I'm new to the site and FE powered vehicles. I've have been pouring over many informative posts on FE engines. Great stuff! I'm soon to receive delivery of a 66 F250 with a good remanufactured 352 4V engine (with edelbrock manifold). This is a 4 speed truck. I plan to use it as an ocassional hauler (auto trailers, boats etc.) and street cruiser. I think I would be happier with the torque and overall performance of a 390 and am trying to firm up my selection criteria.

I would like to use gas with 93 or less octane. What compression ratio engines should meet this criteria? Will a 9.6:1 or a 10.5:1 run on 93 octane?

I've been looking at 61-63 Ford/Mercury 4V 390's because of the HP/Torque and 9.6: CR of some of those engines versus the higher CR 390 engines. I'm not sure if I need to limit my selection to the lower compression engines.

I have located a 62 Z code 330 HP 390 in a galaxie (yet to check it out in person). I've read that the stock CR is 9.6:1 at one place and 10.5:1 at another. I think the 10.5:1 is correct but am not sure?

I've also located a 61 300 HP 390 in a T-Bird which is supposed to be a 9.6:1 CR engine. With either engine I realize that I'll need to have the exhaust valve seats installed. Sorry for being so long with the post. Any guidance here would be appreciated.

 

IMO I would stay with the 352, they are good work engines, good torque and power. The older 390 engines ran the high octane fuel, the 352 should run on reg. Being that the truck is a F250, I don't think you shuold have a problem towing or hauling. I run a HiPro 390 in my 66 F100 4x4, it will only run the 93 octane, my sons 66 F100 with a 352 would pull about the same nad run reg. fuel. If would want to build for higher HP go with the 390's.

 

Bertha66 - Thanks for sharing your experience with two 66 trucks. I've not driven my truck yet. I know it sounds silly to be thinking about a 390 when I've not experienced the 352 yet. I guess I've just been enamored with the pro 390 comments here and else where(lots of HP and 427 ft/lb of torque in a 390 versus 376 ft/lb in the 352). The 390 sounds awsome. I'm 45 but I think I sound like I'm 25 here!

Maybe I should experience the 352 under various conditions before going out to buy a 390. From much of what I've read the 352 is a good truck engine, but also that if an owner is going to spend money enhancing an engine the 390 is a better choice.

Perhaps I'd be a happy camper if I add a pair of those cast iron headers or aftermarket headers to the Edelbrock intake and 4V carb setup. The stock 66 352 produces 208 HP. That's .59 HP per cube which seems pretty paltry compared to 300 HP in a 390 which is .76 HP per cube.

Would reduction of the exhaust restriction on the 352 make much of a difference on the HP. I've also read that the 390 gets better gas mileage than the 352. That seem hard to believe.

 

With a good exhaust you will gain more over the stock exhaust, HP and mileage. When I put the 390 in my truck, it was not that I needed the HP, the 352 was working very good but was on it's last legs, I pulled the 352 for a rebuild but there was notting in the por old engine worth rebuilding. I had the 390, so I rebuilt it and put it in, I did not replace the valve seats, been running it that way sense 1980 with no problems. I did get better mileage, but like I said the 352 was shot. Just because you are 45, I'm 52, does not mean that we don't like them fast and fun.

 

Last 390 I had, had a 10.25 to 1 comp ratio, stock C8AE-H heads, Crane 272 degree Energizer cam (272/272 duration, .523 lift with the non adjustable rockers if I ain't wrong) Stock 68 390 4bbl pistons std bore.(the motor only had 58,000 miles after 34 years) With the ignitial timing set to 12*BTDC (stock distributor fitted with a Pertronix I unit) it was fine running 89 octane fuel. Power was from idle to 5500, smooth idle with only a hint of lope when cold. In it's 4200 lb Merc with a C-6 and 3.70's it ran mid 14's in the 1/4 mile.

 

Alot of your compression depends on the heads. So different 390 had different compression casue the heads and pistons combination was different. I have a '66 F100 that had C8ae-h heads car pistons. With a ford Gt intake 4v and ran good on 89 octane all day long. Used it (at that time) to pull horse trailer, tractors, etc. with old 3 speed on the column. The the 390 will run find on 89 octane. As long as your timming is set right you should not have a problem. The thing is that alot of people rebuild engines and get their heads shved down and raise the compression. Or not enough cam to bleed of the cylinder pressure. These can all play in affect on how the engine will act on the lower octane fuel. I have a12 to 1 engine I run on 93 octane on the street. But do run 114 octane when I raise.

 

You guys are awsome. Thank you for the replies. I think I'll try out the 352 for a while probably with some headers and duel exhaust. I'm guessing that with the Edelbrock intake and 4V carb should produce 250 HP out of the 208 stock HP 352. I don't think any other mods were made to the 352 as a remanufactured engine. It may have been bored out. The current owner does not know. If it's does not already have electronic ignition I'll probably add a petronix unit. Those seem to be the favorite here. If I choose to build a 390 for future use I now know that I can safely go with a 10.5:1 CR engine and run 93 octane if needed. That gives me more options. I'll post some Pics of the truck when it arrives from California in a few days.

 

yes, and if you find after your engine is together that the running (actual) compression is more than you like you can play with your cam timing to let the intake bleed some of the compression off at lower rpms. it stops bleeding compression at higher rpms and raises your compression back up agian but by this time usually detonation doesnt have time to happen. this will effect your vacuum though. someone help me here am I right to say to advance it to bleed it off? but depending on your lift you might want to check piston to valve clearance when doing this. some ways to prevent detonation is to smooth the combustion chamber of sharp edges that may get hot enough to ignite the fuel mix prematurely. that includes your spark plug electode tab! piston dish shape and combuston chamber shape in the head play a large role in this too, but you dont have many options here. yes free up that exhaust as much as you can, step up to a larger valve size its not much more and you want to buy new valves anyway if your rebuilding the heads.