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300 Six - EFI vs Carbed Questions

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Old 09-15-2011, 01:56 PM
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300 Six - EFI vs Carbed Questions

I have a chance to pick up a good running EFI 300-6 out of a '94 F-150 for next to nothing. I am considering replacing the 460/C6 in my '66 F100 truck with it and a C6.
What issues will I face converting the EFI engine to a carburetor?
Can a '70s DuraSpark II distributor be used in the EFI engine?
Can I use the EFI head and exhaust? Will a stock carbed intake work on the EFI head, or do I need to replace it?
Are there any camshaft compatibility issues?

The 385 pattern C6 transmission in there now is not very old, so I would like to simply find a C6 for the 300 and transplant the interior components. I am not sure what transmission is in the donor truck though.
Did the 300 use a C6 in the '90s?
Did it use an automatic overdrive in trucks, such as the E4OD?

My 460 has done real well for towing my trailer rated at 7,000 lbs. I do less towing now, and more driving and gas - well, you see where this is going.
What mileage can I reasonably expect to get with a 300/C6 combination in front of a 3.25 rear ratio? That is, for regular driving. Towing is another matter altogether.
Will I still be able to tow with a 300, even with the reduced power?

Thanks for any and all assistance.

PS: Issues such as engine mounts, accelerator linkages and the like are not a problem, they are easily, if not already solved. CD
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Old 09-15-2011, 03:20 PM
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If i recall correctly its the efi head that has more bolts to hold down the intake/exhaust. i think it takes some minor modification, but nothing big, there is a thread on it here somewhere. but the dizzy will be no issue, however there isn't a hole for a mechanical fuel pump. the 94 would be the e4od, but an 80's sbf c6 would work.

alot of guys report between 15 and 20 mpg, but your results may vary!

you should still be able to tow, just don't expect it to do so quite as swiftly.
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Old 09-19-2011, 04:49 PM
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The head has a fast burn characteristic applied to the chambers in an EFI head. It'll work with the carb, but I can't remember if it's a benefit or a detriment to performance. If it's a detriment, it's not very much, just not optimal.

The head uses 16 bolt holes on the EFI and 13 on the carb'd engine. The 3 extra bolt holes are only for ease of installation, since the EFI manifold setup used 3 pieces, whereas the carb setup used 1 (intake and exhaust were solidly bolted together). This is a complete non-issue.

The EFI's exhaust manifolds are a common bolt-on performance upgrade to carb'd engines. They may require a slight amount of grinding (and I think one of the exhaust manifold's hanging tabs needs to be removed) so that it doesn't bind with the intake manifold. It's not a big deal though.
Other than that, the intake manifold will bolt right up like it was made for it.

The distributor will drop right in.

I *think* the EFI engine uses the same cam as the carb engine.

The biggest issue is what what Muscletruck said. There is no provision on the EFI block for the fuel pump. Not a show-stopper, but something to be aware of. An aftermarket electric pump/regulator will solve it.

The 300 will be able to tow pretty much whatever you throw at it. It just won't do it quickly. If you want to increase the power, though, you can always look into putting in a performance cam and getting yourself a 4bbl intake/carb to bolt onto it. Find yourself a good carb'd 300 head and do a good port and polish on it. It's amazing how quickly the power of the 300 can be boosted.

The 300 uses the same smallblock bolt pattern as the 302 and 351, so any transmission that bolts to those will bolt to the 300.

Gas mileage varies greatly with the 300 from 12 - 20. It depends a lot on vehicle weight, gearing, tire size, etc. The C6 isn't exactly the best on gas either.
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