I've been thinking of building a 390 stroker in the future for my Diplomat ex cop car. I wanted to do the 390 so I can use the original engine and not have to hunt parts down. I saw Hughes sold a stroker kit and Indy has a set of heads for $975 assembled. I'm not wanting to do a 360, 408 etc because I don't want the original 318 sitting around wasting space and I'd rather use what I have if it's worth doing.

What are the problems, if any, with the 390? I know it's under square, not by much, but didn't know if this was serious concern.

Thanks

I've never done one but I have seen posts on really good running 390's. For top end power in a race car the slightly smaller bore on a 318 is a disadvanage but not so much on a street car. A carefully built 390 with a decent set of heads should work great in your application. I wouldn't hesitate if it was mine.

Out of curiosity, can you describe the indy heads you are thinking of using?

I think these are them. I saw the ad in MCG.

http://www.indyheads.com/lax.html

I have a friend who lives nearby with a factory efi'd 390 in a clubcab dakota 4x4...

11:1 static, 236/242 cam, as cast magnum r/t heads, 2bbl efi m1 intake and I think a 52mm throttle body through a 3200 stall and a slipping 4 speed overdrive trans. lol doesnt make much sense on paper...but it hauls ass.

He's run in the 12s with it and mind you once again it's in a 4x4 clubcab dakota. Very heavy.

He's putting the same engine in a dart soon, so it will be a nice thing to see how it runs in the lighter vehicle.

If all I had was a 318 block to work with to build a 4 inch stroke engine, I wouldnt treat it like it's a problem.

No cons... all good!!!! build it!!! 72 extra cubes from a 4" crank is a great bang for the buck..... TBF

what year dippy is it? biggest advantage, if it's an '85 or up, is that it has a factory hydraulic roller cam. if the lifters are in good shape you can reuse them, or stock replacements are $100-140/set vs. $500/set for the retrofit rollers. you can also get the stock roller cam reground by outfits like bullet cams, or trade your core in on a reground cam from hughes.

hughes sells the indy LA-X heads for less money with stock replacment valves:
la-x stock replacment

or upgraded valves
la-x upgraded valves

I like their #1110 springs that are installed on these. they're good to about .550" lift if set up with their recommended IH. I'm running them on some stock magnums on my 318 with a .506" lift roller cam--which was the reground stock cam, ground by bulletcams with their HR259/316 lobes for both intake and exhaust.

they also have the less expensive Enginequest heads, which have LA intake bolt pattern, but magnum rocker gear. one advantage of the magnum rocker gear, is you get the 1.6 ratio rockers stock, and aftermarket rockers are cheaper than comparable quality LA rockers.

EQ "iron ram" stock replacement

EQ iron ram alloy valves

EQ "iron rams" 2.02 valves

the biggest reground roller cam I've seen offered is the huighes 1828 which with 390 cubes should have a very nice powerband from idle to about 5500 rpm. I'd see if they can use the exhaust lobe for the intake and exhaust, making a 2828, personally, and run 1.6 rockers. Bullet Cams will probably want to see the cam before they say how big of a lobe they can get on it, but I prefer the most lift/fastest ramp you can fit. here's bullet's master list for HR cams:

http://bulletcams.com/Masters/HRlobes.htm

look at the .006" lift vs. .050" vs. .2" durations for the different profiles. while my HR259/316 lobe is 10 degrees smaller in .050 duration compared to the comp XE262 it replaced, it is only 3 degrees smaller in .2" duration (127 vs. 130) and has .008" more lobe lift.

if they can fit it on your core, for a 390, I'd use their HR272/340 lobe with 1.6 rockers, personally. the magnum based heads flow well enough on the exhaust that I personally don't think you need a split pattern cam.