I intend to supercharge my '91 F-150 with a 302. Some engine folks I ask tell me to go ahead and stick a rebuilt 302 in before supercharging (seen some with 370 horsepower!) and others tell me to stick a 351 in place of my 302.

Looking at Ford's specs for the 1991 model year, I am not seeing a huge difference in power for the 302 vs 351. While the 351 has more torque, I'm not sure I want to trade the fuel economy and lighter weight of my 302 for the 351. Besides, after supercharger, it will pretty much be irrelevant, anyway, right?

I would rather spend less money on my engine rebuild than shell out $3700 or more for a performance 351 BEFORE shelling out another $4000 for a supercharger. Current engine has 69,000 total miles and uses a little oil on long trips (1200 miles yesterday alone.)
A stronger rebuild coupled with a s.c. would be adequate--no reason to spend upwards of $7000 on a rebuild and a s.c.

Next, as far as superchargers are concerned... I need a performance increase at all RPMs. Guessing that means a Roots unit. What do you folks suggest as far as supercharger brands are concerned. I don't care about everyone knowing I've got a supecharger installed--doesn't have to be loud. The Eaton unit sounds nice.

Thanks for the help! Also appreciate any smart advice on how to go about this the best way, financially. Excited about doing this, because this subdued-looking truck (even has a "Seniors are Special" sticker in the window!) is going to be a sleeeeper!

-Mike

 

Mike
Your '91 is speed-density, you need to convert to mass air before adding a blower.
As to brands, the Eaton would be by far the best, but I don't think a truck-specific kit was ever produced, I may be wrong. BBK has a 302 Mustang kit, but you might need to convert the upper manifold, throttle body and linkage to Mustang spec to get it to fit. I'd call or e-mail them to find out: i'm sure you're not going to be the first to ask the question. Kenne Bell makes a positive displacement screw-type blower kit for 302 trucks, but if you search the site archives, you'll find some negatives -- and some positives on their units. The Vortech S-Trim builds boost in mid range, so it's not as useless on a truck as some of the other centrifugals, but it's not a Roots either.
They have a reputation for being very complete and well thought out kits.
Since you're going to rebuild your engine anyway, consider forged pistons, but keep the stock 8.5:1 CR, they're good life insurance with a blower. Whatever you decide, beef up your AOD or it won't live very long.
Have fun!

 

hi Mike, hows the truck doing? You like it?

I don't know much about Superchargers. But I can tell you about the 351 and the 302s. The 351 despite its 49 cids more, produces only 10-15 more factory hp than the 302. But, it gets worse mileage. I have a friend at school that has a truck Identical to yours, only his has a 351/E40d/94k miles. Same year. The truck is geared the same as mine, and he gets about 14mpg, while I get 20. The 351 is a Windsor engine, and its main purpose is for pulling.

I don't understand why you would want to rebuild your engine with only 70k miles. I know of several 302s pushing 200k before a rebuild. The can/will go over 200k, but with terrible mpgs and performance, and major oil consumption. I used to have a 1983 F-150 302/Aod, that had 160k when I got it and it now has almost 200k. It uses very little oil, and has excellent compression.

Good Luck~~

P.S. You might have better luck posting in engines.

 

StrangeRanger: 302s have 9.0 compression. 351's have 8.8

 

Oops!!
I know my 302HO started off as a 9:1, but I thought the standard 302s had 1/2 point less compression.

 

Actually, you don't have to convert from speed-density. Either SD or mass-air will require a "custom" computer chip once you add the blower, so you can stick with the SD and have your ECU programmed accordingly. Be sure to keep all your engine specs (cam, lifters, valve size, etc) for your programmer. They will need to know as much as possible to get the best performance.

 

Thanks for all the replies so far (keep 'em coming!)

Pastmaster, I'm really enjoying this truck--I like the old thing!! Much better than my new V6/regular cab (and I owe lots less, too!!)

Not too literate on the differences between speed-density systems vs mass air. If someone wouldn't mind explaining this, I'm interested in listening.

I used a bit of oil on my 1200 mile trek Monday... Not much, but a noticeable amount. A rebuild would result in a strong engine, anyhow, so I figured better go ahead and rebuild before supercharging so that I don't have my engine for lunch one day. The tranny will probably be upgraded to an E4OD, although I know the AOD will take some improvements... and I do like the quickness of the shifts--not sure the E4OD or another electronic transmission will duplicate this. The AOD has been really smooth, and I've done some checking around for structural improvements to it.

So no true roots blowers, eh? Dismal. The Kenne Bell sounds good, and Eaton does not make a unit for the truck 302.

Speaking of which, Pastmaster, I'm judging by your earlier reply that you think the 302 is worth keeping and upgrading to the 351 isn't a reasonable idea. I was averaging about 15 mpg at 78mph on the highway--hoping that'll get better at about 67mph. Maybe need a new O2 sensor?

Thanks for the help.

Mike

 

replacing the 302 to a 351 is totally your decision, but I wouldn't trade mine. They are good engines, but I perfer a 302. Yes o2 sensor will give you better mpg, responce. Another 12 dollar sensor that improves performance is the Coolant Temp sensor. It is at the base of the pipe that holds the distributor up. You'll see it, it's facing you. I did it when I replaced all the hoses, and thermostat, and flushing the coolant this summer. the sensor's job is to tell the computer weather the engine is running to lean or to rich. Based off of the temp of the coolant. I noticed the biggest difference after replacing it. Another performance mod that I noticed a difference on my 89 was, advancing the timing and the tps mod. That is the thing about EFi, its true that they don't need more maintence than a carb, but it's the little things that pose a problem. You stated earlier that you noticed a difference in mpg by doing a tuneup, you bet! I honestly don't know much about blowers, other than what their supposed to do. If you get a lower-restriction exhaust, get a FIPK,(the dropins gave me +3mpg, the FIPK is supposed to be 19% more). And of course a chip will help you. You can change the AOd for a E40d, but you'll have to get a computer for the tranny. I honestly don't think, that you'll gain anything replacing the AOD for a E40d, unless of course you need to replace the tranny. A shift kit will do it better. I haven't been impressed with my E40d.

you are probably right about the rebuild. The blowers do need more support.

I wish someone would tell the difference between Mass air and Speed density. I know what years the differences are. 1994+ have MA. Yours and mine of course don't.

 

Whoa, This should be interesting!! I'll be more interested in the Speed Density half, and no, I haven't worked on my truck yet. Waiting for Sat. as it will be in the 60's, but riddle me this Batman. Would the Speed Density be able to "cope" with an increase in intake air from the fender via one on those air kits(k&n,whatever). Sensor problems configuring it all? I think nomo mentioned a custom chip to me earlier. Also noticed an earlier post from nomo about the Speed Density not being able to handle any "major mods"(cams,etc) and said it might be easier to convert over to the mass air with a kit. After I get it running right, I would like that to be my area of first improvement. But again, would that be too much air for the "SD"?

[This message has been edited by JOHNNY MC (edited 01-14-2000).]

[This message has been edited by JOHNNY MC (edited 01-14-2000).]

 

Speed density systems measure manifold absolute pressure (as in "MAP" sensor) or the pressure above perfect vacuum in the intake manifold. Because for a stock engine the volumetric efficiency of the engine is well known by the manufacturer at any given RPM and temperature, the processor looks up the values in a table and meters fuel accordingly. Anything which significantly affects volumetric efficiency, such changes in cam, compression ratio, or adding a blower will cause the computer to misread the charts and run poorly. Minor changes such as air cleaners and cat-backs do not create a problem. Speed density is not all bad. The older speed density Mustangs in stock form were actually quicker than the mass air controlled ones of the same era. The engineers were able to run the speed density controllers much closer to the perfect power producing lean without going over.

Mass air sensors use a hot-wire that is cooled at a known rate by a mass of air flowing over it to get a direct measurement of the air ingested by the engine. As a result they will allow virtually any modification (as long as you upsize the meter, fuel pump and injectors appropriately) without loss of control. Mass air chips may benefit from a little tweaking to maximize performance or resolve drivability issues, but a mass air vehicle will run quite well on the stock processor, meter, pump and injectors up to about 280 flywheel HP.

You can have a speed density controller reprogrammed to accomodate a new engine configuration, if you can find a dyno-tuner who is familiar enough with them. But if your engine is a work in progress, each significant change means a re-burn. At $250-300 or so per burn, it doesn't take long to pay for a do it yourself install of a mass air conversion ($600-650) which lets you piecemeal stuff as you go.

Also if the tree-huggers have instituted smog checks in your area, you're going to find a lot more smog-legal stuff that mates up to mass air and be much more likely to pass with a mass air control.

 

Thanks StrangeRanger. That's enough info to keep "me" quiet and busy for awhile!

[This message has been edited by JOHNNY MC (edited 01-15-2000).]

 

Thanks, still, for all the great replies. It's sounding as though converting to mass air might be a good option... What are the details for how to go about doing this? Keeping things emissions-legal is very important to me (thinking about registering the truck back home in Texas, and they do smog checks there.)

Also, does anyone know how to go about adding "super engine cooling" to my truck. It has the standard radiator, and I'd like to upgrade. Correct me if I'm wrong, but the only difference between super engine cooling and standard is a larger radiator. Is this a simple bolt-in change? Are Ford's radiators worth the price, or should I go with an aftermarket radiator of the same capacity (or better)?

Answers to these two questions are 'preciated! Great resource here!

Thanks again,

Mike

 

The absolute best resource I've found yet on Ford EFI systems is:

Probst, Charles O., Ford Fuel Injection & Electronic Engine Control: 1988-1993. Cambridge, MA. Robert Bentley Publishers, 1993
ISBN 0-8376-0301-3

Also available from Ford SVO as P/N M-1832-Z1

Read it before you do anything. He is noticably short on modification info, but gives a detailed understanding of how everything works. From there you can more readily evaluate what changes will best meet your needs and budget.

The SVO mass air conversion kit for the 87-94 F series 302 truck is:

M-9000-T50 for manual trans
M-9000-T51 for AOD

Suggested retail is $675. some careful shopping should lower that to $600 or so

 

Will the speed-density to mass air conversion in itself add any power/torque/mileage?

Sounds like I need to order an SVO catalog...

Thanks,

Mike

 

The later mass-air trucks were rated at (I believe) 205 HP, so if there were no other changes, that would represent a nominal power gain, but I doubt you could feel it -- or measure it in 1/4 mile times. Likely just a dyno fart.