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Old 04-09-2018, 02:08 PM   #1  
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Default Cadillac 4.9 V8 Conversion in a Lemons Car

I thought you guys might enjoy this. I'm most of the way through this build, swapping a Cadillac 4.9L aluminum block V8 into a '94 miata. This miata was previously crashed, then stripped down, caged, and turned into a 24 hours of Lemons race car with a Geo Metro roof stuck on to make it a "hatchback" of sorts. After racing for a couple seasons and having mild success and good reliability, we decided to go for more power and more fun. No one has run a V8 miata in lemons as far as I know, so it seemed like a good challenge. In order to get a V8 swapped on a lemons budget, we decided to go with a '91 cadillac deville 4.9L V8. These a front wheel drive v8 scrap heaps more or less and we were able to get the whole running car for free.











These motors have the 60 degree GM "Metric" bellhousing, and a rwd AX15 manual transmission from a '98 dodge dakota bolts right up, sort of. The clutch is from a Pontiac Fiero and I picked up a conversion flywheel from LSC for fairly cheap. It turned out that the bellhousing was slightly too long for the input shaft length, so we made a fixture and cut and welded it back, taking about .75" off of the length.



Transmission and engine assembled, ready to drop in:



Hacked away a lot of the firewall to get the engine as far back as possible:



Engine placed to build engine mounts. Its as far back and as low as we could go, without going into the pedal box area:



Transmission cross member:



Frame plated and trans tunnel closed back up, with bracing to the cage:





Custom oil pan to clear the k-member:



Since there was basically no room left to make an efficient exhaust, we decided to go upwards with the headers and out the sides. Seemed like the coolest option at least. So I built some custom headers after machining header plates to fit the Cadillac motor. To go with the lemons theme, I used a lot of bends and tubing from an old set of headers we found in a junk yard from an old dodge:
















The rear end was converted to the Ford 8.8, with an explorer cover with the wings, and solid mounted to the subframe with spherical washers to allow for pinion angle adjustment:



There's no picture of it yet, but we're using a C4 corvette driveshaft with conversion u-joints on both ends, its the perfect length for some reason.

Oh, and all 4 wheels were converted to Mustang 5-lug hubs so we can run 17x9 wheels with the SVT Cobra brakes and 255/40/17 tires.

Up next is fitting the 80's Toyota Supra radiator in, mounting an alternator and routing the serpentine belt, and finishing the wiring.

After its all done, and after including all the money from selling off the miata parts, we're actually at about -$500 on the project. Wheels, tires, and brakes are "safety items", so they're not included in the budget.
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Old 04-09-2018, 02:19 PM   #2  
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I like it!!!!
Lots of thinking out of the box on the build.

Any more information about converting the hubs to 5 lug?
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Old 04-09-2018, 02:20 PM   #3  
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This motor, with starter, flywheel, clutch, and alternator weighs just about 85lbs more than the miata motor in the same condition. Its also shorter both lengthwise and height wise, which is nice. We went through the motor to confirm everything looked good and clearances were right, and did some port and combustion chamber work on the heads. Supposedly that is the biggest restriction on these motors. They also got a 3-angle valve job from an old snap-on valve grinder. Then we took .075" off the deck height of the head and measured the compression ratio to be right at 10.1:1









We also got a little creative with filling the egr holes which were located right in the high pressure area on the 2 middle exhaust ports. Melted a bunch of aluminum, poured and filled them up, then ground the ports into shape. Backyard engineering at its best.



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Old 04-09-2018, 02:24 PM   #4  
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I like it!!!!
Lots of thinking out of the box on the build.

Any more information about converting the hubs to 5 lug?

For the rear, I turned down the Mustang rear hubs to fit into the Miata bearing. It actually worked out really nicely, even the dust seal on the back side of the miata upright fits the Ford 8.8 CV. For the front, I modified the miata spindles to accept the Mustang front hubs. I'll try and get some pics of that soon. The caliper bracket designs are almost done and will be machined soon, so I'll get some pics when those are done.

Pics of the rear:

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Old 04-09-2018, 03:01 PM   #5  
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Found a pic of the front hub setup, but it doesn't show the machining work:

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Old 04-09-2018, 04:30 PM   #6  
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Very cool! This should do very well in Lemons. Was this car at Gingerman last April? It looks familiar, but I can't remember if it was at the race, or if I have just seen pictures of it.
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Old 04-09-2018, 04:43 PM   #7  
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Very cool! This should do very well in Lemons. Was this car at Gingerman last April? It looks familiar, but I can't remember if it was at the race, or if I have just seen pictures of it.
It was there, and last fall too. The car is out in Colorado now and I'm not sure when we'll make it back to the midwest to race again, but hopefully someday it will happen. The first race is in June at High Plains out here near Denver.
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Old 04-09-2018, 05:12 PM   #8  
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Awesome! We were there in the orange and green chop top Supra. We ended up swapping over to ChumpCar and the car is now not eligible for Lemons, but we usually still do the Lemons practice days at Gingerman. Good luck with the build and first race!
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Old 04-11-2018, 07:56 AM   #9  
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That's funny, our car is now not Chump eligible because of the V8 swap, it doesn't work well in their points system.

Update: C4 Corvette Aluminum driveshaft with conversion u-joints just fit right in with no modification necessary. Sometimes things just work out. The front flange was from the dodge with a 1330-7290 conversion joint, and has a good 3-4 inches of engagement in the transmission. The rear flange is from a thunderbird with a 1310-1330 conversion joint. The driveshaft was literally $30 shipped from ebay.

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Old 04-15-2018, 07:55 PM   #10  
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I have one concern. Iím worried the aluminum you added to the heads isnít of the same alloy or heat treatment. I fear it may melt out during racing and totally f up you engine. Maybe not....,
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Old 04-15-2018, 08:23 PM   #11  
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Oh yea, definitely not the same alloy or heat treatment, its aluminum poured into a cast iron head. Plenty of people have done this over the years, so its not anything new. I doubt it will melt, and it has some pretty odd shapes holding it in there, so its not just going to slide out. If it does have small pieces fracture and fall off, its going out the exhaust, not into the engine. This is only in the exhaust port. If it doesn't work, we have plenty of spare engine parts to throw on if needed. The motor and trans have been set up to be removed within an hour, so we can do a drivetrain swap in record time and be back on the track.
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Old 04-15-2018, 11:54 PM   #12  
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Funny, I just saw this post. There was a Ford powered V8 Miata at the Lemons race at Joliet this weekend. Yours should be a weapon when it is done.
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Old 04-16-2018, 01:49 PM   #13  
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Funny, I just saw this post. There was a Ford powered V8 Miata at the Lemons race at Joliet this weekend. Yours should be a weapon when it is done.
Interesting. Did they finish? Did they get penalty laps? Was it fast????
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Old 04-16-2018, 06:07 PM   #14  
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I don’t know if they got any penalty laps. It was in their pit more than it was out. I can’t say that I ever saw it on track in my 2.5 hour stints on either day.
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Old 04-22-2018, 09:37 AM   #15  
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New serpentine layout using a jeep liberty tensioner, sbc A/C delete pulley, and an alternator from an early 90's camaro.




Also, found a new steering wheel center, it fit better upside down. Check out the shifter position, we had to reduce the truck shifter length by about 2.5", but it ended up working out really well:

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Old 05-14-2018, 09:04 AM   #16  
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Splitter needs to be re-done, but its getting close to race ready. Ride height is set and the brakes are all mounted and bled. The 17x9's look pretty huge on this thing, we're going to need some fairly decent size fender flares to pass lemons tech inspection.



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Old 05-14-2018, 10:30 AM   #17  
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The technical aspects of the car are really impressive, as is all the work that has been put into it
..............but.............
it sure is ugly.
Guess that is the whole point.
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Old 05-14-2018, 10:45 AM   #18  
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It is the point indeed. Our car has been called "The epitome of Miata sadness" by one of the judges, which we take as a very high honor.

It would be much harder to get a clean, straight v8 miata with big wheels and brakes into lemons without getting lots of penalty laps.
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Old 05-30-2018, 09:39 AM   #19  
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It runs and drives!! Its hard to tell in this video, but this is one of the steepest hills around, at its at 8000' elevation, so the motor is actually moving the car pretty dang well. Also, the exhaust sounds most excellent. First track day this friday, so we'll see how it performs in the corners.


And the old school corvette dash works:


The donor list:



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Old 06-11-2018, 09:30 AM   #20  
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Well, turns out this is a pretty decent motor. Ended up 4th overall and 1st in C class with the fastest lap of the weekend by 3 seconds. In fact, it was the fastest lap ever for a lemons race at high plains raceway. Sure was fun. Ran all 14.5 hours without missing a beat, passing literally every other car constantly, except for all the fuel stops. As they said at the awards ceremony, this is proof that the HT4100 series motor is the best pushrod engine to ever come out of Detroit.

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Old 06-11-2018, 11:24 AM   #21  
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Very impressive.
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