Engine Help Me With Throttle Body And Injector Sizing

stealth886 · Nov 28, 2016

I am needing help sizing my throttle body and injectors. Here are my engine specs:

331 CI
Edelbrock performer RPM heads, 2.02 intake, 1.60 exhaust
FTI camshaft with 1.72 roller rockers DUR @ .050 is 226/230, lift with 1.72 rockers is .607/.585
Compression ratio is around 10:1
1993 Cobra intake, Lower ported by TMOSS to match heads. Will flow 250 CFM

Estimated flywheel horsepower in the 400 HP range. Everything I see online is pointing to 30 LB injectors up to 425 horsepower. I do have a set of 30 LB injectors, and a 36LB set, not sure what to go with. I also have an ACCUFAB 65MM throttle body, but I am not sure if it will match this combo or not. Please give me your advice. Thanks in advance.

RaggedGT · Nov 28, 2016

The 30lb injectors and 65mm throttle body sound like winners to me.. let's see if we can get the opinions of a couple guys with a lot more knowledge.
@90sickfox @mikestang63

90sickfox · Nov 28, 2016

This will help you out... All you need to know is bore, stroke, and power band for your cam.

http://www.hipermath.com/images/throttle_body_2.jpg?1463161109

If you go to the hipermath website there is a throttle body size calculator. I would think you'd need a 75mm. That's what I have on my 331 turbo project.
http://www.hipermath.com/math_center/racing_calculations

mikestang63 · Nov 28, 2016

I think you should be ok with the 30's if you bump up the fuel pressure. However if you have 36 I would run those so you don't end up maxing them out, as long as you either have a calibrated MAF or can tune to ir. For TB, I would run at least a 75MM. What brand and size MAF are you planning to use? You can go with either a Pro M or LMAF.

What springs are you running on your heads- the ones Ed recommended I hope to match the cam.

stykthyn · Nov 28, 2016

You can bore out the inlet on the cobra to match a 75mm. It's what I run. It's effectively the largest Tb you can use on that intake.

General karthief · Nov 28, 2016

Bigger, better, faster, more.
Thats all I got.
I know, I'm useless.

Gearbanger 101 · Nov 29, 2016

30lb injectors are more than sufficient in a N/A combo to feed 331ci. You'll also be fine with the 65mm throttle body you currently have.

The 3-5hp gain you'll get jumping up to another throttle body size isn't worth the cost.

FWIW, I ran 30lb injectors and my accufab 70mm for years without any major trouble. If you're going to need to spend money on anything, it's going to be a chip and a tune to tie it all together....because something tells me your stock ECU isn't going to like your combo very much. Mine didn't and I ran a less aggressive can than you've got..

I don't know who you recommend that came to you, but if it were me, I'd think about running less cam. You didn't list the LSA, but you don't have the intake, heads or cubes to justify something that big and all its going to do is cause you drivability issues. It's going to be one lazy mofo below 4,000RPM

Grn92LX · Nov 29, 2016

Use the 36's since you have them. I had maxed out 30's on my 347 and had to step up to 42's. You have the 65mm tb so i'd reuse it. If you were buying all new, 75mm would be the minimum you'd want on a stroker but you'd have to open up the inlet on the upper. Stick with the cam Ed designed for you. It's not too "big".

jrichker · Nov 29, 2016

Fuel injector sizing & injector photos

Revised 26-Dec-2014 to add statement about figures are for flywheel HP and not rear wheel HP

Injector HP ratings: this flywheel HP, not rear wheel HP.
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/calcpchg.htm 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

Copied from the FORD RACING PERFORMANCE PARTS catalog:

PROPERLY SIZING FUEL SYSTEM COMPONENTS

Fuel Pumps
The following information is presented assuming the above information has been taken into consideration regarding BSFC, fuel pressure and specific gravity of the fuel being used. Most fuel pumps for electronic fuel injection are rated for flow at 12 volts @ 40 PSI. Most vehicle charging systems operate anywhere from 13.2v to 14.4v. The more voltage you feed a pump, the faster it spins which, obviously, will put out more fuel. Rating a fuel pump at 12 volts then, should offer a fairly conservative fuel flow rating allowing you to safely determine the pump’s ability to supply an adequate amount of fuel for a particular application.

As previously mentioned, engines actually require a certain WEIGHT of fuel, NOT a certain VOLUME of fuel per horsepower. This can offer a bit of confusion since most fuel pumps are rated by volume, and not by weight. To determine the proper fuel pump required, a few mathematical conversions will need to be performed using the following information. There are 3.785 liters in 1 US Gallon. 1 gallon of gasoline (.72 specific gravity @ 65° F) weighs 6.009 LBS.

To be certain that the fuel pump is not run to its very limit, which could potentially be dangerous to the engine, multiply the final output of the fuel pump by 0.9 to determine the capacity of the fuel pump at 90% output. This should offer plenty of ‘cushion’ as to the overall “horsepower capacity” of the fuel pump.

To determine the overall capacity of a fuel pump rated in liters, use the additional following conversions:
(Liters per Hour) / 3.785 = Gallons
Multiply by 6.009 = LBS/HR
Multiply by 0.9 = Capacity at 90%
Divide by BSFC = Horsepower Capacity
So for a 110 LPH fuel pump:
110 / 3.785 = 29.06 Gallons
29.06 x 6.009 = 174.62 LBS/HR
174.62 x 0.9 = 157 LBS/HR @ 90% Capacity
157 / 0.5 = 314 HP safe naturally aspirated “Horsepower Capacity”

Safe “Horsepower Capacity” @ 40 PSI with 12 Volts
60 Liter Pump = 95 LB/HR X .9 = 86 LB/HR, Safe for 170 naturally aspirated Horsepower
88 Liter Pump = 140 LB/HR X .9 = 126 LB/HR, Safe for 250 naturally aspirated Horsepower
110 Liter Pump = 175 LB/HR X .9 = 157 LB/HR, Safe for 315 naturally aspirated Horsepower
155 Liter Pump = 246 LB/HR X .9 = 221 LB/HR, Safe for 440 naturally aspirated Horsepower
190 Liter Pump = 302 LB/HR X .9 = 271 LB/HR, Safe for 540 naturally aspirated Horsepower
255 Liter Pump = 405 LB/HR X .9 = 364 LB/HR, Safe for 700 naturally aspirated Horsepower

Note: For forced induction engines, the above power levels will be reduced because as the pressure required by the pump increases, the flow decreases. In order to do proper fuel pump sizing, a fuel pump map is required, which shows flow rate versus delivery pressure.

That is, a 255 liter per hour pump at 40 PSI may only supply 200 liters per hour at 58 PSI (40 PSI plus 18 lbs of boost). Additionally, if you use a fuel line that is not large enough, this can result in decreased fuel volume due to the pressure drop across the fuel feed line: 255 LPH at the pump may only result in 225 LPH at the fuel rail.

My Comments:

A lot of people oversize the fuel pump by buying a 255LPH pump thinking that the fuel pump regulator will just pass the excess gas back to the tank. It does, but… Did you ever consider that circulating the fuel around as a 255 LPH pump does will cause the gas to pickup engine heat? What happens to hot gasoline? It boils off or pressurizes the fuel tank! With most of the 5.0 Mustangs having the carbon canister removed or disabled, the car stinks like gas, and the gas mileage drops since the hot fuel evaporates away into the air.

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

No.11 · Nov 30, 2016

jrichker said:
My Comments:

A lot of people oversize the fuel pump by buying a 255LPH pump thinking that the fuel pump regulator will just pass the excess gas back to the tank. It does, but… Did you ever consider that circulating the fuel around as a 255 LPH pump does will cause the gas to pickup engine heat? What happens to hot gasoline? It boils off or pressurizes the fuel tank! With most of the 5.0 Mustangs having the carbon canister removed or disabled, the car stinks like gas, and the gas mileage drops since the hot fuel evaporates away into the air.

Thanks for pointing this out. I was one of those who thought, meh, might as well put a 255 in there. Maybe I'll just go with a 155 for now.

A5literMan · Dec 1, 2016

Here's my generic answer-run as big of a MAF,TB,CAI as you can. You don't want any restrictions of airflow. Now with that intake you're going to be limited to a 75mm(at most-with some porting). 65 is too small and a choke point. The intake isn't the best choice IMO but will make lots of mid range power. These comments are for maximizing power potential. If you're not worried about 10-30hp then run the 65/intake/etc etc.

30#inj are going to be the minimum you can run. I'd run the 36's with a matching pro-m meter. I also wouldn't use less than a 190lph pump. I've ran 255's on a couple cars that didn't really need that much pump and had no issues whatsoever. I prefer Walboro.

Don't know what gearbanger is on about but that cam isn't to big and Ed knows his stuff. I do hope you have the proper springs. I assume you do by my previous statement about said cam profile. Lol. It should make plenty of torque in the mid range and pull hard to 6k IMO. You will probably need a tune/chip to maximize driveability/idle and power.

Gearbanger 101 · Dec 1, 2016

A5literMan said:
Don't know what gearbanger is on about but that cam isn't to big and Ed knows his stuff.

I'm running less cam than that, with equivalent heads, a much better intake and a full compliment of intake and exhaust mods on my 10:1 331 and its lazy under 3,500RPM and doesn't really start coming alive until 4,000RPM. So one can choose to take my personal experience into account, or disregard it....I don't really care.

I will however be pulling my cam in the spring, for something a little tamer with better idle quality and a more usable, street friendly power band. No need to have a cam in there that'll spin to 6,500RPM, when the stock ECU ends the party at 6,250RPM. Less cam will be much easier on valve springs as well.

And FWIW, bigger isn't better when it comes to throttle body selection. While WOT may not show any drawbacks, part throttle drivability and tuning can be finicky with big throttle body's on engine that can't utilize them. My advice is to run as big a throttle body as necessary and nothing more. That Cobra intake doesn't have the physical real estate to accept anything larger than a 70mm throttle body, which will still require port matching. And IMO, trading up from a 65mm at this point to a 70mm is wasted money for the hand full of top end horsepower he'd gain.

The 30lb squirters are fine. He's not going to come anywhere close to maxing them out on a mild stroker. Anyone who does likely has other fuel related issues going on.

Regardless, he's going to have enough parts in this car to make retuning the ECU mandatory.....or suffer poor drivability. Id sink my money into that, before ever considering a bigger throttle body.

But again, these are only my opinions.

A5literMan · Dec 1, 2016

Gearbanger 101 said:
I'm running less cam than that, with equivalent heads, a much better intake and a full compliment of intake and exhaust mods on my 10:1 331 and its lazy under 3,500RPM and doesn't really start coming alive until 4,000RPM. So you can choose to take my personal experience into account, or disregard it....I don't really care.

I will however be pulling my cam in the spring, for something a little tamer with better idle quality and a more usable, street friendly power band. No need to have a cam on there that'll spin to 6,500RPM, when the stock ECU ends the party at 6,250RPM. Less cam will be much easier on valve springs as well.

And FWIW, bigger isn't better when it comes to throttle body selection. While WOT may not show any drawbacks, part throttle drivability and tuning can be finicky with big throttle body's on engine that can't utilize them. My advice is to run as big a throttle body as necessary and nothing more. That Cobra intake doesn't have the physical real estate to accept anything larger than a 70mm throttle body, which will still require port matching. And IMO, trading up from a 65mm at this point to a 70mm is wasted money for the hand full of top end horsepower he'd gain.

The 30lb squirters are fine. He's not going to come anywhere close to maxing them out on a mild stroker. Anyone who does likely has other fuel related issues going on.

Regardless, he's going to have enough parts in this car to make retuning the ECU mandatory.....or suffer poor drivability. Is sink my money into that, before ever considering a bigger throttle body.

But again, these are only my opinions.

Well I agree with you on the intake/TB combo. I also agree on the tuning advise. Where we differ is the cam. Without full info on the timing events/etc of the profile it's hard to come to a complete "opinion"-which you also stated in your first response. Heck I have a 70mm on my 302. I don't have any part throttle issues

Where I disagree is that 226/230*@.050 in a 331 is to "big". Will it be lazy in the off idle-2500/3k range? Maybe,slightly,but those heads flow well enough to move enough air in the mid to upper(6-6500) to make up any lowend issues IMO. Probably splitting hairs here is all I'm saying. It really depends on his end goals.

One thing I know for sure is Ed at flowtech has made thousands of cams for these cars and knows his stuff. I will say that my custom(by a different person) was 223/227 for a 302. But I did have more head/intake/tb etc and sold the project before any real world experiences with the combo and it was designed for strip/street duties.

FoxMustangLvr · Dec 1, 2016

stealth886 said:
I am needing help sizing my throttle body and injectors. Here are my engine specs:

331 CI
Edelbrock performer RPM heads, 2.02 intake, 1.60 exhaust
FTI camshaft with 1.72 roller rockers DUR @ .050 is 226/230, lift with 1.72 rockers is .607/.585
Compression ratio is around 10:1
1993 Cobra intake, Lower ported by TMOSS to match heads. Will flow 250 CFM

Estimated flywheel horsepower in the 400 HP range. Everything I see online is pointing to 30 LB injectors up to 425 horsepower. I do have a set of 30 LB injectors, and a 36LB set, not sure what to go with. I also have an ACCUFAB 65MM throttle body, but I am not sure if it will match this combo or not. Please give me your advice. Thanks in advance.

I don't see any need or benefit from running a TB that's any bigger than your upper intake inlet size. So match that accordingly.

mikestang63 · Dec 1, 2016

FWIW, I've seen many a time people look at the specs on Ed's cams and say wtf, but then they outperform every time with great street manners.

RangerJoe · Dec 6, 2016

My combo"

10.7:1 331
AFR 185
Systemax Intake w/ 70mm Accufab & 80mm Pro-M w/ 30 lb Inj.
FTI Cam 227/235 .613 & .588 111.5
Big tube Shorties
STOCK ECU, but does use an extender to bypass review limiter

Runs great, no idle issues, pulls clean to the 6500 shift point, goeso in the 11's on street legal DOT's with full interiorange, AC and PS.

Go with the 36's if you have them. The TB should flow roughly 650 CFM.

Joe

Engine Help Me With Throttle Body And Injector Sizing

stealth886

Member

RaggedGT

Been here over a DECADE and still no CT

90sickfox

Wasn't a pretty sight...and I've got big hands

mikestang63

stykthyn

I want to measure mine. It doesn't look that tall.

General karthief

wonder how much it would cost to ship you a pair

Gearbanger 101

Straight Outta Locash

Grn92LX

Fidanza Man!

jrichker

StangNet's favorite TOOL

No.11

A5literMan

At least it is lumpy...

Gearbanger 101

Straight Outta Locash

A5literMan

At least it is lumpy...

FoxMustangLvr

I love my Pimp

mikestang63

RangerJoe

I leave the horn on while driving

Similar threads

Engine Help Me With Throttle Body And Injector Sizing

Member

Been here over a DECADE and still no CT

Wasn't a pretty sight...and I've got big hands

I want to measure mine. It doesn't look that tall.

wonder how much it would cost to ship you a pair

Straight Outta Locash

Fidanza Man!

StangNet's favorite TOOL

At least it is lumpy...

Straight Outta Locash

At least it is lumpy...

I love my Pimp

I leave the horn on while driving

Similar threads

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