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1981 smallblock to big block conversion



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
502 fit

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
LS6 intake

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.
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
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

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
info /swap

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 ;)
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
502 swap

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
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

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!!
Here we go!

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.
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


:cool :cool "Great big box full of engine!" :cool :cool

: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?

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.


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
Swap notes

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.

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

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

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