the valves from an E88 head, or just use valves from a 280Z?

I could go on forever but I'll stop here for now, thanks again!

heres a few pics on what I've been working with ioncase anyone was interested.

[zwrenchturner]

ok I tried to put all these pics up at once but it didnt work, so heres another

[zwrenchturner]

...and another

[Gav240z]

When you say high compression like 11:1 12:1 is this after shaving the head?

I wouldn't recommend shaving too much as you won't be able to run it on the street.

I believe the early 240z's had flat top pistons in them but can't be certain.

You may have to notch the cylinders for the bigger valves but I am not sure on an L24 and I don't know because I've never done any machine work myself.

The good thing about an L24 is that they like to rev alot more that's why i suggested installing a lighter flywheel and harmonic balancer. It helps the bigger motor turn over.

Don't go too far over budget as it is really easy to do so with any form of build.

Do whatever will make you happy and speak to a professional who works with Z's alot in your area.

[zwrenchturner]

no, I didnt want to shave the head too much, just whatever was necessary to true it out. but yeah, I'm catching the fever and I find myself oogeling over stuff I dont really need.

one step at a time though, first I gotta get these heads done up.

thanks for all your help though, I sure do appreciate it.

[grunt0311]

Here you go

http://geocities.com/zgarage2001/heads.html

Although I prefer a V-8, but have had alot of fun with the L series also.

grunt0311

73 scarab 327

70 rhd still in the garage, still ugly