Engine Build Choices - What Would You Choose?

Discussion in '1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-' started by JTB321, Oct 27, 2013.

  1. Firstly, I'm not an actual Fox body owner but using a 5.o in a Factory Five Cobra. Most of the mechanical parts came out of a '90 GT, engine, T5, 8.8 rear end, spindles and brakes. After 3 years on the road time has come to upgrade the engine!!!

    The original build was standard E7TE block with GT40P heads and E303 cam. Now, the block is off getting machined to +030" and I have to decide what to build. I need to keep the heads/cam but have installed new TFS valve springs. I also now have a Exp upper/lowers and have 30 LB injectors to go with the rebuild. An MS3/MS3X will do the engine management.

    Should I stick with just a 306 using reground standard crank with new pistons OR go for a 331 stroker kit (see link) and live with the limitations of the heads/cam?

    I'd like to hit 300hp to 325hp which should be plenty entertaining for a 2200lb car :nice:


    Roller rockers, new push rods and a full crank/flywheel/damper balance will be used along with whatever else any one can suggest.

    Any comments would be appreciated.
    Thanks, John
  2. Can't speak to that particular kit, but I'd do the 331 over the 306. With those heads, you probably won't make much more power, but you will make a lot more torque, roughly 40 ft lbs, that will be there for almost the entire rpm band. 220 pounds, wow that sounds like fun, especially turning into corners!
  3. I've always wanted to build one of those kit cars. Check out my signature and look at my combo. Scat 331, home ported GT40's, N41 cam and Eddy intake. No dyno numbers, but using HP calculators (3390 lbs, 107.77mph in 1/4) I should be making a little north of 300rwhp, or approximately 340 flywheel HP. The cost of 306 vs 331 was about $300-$400 difference. Well worth it in my opinion.

    A5literMan likes this.
  4. I don't believe in rebuilding 302's as 302's or 306's, i just don't think it's worth the money, machine shop costs are very similar to just doing a 347, which is my preference.

    With that said, i'd rather have a 302 with TW's or afr's than a 347 with gt40 irons.

    Any particular reason you have to stay with the gt40's?
  5. i say 331 if you are going to drive the car on the street a lot. if it is mostly for fun or the track then, go 347. imho, 347's aren't as streetable as a good 331. that's just my .02
  6. Thanks guys, I guess a 331 would allow future upgrades to make more gains. I need to stick with the GT40P's for now for financial reasons but I'll change them out when I need the next boost!!!
    Any estimates what the 331 with my heads and cam would make at the flywheel?

    cheers, John
  7. who is doing the labor?
  8. Has to be me, I've turned every nut and bolt and done every square inch of the body, so other than the machining I am seeing this project through!!

    Cheers, John

  9. John,

    I was in the same boat as you. Also, I did 98% of the work myself. I have a real good friend who owns a machine shop. He is old school, but has a great reputation for quality. He bored, decked and checked my mains, then added new freeze plugs and cam bearings for $300. I bought my rotating assembly (Scat), rings, bearings, balancer and flywheel as a package from Coast High, for around $1350 ( I upgraded rings, bearings and pistons from base kit, adding to cost). I reused my almost new timing chain, reused my TFS 1 cam that I had at the time, I reused my rockers, reused my lifters and reused my ARP bolts. New oil pump was around $35, and all gaskets ran me about $130-$150. I also put $400 in my GT40 heads, which included me porting them, double valve springs, cutting my bowls at the shop, milling, valve seals and a valve job ( probably could skip on some of this and save some $$$). I'm sure there are a few other miscellaneous items that I am leaving out, but that totals about $2235.

    Last spring I trapped 107.77mph in the quarter mile. I weighed the car before making that pass, with me in it. It came in at 3390lbs. Using online HP calculators, that comes out to 305rwhp (345 FWHP?). Not a definite number, but should be fairly close. I think considering you are using an E cam, and I am currently running a N41, plus your heads will probably not be ported, I would say you will probably fall about 15hp or so under me, but who knows, you may build a wild freak!

    Even if you had to buy the things I reused, I think you could still get a well built motor done for well under $3K, maybe even $2.5K. The aluminum headed FRPP 306 crate motor cost around $3600 last time I checked, and it is advertised to make 340FWHP. When I go aluminum heads, with bigger cam and bigger intake, in the spring, I think the 331 investment will really pay off.

  10. Joe, thanks for taking the time to reply in detail and offer good advice, appreciate it. As for my build I am 99% sure I'll go up to a 331 and stick with the GT40P's at the moment which would seem to be the limiting factor. But, heads are a relatively easy swap out in the future if/when I need more power!!
    Now, where is my credit card.........

    Cheers, John
    A5literMan likes this.
  11. I'm going to disagree with everyone above and say stick with a 306. The 331 will be a lot more money for almost no performance gain whatsoever. Those heads will choke out a 306 never mind a 331. I would turn the stock crank, get the stock rods checked out and resized if necessary, get a set of 30 over hypereutectic pistons for it and call it a day. There are better places to spend that additional $2000 on then on a stroker bottom end. If that $2000 is really burning a hole in your pocket you are much better spending it on top end parts than bottom end parts.

  12. Well, I guess that is my 1% doubt about my plan.......
  13. I'm sorta with revhead on this one, especially since this seems to be budget orientated.

    Reason i say sort of is that explorer 5.0's are about $500. Their factory built engines are better and more reliable than any home or rebuilt 306. Buy the engine, sell of the heads and intake and you will only be in the shortblock $250.
    Then take the money you just saved and buy TW's or afr 165's.

    Then while enjoying your h/c/i 302, start building your 347 on the side. You will then be able to use the 165's or wedges as is or have them cnc'ed for more power when it's finsihed.

    Why have fun in the distant future when you can have it now.

    A 331 or 347 still doesn't make much more power with p's choking it. I certainly wouldn't do it. All the power is in the heads.

    BTW, a 331 has no advantage over a 347, i'm not sure why a 331 even exists.
  14. I kinda agree with revhead and 2000xp in that almost all the power is in the topend. But a stroker with gt40s is still going to make more tq than a 302 with 165cc heads in the low to mid range and maybe through the entire rpm band. Also it's easier to add topend stuff later than to add cubic inches. I say do the stroker-gt40s and when you can afford it add some good heads and cam. The either/or debate is a compromise in both directions. Obviously not ideal.
  15. I hate to bring up magazine tests, but it's relevant here. They did this years ago with at MM&FF. They took the top end off of a stock 302 and dropped it on a brand new 342 cid (347 with stock bore) and dynoed it again. It picked up 2hp and 3 ftlb of torque. Most of that can be attributed to it being a new engine. There isn't any real torque gain either.

  16. That still isn't an apple to apple comparison. I know what you're saying but he already has the block at the machine shop,heads and cam. So why build a 306 shortblock? Why not a stroker and then add the heads,etc? Is it a choke point? Most definitely. If I was in the market for internals I'd add the cubes and worry about the rest later. IMO still going to make descent power like Joe's build
  17. It's a lot cheaper to build a 306 than a stroker engine, even if the engine is already at the machine shop. And it is as close as it's going to get to an apple to apple comparison. We are talking about a different Ford iron head, but it's still a Ford iron head. He's got a long way to go on the top end to justify a bigger bottom end. I get pretty frustrated sometimes with internet pure parts shopping advice. Just because something is more expensive doesn't make it better. I can't understand how someone can see Ford making over 400hp out of the new 5.0, and then think "ah, I must need more displacement."

  18. All valid points, but I think this is about long term budget. Yes, 306 is a little cheaper right now, but in two years he is going to want more cubic inches. Then he has to start over.

    Now, of this was a choice of 306 with aluminum heads vs. 331 with iron heads, then I would say go 306. But, it looks like he will be stuck with iron heads either way, so that is really irrelevant. By the way, my 331 gt40 combo spins to the rev limiter without hesitation, never stops pulling.

    My cost were as follows for a 306:

    $300 block work
    $100 crank turning
    $400 pistons
    $rods needing rebuilding for $150, or new ones for $200
    Then what ever cost for bearings, rings and rebalancing. The 20 year old balancer needed replacing, and the flywheel too ($200 for both?)

    That's $1200 right there, not counting bearings or rings (say $150). So now we are at $1350. Still no gaskets, oil pumps or hardware.

    I probably had $1650 in my rotating assembly and block work. Not really financially better to build a 306 in every situation.

    A5literMan likes this.
  19. Way easier to add the topend later. Than being limited by smaller displacement. Umm MM&FF also have done articles showing the power differences between 306-347 builds with the "same" topend kits
    I'm sorry but more displacement has more potential for hp. Why is 347 in your on screen name if you don't believe in displacement? And who said anything about expense being better? That's true no matter which direction you're talking about. More expensive heads/displacement. And as for the "new" 5.0 making 400 hp who cares. They also build a 5.8 for the cobra. Why did they do that? Why not just put the blower on a 5.0? I just don't agree about a 306. I believe in displacement that's why I'm going to build a 9.5" deck motor:nonono: