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Old 11-18-2017, 07:18 PM
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engine decision

ok i am almost to the point in my build that it is time that i need to decide on what i want to do with the engine. That being said it had a 351m in it and that is what i want to put back in it but the original engine isnt in all that good shape. And i do want it to be fuel injected.
so should i try to get a crate motor or should i rebuild the one i have and do the efi upgrade?? what are your guys opinion on it what would you do if it was your truck?

thanks in advance
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Old 11-18-2017, 07:45 PM
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So this is for your '78 F250 SC?

What are you going to do with the truck? How much do you want to spend on the motor? How much power do you want?

The usual fix for the 351M is to make a 400 out of it, put pistons in with 9:1 or better compression, a decent cam, 4bbl intake, and carb to match cam/compression etc. If you want to go EFI, there are several to choose from and it appears they get better all the time.

https://www.summitracing.com/search/...ection-systems

This is from '14:

Car Craft's Giant EFI Test - Hot Rod Network
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Old 11-18-2017, 08:04 PM
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For the basic engine, there are not a lot of 351M crate engines that I know of. The re-builds sold by AP stores seem pretty spotty on quality.

Re-building the one you have is a good option... just need to find a decent shop to help.

The 351M and 400 share the same block, manifolding and accessories. The difference is the crankshaft and pistons. The 400 gains displacement and there are quite a few upgrade parts available for the 400 which is why it is a popular upgrade for the 351M. See TM Meyer.

For the EFI... I run an older FAST system on a hot rod which has been good. As mentioned, there are lots of other good systems out there now.
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Old 11-18-2017, 08:26 PM
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[QUOTE=85e150six4mtod;17600815]So this is for your '78 F250 SC?

What are you going to do with the truck? How much do you want to spend on the motor? How much power do you want?

yes this is for my 78 sc. as far as what i am going to be doing with the truck i will probably pull a trailer occasionally and haul stuff on the flat bed all the time. as far as money i don't want to buy a cheap junk motor and put it in there and have to replace it in a couple years. and i don't want to spend a fortune on one but would like to get a good reliable engine for a decent price. for power i would like to have enough to pull a trailer with out any worries.

thanks for the help guys
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Old 11-18-2017, 08:31 PM
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Quote:
Originally Posted by Blue and White View Post
For the basic engine, there are not a lot of 351M crate engines that I know of. The re-builds sold by AP stores seem pretty spotty on quality.

Re-building the one you have is a good option... just need to find a decent shop to help.

The 351M and 400 share the same block, manifolding and accessories. The difference is the crankshaft and pistons. The 400 gains displacement and there are quite a few upgrade parts available for the 400 which is why it is a popular upgrade for the 351M. See TM Meyer.

For the EFI... I run an older FAST system on a hot rod which has been good. As mentioned, there are lots of other good systems out there now.

does upgrading the engine to a 400 add a lot of power? and to make my 351 a 400 would you have to bore the engine? thanks for your help
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Old 11-18-2017, 08:59 PM
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Originally Posted by lakequ View Post
does upgrading the engine to a 400 add a lot of power? and to make my 351 a 400 would you have to bore the engine? thanks for your help
My experiance going from a stock 351M to a stock 400 didn't give me any noticeable power increase. Others more than likely have had different results. I had another truck with a built 400 that had tons more power, but I suspect you could about get there doing carb/cam on a 351. To make a 400 from a 351 you change the pistons and crank. The bore is the same. 400 pistons have a different compression height to allow the longer stroke of the crank.
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Old 11-18-2017, 09:04 PM
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Put a 460 in it
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Old 11-18-2017, 09:16 PM
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My experiance going from a stock 351M to a stock 400 didn't give me any noticeable power increase. Others more than likely have had different results. I had another truck with a built 400 that had tons more power, but I suspect you could about get there doing carb/cam on a 351. To make a 400 from a 351 you change the pistons and crank. The bore is the same. 400 pistons have a different compression height to allow the longer stroke of the crank.
ok thanks for your input i think if i rebuild the engine i will probably make it a 400 and put a good cam in it with an efi set up
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Old 11-18-2017, 09:16 PM
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A 400 definitely does run better than a 351m if it has the usual mods. 351's are turds and I never would rebuild one let alone waste money on fuel injection for it. I had a 400 in my 79 but switched to a 460. If I didn't have all the stuff to do it I may not have but I didn't know if my 400 was worth messing with. With that being said I do not miss my 400 at all, my 460 is so much better. I'm going to say my mpg is slightly better with my 460 too.
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Old 11-18-2017, 09:17 PM
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Originally Posted by Coleton_henry View Post
Put a 460 in it

i would but i already rebuilt the trans and tcase for the 351 and i don't want to have to go to the gas station every day
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Old 11-18-2017, 09:30 PM
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Originally Posted by lakequ View Post
i would but i already rebuilt the trans and tcase for the 351 and i don't want to have to go to the gas station every day
460 gets better gas mileage than a 351 and a 400 lol
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Old 11-18-2017, 10:07 PM
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i would but i already rebuilt the trans and tcase for the 351 and i don't want to have to go to the gas station every day
They all share the same pattern.
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Old 11-18-2017, 10:10 PM
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460 uses the same transmission/transfer case.
If a 460 interests you, do a search on swapping this engine in. You will likely have to fab up your motor mounts, power steering and alternator brackets.
You have to drive a 351 like you are mad to get the performance of a babied 460. I doubt you would see much difference in fuel mileage.
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Old 11-18-2017, 10:38 PM
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Build a 400 and upgrade the cam, lifters, and springs.

Do some headwork. Smooth out the ports. No need to hog them out significantly.... just remove the rough casting and port-match to the intake and exhaust gaskets.

Weiand Stealth 4V manifold, headers, and dual exhaust.

EFI? Holley's Terminator or Sniper, or FITech. Keep it relatively simple.
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Old 11-18-2017, 11:17 PM
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I've just built a 351C... kind've the performance oriented predecessor of the 351M.

A 400 would be great, but stay away from '4V' ports if you can. They deliver great high rpm usability but its not what these engines are about unless you spend big coin on them.

A standard '2V' is plenty for the street and aftermarkets made a raised '3V' that is the best of both worlds. Either of those is fine and will give good usability and power with something resembling economy if you set it up right.

I'd aim for about 10:1 compression with a decent closed-chamber aftermarket head, a twin-plane intake (RPM Airgap is a good option) and moderate camshaft (something in the .500" lift and 220 duration at .050" ballpark) like an Elgin E-907-P would be fine.

Headers are a must with those upgrades, and a twin 2.5" exhaust system will be more than sufficient for the power it makes while still staying reasonably quiet when you want it to be. It'll let out a good note if you put your foot down, too.

EFI is great but honestly a well set up carb is still fine today. Both my truck and my Valiant run used Holley's that I have put a basic kit through and cleaned up before installing. They run fine and start easy hot or cold. I'd save the money and avoid the hassle of EFI by staying carburetted. If you really do want EFI it is a large investment and installation process as it relies on many sensors. The modern kits are very good and self-tune generally, but as I said a well set up carb is still a good thing.

- boingk
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