ZZ4 Partial Engine / L-48 Compatability?

[Muzz]

Has anyone ever swapped out the stock lower end of a '75 350 L-48 engine with one of the GM Performance Parts ZZ4 Partial Engine assemblies?

I purchased this '75 T-Top with TH-400 from the original owner when it had about 90,000 miles. At 100,000 miles the air condix compressor locked up. In the process of removing it I decided to de-smog the engine. This I did. It ran much better...but I am not one to be easily satisfied.

So, I purchased one of those Competition Cams, 268H I think it was, and had the local performance engine shop install it for me. At that time I also installed an Edelbrock aluminum intake to go with the headers I had put on when I removed all the stock exhaust. When they got it done it ran like a scared rabbit compared to stock trim.

Since it is a daily driver, or was, I didn't mind it not being stock. In a way I regret that now. Gas mileage really improved too!

I had a job change a year of so after the cam install and with it came a company car. So, my vette went into my garage and sat there for extended periods of time without being driven. When I did start it up, in the spring usually, I noticed some smoke but passed it off as oil leaking around the valve stem seals. Turns out that was only part of it.

Well, I couldn't stand having a smokey engine so I decided to just replace the heads with a pair of Aluminum ones from Summit Racing. They had several kits available and the kit I got was fairly mild but it had bigger valves. The new 4" Hooker side pipes with glass packs were purchased too at that time and the whole kit installed. S W E E T!

When I took off the stock heads I found the source of the smoke. Number eight cylindar had antifreeze in it and the cylindar wall had been rusted some. Close inspection of the wall showed lines where in previous winters the piston rested in other positions and the rust lines were visible. One of the head bolts in the corner by #8 leaked antifreeze around it and it got into the cylindar. Possibly the head gasket wasn't making good contact to make it worse. The block isn't cracked from freezing which I first feared.

I didn't realize the damage that had been taking place while it sat there in my garage waiting for some needed attention. Now, when the piston comes to the top of travel it leaks compression where the corrosion was and there is a definite indent where the ring wiped away the weak stuff and made a bump or a dent.

I had a couple "mechanics" inspect the marks I saw and they thought that as long as I didn't push it it would likely be ok. That is just what I wanted to hear as I had this stack of brand new stuff and I was eager to get it installed and go burn some rubber.

I live out in the "sticks" and there isn't a performance engine shop around anymore. Even if there was, they couldn't install the heads and keep the antifreeze from leaking past the bolt on the corner of the block so I doubt they would do it right a second time. Oh yea, I did the work myself when I added the new heads and stuff, and didn't have one leak and it started up and idled to 800 rpm even before I let off pressure on the key the first time I fired it up. Wow, no leaks, no drips, no errors....except for #8 compression leak that is.

This brings me up to date pretty much. I still don't have an engine shop I can take my lower end to and have the necessary boring and decking done to restore the stock block.

I'm considering purchasing a ZZ4 partial engine and pulling all the heads and stuff off my engine and rebuilding with the new lower end.

My local GM dealer can't tell me if the ZZ4 partial engine block is a direct replacement for my '75 350 lower end or not. Strange.

So, I bring my tale of woe to this forum in hopes that someone here, with patience to read this far, (tnx) has had a similar experience and can offer the benefit of that hard won experience to me.

Oh, did I tell you I was eager to get the engine together? Yup, well, last summer my friend that has a body shop and does show cars and street rods for a living finally after 15 years of waiting found a slot to get my car in. I just got it back from him after a year and a half. It now has been fully restored with a show car finish, all new chrome, new bumpers, new interior, the works. It is waay better than stock now. It turned into a regular garage queen street rod!

Now I must find myself a fuzzy suit to wear and remove the engine for the rebuild it should have had two summers ago without so much as a scratch or a smudge!

Story of my life. Impatience has cost me more than a couple fortunes. Too soon old, too late smart.

I need to get this car finished so my wife can have it in a sellable condition as I have terminal emphysema and this engine job will likely be the last project for me. I don't want her to have to peddle a pile of parts and I sure would like to have that car perform like I know it should and take it to the Woodward Avenue Cruise in Detroit to show it off when it is finished.

My goal is to make it perform well, not a hot rod, but responsive to pedal pressure, you know. Oh, and live to see it!

So, please advise if you can and thank you all in advance.

 

[Bill75]

Muzz,

Welcome to the forum!

The ZZ4 is an excellent engine, I bought one and installed it in my 75 in place of the original L-48. In may case I wasen't happy with the performance so I swapped the heads and changed the cam, but I would not buy a short block and install the cast iron heads from your L-48 on the ZZ4. The iron heads are not very good performers, the ZZ4 heads are Alum. and much better. Unless you had some high performance heads like AFR's or Brodix, you're MUCH better off with the ZZ4's and it makes your project much simpler....essentially just drop in the motor. You'll have to change the waterpump to the short style but everything is attached including the intake distributer etc. except the carb. The ZZ4 has a roller cam which would require your to purchase roller lifters and pushrods if you bought a short block........another added expense.

Your project will go much quicker with allot less headaches if you get the motor complete and you'll be VERY happy with the performance, it's an excellent motor.

Best Wishes and good luck.

Bill

 

[Muzz]

Thanks for the info Bill. I already have all the good stuff to put on the ZZ4 partial. It is now on my original L-48 block and runs pretty well but only on seven of the eight as #8 is pretty much just along for the ride.

Heads are Trick-Flow Aluminum 23 degree / 64cc / 195cc / 1.25" springs .480" max lift. 2.02/1.94 valves

Cam flat tappet hydraulic 210/216 dur @ .050", .440/.454" lift 110 lobe sep. with 1.5" roller rockers.

Edelbrock Performer 2101 intake

Jet Performance Products Quadrajet tuned for above combo.

Summit says their TFS-K314-350-400 combo should do 350Hp/400 ft lbs.

Hooker headers with 4" black side pipes w/glass packs....spell that S W E E T !

Now, if I can marry the ZZ4 partial engine, with all the above, to my TH-400, I should be good to go.

One thing I have learned. If you ever need a place to get rid of your extra cash, and then some, buy a ten year old Corvette!

I once had a '68 roadster rag top, close ratio 4-speed manual, 327 350hp and I sold it for $3k so I could buy us a family car!

*Ouch, Ouch! kicks self again*

Like I said, too soon old, too late smart.....


Thanks again for your assistance and advice.

 

[Bill75]

We're always learning, myself included. I can't count the times I've wish I'd have slowed down and thought out something a little more before I pulled the pin!

Well it sounds like all you need is a good block with a crank and pistons. I'm not a good source of info as to weather or not that cam with those lifters will be happy in the ZZ4 block. That motor is made for a roller cam and has a different cam retention method. Somebody will chime in I'm sure and verify that for you. Make sure before you start all this. Too bad there aren't some good shops around you, it might just be more economical to have your block freshened up as long as you have all the rest of the parts.

Bill

 

[Jack]

Me thinks 383 partial engine ( GMPP p/n 12499106 ) will be a better match w/ 195cc runners. Your old flexplate that fits a '75 motor won't fit new 383 or even zz4-350 ... newer motors have a different bolt pattern. It will work (non-roller cam fit in roller block), but I echo what Bill says about your cam & newer block.

You've proven you can assemble a motor. Must be a machine shop within a couple hours of you. Suggest pull your L48 motor, have machine shop machine L48 for overhaul & upgrade ... you reassemble yours as hot 355 or 383.

 

[Muzz]

Thanks Jack.

Taking your advice, I looked again this morning and found a performance machine shop only 13 miles from my home! Google is terrific sometimes.

So, I take my L-48 block and rotating assembly to them and for about $300 it gets the needed attention and I can rebuild using all the goodies I have on hand. I may opt for a new oil pump as long as it is getting spiffed up in that area and maybe have them do all eight holes but the main point is, I can do this and it will be within my budget. Once I get it in and have the machinist inspect it I will know if I need to go the ZZ4 crate motor route or not.

I suspect it is going to be easier than I had figured. Too bad I didn't do this all the last time I had the engine out of the car. Only hard part will be doing it without making a mess of the new paint and stuff.

Thanks much to all on this forum for your advice and words of encouragement. I would welcome hearing from any of you about your similar experiences. I know I must not the first to be in this situation.

 

[Jack]

Realistically, what is your overall budget for this motor job?

Glad you found a machine shop so close. For what you're doing, you don't require a performance ms ... what's most important is using a good ms ... the 2 aren't always 1 in same ... check close ... drive a little further if need be. Also, on surface it seems you have 1 bore that needs an overbore ... chances are, if old chevy has alotta miles on it, all 8 actually need boring. It'll be an odd request to bore less than all 8 ... 'though it is done. I'd expect '75 sbc motor with 100K+ on it to need boring on all 8.

Also, after 100K miles, head bolts don't usually begin leaking into cylinder; it happens but not often. You did not specify if outside mechanics removed heads but it was not necessary to remove heads when they installed cam & intake. Quite likely the intake manifold seal leaked & sucked water into head's intake ports & into #8. Intake water/oil leaks into ports are common, especially so on a new install.

You have 64cc alum heads on a street car ... suggest flattop pistons if you build a 350-355 ... suggest dish aka reverse dome if you build 383.

Let us know what the ms finds.

 

[Muzz]

I work in electronics and have much experience troubleshooting complex communications systems and helping other techs solve the tougher problems over the phone sometimes. It is kind of a joke in servicing that goes something like this: "Is it plugged in?" That is a very basic question you have to answer before ripping out the circuit boards.

You may well imagine my embarassment. The MS tech, quite an experienced individual, advised me to make a few "double checks" before removing the engine. Those he mentioned seemed like they were very basic but made good sense, especially as I mentally went over the tear down and reassembly process.

I have a new compression gauge that I intended to actually check the cylinders with as I suspected the wear marks I saw would require some follow up eventually. Too bad I didn't use it long ago! So, upon his advice, I opened the package and read the instructions. I removed the plugs and inspected each. One was fairly black but it was on the opposite side, #7 I think it is. When I went to remove the plug wire, to my chagrin, I found it was just sitting on the #7 plug loosely. I don't know how or when it came loose but that would certainly account for some of the behaviors I have noted. Little wonder the plug was black.

When I took off the wire to #6 I found it had at some point come in contact with the adjacent very hot Hooker Header pipe and had been arcing through! Two strikes against me now. I had been so very careful yet this happened to me anyway.

Once all the plugs were out I began checking the compression of each and #8 was the highest of all of them, about 177 Lbs. The others were as low as 165 but most were 167 or 168 Lbs. These numbers may well be low, I don't know. 25K miles ago when the engine just turned 100K miles, the lower end was honed and new rings were installed as well as new crank bearings. That is when I had them put in the 268H cam with the stock heads and the Edelbrock 2101 intake.

At this point I am not certain I have anything but a very basic plug wire issue to solve. I think I rather enjoy this embarassing lesson as it is easier to get over than the teardown I had been contemplating.

I share this tale with you all in hopes someone else can benefit from my experience and save yourself a lot of grief. I will report back here how it goes. At least I know where I can have my matching numbers block rejuvinated when it comes time.

Back to the garage.

*shakes head and chuckles at self*

 

[Jack]

Your numbers look fine; their range/variance is also quite acceptable. We rejoice in your discovery.

 

[Bill75]

Well..........there you go! Look at all the money you saved!! Now you can justify some other expendature pretty easily. Congratulations on your find.

Bill

 

[Muzz]

You are correct Bill. Now I can focus on removing the TH-400 and taking it to get refurbished. I have an ace repair facility that will do it for $400 if I remove and install it. Looks like that will be my next project.

After 24 years of working toward getting this car restored/refurbished I am finally running out of items on my to do list and it feels rather strange. Sometimes it is the journey that is treasured, not the destination....or words to that effect. Mom was full of sayings like that.

Thanks again guys.

 

[LVMYVT76]

On your transmission overhaul, are you putting a shift kit in?? Are they giving you a new or rebuilt torch coverter?? Have you checked around at shops for prices?? Yours seems a little high(for our area anyway). But make sure the shop will warranty the job even if you install it, put in good fluids and fill the converter first, lubing the seal, and slide it onto the shaft. Make sure you know how to install a tranny, or get help from someone local that has done a few!!

 

[Muzz]

The TH-400 has a shift kit in it now. The $400 estimate was the high ball park figure and it will likely be less as it isn't in bad condition. I just want it to be as good as I can make it without replacing it. It has 125K miles on it and when this motor starts working like it should I want to make sure the tranny is up for it. Thanks for your advice. I will have an experienced Master Mechanic assistant for the removal and install. Might cost a case of Beer but well worth it.

In an earlier post in this thread I mentioned that one of the plugs was black and the boot was just sitting on the #7 plug. Well I just found out why. When the 90 degree spark plug boot was molded onto the end of the spark plug wire at the spark plug factory someone forgot to install the metal clip to the end of the wire, the one that is supposed to be there to clamp to the plug tip! It has been that way from day one of my rebuild.

I am surprised the engine ran as well as it did on only seven of the eight and here I thought it was a compression problem.

Double check your work, then double check your double checks. Easy to say now....

* moves up one notch on the learning curve *

 

[Bill75]

Yup, you never know sometimes. I found vacuum lines on mine pinched right from the factory.....been that way since 1975 probably driving someone crazy troubleshooting it!

 

[Muzz]

Well folks, new set of plugs and a new set of MSD wires are now installed. It starts, it runs on all 8 as best I can determine, it roars...some. Now I need to get the timing back to where it needs to be and I think it will be tranny project time for my baby.

 

[LVMYVT76]

Its nice to have good friends to help out at times!! Sometimes fellow corvette owners help each other out to the MAX!

 

[Muzz]

Well I got the timing pretty close to optimum based on how well it runs.

Now the BAD news.

Since it was a gorgeous fall day and I had to go to the Dr. for some tests, I decided to take my newly finished and spotless street rod into town. I got about 3 miles from home, traveling at about 45 mph approaching a curve in the road.

The rag joint came apart causing me to have a complete loss of steering. When I realized turning the wheel was useless I was already in the left lane in the middle of the curve. My breaks are very good, but not quite good enough to keep my car from sailing into the ditch!

Fortunately there was nothing in the ditch and it wasn't very deep. No trees or anything that could have made it much worse, no oncoming traffic or pedestrians to run over either, although shortly after a school bus full of kids came by going North. I had been headed South.

As soon as the car came to rest, I immediately put it in reverse and to my amazement was able to back out of the ditch and onto the pavement. A cyclist stopped and help flag traffic while I opened the hood and cranked on the steering gear to get the wheels to turn so I could back the car into a conveniently situated driveway with mowed lawn on each side.

I called the wife to fetch me some tools as the ones I had with me weren't up to the task. Who ever needs 12 point sockets and channel locks anyway?

The State Police officer was understanding and helpful and didn't cite me as it was a clear mechanical failure that caused the car to go off the road. He even escorted me back home.

Back in my garage I inspected the rag joint which had separated, the two pins from the steering gear side slipped out of the holes on the steering shaft side. The steering shaft had at some point been partially pushed back so the gap between the upper and lower shafts was much larger than Chevy intended. I had been driving around with it that way for 35k miles ever since I bought the car back in '85.

I am still shaking a bit from the realization that a much worse situation could have happened, especially considering I wasn't always as conservative behind the wheel as I am these days and all the twisty roads and traffic and the like over the years. These days just knowing the car is capable is enough.

Damage to the car includes 5 or six cracks radiating up from the base of the windshield on the passenger side of the original windscreen which go clear across to the top. The windshield will have to be replaced but I fear what else will get screwed up when the glass tech tears it out and tries to install the new one. I'm told it isn't a simple operation on an old vette with t-tops. The car flexed quite a bit when it hit the ditch judging by the cracks.

The new front bumper I just had put on is a bit smashed on the bottom and one side. Looks like that damage is limited to the bumper for the most part although there is a .50 cent sized chip out of the fiberglass where the bumper was pushed into the left fender.

The right side behind the air vent behind the front wheel has several cracks, again I think the flexing of the plastic car is what caused that.

Oh, both 4" Hooker header side pipes got some minor damage, being pushed up so the door opens and leaves a white mark where contacting them on each side. I was able to readjust them to clear again but one has some dents in it.

The ditch had some moisture in it and of course it got into and on most everything, including the engine compartment that was show room sanitary before this unfortunate excursion.

I got the steering shaft extended back to where GM intended for it to be and the rag joint is now properly secured. The car drives and steers just fine now and the pins protrude the upper flange just as the book describes, about .35 inch. I think it will be ok until I can get it into the local dealership to have the steering column properly serviced...if that is even possible anymore.

I don't need a ZZ4 lower end anymore as once I put the new plugs and wires on this motor and reset the timing all the engine problems are gone. I wonder where i can find a dyno to satisfy my curiosity...

My friend that owns the street rod custom body shop that put all that detail labor into making this car a true show worthy street rod gem was not pleased to hear the above tale of woe. He is clearing out a spot for it again and I suspect it will be late spring before he releases it to me again.

Good thing I still have a decent paying job as this is going to get expensive AGAIN!


Time for a Guinness while I thank my lucky stars.

 

[Muzz]

Well many moons have passed since my last update to this thread. Since that last post I have learned much, most often as usual, the hard way.

I want to highly recommend these "mufflers" for use in 4" Hooker side pipes. They are without a doubt the real deal and makes your car sound the way you always knew it should. I replaced the hooker glass pack units with these and the seat of the pants indicators are telling me it don't get any better short of open headers. Dynamic Exhaust Systems

Yes it is a bit louder and I won't be cruising through any high end gated communities any time soon as I am a big chicken. I once got an excessive noise ticket after I took the spark arrestor thingie out of the brand new muffler on my 80cc Suzuki. Just was unlucky to meet up with one of those officers that just hated motorcycles and the damn hippies that rode them. Yea that was a long time ago, 1967 I think it was. I don't want any repeats.

My car is currently in the hands of a real live pro that specializes in corvette repairs. He has a long list to work on. Rebuild the TH400, install the Hughes Performance 2500 rpm torque converter, replace the 3.08 differential with the new 3.36, install the Willwood drilled/slotted rotors, EBC Yellowstuff 4k brake pads, install the Bilstein shocks to get the ones that were damaged during my ditch diving excursion mentioned earlier in this thread. And finally, rebuild the upper and lower control arms with new tubular units.

I don't expect I will be burning any rubber like they do on those car restoration/hot rod shows on tv I have been watching all winter while I waited for the weather to return in favor of Corvette cruising. That is a fairly narrow window as those of you familiar with Michigan weather will agree. Nine months of winter, two weeks of summer somewhere near the middle of three months of not quite winter weather. We just love it here.

I do know that all I have learned and the improvements I have made to what was a bone stock 1975 L-48 Corvette I purchased in 1985 have transformed a beautiful turd of a car into a gorgeous high(er) performance resto-mod that is a blast to drive and truly cruise-in event ready.

You see when I originally purchased the car I fell in love with the car for its looks and how well it drove. I didn't realize just how poorly it performed because of all the smog equipment and the auto trans. My whole purpose was to find one that I could make as close to new as I could, and make it perform as a Corvette should so that I could leave it to my daughter when that time came and have it be safe and dependable and perform much better than new. It won't be long before she inherits this car as my COPD has reached the terminal end stage.

Now all these many years later and the very liberal expenditure of funds I see that I should have been just a bit more selective and found one with a manual transmission and a rag top as was the 68 roadster I sold to get a grocery getter Honda Civic CVCC back in 1977. Still, it has been fun and I think I have finally achieved all I had originally hoped for. And I am certain she will enjoy it and it will be safe and dependable.

Let this be a lesson your anyone that seeks to find and spiff up a Corvette. You should make sure you start with a manual ragtop if that is what you really want to end up with. You save a lot of money that way. T-tops are nice but they will never be as cool as a rag top and converting to get a manual shift isn't practical.

For those of you that have read this entire book of a thread. How much do you think this car should be insured for at Haggerty or similar? Yea, how much is my car worth? I have no idea. Do you?
Does it matter that I still have everything I took off the car and all that stuff worked when it was replaced with new stuff.

 

[Tom Bryant]

I Believe that you should absolutely keep all of those original parts with the car. It was good that you were able to save your original block. Everything else that you have done to the car could be easily returned to stock with the parts you have saved if you or your daughter would want to some day. As for now I would just drive it and enjoy it.

I watch the auction sell prices closely and nice examples of the flexible bumper C3s have definitely been on the move up over the last couple of years. Even driver quality cars are moving towards the low to mid teens. High quality restorations are in the upper 20s to mid 30s for cars that need nothing. A convertible would bring a little more. The right color combination, options and with the right bidders in the room and it could go much higher.

Take the same car and add obvious mods like the Hooker side pipes, non stock interior, wrong engine and the price will drop. These cars haven't really caught on with the $100k+ resto-mod crowd yet. It's hard to valuate a car without seeing it. You know better that anyone what it would take to replace it. Checking some of the popular evaluation tools and apps I think some are lagging behind recent sales results. Haggerty seems closest at present.

Don't be afraid to insure your car for what you calculate it will take to replace on an agreed value policy. You will fill out the application and submit the required photos and documentation and if they agree on the value you will be guaranteed to receive that amount if you have a total loss. If they have questions or you way over value your car they will contact you.

Just on what you have said I'd estimate the mid to upper 20s with all the ditch rash repaired.

Tom

 

[Evolution1980]

Hey Muzz, I think it's cool that you came back nearly 10 years(!!!) later to update this thread.

You don't have to use Haggerty to insure your car. Most of the general insurance companies will insure it also. As Tom Bryant noted, you'll want to do it for Agreed Value. Otherwise, the car gets blue book value and that is essentially Zero.

As for keeping the original parts, I'd ditch 'em. You story sounds nearly identical to mine, from the original purchase, upgrades, accident, rebuild, etc, and now "many moons later", reflecting on the Lessons Learned and what to do with the original parts. This is where my opinion differs from Tom's. If you have no personal attachment to the original stuff, get rid of it, unless you have plenty of space to store it all. With all the work you've done on your car, it's value "as is" is specific to you. No one in the future is going to buy your car with the intent of putting it back to stock. You have customized your car for you. You didn't buy your car to resell it. You didn't buy your car to store it in pristine condition for the next buyer. If someone really wants an original 1975 Corvette with all original pieces, they are going to find that car. You said the same thing...Find the car you really want and buy that one; not one that is close-but-not-quite. If someone buys your car, it's going to be because they like what you've done to it, or maybe they are going to make their own modifications to it and don't mind modding a car that's already far from original. You car may have a good base for them to expand on it.

Coincidentally, I just tossed into the trash a bunch of my emissions and cruise control stuff. I had been holding on to the OEM stuff for over 20 years. The ROI on my time to clean the stuff up, advertise it (where?), deal with haggling, shipping, and everything else in between simply wasn't worth it. What could it possibly be worth compared to someone that is restoring their 1975 or 1980 Corvette? They don't want old dirty stuff. They are going to pop for new and/or excellent condition originals from any number of vendors that specialize in that type of product.
I had the same conclusion many years ago when it came to my original L48 and TH350. I spent more money keeping it in storage than what it was worth. Eventually I came to that realization and sold it. I've never regretted that decision. I don't regret tossing all the old emissions and cruise control stuff. It was old & rotting. It wasn't worth my time nor effort to hold on to it any more.