Need help deciding on best engine option - Ford Mustang Forum
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post #1 of 8 (permalink) Old 07-25-2019 Thread Starter
65mustang65's Avatar
Joined: Jul 2019
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Need help deciding on best engine option

Hello everyone. So I am trying to decide what I want to do with my 1965 mustang coupe. It is originally an inline 6 but the engine is destroyed beyond repair. I am wondering if I should put another inline 6 in and build it up or put a stock 351W out of an '88. I am want something I can cruise with so good gas mileage but want there to be some power there if I need to step on the gas to go for like merging or quick acceleration. I have a 1969 donor mustang that I plan to put the 8" rear with 3.55 gears and a T5 in and the front spindles in so if I went with the 351 what else would I need? What do you all think would be my best option?

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post #2 of 8 (permalink) Old 07-25-2019
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There are a number of threads about dropping motors in 64-66 cars/ Some disagreement about the fitment of a 351W (slightly wider and the deck heights higher) fitting in the 64-66 frame rails.

As long as you have your eyes open going in. A 6 to V8 swap is not just chucking a motor in. You can retain the stock steering box everything else from there down and back is different. Adding a 3rd gen V8 like the 8. (what is a stock 351 w in that year out of? Not a mustang for sure.)means a lot of the accessories will have to change also. meaning custom fab of radiator mounts ect. Using the 88 engine and trans is okay you will have to have a driveshaft made to match the front and back yokes and the length (drives shafts custom made are relatively cheap) .

Having given all the standard warnings!! a T5 running 3:55 gears (you are gong posi right?) will still yield decent fuel economy. A mild street build in the 400 hp range is very doable for a reasonable price.Basically a cam change, a little more air a little more fuel and decent exhaust) If at all possible try and maintain fuel injection, (fuel delivery and a good tune will help make that 400hp a reality) i

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post #3 of 8 (permalink) Old 07-25-2019
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A 351W will be difficult to fit between the shock towers. I'm not even sure if it would fit with manifolds, much less headers (there are swap headers for it, though). It's also a fair bit heavier, which will require stiffer springs (at least 600 lbs for a comfy ride, and 7-800 lbs for a sporty ride). They also don't get great fuel economy because of the longer stroke and larger main bearings. An Explorer V8 could be a good option, however. Keep the fuel injection, or convert it to carb and distributor. I'd second the T5, and I've had upwards of 25 mpg with one and a 262 flat tappet camshaft.

If you do go the I6 route, a 240 would be a good starting point, but for power, you'll want to get rid of the integral log intake manifold. This means either custom fab (I've wanted to put Weber side drafts on one for a while) or swapping the cylinder head for a Clifford one or an Australian head. There's also camshafts available for it, and T5 swap bellhousings. I'd also still upgrade the spindles and rear end even if you do stick with the six. I've heard of stock sixxers breaking rear axles, so an 8" would still help.

Proud owner of a '65 289 coupe. Equipped with Edelbrock Performer intake, Quick Fuel 680HR carb, ported stock heads, 282 Magnum solid cam, Hedman longtube headers, MSD ignition, and decked and ported heads. T5 transmission with hydraulic clutch. Griggs Racing GR350 suspension. 8.8 rear end. Griggs front & Wilwood rear brakes. Many more mods to come!
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post #4 of 8 (permalink) Old 07-25-2019
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The best engine is the one the car was designed with, changing the motor includes all the suspension, brakes and everything else that supports the power plant in a car. If you want a v8 Mustang, buy a v8 Mustang.
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post #5 of 8 (permalink) Old 07-30-2019
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Everyone discounts the I6 but keep in mind that it is the smoothest configuration because of the way it is naturally balanced. The only exception is a V12 which is essentially two I6 engines spliced together.

You mentioned that you wanted good gas mileage so I assume that is your first priority. Have a local shop rebuild your I6.
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post #6 of 8 (permalink) Old 08-05-2019
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My suggestion is to find a newer 200. I found one out of a 1980 Fairmont that runs, and it was inexpensive. It has a better flowing head than the 60's version, and has valve seats made for running unleaded fuel. Plus it's a bolt in.
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post #7 of 8 (permalink) Old 08-06-2019
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Look into Vintage Inlines. You can do quite a bit with the 6 if you want more power.

As far as gas mileage, you need a taller top gear. AOD or other 4-5 speed transmission. I can drive my '66 i6 around town all day on hardly any gas. But take a long trip on a freeway and you'd think it was a big block with dual quads.
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post #8 of 8 (permalink) Old 08-06-2019
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Small block 289 or 302 is about the easiest. I'm not fond of the 6's. Its your car to do as you wish and any engine can be made to fit.

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