360 FE with 390 FE crank and rods, is this a good thing or a bad thing?
I'm sure this question has been addressed here somewhere else. If someone can point me to the right tread that would be greatly appreciated.
I'm the proud new owner of a 70 F250 2wd camper special. It was free, so I can't beat the price. (The old owner had the truck for a very long time and just didn't want to pay the insurance anymore.) The truck runs very strong.
He told me it has a 360 that was rebuild not too long ago using 390 crank and rods. I have not measured the stroke yet to verify the story but, the old owner insisted that it was true.
If so, does this make the engine a 360 or 390? Which tuning specs do I use? How does this change compression ratio's? Is this a performace enhancement over the stock 360? Is this engine worth modifying further with intake, heads, cam, and exhaust improvements, or should I seek to install another engine?
I'm not looking to race the truck at the local strip, but I do want strong street performance.
Allot of questions I know, I just need a little direction. Any ideas?
And to answer your question directly, yes, most of us would consider this a good thing...!
You don't need to worry about replacing it, as long as it's a good sound strong-running motor. The typical performance enhancements can help, such as aftermarket aluminum intake with 4bbl carb, headers and dual exhaust, and as John said, electronic ignition (I favor the Duraspark conversion 'cause it's easy to do, can be done cheaply with scrounged parts and with the addition of a late-model TFI coil puts out a very nice hot spark.)
The commonly available Edelbrock Performer intake is nice for weight savings and bling and with a 4bbl on top of course gives a performance advantage over the stock cast iron 2bbl setup, but has small intake runners and adds virtually no performance upgrade over a stock-type cast-iron 4bbl manifold as fitted to some passenger car FE applications, but there are other manifolds available that will be a step up in performance. Edelbrock or Holley carb...? Probably a matter of personal preference more than anything.
Headers can be a can of worms. Stay away from cheappies as you want good quality units like Sanderson's with nice thick flanges to aid in sealing. The most common problem (other than sealing difficulties common to most headers) is starter heat and access. Most of the brands of headers available for the FE engine route the tubes very close to starter and tend to toast it, and then you have to remove the header to replace the starter. One of our members here (fastmover) has the Sandersons and is quite happy with them. (BTW, he also has a a 360 rebuilt into a 390.) The solution I would take is to install a brand new high-quality starter and then install a heat shield over it (such as starter insulation blanket) before installing the headers, and then you should have little worry about the starter. Even going the extra bucks for a hi-torque mini starter can be worth the investment as it gets the body of the starter farther away from those hot header tubes. Wrap it with an insulation blanket and fahgeddaboudit...
Well, hope that gives you a few things to think about, and don't hesitate to ask if you have any more questions. We have an incredible wealth of knowledge and experience to draw from here, and there aren't many things you can do to a truck that haven't already been done by someone here.
I've confirmed by measuring the stroke difference from the #1 and #4 cylinders that it has a 3.78 stroke, from my research that is consistent with the 390 crank assy. I will upgrade the ignition to the Duraspark this weekend. I suppose then I need to set the timing according to 390 specs, not to the 360 sticker on the side of the valve cover. What is ideal 390 ignition timing set at? I'll get a manual this weekend to help me out too.
As far as headers, they are certainly in my future plans but, I'm fine with the stock units for now; except there are no gaskets between the manifolds and the heads! What's up with that? I did some more internet research and discovered that some FE trucks came from the factory without manifold gaskets. Is this true? So needless to say, the engine snaps and pops and blows fire out between the heads and manifolds in a few places. If that's not a fire waiting to happen, I don't know what is! Just add a little fuel leak. Sounds terrible too! Manifolds may be cracked and causing my leaks. In any case, I'm sure I can get gaskets and fix this problem. Otherwise, good headers may be coming soon...
What about splitting the stock exhaust system into a dual pipe and muffler system with balancing tubes? Does in make a big difference other than sound?
Thanks TigerDan, I'll go with a car 4 bbl manifold instead of the performance aftermarket units. I also plan to go with a 650 cfm Edelbrock AVS w/ electric choke. I used one on my last SBC build and loved it. It was nearly perfect right out of the box. I also have a 750 double pump Holley unit that I might play with too. That's the fun of tinkering right?
Last edited by grockin2004; 01-14-2010 at 01:28 AM.
Reason: spelling correction
The manifolds didn't use gaskets, but can. Dual exhaust is one of the better things that you can do. The truck will perform excellent as a daily driver without headers. Headers bring on problems of their own, loud, hot, and eat starters. It will turn a 15 min starter change out into hours because the header has to be taken down.
Stay at or below 600 cfms on the carb, the engine cant use much more. You will be dumping it on the road like most others.
Yes, I agree with most of that...and the Edelbrock 600 is what I run on mine, it's just about right. But as for the headers, it's all a matter of preference really. I did explain the issues with them and some work-arounds, and they just flow so much better than the restrictive FE flat manifolds that I feel they're worth the hassle (and I personally love the sound!) And yes, duals is a must and it's worthwhile to add the crossover tube.
And when you have to remove the manifolds anyway to install gaskets, it would be a good time to install headers and duals. If you do go with headers, be sure to use good quality header gaskets, not the typical old-school guaranteed-to-blow-out header gaskets but some of the new blow-out proof gaskets that seal better, like the dead soft copper gaskets, and then ad the locking header bolts on top of that.
Again, good information, thanks. It has a 500 cfm 2 bbl Holley carburetor. Probably good enough. The engine is a strong stump puller. Very good torque!
Even with a 4 bbl. how often do you think the secondaries are actually used in normal daily driving. May 1 or 2 % of the time. If even that much! Honestly, my last work truck with a carburetor, I dis-connected the secondaries and never noticed the difference as far as daily driving. Sure when I had a good load on board or towed a heavy trailer I noticed a little, at least I thought I did! Of course, in my hot rods, when I press the woo-hoo pedal, 4 barrels is a minimum.
I'm gathering the pieces to put dual exhaust in it this weekend. I'll leave the manifolds alone for now, just going to install gaskets. Truck sounds awful, snapping and popping from the manifolds and a couple other leaks under the truck...
i switched to four bbl because of the obvious but it also actually will save you gas. the primaries are smaller than in the 2bbl, so if you keep your foot out of it youll save gas but will also have the extra backup power if needed. just a tip
Dual exhaust might not fit if you've got the aux. gas tank. I ran dual pipes into a magnaflow, then out from there with a single 3". I think its as good as a dual set-up.
If you go to the expense of changing your manifold and card, its really not worth the hassel and cost unless you go to the right cam as well.
Mine has duals, one on each side and an aux. tank...it was set up that way when I got it. They ran the pipes under the frame rail up front and then down the sides of the frame outside the frame rails. So far I've never hit the pipes on anything where they run under the frame. When I swap the motor though I'll go single 4" exhaust.
As you said it runs very strong, don't worry about 360 or 390 "book" timing, just check where it's at before you mess with it- in the old "if it ain't broke don't fix it" style-so you know where to put it back to. Bump it a couple degrees and drive it in both directions, and see where it runs the best.
What are you trying to do with it, and why do you feel it needs to be modified, as you said it runs very strong- F250 4x2's aren't really hot rod material, I'd put some duals on it and leave 'er be and enjoy it