I'm SO glad I came across this forum =) I've been wanting to do a v8 miata swap for the past two years and finally found the time and $ (its always one or the other isnt it!). I have a shop full of 9 miatas, mostly with body damage, and picked one for the donor. Engine is freshly pulled from a 76 stingray with 77k original miles.
I've never done a swap like this so I hope to read ton on others builds and ask questions, and of course, post pics of my build along the way.
As I'm always asked, " Why go with a crappy smog year SBC when you could go LSx?!". The answer; simplicity and nostalgia. The SBC's allow super cheap HP and are cake maintain. I wanted a toy that let me work on it when I wanted and drive it when I didnt; not turn in to a jack stand king everytime I got greasy.

The donor car


The engine




I bought a trans that was a waste, some 5 speed from an old sunbird. I suppose It'll just be used for mockup. Anyone here from NY? I'd love to see some swaps in person

 

Good luck with it!

If you can pin 5.7MX or Rugger down, both have finished their own SBC builds and might be able to give you tips they've learned along the way

 

I'm also using a Gen I small block....weighs a bit more but a hellofalot cheaper HP and much easier to install and maintain (in my opinion). I would suggest that you do some work on your motor.....it's a real dog! Low compression, smog motor and with the low HP output and the additional weight I'm not really sure you'll see much improvement in performance....unless you do some mods your money would be better spent modifying your Miata engine....good luck and please keep us posted. Thanks, Tony

 

A close friend of mine has been building SBC based drag cars for years, in the winter its being sent to him for a mild build (cam/built alum heads/intake manifold/larger carb). It's going to cost me pennys, I'm sure he'll give me most of the parts. I'll still probably end up still replacing this motor with something more stout, but not for a year or two.

 

Welcome, I suggest doing some measurements of your donor motor on length and height verse the LS or 5.0 motors. I used a LSX motor and still had issues with hood clearance and firewall. The LS block without the radiator is pretty short and no carb helps with the height. Are you going to make your own K member mods? What do yoou plan on doing for a differential? Good Luck and have fun!

 

I don't even know where to start. Landon (MX5.7) is probably more of a pro regarding the SBC and miata combo. However, the exhausts are challenging, and there isn't much room in the tunnel. I ended up doing a mod to my subframe so that I could run block huggers. I also have sides exit exhausts which further complicated things. What are you planning on running for tranny? I'm running a Muncie 4sp. I wish that I had a 5 or 6 speed due to the higher rpms and noise. Go ahead and put in some dynomat or equivalent on the tranny tunnel. The heat is nearly torture. Run AC if you can. These cars are freakin hot in the summer. PRC made my radiator for me. Be sure and seal around yours really well, or you'll have cooling issues. Landon and his friend were able to tuck a carbureted SBC under the stock hood of a miata. Find out how he did it. It will save you trouble.

 

Hey guys! Making progress on the Miata. Does anyone have any pictures of the motormounts people have made and where they were tied to? I'm just about ready to make some and drop her in. Tunnel is cut out,bay is stripped, and subframe out =)

 

Here ya go. They are solid mounts. I feel none of the torque through the body of the car. I was pushing the weld a bit on the mounts. They are not pretty, but they are holding.

edit: those mounts are available at most drag race shops and speedwaymotors.com
http://www.speedwaymotors.com/Steel-...unts,3277.html
Search "small block chevy motor mount" on speedway. There are many options. The lower part of mine was made with pieces that I bought from the scrap yard.

 

Also, check out Stein's front subframe mod. It would make your life eternally easier if you do that mod.

http://forum.miata.net/vb/showthread...=353302&page=2

For that matter, check out his rear subframe mod, too. That guy can work metal.

 

Coming along!

 

Some inspiration.

 

mx5.7 - Can you show how you did your motor mounts? I have an idea on how I want to tie mine in, but it looks like you have yours tied to your frame rail in front of your shock tower?

 

From what I remember of the 77 Vette engine, it is pretty anemic (my MSM Miata has more power). You might want to do some upgrades before you slap it in.

 

Not a big deal, set of vortec heads and 750cfm carbs will make a HUGE difference. Not too $$ to get the engine over the 300hp mark. The goal with the project was cheap and easy, and the standard 350 block delivers just that. For now I want the car moving under it own power before I tear in to the engine.

 

That is exactly what I did. I used three plates of steel to box a small area of the "frame rail", and bolted through that top to bottom. Then I made a "cradle" that goes down under the oil pan and to the other side out of rectangular tubing. On that cradle I welded to pieces of round tubing that I could slide the bolts through for the factory style motor mounts.

 

I did it this way:



With these motor mounts:


http://www.speedwaymotors.com/Steel-...unts,3277.html

 

mx5.7 - I started making my mounts the way you described yours, but ran in to a little "issue". Is your cradle made up of 3 pieces? If this is one piece, I don't see how it can be removed. Any pictures of yours by any chance?

 

It is one piece and I have never removed it. Sorry no pics.

 

Ended up combining both ideas for mounting to something I felt comfortable with. I liked the idea of having a cradle for the engine, but not having it permanently tied to the frame, so it had to be removable. A plate will be welded to the upper subframe (pictured with tape holding it on), and roundbar will be welded back to the cradle. Once in place additional gussets will make it nice and secure. Should hold up great.

 

Good looking stuff. How well does the distributor fit back by the firewall? I remember that always being a problem area with SBC builds.

-Jason

 

Not directly Miata-related, but speaking towards the old-school Chevy V8 vs. LS.

I started a big block Chevy swap in my Datsun about 12 years ago. To truly do these engines justice (SBC and BBC are sufficiently similar to cover both in one swoop), you're looking at:

- modern heads (AFR, Brodix, Canfield,...), with some porting
- mechanical roller cam and associated valvetrain
- crank and rods (SBC) or at least careful machining on stock parts (BBC)
- bore/hone, decking, etc. etc. at the machine shop
- pistons, and balancing of the rotating assembly
- proper oil pump, drag-race pan
- intake, carb, ignition, etc.

That's about $4K in parts, if you are clever and stay modest. I have around $7K in my BBC, and that's with the factory block, crank and rods. Heads alone were $2K+ ! This is a 461, "maybe" making around 550 hp.

Sometimes the hardest part of a swap isn't the swap itself, but building the engine! It can all be done, and it can be very rewarding to build and to enjoy once it's on the road. But it's not cheap and it's not simple.