Carb to EFI: Speed Density or Mass Air?

Chris in NY · 10-11-2001, 12:25 PM

Hello all. I will be converting my 500HP 408 Windsor (in a street '71 Mustang) from 750 DP / Victor Jr. to EFI. The whole EFI aftermarket clearly favors speed density, but I can't figure out why mass air isn't a better choice. For example, the FRPP EPEC seems to be offer plenty of tunability for a mass air install and you can get large diameter mass air meters, which should be low restriction. Also, my thought is that plumbing the Victor Jr. for EFI will make best power for my application versus the two piece EFI intakes. Thanks for any opinions/thoughts/experience.

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'71 Mach1, 408, TKO, Baer Claws, GlobalWest suspension, 17's, etc. Runs 12.76 @ 112, but its a road race car.

Dark_5.0 · 10-11-2001, 12:43 PM

Mass air for sure this is an easy one you would probably never even get that monster to run off of a speed density set-up.

Sounds like a good project .....Good luck!

------------------
88 mustang gt convertible bored to 306 BBk equal length headers, mac cold air fender kit, 3.73 FMS gears, Steeds Tri-ax shifter, Steeda underdrive pullies, Custom off road X-pipe, 2 chamber flow masters, cowl hood, nitto drag radials, ford racing clutch, 160* thermostat 16 degrees of timing electric fan off 94' t-bird jacobs electronics cap and wires. Edelbrock 1 1/2 inch drop springs. (Best E.T. 14.79@93mph @3000ft)

jimberg · 10-11-2001, 12:49 PM

I don't believe that the aftermarket favors speed density at all. Everything out there for EFI is more for MAF. You should definitely go with MAF.

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351W 89 Mustang GT Convertible

Yan88gt · 10-11-2001, 06:16 PM

Go at wmsracing.com and check there sds injection. Cheap and easy to tune.

Unit 5302 · 10-11-2001, 06:31 PM

The market favors MAF over SD by a mile. Most modifications have some sort of directive "for MAF equipped cars" because more is known about how to tune them.

MAF is the clear choice on your car.

Stang Runner · 10-11-2001, 08:44 PM

If you have the $$ go with a DFI kit!

------------------
14.28@103.0 on a G-Tech Engine: Steal Mounts, Under drive pulleys, K&N, Home ported Lower Intake, No power steering, No A/C
Drive Train: 3.55, T-5z,

Real power STUFF I Have and will put some time: Mac cold intake, 70MM TB, Valve covers (COOL ONES)255 Fuel pump NOS Dry 75HP, AFR 165 58cc, GT-40 Intake.
Next to get: Rocker Arms,Cam,Injectors 24, What might I need???See It at www.computerconquest.com

Chris in NY · 10-11-2001, 08:53 PM

Thank you all for your replies. A point of clarification: When I say the aftermarket favors speed density, I mean the Accel DFI, Simple Digital Systems, Speed Pro and other engine management systems all are speed density. The stock Ford EEC and the FRPP EPEC units are two of the few that are set up for mass air. And I believe many of the heavy duty Mustang drag racers are running the speed density systems. That's what I don't get. Again, thank you all for any comments.

jwboner · 10-12-2001, 03:23 AM

I know a guy(can't really call him a friend) that has a 1100hp, Speed Pro, twin turbo, street legal car(which I've never seen him drive on the street). The good systems have a much higher level of adjustability and programability than mass air which does much of the calculating on its own and leaves the person out of the tuning process, you can give it an idea of what you want but it still does its own thing. But then again I am not an expert on mass air.

------------------
65 fastback
347 DFI injected, TFS heads, T5, 4.11 9", tc subframe conns, torq thrust D's
A little history lesson using today's tech.

10-11-2001, 12:25 PM	#1
Chris in NY Registered Member Join Date: Mar 2000 Location: Rochester, NY USA Posts: 19	Carb to EFI: Speed Density or Mass Air? Hello all. I will be converting my 500HP 408 Windsor (in a street '71 Mustang) from 750 DP / Victor Jr. to EFI. The whole EFI aftermarket clearly favors speed density, but I can't figure out why mass air isn't a better choice. For example, the FRPP EPEC seems to be offer plenty of tunability for a mass air install and you can get large diameter mass air meters, which should be low restriction. Also, my thought is that plumbing the Victor Jr. for EFI will make best power for my application versus the two piece EFI intakes. Thanks for any opinions/thoughts/experience. ------------------ '71 Mach1, 408, TKO, Baer Claws, GlobalWest suspension, 17's, etc. Runs 12.76 @ 112, but its a road race car.

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10-11-2001, 12:43 PM	#2
Dark_5.0 Registered Member Join Date: Apr 2001 Location: Staging lane Posts: 4,337	Mass air for sure this is an easy one you would probably never even get that monster to run off of a speed density set-up. Sounds like a good project .....Good luck! ------------------ 88 mustang gt convertible bored to 306 BBk equal length headers, mac cold air fender kit, 3.73 FMS gears, Steeds Tri-ax shifter, Steeda underdrive pullies, Custom off road X-pipe, 2 chamber flow masters, cowl hood, nitto drag radials, ford racing clutch, 160* thermostat 16 degrees of timing electric fan off 94' t-bird jacobs electronics cap and wires. Edelbrock 1 1/2 inch drop springs. (Best E.T. 14.79@93mph @3000ft)

10-11-2001, 12:49 PM	#3
jimberg Registered Member Join Date: Oct 1998 Location: Rogers, MN Posts: 2,089	I don't believe that the aftermarket favors speed density at all. Everything out there for EFI is more for MAF. You should definitely go with MAF. ------------------ 351W 89 Mustang GT Convertible

10-11-2001, 06:16 PM	#4
Yan88gt Registered Member Join Date: Jun 2001 Location: Quebec canada Posts: 92	Go at wmsracing.com and check there sds injection. Cheap and easy to tune.

10-11-2001, 06:31 PM	#5
Unit 5302 Registered Member Join Date: May 1999 Posts: 5,246	The market favors MAF over SD by a mile. Most modifications have some sort of directive "for MAF equipped cars" because more is known about how to tune them. MAF is the clear choice on your car.

10-11-2001, 08:44 PM	#6
Stang Runner Registered Member Join Date: Jun 1999 Location: Walker, MI, USA Posts: 1,202	If you have the $$ go with a DFI kit! ------------------ 14.28@103.0 on a G-Tech Engine: Steal Mounts, Under drive pulleys, K&N, Home ported Lower Intake, No power steering, No A/C Drive Train: 3.55, T-5z, Real power STUFF I Have and will put some time: Mac cold intake, 70MM TB, Valve covers (COOL ONES)255 Fuel pump NOS Dry 75HP, AFR 165 58cc, GT-40 Intake. Next to get: Rocker Arms,Cam,Injectors 24, What might I need???See It at www.computerconquest.com

10-11-2001, 08:53 PM	#7
Chris in NY Registered Member Join Date: Mar 2000 Location: Rochester, NY USA Posts: 19	Thank you all for your replies. A point of clarification: When I say the aftermarket favors speed density, I mean the Accel DFI, Simple Digital Systems, Speed Pro and other engine management systems all are speed density. The stock Ford EEC and the FRPP EPEC units are two of the few that are set up for mass air. And I believe many of the heavy duty Mustang drag racers are running the speed density systems. That's what I don't get. Again, thank you all for any comments.

10-12-2001, 03:23 AM	#8
jwboner Registered Member Join Date: Jun 2001 Location: Under the hood Posts: 164	I know a guy(can't really call him a friend) that has a 1100hp, Speed Pro, twin turbo, street legal car(which I've never seen him drive on the street). The good systems have a much higher level of adjustability and programability than mass air which does much of the calculating on its own and leaves the person out of the tuning process, you can give it an idea of what you want but it still does its own thing. But then again I am not an expert on mass air. ------------------ 65 fastback 347 DFI injected, TFS heads, T5, 4.11 9", tc subframe conns, torq thrust D's A little history lesson using today's tech.