347 VS. 331

What's up everyone!? I've been looking and looking, talking and talking, but would really love to get a great answer on building either a 331 or a 347 for my 65 Mustang. I have heard so many horror stories about the 347 being weak and having massive issues with the rods and the side thrust being too much for a stock 302 block, and it just doesn't handle the build very well. I have also talked to some engine builders who say that the 347 is just as reliable as anything, but could you really trust somebody who wants you to spend $8k in their shop?
 
  • Sponsors (?)


I've also been heavily researching for a 347 build. Early on, the 347s were victims of poor geometry in stock blocks and lack of properly designed aftermarket parts. Guys were grinding out clearances and cobbling together mismatched parts to make them work. Stroker parts and knowledge are much better these days, if you go with a stroker kit from a reputable company it will last a long long time. I personally would never use a stock block for a stroker even with the improved piston designs and proper clearancing, an aftermarket block such as Dart is designed from the beginning for stroker builds and inherent weaknesses of factory blocks have been addressed in the design. Many of the old issues can be avoided just by using an aftermarket block. As far as side thrust and rod ratio, today's oils and piston skirt coatings are more advanced and able to withstand the abuse better. No reason anymore to believe a stroker wouldn't last as long as a stock 302 if properly built.
 
  • Like
Reactions: 2 users
I agree with above, all correct statements except I have had great success using a stock block for a stroker. The original horror stories started when a shop in carolina first came up with the 347 as an option for the 302. Their mistake was using too long of a rod and using very low tension oil rings and combine that with the internet and the myth lives on today, 25 years later. Same with TW heads. They had issues at first release with their cheap cast iron valve guides and again, thanks to the internet, the myth lives on today. They offered to replace every set sold with new bronze guides and then quit offering the pedestal mount versions altogether. 347 will make more hp than an equally modified stock stroke 351 because of the differences in rotational weight.
 
  • Like
Reactions: 2 users
Modern built 347 - I went and did the 347 on my 65 - I basically got to the point after reading up that if I am not racing it or beating the piss out of it routinely go big- Go for the 347. Late to the thread but just finishing up my 347 build and waiting on a torque converter to start running!
 
Modern built 347 - I went and did the 347 on my 65 - I basically got to the point after reading up that if I am not racing it or beating the piss out of it routinely go big- Go for the 347. Late to the thread but just finishing up my 347 build and waiting on a torque converter to start running!
how did the build go?
 
What's up everyone!? I've been looking and looking, talking and talking, but would really love to get a great answer on building either a 331 or a 347 for my 65 Mustang. I have heard so many horror stories about the 347 being weak and having massive issues with the rods and the side thrust being too much for a stock 302 block, and it just doesn't handle the build very well. I have also talked to some engine builders who say that the 347 is just as reliable as anything, but could you really trust somebody who wants you to spend $8k in their shop?
did you ever make a decision? I'm pondering doing a 347 for my 95 and the guy I want to build my engine in TX said a 331 would be better because of " Rods too short and not reliable, side loads piston in the bore too much and creates a ton of wear in the skirt " when it comes to the 347.
 
I've also been heavily researching for a 347 build. Early on, the 347s were victims of poor geometry in stock blocks and lack of properly designed aftermarket parts. Guys were grinding out clearances and cobbling together mismatched parts to make them work. Stroker parts and knowledge are much better these days, if you go with a stroker kit from a reputable company it will last a long long time. I personally would never use a stock block for a stroker even with the improved piston designs and proper clearancing, an aftermarket block such as Dart is designed from the beginning for stroker builds and inherent weaknesses of factory blocks have been addressed in the design. Many of the old issues can be avoided just by using an aftermarket block. As far as side thrust and rod ratio, today's oils and piston skirt coatings are more advanced and able to withstand the abuse better. No reason anymore to believe a stroker wouldn't last as long as a stock 302 if properly built.
hey did you decide on anything?
 
Being the OP is long gone I thoght I would provide my take on them. I went with a 331 due to the rotating assembly was cheap due to the guy was going through a divorce. However, I would have preferred a 347 as they make more torque which is a function of cubic inches.

As far as I know all the old “side loading”, “wrist pin is too high”, “geometry is not good”, etc. was engineered out of the good kits so I would not shy away from a 347 at all.
 
  • Like
Reactions: 1 user
Being the OP is long gone I thoght I would provide my take on them. I went with a 331 due to the rotating assembly was cheap due to the guy was going through a divorce. However, I would have preferred a 347 as they make more torque which is a function of cubic inches.

As far as I know all the old “side loading”, “wrist pin is too high”, “geometry is not good”, etc. was engineered out of the good kits so I would not shy away from a 347 at all.
oh wow long gone as in gone gone? I have to call my guy in tx to see what it would cost to build a 331 as he told me " Rods too short and not reliable, side loads piston in the bore too much and creates a ton of wear in the skirt " ....

So when I talk to him I will have that conversation and ask him why he still feels that way and if he has built any modern 347s with the kits now that are not what the old stuff used to be/have. I mean I think I'll be happy with a 331 as well as the 347 overall so not going to fret it if he doesn't want to build the 347. I've known him since around 2012 13 and always like how he talks about the whole scope of building and horsepower, torque, air speed, ect ect as to how putting together a combo that matches and the whole shabang. If the price is right I will definitely let him do my build but will also look into longblocks from the reputable places as well. I will likely want to put a certain head and intake over what comes on them depends on who I get it from. Some of the places like Prestige Motorsports I love the fact that they dyno their engines and I've seen a lot of videos of their builds. In that case I might go with the heads and cam that comes with their combo but ofcourse we'll talk about what intake I'll use to match the heads and let them build the cam off of that.
 
You are better off talking to Ed Curtis at Flow Induction Systems and let him spec the cam, heads, and intake(s). From there buy a full rotating assembly from the likes of Scat, Skip White Performance, Coast High Performance, Eagle, etc. Ed will need to know the the cubic inches, compression, fuel system, exhaust, trans, gears, etc. You can download his custom cam shaft data sheet here and that will give you and idea as to what he will be looking for. You can ignore the heads and intake if you want him to spec those for you.


Have your engine builder / machinist build it and I would strongly suggest putting it on an engine dyno before you stab it in the car. Too many people think they know how to put the parts together and end up not achieving their goal(s) because of mismatched parts.
 
You are better off talking to Ed Curtis at Flow Induction Systems and let him spec the cam, heads, and intake(s). From there buy a full rotating assembly from the likes of Scat, Skip White Performance, Coast High Performance, Eagle, etc. Ed will need to know the the cubic inches, compression, fuel system, exhaust, trans, gears, etc. You can download his custom cam shaft data sheet here and that will give you and idea as to what he will be looking for. You can ignore the heads and intake if you want him to spec those for you.


Have your engine builder / machinist build it and I would strongly suggest putting it on an engine dyno before you stab it in the car. Too many people think they know how to put the parts together and end up not achieving their goal(s) because of mismatched parts.
I actually sent Ed an email recently so I'm just waiting on a waiting a reply. I have not made any final decisions yet I just and I am just getting things in play and I'll talk to my builder extensively since I first met him and he's mentioned that and he knows Ed Curtis and those guys very well he's done some cams and stuff for customers that it was something along the lines of he was working with Ed or have worked with some cams done from it or after it or something along those lines I can't remember exactly but trust me when I say I know I trust this guy to put a combo together and that's why I'm waiting I actually haven't talked to him yet I'm going to give him a call right now and actually. But I'm going to get his combo a few of his intended combos for my build and make me a spec sheet and then give me a price and I'm going to see if that's the way I want to go. So nothing is out of the water yet I'm just kind of getting my ducks in order....


Speech to text while I'm exercising LOL so I was going to make one long sense but I know that sometime hard to read and keep up with but yeah so I'm just having options right now and he is one of the guys who are definitely trust to build my engine and to put a properly matched combo together. So between him and Ed or prestige Motorsports that will likely be the way I will go either for 3:31 or 3:47. But yeah I definitely know people have had great success with Ed as well so it just depends on you know length of time you know on how long it will take him to do it etc etc you know I'm in no rush but I definitely want this one to be right and I feel one of these three will definitely do me right or all three of them will any of them.
 
You are better off talking to Ed Curtis at Flow Induction Systems and let him spec the cam, heads, and intake(s). From there buy a full rotating assembly from the likes of Scat, Skip White Performance, Coast High Performance, Eagle, etc. Ed will need to know the the cubic inches, compression, fuel system, exhaust, trans, gears, etc. You can download his custom cam shaft data sheet here and that will give you and idea as to what he will be looking for. You can ignore the heads and intake if you want him to spec those for you.


Have your engine builder / machinist build it and I would strongly suggest putting it on an engine dyno before you stab it in the car. Too many people think they know how to put the parts together and end up not achieving their goal(s) because of mismatched parts.
Forgot to mention he grinds his own cams as well and he ground regrind the can that I had in my setup back in 2014 when I had a broken spring on number two. I sent my cam to him and he reground the E cam
 
He shows up here from time to time and repeats the mantra above.
talked to Shaun this evening and I'm likely going to have him build a 331.

stock block 302,
Brodix 17 degree 165's bare and he'll use a 1.94 intake valve and I believe 1.57 exhaust and change/upgrade some other components. I believe he'll get them bare.
custom cam
either a performer 2, Systemax 2 or Trick Flow intake. I don't like the flat look of the regular TF uppers but one of those will likely better match my combo. Going to do some research on similiar builds to get some insight
 
  • Like
Reactions: 1 user
If you didn't fill out the form then he will not reply.
Loved the guy. Really helped me when I was new to the game. I've had 2 of his cams. I reached out to him for a 3rd w/ addl valvetrain components... several months passed. Reached back out again; was directed to fill out the form. Did so, and asked if he had everything he needed, which he affirmed. Months went by again; so, I reached out a 3rd time and he acted like he didn't know anything about my order. So, my Ed days are over. If you can get his attention & support, I think he's the best in the biz. If not, he's more towards the opposite.

edit: maybe they're no so over... He's agreed to help me on a new build. Excited!
 
Last edited:
  • Like
Reactions: 1 user