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Engine rebuild advice? Suggestions?


rdefabri

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All:

New to the forum, made a few posts. I am 20+ years out of the Z game, but recently purchased a 1972 240Z, numbers matching. The previous owner kept it mostly original, but did add a 5-speed and a 4.11 R180.

The car needs a rebuild, it doesn't have spunk to it. I considered doing a resto on it, but given the tranny and rear-end, perhaps a "resto-mod" or stealth Z is in order.

I considered the idea of the Rebello 2.7L, but searching this board indicates this is a $4,000- $5,000 expense :eek: So I started thinking I could do this on my own if I were to obtain a 260 crank and rods, add higher compression pistons, and maybe have Rebello do an Improved Touring job on the head.

Yes, this is only a 2.6L, but for maybe $2,000 plus my time, I am thinking I could come close to the 200 or so HP Rebello advertises.

Any thoughts? Am I a nut? I don't want to pull the block and rebore if I can avoid it, my funds are low.

Thanks in advance!

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If it's worn bad enough to require a rebuild, it probably NEEDS to be bored anyway.

If you're not going to be stuck on numbers matching, find a decent 2.8 from a 280ZX and use it as your starting point. You should be able to get an '82 or '83 with flat-top pistons for a few hundred bucks. Then put your IT head on that instead.

While the following site may not have perfect info, it can be used as a good starting point.

http://www.geocities.com/zgarage2001/engine.html

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Arne,

Thanks for the feedback, I know Bryan Little's site well! Unfortunately, I want to keep numbers matching. Otherwise, his site was what kept me motivated to someday get back into the Z game!

I know these motors fairly well, I only have 148K miles on it, so I don't think it needs to be re-bored. When I tear it down that should indicate whether or not I should.

Assuming I don't need a rebore, and I want to keep my numbers matching, am I still crazy or does this sound like a reasonable plan to getting some more oomph out of my 240?

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I just got home and read your post. I know it is important to some restorers to keep the numbers correct. I know the value of these cars will be greater if you have the original engine in the car. Here is what I would do. Take you engine out and buy yourself a 260 engine long block. If you install the 260 crank and rods and bore the 240 block .060 over with a new set of standard pistons, you will have 2658 cc's with about 10:1 compression. (Or, install the stock 260 pistons with new rings. CR will be 9.6 and you will still have 2565 cc's) It will essentially be a 260 engine in your 240 block. Do a head rebuild, take .010 off and bolt on your 240 head. 280 valves are another option) It will have a lot of torque and be fun to drive. Your stock SU's and exhaust manifold will work fine with a mild cam. It will perform and look stock for the "purists". Just an idea from the old racer!

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Nice suggestion! But how about just dropping in a L28 crank in the original motor?

That gives me the extra torque, but numbers would still match. I'd also be around 9.5:1 compression, so I think I could make some decent power like that.

Visually, it would still be numbers matching with no modifications to the block (I'd store the 240 crank).

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Yep, that's what I meant!

Still debating whether it's worth it. The added displacement may only be worth 10HP at crank, so it's not much. I think with a cylinder head job from a good supplier, I could squeeze decent HP while being streetable and getting more ponies.

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If you want HP, you will need to spend money. By placing a 260/280 crank with rods in your 240 block, you will have a bit more then 10 hp. You will also be increasing you CR by nearly 1 point. With a bigger cam and some head mods you could be looking at 20-25 hp. When you say you want 175-180 hp w/o spending any money and using the 240 engine, we have a problem. I don't think you can have it both ways. I would just rebuild your 240 engine and put it in as a new stocker. IMHO, You cannot get any better then that.

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Well, I am not saying I won't spend money, I don't want to drop $5K into a full blown Rebello/Sunbelt motor.

About 20 years ago I had a 280 that I modified a bit and it responded well for little dollars (sort of the Bryan Little/Z Car Garage thing).

I am budgeting about $2K or so on engine work. The car has good compression, and doesn't burn oil, but seems a bit sluggish off the line. The previous owner told me that the guy he purchased it from put in a new cam. If he did, I can't tell, or he just dumped in a cam without other mods (porting, etc.).

For $2K, I think I could get a first rate head re-work. Maybe specify some mods, but I think that's reasonable. If I do that + the 280 crank and rods (which I already have in my possession), I think I could get to the 180 mark.

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Did you really say you wanted 190 hp to the "Rear Wheels"? Wow, I have dyno'd a couple of cars and you will be looking at crank HP rating of 220-225 hp. Doubt if you can get that out of a "stock" 240 no matter how many mods you make. You are stymied be the exhaust manifold, the SU's and port size. How about just putting a rebuilt 240 engine in your car and being satisfied. Think how smooth that baby will run!

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Yeah, isn't that strange? I thought the same, unless it just isn't a 4.11 diff. I've only had the car for about 2 months, and with children it's impossible to get free time :rolleyes:

Ok, let's reset the thread. I wanted to get 225 at the crank if I went for the Rebello stroker (at least that's what they advertised). I know my way around cars well enough to know what I can and can't get and how much to pay (I may be a newbie to this forum, but I am no newbie to cars, hot rodding, etc.)

I realize now that the Rebello stroker is not the way to go ($$$). That's why I suggested the 280 crank/rods. With that extra displacement + a good head rework, I have to be realistic about what I can get. Given the $2K budget (I have been told that a Sunbelt job is $1,500 or so) I think 190 at the crank should be attainable or somwhere close to that.

I am curious if I really have the 4.11 gears, I have to take a closer look at it. The thing doesn't move out at all, in fact it's much slower than the Z I had 20 years ago. In fact my 1997 Saturn SC2 is much peppier, leading me to believe a) it's not a 4.11 or B) there's something wrong with the engine.

My guess is that it's a, since the engine seems to be fine, but then again I need to rip the thing apart to see.

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I too have built lots of engines. Some I built the old fashioned... I kept breaking them until I figured out how to make the last. I guess we learned from the school of hard knocks. I am wondering if you have one of the "long" 1st gear 5-speeds with the stock 3.36 diff. That will make the Z bog down in a hurry. I guess you can use the old method of counting wheel turns and drive shaft turns to get your ratio. 10 turns of the D/S = ?? turns of the wheel. If you do have a 4.11, your wheel should turn 4 times while the D/S turns 10. Now if the wheel only turns 3 1/3 revolutions, then you have a 3.36. I think the wheel rate is doubled if you have one wheel on the ground. (ring gear/spider gears) It's been a long time since I did a diff like this but I think I have the info you need. We will be curious when you know the ratio. If you do have a 4.11, I haven't got a clue what the problem is.

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That's certainly one way!!

I could also pull the rear cover and I think there is a stamping inside that should indicate if it's a 4.11. I am pretty sure the diff has been changed, or minimally cleaned, it looks rather new.

The 5-speed is a Motorsport Auto unit. Don't know if they still sell them, but it's not a T-5 from a Mustang or ZX. I am curious if MSA just rebadged or mimicked what was in a T-5, but I am not up to speed on what the gearing was in them.

Here's what is interesting. When I am below 3000 RPMs, the motor coughs and such, but once you get past 3000, the thing takes off. I figured that was due to the cam, I bet the previous previous owner dumped something in there without doing the port/valves/exhaust, etc. It doesn't burble at idle, so it can't be too hot of a cam, but it's sluggish at low revs.

I also noticed it ticks a bit. I know the Z's are known for this, but it seems pretty loud. I have good oil pressure, and it's not smoking, so maybe there's just a need to get that head off and have it done.

It will take me some time. I have to start tinkering with the E-type too -- while quite similar to the Z, it's different enough to scare me more.

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Have you adjusted the valves, timing & carbs? If it's ticking a bit could be the valves need adjusting. Adjusting the timing & carbs won't yield as much improvement in performance until the valves are set.

I recently looked at a '72 Z with a 4 bbl intake and Holley carb. It had a 5 speed in it, not sure what kind, and I'm not sure about the differential gearing. But, it was quick, it would put you back in your seat when you took off from a start. The guy said the engine was out of a '73 so it would be an L24. The rest of the car was too far gone for my liking, but I've been thinking it might be worth it for the drive train... I know you want to keep the stock engine in the car, perhaps swapping out to a 4 bbl might be an option, though...

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To me from what you describe the performance is like , if the engine is in proper tune that is . The engine is over cammed for the gearing . Installing a performance cam in a engine changes the RPM where the engine makes power . A radical cam will require the engine to spool up to much higher Rs to perform at it's best . When you are driving down the freeway / turnpike in 4th gear what are your RPM vs MPH ? This is one thought. If you are concerned with numbers matching and you do not want to install a later engine then I think you need to rethink your 190 HP figures . Especially if you don't have deep pockets. Since the car has been modified already , 5 speed , different diff, and the engine has been modified , numbers matching really is no longer a factor. Now keeping it all stock then yes keep numbers matching . Some day someone may want to strip it down and restore it to origional . This is where the numbers matching come in for show judging. My 2 ¢

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Rich, I forgot to mention in my previous reply that my engine really takes off at around 3000 rpms, too, seems to be the start of the power band. It is smooth up to that point, no coughing or sputtering, but it's not real quick.

I had the engine rebuilt last spring, it's a '73 L24, but has an earlier E88 head (the original head developed a crack), round top carbies & intake from a '71 and an MSA header & turbo exhaust system. I think the block, pistons, crank & bearings hold up real well on the old Z engines. I could have gotten away with only replacing the head, the cylinders were barely worn, no ridges at the top or anything, a faint trace of the hone pattern still visible on the walls, etc... I spent just under $2k to have the engine rebuilt.

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...snip.... I think the block, pistons, crank & bearings hold up real well on the old Z engines. I could have gotten away with only replacing the head, the cylinders were barely worn, no ridges at the top or anything, a faint trace of the hone pattern still visible on the walls, etc... I spent just under $2k to have the engine rebuilt.

I think Kens observation is pretty typical. You can have 150k miles and still see the hone marks on the cylinder walls. The tolerances on these old engines are pretty loose by todays standards.

I have a question form all this talk of putting a 280 crank and rods on an L24 block. Wouldn't you need to do the extra balancing work the same as for a stroker. If you are trying to throw around that extra length at higher 240 type RPMs, I would think the same kind of machine work would be involved as putting the LD28 crank in a L28 block. Please feel free to explain the error in my logic. Are the rods shorter?

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The tranny ratios are as follow:

4-speed 1st gear - 3.549

5-speed 1st gear - 3.062

You really will have quite a difference in low gear with the 5-speed.

I agree with Beandip. If your car has been modified, why not put a 280ZX engine in the car? I have my original 4-speed, 3.36 diff and 240Z engine stashed away in my shop. If I want to show this car as an original numbers correct model, I will only need to re-install these original parts. If you do not have these parts for your car, oops! I also wanted the car to appear original. I like the look of the original 240Z. I even put the BRE front and rear spook/spoilers on the car. I kept all of the original parts in the engine compartment. It is a 3.0 liter but looks like a 240 (unless you look close!) Maybe you are looking at doing something that you don't really need to do. What do you think?

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Well, that's the dilemma.

Since it's numbers matching, I like the idea of keeping it original. I could always score a 4-speed and ditch the rear end (what ever it is). I have the slotted mags, and I actually prefer the steel wheel/hubcap combo.

The only other mod appears to be the seats, they have Recaros (which suck horribly).

It's close enough to "original" to restore, but I don't want a trailer queen. I don't care about winning concours events or anything like that, but I do recognize the historical significance of the Z. It's why I bought a 240 instead of a 1977 or 1978 280Z.

To be honest, when I bought the car, I assumed the thing wasn't quite as original as it is. I was fully prepared to modify it heavily. But now I am having second thoughts.

On the subject of the L28 crank, it's definitely different from the LD28. I am 90% certain you can use the L28 crank and rods with no issue (that's essentially what a 260Z is). I'd never put it in without first balancing, but Z cranks are legendary for being balanced.

I think the answer is to forgo the L28 crank, just send the head out for the rework/valves, etc. If I truly have a 4.11, then in stock form, the refreshed engine should move enough for me.

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Good thinking. Keep her stock and you will continue to love her. Touch up the valves, maybe do a gasket port job, take .020 off the head, put in some new valve seals and maybe a mild camshaft and there you go! (Check the guides to make certain you do not have too much play) It will be amazing how good a fresh head will make your engine run. You are on the right track!

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I know it is cool to run the steel wheels but... Nothing makes a Z more unstable than running 5" wheels with 175X14 tires. They are very sqirmmy. How about getting a set of 6.5 steel wheels for the Z and run the stock "D" hubcaps? Having the extra rim width and wider tires really will help the handling. And only an expert will know the difference!

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