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V8 on the cheap: 240 lb-ft torque & 6" rear end


Old 11-18-2017, 01:30 PM
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Default V8 on the cheap: 240 lb-ft torque & 6" rear end

OK..... first post other than the introduction. ('91 NA, completely stock 230k miles)

Initial fact finding post with a couple questions, as I'll be reading this site a bit for tidbits of knowledge. I apologize if this is asked too often or repeatedly. I haven't began my knowledge quest for V8 upgrades yet.

Question # 1:
Who's broken an NA 1.6 rear? What breaks?

Question #2:
How much torque did you apply? (was it more than 240 lb-ft ?)

Question #3:
What clutch master and slave is used with a T-5 or T-56 in a Miata (N/A)?

General idea and the reason for my joining this forum. I want to V8 a Miata ... on the cheap.
V8 swap on the cheap;
Not interested in making BIG power like with a traditional LS or 302 swap: I don't have an LS or 302 lying around.
I do have four 215 V8s, a decent Camaro T-5 (NWC) with 0.63 OD and a LT1 T-56 6-speed at my disposal (and a couple 1.6 rears).
Just thinking an AFFORDABLE swap using mostly existing parts inventory ... for fun, ... not serious competition or daily road use.
V8 sound, top down cruising and not emptying the wallet ... mostly V8 sound cool factor... because it won't be a real hot rod with only 150 HP and 200 lb-ft TQ. lol.

I'm a fan of the old '61-63 Buick/Olds 215 aluminum V8s (later Rover V8s) . Power output ranges from 150-200 hp and 200-240 lb-ft torque.
I run them in a couple Chevy Vegas (6.5" and 7.5" rears). ... not because of the increased power output solely, but because of the unchanged/improved handling.
They're 320 lbs fully dressed (20-30 lbs heavier than the Vega 4-cylinder) so stock handling isn't compromised... probably improved with the lower center of gravity vs the 90 lb cast iron sohc Chevy Vega head sitting way up top on the engine. Unchanged or improved handling and double the power in a Vega. Win!

Figured the Miata 1.6 would have a similar weight (300 lbs).... and I'd love to double the torque output. Miata turbo and supercharger kits can cost a couple thousand dollars to do. I'm thinking I can do this fairly cheap.

I've gotten pictures of the engine perches and mounts for a NA Miata (for a Rover swap) that I can probably have fabbed up.... so the engine swap shouldn't be a major obstacle.
PICS NOT MY CAR (from internet) :

So this swap has been done (with an RX7 rear I believe) and I don't expect the mechanics of swapping one in will be that difficult (maybe routing exhaust).
I've considered swapping in a 1.8 rear for upgraded strength and associated axles/hubs to maintain the Miata wheels/tires. I just can't seem to grasp the Ford 8.8 (or 7.5) swap price .... my car is cheap, the engines are cheap.... the t-5 is cheap (not the T-56). So...... trying to feel this out on the cheap! lol.

I understand about finding the weak link in this thought process of doubling the torque of a Miata (rear end). The diffs will be open and I doubt the car will "hook" very well.... so it shouldn't be shock loaded much if driven responsibly. I can accept the consequences if the rear grenades (I have access to spares). It won't be shock loaded as it will mostly be driven in the field mostly at first (rallycross) for major testing purposes. If successful, a suitable rear swap may ensue for street use.

Initial ideas for swap:
-215 V8 with carburetor (no computer wiring for fuel injection) just ignition power to HEI distributor
-Stock brakes/suspension (no appreciable weight gain with 215 v8)
-T-5 or T-56 trans ... need a deep overdrive to compensate for the Miata 4.3 rear gear (70 mph is about 3500 rpm)
-Fab Trans crossmember
-Some hydraulic clutch set up?
-stock 6" 1.6 rear/axles (initially)
-'Fab/shorten driveshaft with GM spline slip yoke/Miata rear u-joint.
-Fab/shorten brace (torque arm?) from trans tailshaft to rear end
-Upgrade radiator/fans
-Gauges ? (prefer to use Miata gauges if possible with Oil/temp sender swap..... Tach re-calibration?)

Question #4:
What am I missing?
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Old 11-18-2017, 02:39 PM
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You are definitely wanting to follow a path not followed too often.

I do seem to remember the old Buick V8's being popular due to their aluminum construction back when that was unheard of.
Didn't Triumph use them in the TR8?

For the engine specific question, I will just stay completely away from those because that is for somebody that knows about such things.

Not directly effecting the swap so why not leave them factory and decide after completing the swap if the need upgrading?

both will handle the HP levels of the Buick engine so it probably comes down to coming up with a bell housing and the pilot shaft diameter and all those other little things that make a transmission work. You will probably be wanting the extra overdrive that the T56 gives as it sure cuts down on the RPM over the T5 in top gear but the trade off will be the extra weight of the 6 speed. Be aware that you will almost definitely be forced to do transmission tunnel surgery with either transmission as the bell housing tries to use the same real estate as the front portion of the tunnel.
For the hydraulic clutch setup, you could probably visit a salvage and grab the whole assembly from a manual Camaro or Firebird. Make yourself an adaptor plate to bolt the unit to the firewall and then grind on the Miata clutch rod to fit. That part is actually pretty simple.

Rear end assembly;
Stick with the factory rear end as it is not directly tied into the swap except for driveshaft yolk and the brace that connects the rear end to the transmission.

Radiator & Fans;
Try the factory Miata radiator and see if the connections will work for you. Since you are doing a swap that doesn't have several build threads to use as a starting point, the radiator is one of those things that you will have to work thru. You won't know if it is large enough till you finish and do some driving.

The temperature and pressure gauges are dependent on using the Miata sensors so you will need to figure out how to adapt them to your block.
The tachometer is something that I have no input on but the Ford swap guys can probably walk you thru that.
Same with the speedometer as the Ford guys commonly use T5's for their swaps. GM swaps normally use a computer, which give an electronic speedometer signal.

What are you missing?
Engine cross member fit with respect to the oil pan and exhaust manifolds.
Exhaust headers or manifolds could be a real problem area because the real estate available is not as generous as some other cars.
Fuel pressure since the Miata has a tank mounted pump and you are wanting to feed a carb. The Ford guys can help with that but I am guessing an adjustable regulator will work.
Actual location of the engine in the bay. You probably need to back into that item. Presuming you go with the Camaro T5, the shifter is in approx. the correct location to fit correctly in the Miata opening. Start with that location and work forward to determine the motor mount location and oil pan location. Cut and weld the cross member to fit.

Since you mention wanting to do the swap on the cheap most of my recommendations involve installing the Buick engine and T5 transmission while retaining as much of the original Miata components as possible.
To me "On the Cheap" means to get it up and running and thrash it to find out if anything is going to fail then upgrade system by system as it fails. Given the low HP numbers you mention from the engine, I am thinking the balance of the drivetrain will be fine except for normal wear and tear.
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Old 11-18-2017, 09:41 PM
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Thanks for the reply BGordon.
Yes, the 215 was sold to British Leyland around '65. They used it in several of their cars over the years. MGB, Triumph TR8, Morgan 8, Rover, etc.... Engine is a proven design and very lightweight.
Obviously, not a powerhouse ... but it's virtues are it only weighs 300 lbs and has up to 200 hp. I've run them in a couple Vegas over the years. GREAT combo! D&D Fabrications performed over 2200 Vega swaps back in the 70s and 80s. Now that the Vegas are rusted away (or melted away), they've turned to the MG platform for their swap fodder. Home They have lots of 215 "upgrades" available. Stroker kits, cams, intakes, etc.

Ever since I owned my first 215 powered Vega, I've thought a Miata would be a good swap (following the MG idea). Now that I own a couple Miatas, there may be a possible swap in my future.
I read this thread on Miata.net ... https://forum.miata.net/vb/showthread.php?t=139941 ... much to my dismay.... but it involved a lot of EXTRA obstacles by not keeping it simple (my plan is more simple ... or cheap). He eventually decided to go the LS route after posting a couple videos of it running with the Rover engine swapped in....
.... and doing a burnout....

Obstacles to be expected in my "cheap" swap (based on Cory's swap in the thread listed above):
- Oil pan / K-frame / steering rack clearance Oil pickup tube re-route.
- Hood brace clearance issues. Once the engine and trans are positioned, there appears to be some interference with a carb hat (even with a \shortened TB injection hat), the large HEI distributor up front..... as well as the alternator/bracket.
- Shifter hole alignment ... with T-56... I'm not afraid to cut a new hole.
- Exhaust manifold/downpipe routing .... the 215 is wider than a Ford v8. My thoughts would be to "redneck engineer" a log-type manifold out of pipe like those used on "derby" cars and rat rods to ease routing as needed..... not pretty, but works.

or even some forward swept items like the turbo guys use...... Buick 215 manifolds can be swapped to either side (if I remember correctly).

- Heat shielding for fuel lines and brake lines.
- Fuel Pressure for a carb.... reducer or even de-energize the in-tank pump and use an in-line electric pump.
I have an extra carbed 215 that works..... so that would be a cheap swap.
-- I've heard FI Tech or another company is making their self-learning throttle body type injection kits for smaller engines (currently 200 hp and up). When the lower HP systems become available ..... That would be ideal.. (later $$$).

Most issues could be resolved affordably.... hopefully. My main concern/question was the strength of the NA Miata rear diff.
My calculations show at 4.3 geared NA rear gear traveling at 70 mph on 185/60/14s would net:
about 2600 rpm with a 0.63 OD T-5
about 2225 rpm with a 0.50 OD T-56
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Old 11-20-2017, 08:23 AM
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Good plan.
Sounds like you could look over the Ford build threads that utilize a carburetor and follow about 90% of what they do.
The rear end is going to be the least of your worries.
The Honda 4 cylinder & V6 swaps use the factory Miata transmission and rear end and seem to hold up as long as the driver isn't drifting and drag racing every time the car gets started.
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Old 11-23-2017, 04:57 PM
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Sounds like you have a plan and know the right questions. Seems that over the years I've read a "few" as in 3 or 4 well executed Buick al swaps.

Good Luck!!!!!!!
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Old 11-23-2017, 07:50 PM
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1.6 diffs are easy to break. But worse is the gearing. You'll be reving up that engine to 4K+ rpms at reasonable hiway speed.
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Old 12-22-2017, 10:28 AM
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Originally Posted by MX-Brad View Post
1.6 diffs are easy to break. But worse is the gearing. You'll be reving up that engine to 4K+ rpms at reasonable hiway speed.
That's why I want to use the T-56 6-speed I've got lying around. It's got an overdrive of 0.50. So my calcs show about 2200-2300 rpm at 70 mph.... with stock 14" tires and a 1.6L 4.3 rear..

Well........... just picked up my 3rd NA Miata. A '94. So it has the larger rear (Torsen, I think... pic is on gravel driveway, so It doesn't prove much).... and it should have the marginally better 4.1 gearing.

Power windows, power mirrors and cruise (cruise is inoperable at the moment) No ABS.
This could be the car that gets the 215. 195k miles and runs fine. Hate to pull a good running engine and "ATTEMPT" something that isn't exactly a direct bolt-in engine swap. But the price was right and I won't have to mangle my '91 Rally car ... or the really rare '93 L.E.
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