Ford Mustang Forums banner

1 - 20 of 49 Posts

·
Registered
Joined
·
956 Posts
Discussion Starter #1
The title pretty much says it all!

We have a '91 RX-7, and we're tired of feeding it rotary engines. We blew the coolant seal/cracked iron on the first, broken apex seal on our second motor we bought used, and don't want to sink the money into tuning our third motor which is bridgeported.

I have a 40,000 mile 5.0/T5 setup with wiring harness and computer that will be going into the car.

We don't care about making tons of power, stock this thing will pump out more than the little 13b, and have torque all over the place.

The motor will be stock for the time being. I am pulling the heads to replace the top end gaskets, and looking to replace/fix anything for longevity sake. This is an endurance race, so its going to need to last!

We will keep the rev's down, with stock intake and heads it won't be making any steam up top anyways. That being said, I still want to install ARP rod bolts and new valve springs.

Along with head gaskets(any recommendations?), I will use ARP head bolts. They will be reuseable in case we need to change a head gasket at the track. I'll also use the nice rubber/reinforced valve cover gaskets, so we can reuse them.

185 T-stat and the car already has an electric fan wired up to help keep things cool.

How does this look to everyone? Am I spending money on anything thats a waste? Am I missing anything?

Oiling is still on my mind, I will be running the stock double sump pan, but still looking up plans on how to modify it. Additionally, an ARP or Ford Racing oil pump driveshaft will be cheap insurance. Should I just run the stock oil pump?

Sorry for the long-winded thread, hopefully I'll give some ideas to others looking to build something similar. Thanks!
 

·
Registered
Joined
·
763 Posts
isn't the car supposed to cost less than 500$?
 

·
Registered
Joined
·
5,521 Posts
I have an 80 RX7; the little 12A is a surprising motor. As I recall the stock rear gear is in the 3.90 - 4.xx range which means your revs won't be all that low even with the T-5's 5th gear. With stock springs on the heads you will probably be done at 5500. I think I'd do a stock 195 t-stat so you are assured the computer will go closed loop. Sounds fun though. Using a conversion kit?
 

·
Registered
Joined
·
956 Posts
Discussion Starter #4
isn't the car supposed to cost less than 500$?
We got a nice low residual value after we blew the motor at the last race. The rest of it is to do a good job hiding it all, and bribing the judges.

We'll take any penalty laps, just to get the car on the track. We don't plan on winning, just having a good time! It'll cancel out for the next race and we ought to be able to race with no penalty next time out.
 

·
Registered
Joined
·
956 Posts
Discussion Starter #5 (Edited)
I have an 80 RX7; the little 12A is a surprising motor. As I recall the stock rear gear is in the 3.90 - 4.xx range which means your revs won't be all that low even with the T-5's 5th gear. With stock springs on the heads you will probably be done at 5500. I think I'd do a stock 195 t-stat so you are assured the computer will go closed loop. Sounds fun though. Using a conversion kit?
My first lemons race was in an FB with a 12A, that thing was so much fun. Light, nimble, very well balanced and revved forever.

Not sure what gears are in this car, I'll need to check it out. Its a convertible, and has 4 piston calipers up front from the factory, and discs out rear. We loaded them up with Hawk Blue's...I think they'll be just fine!

As far as RPM, there aren't many long straights in Lemons, they try to tame the top speeds with tire chicanes. Of the races I've been in, I think 95 was the fastest we got. This car will have more power though so it will be capable of more.

Any recommendations on valve springs? I don't WANT to rev it high, but having the ability would be nice in tight situations.

We're going with the Granny's Speed kit, and keeping the RX7 style hydraulic clutch setup.
 

·
Registered
Joined
·
1,068 Posts
May I suggest a ford n/a 2.3 instead? Yes the 302 will have way more power all around, but you are asking for rear axle trouble and they are going to nail your ass to a wall if you do a halfway proper V8 conversion in that car.

Now, you grab an el-cheapo 2.3 carb motor, a used e-bay cam, mill the hell out out the head to get the static CR up, do a half ass port job with a decent valve job and it will run. It will be cheaper, you will fly through BS tech, and you can beat the #### out of it (7k RPM's) all day long.

No wait, don't do any of that. Our team wants to be the first to win with a n/a 2.3.....
 

·
Registered
Joined
·
956 Posts
Discussion Starter #7
May I suggest a ford n/a 2.3 instead? Yes the 302 will have way more power all around, but you are asking for rear axle trouble and they are going to nail your ass to a wall if you do a halfway proper V8 conversion in that car.

Now, you grab an el-cheapo 2.3 carb motor, a used e-bay cam, mill the hell out out the head to get the static CR up, do a half ass port job with a decent valve job and it will run. It will be cheaper, you will fly through BS tech, and you can beat the #### out of it (7k RPM's) all day long.

No wait, don't do any of that. Our team wants to be the first to win with a n/a 2.3.....
Not a bad idea, but we have the motor and tranny already from an earlier project! :cool:
 

·
Registered
Joined
·
956 Posts
Discussion Starter #8
Does anyone have an opinion on the valvesprings? The heads will be off while I do the top-end gaskets, it would be a good time to do get the springs done.

Whats the failure rate on stock, low mileage pieces? What about when you show them long run time and high temps, as with an endurance race?
 

·
Registered
Joined
·
1,554 Posts
Does anyone have an opinion on the valvesprings? The heads will be off while I do the top-end gaskets, it would be a good time to do get the springs done.

Whats the failure rate on stock, low mileage pieces? What about when you show them long run time and high temps, as with an endurance race?
I think oiling tends to be the major killer for 5.0's at lemons. Hunt around for levyracing, they campaign a 5.0L in lemons.
 

·
Registered
Joined
·
956 Posts
Discussion Starter #10
I think oiling tends to be the major killer for 5.0's at lemons. Hunt around for levyracing, they campaign a 5.0L in lemons.
I'll look into it! For now its looking like some simple baffles, a larger oil filter if possible, and a half or full quart of extra oil.
 

·
Registered
Joined
·
956 Posts
Discussion Starter #11
We pulled the motor apart last night. The main and rod bearings have some wear, my buddy said they'd likely last for another 50k of street driving. We're doing anything BUT street driving, so I'm going to plasti-gauge a fresh set and go from there. What clearances should I look to run for this type of application- endurance road racing?

None of the bearings had spun, and the journals all look good with no gouging, so I'll likely clean it all up really well and just install the new ones.

I'll need to post pics later, but I've also started removing the factory MAzda wiring harness. This thing is a mess, but its so large it'll really help offset some of the weight we've gained going with the V8.

Still waiting on the Granny Speed kit before I can get it all installed, I'll keep you all updated.
 

·
Registered
Joined
·
2,133 Posts
Does anyone have an opinion on the valvesprings? The heads will be off while I do the top-end gaskets, it would be a good time to do get the springs done.
I have some 5.0L valve springs you can have. No idea what the seat pressures are though. You'll want to have a machine shop check them. Wayne Calvert can do this.
 

·
Registered
Joined
·
956 Posts
Discussion Starter #13
I have some 5.0L valve springs you can have. No idea what the seat pressures are though. You'll want to have a machine shop check them. Wayne Calvert can do this.
I went ahead with the Trick Flow kit, good to .54X" lift and comes with springs, retainers, locks, and valve seals. thanks though!

I'll clean the heads and hand-lap the valves, but thats about all the work these stock heads will see.
 

·
Registered
Joined
·
956 Posts
Discussion Starter #14
Here is a picture of the car at the first race....where it blew up after 15 laps!


What it looked like a few days ago


A picture of whats to come!


Motor stripped down, it'll get new bearings. I hope the rings are alright, all the cylinder walls look good.
 

·
Registered
Joined
·
191 Posts
FWIW, make sure you run a decent oil cooler. With the stock motor you'll have oil temps over 300 degrees within a few laps. Even the FMS unit will drop it to 240 or so.

With the stock top end you might consider a higher OD for the T5. The car won't pull the .68 OD. The .80 would be ideal. Give Bruce at Modern Driveline or Tony at Astro a buzz. Of course your rear gear will determine quite a bit too.

Just my $.02
 

·
Registered
Joined
·
956 Posts
Discussion Starter #16
FWIW, make sure you run a decent oil cooler. With the stock motor you'll have oil temps over 300 degrees within a few laps. Even the FMS unit will drop it to 240 or so.

With the stock top end you might consider a higher OD for the T5. The car won't pull the .68 OD. The .80 would be ideal. Give Bruce at Modern Driveline or Tony at Astro a buzz. Of course your rear gear will determine quite a bit too.

Just my $.02
The oil cooler is a good idea. The RX7 has one from the factory, but its lines are terrible and leaky anyways. It'd be easier and likely cheaper to go with a new system from scratch.

We'll need to find a place in the budget for it during the season.
 

·
Registered
Joined
·
910 Posts
Keep it cool! I've done 8 LeMons races and have seen several 5.0s suffer because they overheat. Get a good radiator, oil cooler, and lots of air flow.
 

·
Registered
Joined
·
956 Posts
Discussion Starter #18
Keep it cool! I've done 8 LeMons races and have seen several 5.0s suffer because they overheat. Get a good radiator, oil cooler, and lots of air flow.
I am going to run the stock RX-7 radiator for now. Its larger than the stock 5.0 radiator, too. I don't see it going long term, I just want to get the car movign under its own power.

It will likely get a larger radiator and a "newer" balancer before it sees its first Lemons race. I'd like to get some miles under its belt for shakedown purposes, whether it be at the drag strip, auto-X, or a trackday.

For an update, the rings were way out of spec, and the pistons a tad undersized. The clearance between the pistons and bore was ok though so we touched up the cylinders with a 3-stone on a drill, and installed new rings.

The shortblock is back together- ended up taking new rings, main and rod bearings, timing chain (no gears, just chain), ARP head bolts, Trick Flow valve spring kit, and of course all new gaskets.

Thankfully, a lot of these costs will be offset by selling off the RX-7 parts.

The motor mount stuff finally came in, the kit is very straightforward. 5 attachment points, no cutting/drilling/welding, and its installed. The transmission mount even uses the stock mounting locations and hardware.

All I'm lacking now is a starter and shifter(which I'll need to buy), and the tranny/bellhousing, which is at a buddy's house.

Its coming along, I'm excited to get it running! I'm going to estimate a stock power output of 195 hp and 290 tq- which should get this light car up to speed pretty quickly!
 

·
Registered
Joined
·
191 Posts
The oil cooler is a good idea. The RX7 has one from the factory, but its lines are terrible and leaky anyways. It'd be easier and likely cheaper to go with a new system from scratch.

We'll need to find a place in the budget for it during the season.
Yep, or you could get new fittings for the RX cooler. A couple buddies are dropping an LS1 in their RX-7, so we've been going through the trials of what can get reused and what needs to be bought/fabbed.

The factory cooler was pretty nice.
 

·
Registered
Joined
·
956 Posts
Discussion Starter #20
Yep, or you could get new fittings for the RX cooler. A couple buddies are dropping an LS1 in their RX-7, so we've been going through the trials of what can get reused and what needs to be bought/fabbed.

The factory cooler was pretty nice.
Its a decent cooler, where did your buddies find the fittings at?

Thanks!
 
1 - 20 of 49 Posts
Top