DIY 306 Miata Swap

Morning all,

Wanted to introduce myself. My name is John and I'm in the process of doing a 306 swap into a 99 Miata. I did a DIY turbo on one of my other 99 Miatas but I was capped at low 200's unless I went forged internals, and then a 6 speed and upgraded diff, so I decided that I wanted to go V8.

I'm doing it without a kit as I love fab work. I'm a little slow on electrical and this is my first 5.0 so I will be looking to you for help on the Ford part of this.

Motor is a 306 with .030 TRW pistons, AFR 165's, E303, ported Explorer mani, balanced and polished crank, 1.6 RR, BBK 65mm TB and EGR.

I have a 90MM LMAF, 30lb and a Quarterhorse for tuning to go in after I get it running.

Clutch is a King Cobra and Trans is WCT5.

Rear end is 8.8 IRS from a V8 T-bird and I'm adding 3.73's and a Trac Loc diff. Axles are factory shortened units from Factory Five Racing's Cobra kits and rebroached Miata hubs to accept them.

After the car is running it's getting stripped down for a full repaint/color change to TItanium, which is a deep metallic silver. I also have a factory hard top that will be painted then.

Anyway, I'll post up a few in progress pics in a few minutes.

Jig for subframe.

Subframe after mods.

Motor is in, at least as far as the mounting goes. I actually did it twice. The first time I had it all the way back to the power steering cooling loop. It fit well. But then I started looking at the trans and where the shifter fell and it was too far forward. It also looked like the water pump would infringe on the radiator's space.

So, I redid the mounts, bent the cooling loop down and was able to move the motor back another 1 1/4". That put the shifter right at the front edge of the hole which seems OK to work with. Sorry, the side view is before I moved it back and I didn't get another shot. Now, the left head is about 1 TO 1 1/2" from the firewall.




After that I looked at the radiator. I have a 52mm Koyo that I carried over from the turbo car. With the motor moved back, all that I had to do is relocate the lower radiator mounts forward 2" and down 1/2". Basically, I moved the rear bolt hole to the front hole. Did a little trimming so everthing would clear and dropped it in. Slight bend on the stock upper mounting brackets and everything fit perfectly. Need to cut all of the stock Miata fan mounting points off of it yet. There is 1/4" gap from the end of the WP to the radiator. I could cut 1/8" or whatever protrudes through the pulley off of the tip of the pump shaft if I want another bit of clearance.



Headers fit with no problem, other than the notching that I had to do on the passenger side. After moving it back, it was discovered that I wouldn't have had to notch as far forward, thus as tall but everything is boxed and I'm not about to do it again.



Here's a shot that shows how busy the left mount is. All lines clear by 1/4", plenty of clearance on steering u-joint and collector of header. I have to replace the return line on the PS because it was kinked when The pump hung off of it while installing and dismounting the rack half a dozen times. I have another rack to rob parts off of.

timeless2 said:

Power to weight ratio rocks.

Click to expand...

Yeah, I'm hoping for 320WHP with a good tune and 2500 lbs wet. It's a base model car (no power anything except steering) and they are supposed to be2200 lbs. Ford swap is usually 200-ish lbs heavier, but I'm thinking 250 with the 8.8 over the 7.5 and a few other things but the AFR's will help me gain back about 40 over the iron heads.