Fox T-Bird/Cougar Forums

Hey all,

Just thought I'd pick your brains for some advice. I recently bought a low mile/cosmetic wear and tear 20th anniversary model intending on using it's V8 driveline as a donor to my 88 LS V6 which I recently blew the transmission on. I got a great deal on the 20th and have been using it as my daily over the last few days. I've really been enjoying it and am now wondering if should just keep this car as my daily driver and give it a few upgrades with parts I already have stockpiled for my other car. I was wondering if throwing on my pair of refreshed GT40 heads would be a direct swap. I also have an explorer upper/lower, 60mm throttle body, and stock mustang headers that I could use too. Anything I should be aware of when swapping these parts in? The engine is bone stock right now...

Thanks!

If you got the h.o. cam and you are tearing into it that far, just throw it in and do a full h.o. conversion.

The gt40's usually clear, but make sure you check.

If you use the Mustang headers, you'll need to ditch the Y-pipe.  The s are wrong, and the pipes are too small.  Additionally, on HO engines, the oxygen sensors are in the top of the H-pipe, not the manifolds, and your stockers won't reach, so you'll need those, too.  So basically, headers will cost you a full exhaust and sensors. #worthit.

Check for clearance but try and use the HO cam/computer/injectors if you're swapping GT40 heads/intake on.

Thanks for the replies!

Haystack:
"If you got the h.o. cam and you are tearing into it that far, just throw it in and do a full h.o. conversion."

I'd like to keep the bottom end of the engine intact for now. I want to keep driving this as my daily and don't want it out of commission for a day. With careful planning I antite that swapping the heads/intake won't put me out of commission for over a weekend.

"The gt40's usually clear, but make sure you check."

How do I check the clearance?

TheFoeYouKnow:

"Additionally, on HO engines, the oxygen sensors are in the top of the H-pipe, not the manifolds, and your stockers won't reach, so you'll need those, too."

When I go with the full exhaust setup, will I have to splice into my existing wiring harness to get the new o2 sensors to reach their new locations? Also, which model sensors do I need?

Thanks!

Just get Mustang or Mark VII sensors
 There's a couple of reasons why you can't splice or extend an oxygen sensor. They're not expensive, and new ones give a nice improvement to drivability. The HO swap is sort of an all or nothing proposition. Heads, cam, intake, Injectors, EEC. The whole burrito. You can do it in a weekend.

You can extend the oxygen sensor harness without issue. Extending the wires on the oxygen sensor itself is a no no. The other option is to just buy an oxygen sensor extension harness: https://lmr.com/item/SVE-1676A/Mustang-SVE-50L-46L-SVE-O2-Sensor-Extensions

So you need to plan this and do some research for a full HO swap.  It has been discussed on here several times and the wiring has also been discussed. Use the search function and you will find what you need.  This can be done in a long weekend but you have to plan and having an extra set of hands that know how to wrench would be extremely helpful.

I assume you are following the coolcats write up.

It is dead on, but, you really do need to do the cam injectors and computer all in one go. The h.I'm computer can'trun stock injectors (correctly at least) and the two cams have different firibg orders.

If you swap the whole top end, its easily doable in 8hrs. Leave the upper intake and exhaust.

You really should do the fuel pump as well, but those can all be done in a few hours afterwords.

Personally, I'd just wait till I had a free weekend and do the whole h.o. swap so you aren't rushing things and have the ability to hit a parts store if needed.

The gt40 heads have larger valves. Because of that, they might not clear. H.o. pistons have valve reliefs to get a bit more room, while s.o. pistons are flat tops. Anytime you mess with cams or heads, you need to make sure nothing touches before bolting stuff on.

Checking the valve to piston clearance commonly known a claying the motor:

Get some modeling clay and place some on top of the piston about 1/4” thick, install the cylinder head with a previously compressed head gasket or you can sacrifice a new one, torque the head to spec, install one set of push rods for one cylinder, and install the rockers for that cylinder. Be sure to tighten the rocker but per the rocker design (pedestal or stud mount). Once you have done this rotate the motor by hand over one full revolution (go slow to make sure the piston and valve do not touch) and stop. Uninstall the rockers, pushrods, and head. From here you may or may not see valve indentions in the clay. If you do then you need to measure the thickness of the clay at its thinnest spot. This is your valve to piston clearance. Minimum clearance is generally accepted to be 0.125”.

Searched a bit and found this easy to follow write up at Late Model Restoration.

https://lmr.com/products/how-to-check-mustang-302-351-piston-to-valve-clearance-85-95

Thanks for all the responses guys. It sounds like a lot of folks advocate for going the whole way with the swap, which I can understand from a cost/time vs performance aspect. The fact that the H.O. conversion has been done to our cars by so many people is a testament to the greatness of the mod. That said, I still have a reservation and one question. My reservation is that because I'm using this as my daily driver I cannot have it out of commission for over a weekend so I would rather not risk doing the cam/injectors/computer/fuel pump/misc.  This leads me to my question. IF my heads end up clearing, is there anything wrong with installing GT40 heads on a stock motor, adding a 60mm throttle body to the stock intake, and getting a full dual exhaust system installed? I get that it's not the most optimal configuration but will I have problems? If I do what I'm proposing, I will have the heads and exhaust in place for later in the event that I decide to do the full conversion.

Thoughts?

You're still going to run out of fuel right away, and the stock intake wont take a 60mm TB.  The blade will hit the opening on the EGR cooler.  If you have time to do the heads, you have time to do the cam. The cam is only a couple more hours work at that point. The intake will be off and apart to do either the heads OR the cam, so swapping the injectors at that time is 30 minutes work at most, and swapping the EEC is another 20 minutes.
What WILL take time is futzing with the exhaust.  If you have to put something off, put off the exhaust.  The stock manifolds will still bolt to the GT40 heads, so you can tackle the exhaust the next Saturday or whatever.  You have to know that the pipes from the H or X pipe to the lers will have to be MADE in 2 1/2 or extended if you get the 2 1/4 ones for Mustang.

Makes sense. I'll likely take the car to an exhaust shop to have them deal with this part of the build. I don't have an experience with bending/fitting the exhaust plumbing and not really much interest. I'd rather someone with the right tools and know how take care of it. Right now I'm just waiting for the weather to warm up. It's been bitter cold here lately and I can't work on anything!

What about the wiring that will need to be addressed in the EEC harness going from SD to MAF?

https://lmr.com/products/install-fox-body-mustang-mass-air-conversion

Not a huge deal but you need to be aware of what you need to change.  You also need to know that an A9P or A9L EEC will work with an automatic trans car or a manual car as long as you pay attention to the wiring.

Manual/Automatic EECs
There is a hardware difference between an auto processor & a manual processor. The difference is the way the NDS [neutral drive switch, manual transmission] & the NSS [neutral safety switch, auto transmission] are wired. They are both wired to the same pin#30 but the auto trans wiring grounds the pin to the starter solenoid & the manual grounds to signal return, during crank mode there is a voltage spike sent to pin-30 so the auto trans processor has a diode on pin 30 where as the manual processor doesn't, most of the time this won't cause a problem unless you get into a prolonged crank condition.

Those that want to convert their automatics to manuals, and swap the ECM, need to clip the wire going to pin 30 or else the ECM will fry the trace off the board. This leaves the manual EEC unable to dump codes, which looks for the loop through the neutral sensing switch of the T5 transmission.

O2 Sensor Wiring
Make sure you have a 5 speed O2 sensor harness when using an A9L or you will fry the trace also. The damage is common when people mismatch harnesses and use an automatic O2 sensor harness with an A9L computer.
For a Manual: The looped wire should connect the Blue/Yellow wire to the Purple/Yellow wire.
For an Auto: The looped wire should connect the White/Pink wire to the Purple/ Yellow wire.
If the white/pink wire( start voltage) is connected to the blue/yellow wire. It will fry "ANY" ECM you put in there. No matter if it’s an Auto or Manual ECM

I didn't think he was going MAF.  Sounded like he was staying SD for now, in which case it's not a thing.  But he WILL need either HO O2 sensors or extensions when he does the exhaust.  If he stays SD, he should be just fine with the harness he has.  Since he already HAS a 5.0, we can assume he has an automatic, and since SD 5.0 HO Mustang EECs are pretty much a 1 or 2 year thing, the chances of ending up with one for his HO swap are slim.  To that end, be sure you know what EEC codes will work ahead of time.  Any A9L, A9P or really A9x is MAF, and IF you're going MAF, get an A9P so you don't have to change any harnesses.  If you're not going to end up needing a tune, you'll like the spark tables in the A9P better.  For SD, look for Mark VII EECs, there is literally no chance of getting one that will give you trouble.  Marks have a speed limiter, though, so think about installing a toggle switch in the VSS wire to the EEC if that's something that bothers you.

What's the speed limit in the Mark VII EEC?

First, if your speedo stops counting at 85, unlock it so it keeps counting.  When I had a Mark VII EEC, I ran into the limiter at 116 while I was chasing a Mercedes SL on the freeway.  This pissed me off so bad, I put a switch in the VSS to the EEC.  Mustang EECs have their limiter set to 127.5 and this is the value that disables the limiter.  If you were going to tune a SD EEC, this is the value you'd set the limiters to.  But you're not going to tune a SD EEC, because definition files for them don't exist that I know of, and as your thread title states, you're going for "Mid-Output".

Regerding your oxygen sensors.... Bosch makes longer wired ones that will work with an exhaust where the sensor bung is further downstream. The Bosch part # is 13942 for the standard length and 13953 for the longer wire sensor....

I also recommend doing the cam/eec/heads/intake all together. You're most of the way to the cam with heads/intake off, as Foe stated, it's not that much more time/work to get the cam out.

I'd say in your case if you could find an HO block, or even a decent bottom end, clean 'er up nice and work that over, then when it's time, drop it in and wire it and plumb it and run it...

Don't forget the little stuff too, new wires, probable keep some dollars on hands for a new hose in case one gets cut or just needs replaced, belts, mounts, etc.

It's the little shiznit that will hang you up and make you question everything in the universe.

Don't forget the PB blaster, some of the exhaust manifold bolts are a real motherfawker.

Keep us updated as you make progress.

I dont think ive ever read more true words.