View Full Version : 1981 smallblock to big block conversion

04-27-01, 09:27 AM
Hello fellow Corvette owners. I have just purchased by first Corvette, a 1981 4 speed
coupe. I love the looks of the car but it just has no power. I have purchased a Richmond
5 speed and was in the process of researching a 400+ cu. in small block for the car. After
several months of workit became clear that I could purchase a ZZ502 crate engine from GM
for less than this buildup was going to cost. The big question it WILL IT FIT. I contacted
GM and they were not sure. They thought their might be a clearance problem with the
hood. A couple of weeeks ago I attended a big Car show at Charlotte and talked with
a guy running the GM engine display and he thought the 502 would fit with the right intake.

I really like the looks of the car and don't want to change the hood to a "big block" style
hood. HAS ANYBODY OUT HERE TRIED THIS???? Any help would really be appreciated.
I can always go with the small block but the 502 would reallly be nice it it will fit.

Thanks in advance for your help. gwtill

04-27-01, 10:17 AM
get the 502 it will bolt in with just a change to heavier frount springs and a 1970 LS6 chevell intake(can you say E-baY) all other swap parts are availlable just use c3 bbc vette parts youll have a nice car when your doneINFO: the 502 is available with both oval and req ports ,ovals better for street and reqs better for race and the ls6 intake in the chevy performanes parts catalogs not the same,that 1s a high rise the chevells came with a low rise req port for hood clearance

Tom Bryant
04-27-01, 11:19 AM
I agree with Paul. I had a LS6 '70 El Camino and the intake was a very low profile aluminum piece. I think it was designed with Corvette use in mind although it wasn't used in '70 on Corvettes. The oval ports will give you better low end and throttle response on the street. The rectangular ports are good for high rpm and give up a lot in the low to mid range, where you will spend most of your time, due to lower port velocities. In other words, more sluggish performance until you are cranking on it hard.

You should be able to buy everything to do the swap from Chevy or the Corvette parts houses for '68-'75 big block Corvettes.

Have fun and send pictures.

Welcome to the CAC.

04-27-01, 02:46 PM
Thanks Paul and Tom, Most everything I had read suggested the need for a big block
hood. While I have nothing against the big block hood on the right car, it just wouldn't
look right on an my 81.

I welcome any additional help I can get. Hopefully there is someone out there who has
actually done this swap. I would really like hear from them (there is no substitute for
experience). In the meantime keep the good info coming.

Thanks Again! Gary

04-27-01, 03:11 PM
Just thought of a couple more questions. Will the HEI distributor on the zz502 fit or will I
have to go with a small diameter distributor? Will the oil pan that comes stock of the
zz502 fit the corvette? Thanks again, Gary

04-27-01, 04:51 PM
the hei should fit fine if for some reason you want to change intakes(like to the 70 low profile one) that also will fit with the hei only a few highrise manifolds wont fit most will(hei)but few other intakes will allow you to fully close the hood the oil pan should fit but you may have to notch the front inch or two of the pan and reweld it (very unlikely) but any muffler shop can do this simple welding job,just mark the pan carefully as to the minor mod you want done after test fitting engine (the last 1976 vette i put a 502 in did not need any thing done to pan) good luck and enjoy !!!! :D

04-27-01, 05:02 PM
thought you mite want to know some 502s don't have a place drilled for the clutch pivot lever stud from the factory or any place to mount a manual fuelpump(fore warned is fore armed as they say) electric pump/drill and tap BEFORE INSTALL IF YOURS doe,s not ;)

04-27-01, 05:18 PM
Thanks for the heads-up on the fuel pump and clutch pivot. I was aware of the missing pivot hole
but not aware of the fuel pump. What kind of air breather did you use? I assume it was a drop base.
Will my stock smallblock filter work? Thanks, Gary

04-27-01, 06:55 PM
502s dont come from chevy with a flywheel they come with a flexplate! chevy flywheels are not sfi certified (blow proof) get a stainless or aluminum one that fits 11" clutch and preasure plates and dont forget a lakewood bell houseing because if any nasty stuff comes off the clutch you dont want it embeded in any tender parts of your anatomy and yes the air filter used was a 14" crhome drop base with a 2" filter and you can save weight by swapping to an aluminum waterpump if you get the aluminum heads you dont need to change front springs as a bbc with the aluminum heads weighs almost the same as an all iron sbc

04-28-01, 08:22 AM
Paul, I received some information last night cautioning me to make sure I checked the 1970 LS6 manifold for interference problems with the roller lifter retention system. This gentleman had tried a 1980 454 truck low rise intake and it would not fit because of interference with the roller lifter retention system.

Did your 502 use the factory roller lifters and if so did you have any interference problems? I still have not been able to find a part number or casting number for the manifold you recommended so I can't begin to search for one. If you don't have any additional information on the manifold I will contact GM Monday to see if they can help. Thanks, Gary

04-28-01, 10:59 AM
yes to roller lifters and no to any problems but the intake I used did not have an oil splash sheild attached to the bottom(came that way to me) I would look on the chevell chat rooms for the (casting/part #) also my e-mail got erased this morning so if there were any mesages I did not get them!!

04-30-01, 06:35 PM
The project is officially underway. Called about ordering a 502 today. Figured it would take at least a month, everything else does. Turns out the dealer had 1 in stock, wanted to sell, said drive down and pick it up. So I just got back with a great big box full of engine. I am sure I will be needing some miscellaneous mounting brackets for alternator, power steering, air conditioning etc. I'll keep you posted.

04-30-01, 07:00 PM
It's official eh? And you've already eliminated a month of waiting! :cool

Can't wait to see the results. Good luck and keep us posted. :J


Tom Bryant
04-30-01, 10:15 PM
:cool :cool "Great big box full of engine!" :cool :cool


05-10-01, 09:36 AM
:confused Help! Started to day on the 502. I see two immediate problems.

1. Clutch pivot hole: There is a boss over the oil filter where the rear pivot hole could be located. The Corvette however uses the front clutch pivot hole on the small block. Guess what! There is no boss where the front pivot hole should be located!!!! I got on the Sallee Cheverolet forum and was told that Sallee makes a bracket that can be bolted to the block that will allow mounting of the clutch pivot in the forward location. Since I have not seen it I don't know whether it will intefere with my headers or any other parts of the car. Anyhone out there have any suggestions? Does GM have a solution for this?

2. After opening the heads and comparing them with the LS6 intake I noticed a SERIOUS port mismatch. I knew the ports would not not be the same size but I didn't know they wouldn't be in the same location. I haven't taken the splash guard off of the manifold yet so I am still not positive the LS6 manifold will physically fit but from a port location standpoint it is way off. In order to use this manifold I will have to physically relocate the ports. This will require removing about 1/4 inch from the bottom of the manifold port and adding about 3/8 inch to the top of the manifold port. If this were done I could get a close match. There appears to be enough metal on the bottom to allow removal of the necessary amount but I really don't know what to do about the top. I probably could have it built up by welding it would cost big$$$ since a lot of metal would have to be added. There may be some form of epoxy out there that could be used but I certainly wouldn't to use anything that might come off and get into the engine. Obviously this would change the angle that the air/fuel mixture entered the head and I am also not sure what that would do the the flow numbers (aka horsepower). I know I could go to a different hood and use the 502 manifold but I would really perfer to the the stock appearance. Any ideas?

Tom Bryant
05-10-01, 11:22 AM
Did you contact Sallee for their recomendation on the manifold? Maybe there is a n alternative that we don't know about. Might contact Edelbrock too. Never hurts to ask.

I have seen the clutch ball adapter before but I don't know what header clearance problems you would have. If it won't fit you may need to go to a hydraulic throwout bearing setup.


05-12-01, 07:24 AM
Tom, Yes, I have talked to Sallee and Edelbrock. Nothing available. I even checked Edelbrock's MPFI but that is also too tall. Looks like its make the LS6 manifold work or get another hood

05-12-01, 11:25 AM
So far so good. I have been running into small problems along the way but I expected that. The 502 is pretty much finished with the exception of a couple of missing parts but they should be in in a week or two. That 502 looks so good on my engine stand that it will be difficult to cover it up with a hood! Grumpyvette has been a lot of help ( no substitute for experience). Unfortunately this is a very busy time of year for me so I don't have a lot of time to work on the swap.

Having never ordered a complete engine kit before one things stands out. Weight! Those things are heavy (over 700 pounds). Make sure you are equipped to unload it and handle it safely. Don't think you are going to get a couple of guys in the neighborhood to unload it when it arrives unless your neighbors are the offensive line of the Dallas Cowboys. Just my humble opinion.

Tom Bryant
05-12-01, 01:17 PM
I know what you mean. I used to play with the early iron Hemi engines in the '60s. Don't want one of those to start whipping on you either. :Twist


05-15-01, 10:14 AM
I am considering using a big block hood so I can take advantage of the Hi-rise manifold.
I have seen many different styles of hi-rise hoods and most of them will probably provide
the necessary clearance but never having used them I was wondering about the quality
of these aftermarket parts. Anyone have any experience on this?

I also have been looking at some stock hoods from earlier model corvettes that provide
additional clearance, L88, big block etc. I feel like these might be better quality and were wondering which hoods from the earlier models will fit the 1981 with no modifications.

I will be putting the car in the shop soon and I was wondering what is the best way to
do the swap. I know the hood will have to come off and I was wondering about taking
the whole front of the car off. How much work would this be? How difficult is it to re-install
and get it aligned properly? Any danger of cracking the fiberglass, etc.? Comments

05-16-01, 03:12 PM
the ecklers part #10420 will fit your vette the 73-76 and the 68-72 vette hoods will not even though they look simular ;)

Tom Bryant
05-17-01, 12:35 AM
You're kidding, right? It doesn't unbolt. You would have to cut it off and more than likely replace the fenders and side panels with new parts, new paint job ect. I think once you get the hood and radiator out of the way it will be easier to work on. You will have to do a lot from underneath and if you knew someone with a lift it would be even easier.


05-17-01, 06:25 AM
Thanks Tom,

No I wasn't kidding. While I have worked on cars most of my life this is my first Corvette. I have seen the entire front end for sale in several catalogs so I didn't know how difficult it would be to remove it. This is a great forum and I appreciate all the help that has been offered. I am asking every question I can think of because I would rather ask a dumb question than not ask and do something dumb. Thanks again, Gary

05-17-01, 06:59 AM
you do not have to do anything but pull the hood off and the radiator out to install the engine after that pulling the sbc out with a engine crane and reinstalling the bbc is not hard at all. it really helps if you have an engine tilter(summit has one for $65 part #sum-g1022) and a swivel mounted on the attachment ring so that you can turn and tilt the engine to line it up easily with the trans and mounts(2000lb swivels are available at most big hardware stores and you use two of those chain repair links that screw together on one side (2000lb size) remember you will be under that engine at some point if only with your hands and you cant lift it off if you use cheap 800lb rated swivels and links that might break ,the differance in cost is less than $15

05-17-01, 07:25 AM
You are 100% right about the engine tilter. I bought one many years ago and it was a very good investment. I have never used a swivel, but it might be helpful.

Tom Bryant
05-17-01, 11:33 AM
Great advise from Grumpy. I think I will get on down to the hardware and get a few new accessories for my engine crane.
Have you decided on a hood yet?


05-17-01, 12:48 PM
Tom, Not yet, I really want to see some up close and personal before I decide which way to go. I can always use the LS6 intake for a while if necessary. Does anyone know if there are any Corvette clubs around the Raleigh, Durham, NC area? I am only about an hour away from either city. I would certainly think there should be a few hi rise hoods in that area.

If you don't already have an engine tilt I would definitely recommend it. Once you use one you'll wonder how you got along without it.


Tom Bryant
05-17-01, 03:21 PM
I went into the "Site Resources" area and searched Corvette clubs in North Carolina and came up with these. There is a lot of information lurking in this site and I'm always finding something I didn't know was there.

Caro Vettes Corvette Club
PO Box 1654
Jacksonville NC 28541-1654
Website: http://www.58fuelie.com/Caro-vettes/

Corvettes International

Raleigh NC
Website: http://www.corvettesinternational.com/

Queen City Corvette Club
PO Box 473072
Charlotte NC 28247-3072
Website: http://www.queencitycorvette.com/

Twin Rivers Corvette Club

New Bern NC
Website: http://www.always-online.com/trcc/
Site Resources

05-17-01, 03:51 PM

Thanks, I will check out the one in Raleigh. Gary

05-18-01, 07:58 AM
just thought id give you some ideas as to how to remove and reinstall that hood while keeping the alignment just right
(1) before you loosen the first bolt clean the hinge and the area around it with fantastic/409/or something like that, that will remove all grease/oil
(2)lightly spray the hinge base area where it meats the hood surface with white paint( just a very light dusting coat)
(3) let it dry
( 4)now remove the bolts that go into the hood itself and leave the ones going into the car alone
(6)when you finish working on the car(you are using fender protector mats aren't, you) the exact spot where the hinge mounts to the hood will be VERY clearly marked(outlined in white dusted paint)
(7) match hood to outline and tighten bolts
(8)spray area with the normal under hood color to hide any white paint dust
(9) let dry; and your done!

05-18-01, 08:34 PM
I already have the hood marked and I even used white paint (great minds think alike) hehehe.
Yes I am using fender covers.

You had mentioned earlier that the earlier big block hoods would not fit my car. I was wondering what the difference was between the earlier big block hoods and the one on my car? They sure look the same with the obvious exception of the height of the hood.

Where did the name grumpyvette come from? Are you the "Bill jenkins" of the Corvette world?

05-18-01, 08:55 PM

I sure hope you are taking pictures as you go along with this project, I really want to see how it comes out! As for a hood, I have the L-88 hood on my '81. When I started making engine mods and added headers/sidepipes the stock hood wouldn't close all the way. I bought the hood from Eckler's for about $499 plus $50 truck shipping, the hood comes ready to paint BUT more than likely you'll have to fit it first and do a bit of sanding, then re-primer and paint it. I believe it gives you almost 4 inches of additional clearance over stock. I'm thinking of adding in the aircleaner insert to the hood and converting to a complete L-88 aircleaner setup once my motor is ready to install.

05-19-01, 07:51 AM
Scott, I am taking pictures. Unfortunately I don't have a digital camera so I can't get the on the net until they are developed. My son has a digital and he came home this weekend and we were planning to take some pictures with his camera andput them on the forum. He remembered to bring the camera but forgot the software and download cable. We will still take some pictures and upload them soon. Gary

05-20-01, 05:05 PM
I had some pictures developed and I just got the prints back. I will try to scan some of the prints in soon. Hopefully I will get the digital camera working soon. Since I have never sent any pictures... How do you do it and what are the rules? I will continue to take pictures as I go along and will be glad to share them with the forum.

05-23-01, 03:44 PM
How do you send pictures to the forum?

05-23-01, 03:54 PM
gwtill, You can post it as an attachment; it's pretty much self-explanatory when you click the attachment button. Or you can insert it directly into a post as an image: (your image[/i m g]) - [i]spaces inserted so you can see the commands in the brackets.

05-31-01, 04:42 PM
Hey Guys! I finished up the engine and am getting ready for the transplant. I need brackets from a 70 or 71 big block Corvette for my accessories, alternator, P.S., & AC. Anybody got any laying around? I am going to try to attach a few pictures just to see how it works. Let me know if you want more. Thanks, Gary

05-31-01, 04:48 PM
One more shot.

05-31-01, 05:48 PM
Wow that looks Go Go Go Go GOOD now I want one:upthumbs :W:

05-31-01, 05:51 PM
Originally posted by billagroom
Wow that looks Go Go Go Go GOOD now I want one:upthumbs :W:

Yeah, me too now. :L

05-31-01, 09:09 PM

Beautiful!! I'm afraid if I built an engine that looked like that I'd run it one time and park it. I wouldn't want it to get dirty. Just kidding, too bad you're going to hide it under the hood.

Did you build the motor? What was done to it? Let us know how it goes.

05-31-01, 09:11 PM
Beautiful, Breathtaking http://www.corvetteactioncenter.com/forums/images/icons/icon14.gif . http://www.corvetteactioncenter.com/forums/images/icons/icon14.gif


05-31-01, 10:33 PM
Al, I bought the 502 engine kit. The shortblock was assembled but I did everything else. I thoroughly checked over the shortblock and did a lot of extra cleaning and detailing. It was amazing how dirty the bores were. The entire kit was packaged quite well but was not sealed against dust. I have some photos of the contents. These are photos that I took with a regular camera and scanned in to a MS word document. The document is quite large and may take a few minutes to download. If you don't have MS word you may not be able to view it. If you want me to put it on the forum or email it to you let me know. Gary

Tom Bryant
05-31-01, 11:55 PM
I noticed in your 1st picture that you have it plugged in. Is it electric? Ought to be really fast until you run out of extension cord.


06-01-01, 12:13 AM
Tom, All I need is 1320 feet and I'm home free! The cord actually goes to the dehumidifier in the bottom left corner. Wouldn't want my baby to get musty. Gary

07-05-01, 04:27 PM
I'm wondering what's happened with Gary (gwtill) and his big block crate motor swap into his '81. I hope it's simply that he's having way too much fun with it ... no time to visit.

07-05-01, 05:13 PM
Unfortunately I have been traveling or tied up for almost a month and have not had any time to work on it. Hopefully I will get a little free time toward the end of July

07-26-01, 08:30 PM
Hey guys, The 81 engine is out and the 502 is ready for test fitting but.....I need the mounting brackets and pulleys from a big block. Anyone out there got any???????

Thanks, Gary

Tom Bryant
07-26-01, 10:45 PM

Might try Paragon Reproductions for used ones. They probably have the new ones too. I see Ecklers has all of the BB accessory mounting brackets and pulleys also. Of course engine mounts and frame brackets are the same.



07-27-01, 07:51 AM
Tom, Thanks for the reply. I'm not familiar with Paragon. Do you have an phone number? I will also look on the web and see if they are listed.