What Is The Best Throttle Body Size For Me?

BKM48198 · Sep 3, 2014

I put an Explorer motor together for my Mustang a few months ago and it's running great but looking for a little more from it. It's a 96 Explorer 5.0 with gt40 (3 bar) heads and Explorer intake. It got new bearings, oil pump, ARP bolts, TFS valve springs and my old Mustang cam. It also has a 65mm TB on it now but I'm wondering if 70 or 75 mm would be better. Would it be better to leave the TB alone and go up to 24lb injectors & mass air or is the 19lb enough? I have 3.73 gears with an AOD that is stock, that is why I didn't change to a different cam yet, need to get a higher stall convertor before the cam change, hopefully that will be for next Spring. If I drop out of OD and floor it it does chirp the tires at 60mph and loves the higher rpms, just seems like I lost a little bottom end but makes up for it over 2500rpm up to 6500rpm.

deathb4dismount · Sep 3, 2014

What MAF do you have?

BKM48198 · Sep 4, 2014

deathb4dismount said:
What MAF do you have?

stock OEM mass air & Explorer injectors

jrichker · Sep 4, 2014

Stick with the 65 MM throttle body you have now. Try to avoid big changes in sizes for the intake track. When there is a large change in size you end up with turbulence which disturbs the smooth, fast flow of air.

A 70 MM or 73 MM MAF would be a good choice with a 65 MM TB.

If you stay with stock 19 Lb. injectors a 70 MM MAF from a 94-95 Mustang would be a good choice, and not expensive either.
94-95 Mustang GT MAF - $40-$100. It is 70 MM instead of the stock 55 MM on regular stangs built prior to 94. It uses a slip on duct on the side that goes to the throttle body and a 4 bolt flange on the other. You need a flange adapter to fit the stock slip on air ducting that goes to the air box. Wiring plugs right in with no changes. *1 *2

*1.) Metal flange adapter http://www.kustomz.com/components.html Buy the TR70 for $40. Or spend some time on eBay looking for one that may fit.

*2.) MAF & sensor interchange
The 94-95 Mustang 5.0 MAF & sensor is also found on:
1995-94 Mustang 3.8L F2VF-12B579-A2A,
1994-92 Crown Victoria 4.6L F2VF-12B579-A2A,
1995-94 Mustang, Mustang Cobra 5.0L F2VF-12B579-A2A,
1994-92 Town Car 4.6L F2VF-12B579-A2A,
1994-92 Grand Marquis 4.6L F2VF-12B579-A2A,
Evidently the –A1A, -A2A, AA, etc. on the end of the part number is a minor variant that did not change the operating specs. You should be able to ignore it and have everything work good.

Fuel injector sizing & injector photos

Revised 11-Dec-2011 to add larger injector sizes to injector table

Injector HP ratings: divide flow rating by.5 and multiply the result by the number of injectors. This uses a 100% duty cycle. These ratings are for naturally aspirated engines at the flywheel.

Example:
19/.5 = 38, 38 x 8 = 304 HP
24/.5 = 48, 48 x 8 = 384 HP
30/.5 = 60, 60 x 8 = 480 HP
36/.5 = 72, 72 x 8 = 576 HP
42/.5 = 84, 84 x 8 = 672 HP

The preferred duty cycle is about 85% maximum, so for a safety factor multiply the final figure times .85.

19/.5 = 38, 38 x 8 = 304 HP x .85 = 258 HP
24/.5 = 48, 48 x 8 = 384 HP x .85 = 326 HP
30/.5 = 60, 60 x 8 = 480 HP x .85 = 408 HP
36/.5 = 72, 72 x 8 = 576 HP x .85 = 490 HP
42/.5 = 84, 84 x 8 = 672 HP x .85 = 571 HP

Remember that the above ratings are at 39 PSI. Increasing the pressure will effectively increase the flow rating. Example: a 19 lb injector will flow 24 lbs at 63 PSI, and a 24 lb injector will flow 30 lbs at 63 PSI.

See http://users.erols.com/srweiss/#jcalc to get the calculators used in these examples.

Here's the duty cycle explanation. Duty cycle is how much of the time the intake is open the injectors are turned on. The 85% figure means that for 85% of the time the intake valve is open, the injectors are spraying. The idea is that you want some percentage of the duty cycle left over so that you have some room to grow the process.

If you are at 100% and you need more fuel, all you can do is turn up the fuel pressure. That means the whole fuel curve from idle to WOT is affected. Maybe you are already too rich at idle, and turning up the fuel pressure makes it worse. If you had some injector duty cycle left to play with, a custom tune could use that where it is needed. That would not over richen the whole range from idle to WOT.

If you did turn up the fuel pressure, you might be able to change the injector duty cycle to get the air/fuel mixture ratio you want since the injectors will have extra fuel delivery capability.

With larger than stock injectors or higher that stock fuel pressure, you will need an aftermarket MAF that matches the injector size. The MAF “lies” to the computer to get a fuel delivery schedule that meets the engine’s needs and isn’t too rich or too lean. The best strategy is an aftermarket MAF and a custom tune to insure the best air/fuel ratio over all the RPM range.

Don't forget to increase the fuel pump size when you increase injector size or significantly increase the fuel pressure

Diagram courtesy of Tmoss & Stang&2birds

madspeed · Sep 4, 2014

i would stick with what you have, it fits the rest of the combo

90lxwhite · Sep 4, 2014

jrichker said:
Stick with the 65 MM throttle body you have now. Try to avoid big changes in sizes for the intake track. When there is a large change in size you end up with turbulence which disturbs the smooth, fast flow of air.

A 70 MM or 73 MM MAF would be a good choice with a 65 MM TB.

If you stay with stock 19 Lb. injectors a 70 MM MAF from a 94-95 Mustang would be a good choice, and not expensive either.
94-95 Mustang GT MAF - $40-$100. It is 70 MM instead of the stock 55 MM on regular stangs built prior to 94. It uses a slip on duct on the side that goes to the throttle body and a 4 bolt flange on the other. You need a flange adapter to fit the stock slip on air ducting that goes to the air box. Wiring plugs right in with no changes. *1 *2

*1.) Metal flange adapter http://www.kustomz.com/components.html Buy the TR70 for $40. Or spend some time on eBay looking for one that may fit.

*2.) MAF & sensor interchange
The 94-95 Mustang 5.0 MAF & sensor is also found on:
1995-94 Mustang 3.8L F2VF-12B579-A2A,
1994-92 Crown Victoria 4.6L F2VF-12B579-A2A,
1995-94 Mustang, Mustang Cobra 5.0L F2VF-12B579-A2A,
1994-92 Town Car 4.6L F2VF-12B579-A2A,
1994-92 Grand Marquis 4.6L F2VF-12B579-A2A,
Evidently the –A1A, -A2A, AA, etc. on the end of the part number is a minor variant that did not change the operating specs. You should be able to ignore it and have everything work good.

Fuel injector sizing & injector photos

Revised 11-Dec-2011 to add larger injector sizes to injector table

Injector HP ratings: divide flow rating by.5 and multiply the result by the number of injectors. This uses a 100% duty cycle. These ratings are for naturally aspirated engines at the flywheel.

Example:
19/.5 = 38, 38 x 8 = 304 HP
24/.5 = 48, 48 x 8 = 384 HP
30/.5 = 60, 60 x 8 = 480 HP
36/.5 = 72, 72 x 8 = 576 HP
42/.5 = 84, 84 x 8 = 672 HP

The preferred duty cycle is about 85% maximum, so for a safety factor multiply the final figure times .85.

19/.5 = 38, 38 x 8 = 304 HP x .85 = 258 HP
24/.5 = 48, 48 x 8 = 384 HP x .85 = 326 HP
30/.5 = 60, 60 x 8 = 480 HP x .85 = 408 HP
36/.5 = 72, 72 x 8 = 576 HP x .85 = 490 HP
42/.5 = 84, 84 x 8 = 672 HP x .85 = 571 HP

Remember that the above ratings are at 39 PSI. Increasing the pressure will effectively increase the flow rating. Example: a 19 lb injector will flow 24 lbs at 63 PSI, and a 24 lb injector will flow 30 lbs at 63 PSI.

See http://users.erols.com/srweiss/#jcalc to get the calculators used in these examples.

Here's the duty cycle explanation. Duty cycle is how much of the time the intake is open the injectors are turned on. The 85% figure means that for 85% of the time the intake valve is open, the injectors are spraying. The idea is that you want some percentage of the duty cycle left over so that you have some room to grow the process.

If you are at 100% and you need more fuel, all you can do is turn up the fuel pressure. That means the whole fuel curve from idle to WOT is affected. Maybe you are already too rich at idle, and turning up the fuel pressure makes it worse. If you had some injector duty cycle left to play with, a custom tune could use that where it is needed. That would not over richen the whole range from idle to WOT.

If you did turn up the fuel pressure, you might be able to change the injector duty cycle to get the air/fuel mixture ratio you want since the injectors will have extra fuel delivery capability.

With larger than stock injectors or higher that stock fuel pressure, you will need an aftermarket MAF that matches the injector size. The MAF “lies” to the computer to get a fuel delivery schedule that meets the engine’s needs and isn’t too rich or too lean. The best strategy is an aftermarket MAF and a custom tune to insure the best air/fuel ratio over all the RPM range.

Don't forget to increase the fuel pump size when you increase injector size or significantly increase the fuel pressure

Diagram courtesy of Tmoss & Stang&2birds

See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring http://www.veryuseful.com/mustang/tech/engine/ Everyone should bookmark this site.

Ignition switch wiring
http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

Fuel, alternator, A/C and ignition wiring
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

Vacuum diagram 89-93 Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg

HVAC vacuum diagram
http://www.veryuseful.com/mustang/tech/engine/images/Mustang_AC_heat_vacuum_controls.gif

TFI module differences & pinout
http://www.veryuseful.com/mustang/tech/engine/images/TFI_5.0_comparison.gif

Fuse box layout
http://www.veryuseful.com/mustang/tech/engine/images/MustangFuseBox.gif

That's what she said.

deathb4dismount · Sep 4, 2014

I like how you guys knew exactly what I was getting at

FoxMustangLvr · Sep 4, 2014

BKM48198 said:
I put an Explorer motor together for my Mustang a few months ago and it's running great but looking for a little more from it. It's a 96 Explorer 5.0 with gt40 (3 bar) heads and Explorer intake. It got new bearings, oil pump, ARP bolts, TFS valve springs and my old Mustang cam. It also has a 65mm TB on it now but I'm wondering if 70 or 75 mm would be better. Would it be better to leave the TB alone and go up to 24lb injectors & mass air or is the 19lb enough? I have 3.73 gears with an AOD that is stock, that is why I didn't change to a different cam yet, need to get a higher stall convertor before the cam change, hopefully that will be for next Spring. If I drop out of OD and floor it it does chirp the tires at 60mph and loves the higher rpms, just seems like I lost a little bottom end but makes up for it over 2500rpm up to 6500rpm.

You're not really going to gain anything, stick with what you have and save for some aluminum heads, long tube headers, better cam and porting that explorer intake. Or just get a Vortech S/C.

BKM48198 · Sep 4, 2014

FoxMustangLvr said:
You're not really going to gain anything, stick with what you have and save for some aluminum heads, long tube headers, better cam and porting that explorer intake. Or just get a Vortech S/C.

My Mustang is a Daily Driver during the summer months and I don't plan on ever racing it, I am the original owner and probably won't get aluminum heads. I am just looking to get the most out of the motor I have now with maybe a cam change at the most. If a larger MAF or TB or injectors will make a little more power I'll change them but it sounds like a larger MAF will help flow more air and might be what I am looking for. I have already talked with someone about porting the intake and was told it really isn't worth doing unless I do get better heads, he said it might gain me 5hp.

mikestang63 · Sep 4, 2014

I wouldnt waste your money on porting the intake with stock E7 heads. If you feel the need to change anything find a 94-95 GT MAF that is 70MM and either buy or fab up an adapter to make it work with the stock intake tube. For about $50 that will give you better throttle response and a few hp.

Other than that, save up for when you do a head and cam change.

FoxMustangLvr · Sep 4, 2014

BKM48198 said:
My Mustang is a Daily Driver during the summer months and I don't plan on ever racing it, I am the original owner and probably won't get aluminum heads. I am just looking to get the most out of the motor I have now with maybe a cam change at the most. If a larger MAF or TB or injectors will make a little more power I'll change them but it sounds like a larger MAF will help flow more air and might be what I am looking for. I have already talked with someone about porting the intake and was told it really isn't worth doing unless I do get better heads, he said it might gain me 5hp.

Injectors only feed higher HP, if you go up in HP then you need bigger injectors. By only increasing your injector size you'll be accomplishing nothing positive for your car. If you upgrade your heads to TFS, AFR of Eddie then you'll need the 24lb or 30lb injectors.

You can change to a bigger MAF like mentioned in an earlier post, 70mm TB since you have the GT40 heads. I'd get long tubes and swap your slush box for a T5 and it'd be a more fun car to drive.

BKM48198 · Sep 4, 2014

mikestang63 said:
I wouldnt waste your money on porting the intake with stock E7 heads. If you feel the need to change anything find a 94-95 GT MAF that is 70MM and either buy or fab up an adapter to make it work with the stock intake tube. For about $50 that will give you better throttle response and a few hp.

Other than that, save up for when you do a head and cam change.

I have gt40 heads with TFS valve springs, I can get a MAF for about $23 from a U-Pull it yard and ebay has an adapter for $11, so I think I'll try the 70mm MAF and see how if it helps.

BKM48198 · Sep 4, 2014

FoxMustangLvr said:
Injectors only feed higher HP, if you go up in HP then you need bigger injectors. By only increasing your injector size you'll be accomplishing nothing positive for your car. If you upgrade your heads to TFS, AFR of Eddie then you'll need the 24lb or 30lb injectors.

You can change to a bigger MAF like mentioned in an earlier post, 70mm TB since you have the GT40 heads. I'd get long tubes and swap your slush box for a T5 and it'd be a more fun car to drive.

I'm 51 years OLD and have thought about a 5 speed but I enjoy my Mustang with an AOD, I had a built trans and 10 inch convertor for a while ( years ago) but now just enjoy being able to drive it anywhere without problems. I have BBK shorty headers, ford racing H pipe, and flowmasters that are in great condition, I'd rather redo the interior than buy a complete new exhaust right now, after 24 years the seats could use new covers.

89stang1 · Sep 5, 2014

BKM48198 said:
I'm 51 years OLD and have thought about a 5 speed but I enjoy my Mustang with an AOD, I had a built trans and 10 inch convertor for a while ( years ago) but now just enjoy being able to drive it anywhere without problems. I have BBK shorty headers, ford racing H pipe, and flowmasters that are in great condition, I'd rather redo the interior than buy a complete new exhaust right now, after 24 years the seats could use new covers.

Im your age and i would only own a stick in a sports car but i also own a heavily modified banshee i ride in sand with paddle tires hill climbing & drag racing etc. your as old as you feel but different strokes for different folks

FoxMustangLvr · Sep 5, 2014

89stang1 said:
Im your age and i would only own a stick in a sports car but i also own a heavily modified banshee i ride in sand with paddle tires hill climbing & drag racing etc. your as old as you feel but different strokes for different folks

I miss my old Banshee. I had a 6" extended swing arm, taller haulers and a pretty fast motor with Werks PEP suspension. Dropped the front gear to a 13 tooth and launched in second gear. I loved drag racing and hill climbing out at Glamis sand dunes and duning as well. Now (i'm 38) I ride a YZ.

Gearbanger 101 · Sep 5, 2014

Seems simple to me. Don't want to change the heads, then I probably wouldn't change the camshaft either. If getting into the engine isn't your thing, then the next logical choice would be to save up for a power adder.

More jam than any set of heads is going to get you, far less work improved driveability and when you're not stomping on it, you won't use any more fuel than stock.

Dropping that much cake on a power adder in one shot seems like it would hurt, but if you take the cost, time and effort involved at doing these small bolt ons one and a time, you're really not far off the mark....and the power rewards are that much greater.

89stang1 · Sep 5, 2014

FoxMustangLvr said:
I miss my old Banshee. I had a 6" extended swing arm, taller haulers and a pretty fast motor with Werks PEP suspension. Dropped the front gear to a 13 tooth and launched in second gear. I loved drag racing and hill climbing out at Glamis sand dunes and duning as well. Now (i'm 38) I ride a YZ.

Ive owned my banshee for 14 years never gonna let it go, theres not much more i can do powerwise its big bore, ported, bigger carbs, timing adv, 15cc domes in cool head has works suspension. You got me jealous mentioning Glamis its always been a dream of mine to ride there!
heres a cell phone pic from last weekend of my banshee....sorry for the thread hijack

BKM48198 · Sep 5, 2014

Gearbanger 101 said:
Seems simple to me. Don't want to change the heads, then I probably wouldn't change the camshaft either. If getting into the engine isn't your thing, then the next logical choice would be to save up for a power adder.

More jam than any set of heads is going to get you, far less work improved driveability and when you're not stomping on it, you won't use any more fuel than stock.

Dropping that much cake on a power adder in one shot seems like it would hurt, but if you take the cost, time and effort involved at doing these small bolt ons one and a time, you're really not far off the mark....and the power rewards are that much greater.

I just put this motor together and have only had it in for about 3 months. I don't WANT a power adder like turbo or supercharger, not even sure I want to change cams, just want to get everything I can out of the motor as it is now. Maybe someday I'll buy another Mustang and build it for more power but I bought this car New in 1989 (1990 GT) and I want to keep it close to stock and looking mostly stock. I have kept all the OE parts so if someday I want to go back I can get it about 99% stock, I don't have the OE battery or mufflers, but I have almost everything else. As far as getting into the motor, I bought a junkyard Explorer motor and took it completely apart, had a machine shop hot tank the heads and polish the crank, I did all the labor putting it together myself, I wanted a little more power than the old motor had, it spins the tires if I hit 2nd or 3rd gear hard (@ 6000rpm) that is all I need. Not everyone wants a race car with 400hp or more. My Mustang has 200,000 miles on it but looks almost new and runs better than new, once the interior is redone it will be ready for another 24 years of me driving it if I make it that long.

BKM48198 · Sep 5, 2014

89stang1 said:
Im your age and i would only own a stick in a sports car but i also own a heavily modified banshee i ride in sand with paddle tires hill climbing & drag racing etc. your as old as you feel but different strokes for different folks

I had an AOD that was built to be a pro-street trans with the 10 in convertor and it was fun to drive but now I just want to keep it looking good and running good, I've heard changing the pedals is a PITA and knowing how I would drive it with a stick I'd be buying more parts after breaking them. I would be launching it hard seeing just how much it could take. I blew my OE block apart, snapped the crank, twisted some rods, had parts blow out the front of the motor and parts all over the ground, luckily I had no body damage just the motor was trash so after that I just want to keep the car looking good and running good, it blew without any power adder or nitrous ever on it. I sold my bikes, had a 73 & 74 Suzuki TS400 dirt bike, I want to get another one because I miss the dirt, unfortunately divorce caused me to have to sell them.....but I kept my Mustang.

BKM48198 · Sep 5, 2014

400

BKM48198
Sep 5, 2014

........My 73 TS400 parked in front of my 73 Mercury Montego GT .........wish I had not sold that car, it was a Q code...had a 351CJ motor but ended up with a 429 before I sold it.

What Is The Best Throttle Body Size For Me?

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