Thread: Which to choose 390FE or 460

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Hey all,
Here is my problem, I have a 4200lb 1968 XL Galaxie 500 with a original 390fe, C6 auto and 9" rear. I want to run about 750 hp but from what I have been told a 390 can't handle it very long here is my options for the 390:

390 block with 427 cross bolted mains
Scat 445 Stroker kit with 8.0 to 1 compression
Blue Thunder Stage X or Edelbrock Stage 5 Heads
Large Bore 6-71 Supercharger
T-56 Transzilla Manual Transmission

Or I could do a 460 with a stroker hit, nice heads and a supercharger that I know can handle over 1000hp.

What do I do, I am torn between the two, I would like to keep the original block, but I want to run the car every once in awhile at the track. I want it to not be at its breaking point.

Help me out guys!

If it's only going to the track occasionally, why is it you need 750hp for cruising??? Reason I ask, a 750 hp engine lugging around on the street in congested traffic is going to be a whole lot more problems then it's worth. Either engine is going to take in the neighborhood of $10K to build, probably a lot more and just isn't going to last in normal street use. Either engine built to that level of performance is going to be very maintenance intensive, and probably not live very long. 750 horse engines belong on the drag strip, and even then weekly inspections are in order to keep everything working good and staying together....

Even in a heavy boat like your Galaxie, a well built 390 with good heads is going to pull you around in traffic just fine.

Just thought maybe a reality check was in order, not meaning to burst your bubble.... If you can afford the $$$$$ for the build and don't mind working constantly to keep the thing running right, have a ball....

Dave,
Well this is the reason I am going with a supercharged engine, I can have like a 5 psi pulley on it for 500 to 600 hp and if I decide to I can go up to 10 or 12 psi if I want to run it from time to time. I want it to be for going to car shows and possible the Hot Rod power tour. I want a big displacement motor with a 5-speed trans and a supercharger so I can puts around without even creating boost, but have it when I want it, Is that too much to ask for, haha.
I understand it is going to probably cost arount $10,000 to $15,000 for the engine but thats fine, if it takes 5 years I could care less, I want this car the way I have dreamed it to be.
My uncle just finished his 1971 dodge Demon with a 340 stroked to like a 380 with about 500hp and a torque flight 727. It is a rough ride, but nice. I just don't want to have 12.1 to 1 compression and a rough idle. Thats why I like the 5-speed and a supercharger, I can have a easy idle cam with a supercharger and still make great power.

I am open to any suggestions and comments, reality checks are very welcome.

If your spending that kinda cash start with a good iron Genesis or aluminum Pond 427 block. You'll be glad you did. Keith Craft or Survival can hook you up with something nice. That's if you want to keep it a FE engine.

Sounds like you have a handle on it, Chris..... I've ran a couple blown engines, but nothing that was built for economy!!!!!

For streetability and no problems finding fuel, keep the compression down around 8 or 8.5. Heads need to flow good, especially the exhaust side. For the cam, I'd do the cam card sheet with Comp or one of the other cam builders detailing exactly what is going in the engine. A friend of mine is running a blown BBF with a TBI unit on top of the blower!!!!! Don't know the details on the electronics, other then it came from FAST and has many built in features including a spark retard unit to pull out some of the timing at higher RPM.....

If you want to really get crazy on displacement, there are some aluminum mountain motor aluminum blocks that will put the cubes around 800 inches and the horsepower out in the twilight zone!!!!!! Depends on how hard you want to search (there are used blocks out there, but be careful) and again, how much you want to spend.

whats a large bore 6:71????

Well if I can get my stock 390 block with an addition of 427 cross bolted mains on it to handle 800hp, then I will keep the 390 block and stroke it with the 445 stroker kit from survival.

As for the supercharger, if I go too small like a 6-71, I'll build boost at low rpm but if it is too small it will drop off in high rpm and create alot of heat. If I go too big like a 8-71 it might be to much and not create power at low rpm.
I contacted superchargerusa.com and explained my build and they suggested their "Large Bore 6-71" It is a 6-71 with I believe a larger case, so its like an inbetween of the 6-71 and 8-71.

The 8:71 is just like a 6:71 except aprox 3/4 inch longer---hardly any difference unless you are running it at 45-50 % over---
a large bore must mean that they have over bored a 6:71 case and come up with some sort of roter to fit it---however there is a standard distance between the rotors so the gears mesh properly so they must have a completely different blower and are just calling it an big bore 6:71--this would take different endplates, gears, cases, rotors---everything but maybe they use the 6:71 manifold bolt pattern---i would like to hear more about what they have done

HERES THE E-MAIL

Sounds all good to me Chris

The 671 large bore blower is the best choice here for 750 reliable hp and no heat problems. If you decide to go bigger on the blower, the lower rpm torque numbers will be down.

Here is the kit.

7521 FORD 390-428, 671 BLOWER KIT, 2V EVERYTHING POLISHED - 8MM 4112.00



3876-80 FORD 390-460 NEUTRAL BALANC CRANK HUB 109.23


4910 DUAL DOUBLE PUMP CARB LINKAGE MOUNTED SIDEWAYS 119.95


4800 DOUBLE PUMP HOLLEY FUEL LINE KIT, SIDEWAYS MOUNT 161.23
4805 SIDEWAYS MOUNT FUEL LINE TO 107P ADAPTER 51.23


3 Year Warranty (Parts and labor included)

The USA 671's and 871blowers are currently at 8-10 weeks delivery. I know you said you're not in a hurry, but please allow enough time from a deposit date if this is something that you want.

Thank you and call me if you have any questions or want to talk more

Thank you

Tim E. Posik
President / Senior Design Engineer
Supercharger USA Co.
Supercharger Manufacturing Division
1120 S. Cypress St. unit #C
La Habra CA, 90631
714-578-8200 (o) 714-578-8260 (f)
susa@sbcglobal.net www.superchargerusa.com

Originally Posted by jerry clayton

The 8:71 is just like a 6:71 except aprox 3/4 inch longer---hardly any difference unless you are running it at 45-50 % over---
a large bore must mean that they have over bored a 6:71 case and come up with some sort of roter to fit it---however there is a standard distance between the rotors so the gears mesh properly so they must have a completely different blower and are just calling it an big bore 6:71--this would take different endplates, gears, cases, rotors---everything but maybe they use the 6:71 manifold bolt pattern---i would like to hear more about what they have done

Jerry, I was as surprised as you appear to be when, a couple of years ago, I discovered that there are large bore and small bore 6-71's. I found this out competely by accident when reading through specs on Blower Drive Service's site. Begin reading here...
BDS Street Blower Boost Charts
on this page...
http://www.blowerdriveservice.com/techcharts.php

Just shows to go ya, we're never too old to learn something new.

Found this on their site thanks Jerry:

There are two different 671 blowers commonly used. They are the larger diameter blower and the small diameter blower. The large bore blower (case thickness 1/2"-) is approximately 11 percent larger in volume than the small bore. The small bore blower (case thickness 3/4"+) is recommended for 370 CID engines or less for street applications. The larger bore blower is recommended for 371-500 CID engines in high performance, racing applications.

I guess you could make up some rotors that actually had a skinnier center that allowed a largerdiameter lobe on the same center line gears, etc, but i think that the displaced volume is what passes thru the middle ---in other words---the volume will be effected by the area between the centerlines of the rotor shafts and any extra put on the rotor lobe will be offset by the amount necessary to remove from the rotor valley where the lobe must fit.

I was the first person to use 8:71 rotors and got them from Ed Isky----Donovan had a
6:71 case mold made longer to put the rotors in---they were the same cross section for the end plates and the 6:71 mounting was how all the manifolds were made--Van Luven assembled it and we were able to run it slower, make more power and go quicker!!!

I will play around next week and see if I can come up with how much you could increase the volume without moving the gears

Originally Posted by jerry clayton

I guess you could make up some rotors that actually had a skinnier center that allowed a largerdiameter lobe on the same center line gears, etc, but i think that the displaced volume is what passes thru the middle ---

Jerry, if you're saying air passes from atmosphere to the intake valve through the middle of the blower, then one of us is confused. I believe the air is moved from atmosphere around the inner diameter of the case, between the lobe and the case, but I could be wrong.

Yes the air passes around the outter part between the rotor and housing, but is compressed as the rotors mesh together in the middle---it is a positive displacement and I don't see how they can get any more volume out of it without some fancy manipulation of rotor design to change the displaced volume in the middle without spreading the rotor centerlines and doing new end plate/housings and gears-- they also must have custom cases as the GMC cases are not 3/4 in thick--about the only thing 6:71 about this would be the mounting pattern at the manifold.

i'm not a fan of superchargers or nox. i do like large engines. i would go with a 460 for get the 390 it;s a good engine but would not be my choice for a hi-po engine. i have a 429 that displaces 494 cubics. has a mild torquer type cam and offy intake with a 750 carter afb, police interceptor heads.(STANDARD heads with cobra jet valves,polished chambers and ported and polished exhaust.) headers in a 1969 galaxie sportsroof. the car is a strip model. only weights 3400 pounds. no p/s,no p/b,no a/c. and factory 4-speed. never aproblem . no maintance headaches. i bought it new in 1969. 429/4-speed. just my suggestion. i'm was a detroit deisel repair man and worked on 4-71,6-71,8-71,and 16-71's. they wear out in due time.