306, 331, or 347 - Which one?

2MANYMUSTANGS

2MANYMUSTANGS

Club Member
Alright Motown Members, I am looking at rebuilding the engine in my '90 LX (5.0). The rotating assembly is good but the block needs to be bored and decked. My question is: am I better off building a 306, 331, or a 347? I would be happy with something around 400 - 425 HP. But, I don't really have a lot of cash to spend. I have about $1000 for the short block. I will assemble it myself. I have a decent set of ported heads, a ported and reworked GT40 tubular intake, a new E303 cam, new roller lifters, timing chain, pump, & shaft.
 
1k to spend on the short block I would say 306 is your only option, a nice 12:1 306 will make some nice power. 317,331,347 stroker kits are about 1k or better, then machine work
 
A friend is building a 347. He has has about $800 in machining, and another $700 in assembly of the short block and cam.

he bought the rotating assembly elsewhere and planned on doing it himself, but decided to have them assemble it.
 
smooth said:
1k to spend on the short block I would say 306 is your only option, a nice 12:1 306 will make some nice power. 317,331,347 stroker kits are about 1k or better, then machine work
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Sounds like I need to scratch together some more $$$. I really want to stay away from high compression. I was thinking about 10.3:1 max. That way I can still run pump gas.
 
I'm doing a 331 right now. Scat cast steel crank, H-beams, and Mahle flat-tops.
I paid $250 for the crank, $200 for the rods, and $550 for the piston kit. (with rings , pins and locks)
That is a $grand with no machine work. You can go on Flea-Bay and save a couple bucks, but you will pay more than what you thought you saved buying cheap parts and trying to make them right. You CAN do a 306 for less using a stock crank and rods. Lots of guys on here make 350+ to the wheels with a 306.
I don't think he advertised budget has a stroker in it.
 
Rod ratio is better on a 331 for a street motor. With a traditional 347 you are putting extra stress on the piston skirts. I wouldnt be scared to run 11:1.
 
I think I can scratch together a little bit more money. If I do a 306 I can probably put it together for $1000 but if I want a stroker sounds like I need around $2000 to do the short block. I have quite a few new parts to finish the engine. Here is basically what I have:

a new E303 cam shaft, new set roller lifters, new timing chain set, new oil pump and harden shaft, on you set of GT40 X heads with 58 CC combustion chambers, and a fully worked GT 40 tubular upper intake manifold.

The car is set up like an autocross car (big brakes, lots of stiffening, and upgraded suspension). But, it is really just a driver. I am shooting for 400ish horsepower. I guess the original intent of this thread was to see if I can get there with a 306 if I can't would I be better off with the 331 or the 347.
 
Your car sounds an awful lot like mine!
$2K will get you into a 331 with quality parts.
The decision for me was that I want more cubes, but am on a budget. Someone mentioned the 347 rod ratio being less than optimal, and that is true. (331 has the same issue, just not quite as bad.) It can cause accelerated wear that impacts durability. I am not one of those guys who pulls the engine every winter, so I went with the lesser of the potential issues.

I think the parts you have will NOT get you the 400 number at the flywheel with a 306. You will be closer with the 331. And MAYBE get there with the 347, but you may pay a penalty in durability. If you are putting 3000 or more miles on the car per year, or open-tracking on a regular basis, I think the 347 will need freshening far sooner than you would like.

With that I have a set of old Edelbrock Performer RPM's, a 220 / 224 Comp roller, and an Explorer upper & lower. I'm planning an Aviaid road race pan and all the other goodies (similar to your list) to build the engine complete. With my 60cc chambers, I am just under 10:1. I expect to make about 375-390 on pump premium after a tune.

Good luck!!
 
SuperStang90 said:
Rod ratio is better on a 331 for a street motor. With a traditional 347 you are putting extra stress on the piston skirts. I wouldnt be scared to run 11:1.
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That makes sense. I was leaning more towad the 331 mainly because of where the wrist pin sits in relation to the bottom piston ring. I want something that will be strong but also reliable. last thing I want is an expensive bomb.
 
i wouldn't even waste time or $ rebuilding a stock blocked 302 based motor. find a decent 351w block or just buy a remanufactured 302 or something to keep ya going. You can get remanufactured or stock 351w cheaper then you would have into a 302 based stock block stroker. The 351w would make and handle more power then a 302 based stock block stroker. then you will just need a gt40 351w lower and a set of headers for a 351w in a fox. can usually find both cheap fairly easy
 
OldbutNew said:
Your car sounds an awful lot like mine!
$2K will get you into a 331 with quality parts.
The decision for me was that I want more cubes, but am on a budget. Someone mentioned the 347 rod ratio being less than optimal, and that is true. (331 has the same issue, just not quite as bad.) It can cause accelerated wear that impacts durability. I am not one of those guys who pulls the engine every winter, so I went with the lesser of the potential issues.

I think the parts you have will NOT get you the 400 number at the flywheel with a 306. You will be closer with the 331. And MAYBE get there with the 347, but you may pay a penalty in durability. If you are putting 3000 or more miles on the car per year, or open-tracking on a regular basis, I think the 347 will need freshening far sooner than you would like.

With that I have a set of old Edelbrock Performer RPM's, a 220 / 224 Comp roller, and an Explorer upper & lower. I'm planning an Aviaid road race pan and all the other goodies (similar to your list) to build the engine complete. With my 60cc chambers, I am just under 10:1. I expect to make about 375-390 on pump premium after a tune.

Good luck!!
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Thanks for all your help. Between your input and info from SuperStang I think you guys convinced me to build a 331; really for most of the reasons that you mentioned. I really didn't plan on building an engine for this car so I am definately on a budget. I could spend more but at this point I could have bought a car that was done and probably nicer that mine is for what I have into it. And I am looking for something to just have some fun with. I could probably build something that would be more powerful but I am not really looking for a 1/4 mile car. I have had a few of those and while they are fun, I hated having to run Turbo Blue and really only being able to drive the car on the track.

+1 for both of you! Thanks again all!
 
2MANYMUSTANGS said:
Thanks for all your help. Between your input and info from SuperStang I think you guys convinced me to build a 331; really for most of the reasons that you mentioned. I really didn't plan on building an engine for this car so I am definately on a budget. I could spend more but at this point I could have bought a car that was done and probably nicer that mine is for what I have into it. And I am looking for something to just have some fun with. I could probably build something that would be more powerful but I am not really looking for a 1/4 mile car. I have had a few of those and while they are fun, I hated having to run Turbo Blue and really only being able to drive the car on the track.

+1 for both of you! Thanks again all!
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just a few little tips...im in the middle of building my first engine.

between block machine work, balance, bearings, a harmonic balancer, and some piston rings, and a used cam....ive got 1400$ in my short block...i already had the crank, rods, and pistons and block.

dont skimp out on parts to save a few $, spend money where it needs to be spent.

measure everything 2 times, and do alot of research, and keep it clean!

if you plan on doing this, you may want to start dropping it off soon, if you wait a little while longer, every machine shop will be backed up so much that you'll be waiting a while for you stuff to come back.
 
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