331 vs. 347

[Mustang88LXKid]

I chose a 331 for reliabilty, I'd use a 347 if I was building a track car, but my car is for a daily driver.. I did not want to take the chances, plus 10-15 hp can be maid up with a power adder, so why worry about 10-15 hp.. That doesnt mean anything for a street car unless it was track car.. And since it is a street car why worry about it, you'll blow the doors off of 95 % of the cars on street.. Cops wont catch you :oD ... put on a A trim if funds are limited, thats 80-100 rwhp right there.. Your engine will love you !!

Ok, umm 331 USED to be better for the street. Now the 347 works and does NOT cause wear in the engines now. I have had different brands have confirmed that they do not. I have talked to Accufab and the person I talked to worked on the 347 for the 5.0L mustang and he said it was fine. He said they used to hurt the engine's life, but now they do not. He told me go for the bigger CID because they are the same price, why go smaller? And if you are paranoid about the life you can just not over bore and it will be a 342. Better than the 331. So a 347 isnt for racing, it is a daily driver too. I have more facts to prove it too, if want.

 

[Sam8950]

my buddy had a 347 from CHP two years ago and his motor used to burn a lot of oil.. Thats another reason why i chose 331...

I think that's been fixed with the more recent versions. I'd really like to hear from anyone who has a CHP 347 (or even 331) that's newer than two years.

 

[93cobra12]

Two years is a while back to make changes, but every highly respected racing company out here in Washington lead me to the 331 side.. Orginally i wanted a 347, but they highly recommended 331, Two racing companies out here.. One of them had a 347 and he wished he had a 331.. I dont know if they were trying to gain more experiences with those short blocks but two companies told me about them.. I dont know, i guess its who you talk too and what you want it for...

 

[Gearbanger 101]

Ok, umm 331 USED to be better for the street. Now the 347 works and does NOT cause wear in the engines now.

Although the oil consumption issue has been addressed, don’t be fooled into thinking the 347 is still a wear-proof motor. The fact of the matter still remains that even if it is ever so slight, the side-wall load that the 347’s rod ratio continues to put on the cylinder walls will make it’s self apparent as the miles pile up. Maybe not for the first 100k, sooner or later physics will catch up with it. This by no means makes the 347 a bad buy what’s so ever. Like was said earlier, there truly is still no replacement for displacement and the larger displacement still does have the ability to make more overall torque and horsepower over the smaller 331. But the fact of the matter remains that the reason most people make the decision to choose the 331 over the 347 isn’t based on horsepower alone.

Aside from the fact that the 331’s bore and stroke dimensions make it less prone to wear, its rod ratio also promotes a faster, freer revving combination, compared to that of the 347. This is likely the main reason the 331’s are favored in most cases. Another reason is that its rod/stroke ratio allows the piston travel to remains at the top and bottom of the bore fractionally longer with each stroke than the larger 347. Thus allowing a deeper intake charge and more efficient combustion charge in the process. Although the 347 still breaths a little deeper than the 331overall, the 331 still makes better use of the incoming airflow and translates those numbers to the dyno. That’s why there’s usually such a marginal difference in power between the two of these engines, despite the difference in displacement.

 

[billetunderwear]

347's also have higher piston speed than a 331 at a given RPM. Inertia is also something to consider. The 347 piston must come to a more abrupt stop and change direction more quickly than the 331 piston. With more speed and a quicker stop, I could see slightly more potential for a failure in the rotating assembly. However, this is all in my head... I have no idea how much the added stress would actually affect a real world engine. Rick91gt knows what he's talking about from hands on experience and I don't, so you should listen to him.

-Dave

 

[90Notch]

The only reason I would ever consider a 331ci over a 347ci is if it was going to be a blown motor (331ci pistons have more meat on the top than 347ci) or cost. This long rod crap you all are talking is just that crap! Take a look at other motors, Honda(Acura) for one will anyone argue that one of their motors won't easily last well over 100,000 miles? No, they have a worse rod ratio than a 347 and make the same if not more HP/per cubic inch plus they rev higher than most 347s around.

Also, my last Eagle 331 (got a deal on all forged kit that I couldn't pass) had the piston pin interesect the oil ring groove and did not require notching of block (Eagle I Beam rods).

If (THIS IS THE KEY) the motor is properly built a 347 will last just as long as a 331! As for reliability, they are as a reliable as a built 302/6 motor, you all have to consider that most strokers are not mild builds nor are they driven like a grocery getter...that's why many need rebuilds after 50,000 miles not because of the internal parts wearing faster.

 

[sleeper89]

like 90Notch said - pick the stroker you want based on performance/cost/etc not on rod ratio's and the like. when i rebuilt my 302 i had my block clearanced for a 347 stroker crank, just in case i decide to go that route. in the last 2yrs the 347's have come a long way and if i were buying i'd get the CHP 347e. Yes, the 347 will have higher piston speed and a worse rod ratio but all else being equal the longevity difference would be minimal on a street car. besides, how often do us "performance guys" let our built engines get over 100k miles? sure it happens a lot on the stock motor but it's relatively uncommon for built motors.

put my vote in for the 347e, but you WILL NOT be disappointed either way.

-steve

 

[stangboy]

I think that's been fixed with the more recent versions. I'd really like to hear from anyone who has a CHP 347 (or even 331) that's newer than two years.

Well, my boy Mitchstang just bought a CHP 331 stroker kit(forged everything ). The block and rotating assembly are at the machine shop as we speak. He's still trying to decide on what heads and intake he wants to use though. So, it may not be running until this summer. I'm sure he'll let everybody on here know when its running. I'll let yall know too, cause he won't be running it hard until he can handle the power of a worked V8. I gotta teach him a thing or 2 . He drives a stock Honda Civic right now. He already told me that I'll be his driver when somebody wants to race him....or should I say his car.

 

[93cobra12]

" Ok, umm I have more facts to prove it too "

Mustangboy, lets see those facts !

 

[90Notch]

"He's still trying to decide on what heads and intake he wants to use though"

AFr 185s and old RPM intake unless he wants to match new RPM II to heads

"I plan on buying a 347e from CHP."

Why? Get the longest rod possible and make sure block is prepper properly and it'll last for a long time!

 

[93cobra12]

I built my car up for a supercharger, not so much hi-reving, the most i'd go is 6300, But this motor is for a supercharger.. I have the aluminum flywheel, 3:73 gears, a blower cam, a 331 w/ all forged internals, 185 afr heads.. So thats basically why I chose a 331, along with all the builders I talked too who recommended a 331.. Dont get me wrong, my buddies 347 was crazy fast, I loved it !! You can make serious hp from a 347, but im for the 331's...

 

[DavidF]

I’m running a CHP 347, and have so for almost two years. I have about 20K on it so far and do not have any oil consumption problems yet. I chose this motor over the 331 mainly for the extra torque and HP knowing I wanted to keep it N/A. As far as wear goes, IMO when ever you run with a power adder you put way more stress on engine components and there for the life of the engine decreases as well. As for me I love my combo, it’s a daily driver and have taken it as far as Las Vegas (in the summer) with no problems. But if the 347 still worries you, you can’t go wrong with the 331.

 

[usedtobe 67p51d]

I went with a 331. 343 hp @6300 and stays at 340 untill 6800. torque is lower than I hoped for 323#'s but the motor hasn't been tuned. this is rear wheel hp tremec, 9" 4.11's in a '67 fastback

 

[Gearbanger 101]

you all have to consider that most strokers are not mild builds nor are they driven like a grocery getter...that's why many need rebuilds after 50,000 miles not because of the internal parts wearing faster.

You know...3-4 years ago I might have agreed with you, but the cost of most of these kits have come way down in price and their reliability has gone up. It's nothing for most people who are making more than minumum wage now, to opt for a stroker rebuild rather than a basic. That's why I think you're starting to see more and more of them on the road and in tech forums. It's not the all out racer buying these anymore. People are purchaseing these kits like a "regular bolt-on" now adays. And why not, what's going to give them a better bang for the buck and make everything else in their combo work better besides a gear swap? Nope....popping the hood and seeing a stock looking 302 block doesn't mean anything anymore. I know I'd lye through my teeth if anyone I didn't know asked me what I was running under the hood. "Yeah, it's just a stock 302 with a couple of bolt-ons ................ ."

 

[CobraGT87]

"He's still trying to decide on what heads and intake he wants to use though"

AFr 185s and old RPM intake unless he wants to match new RPM II to heads

"I plan on buying a 347e from CHP."

Why? Get the longest rod possible and make sure block is prepper properly and it'll last for a long time!

Just remember, the 347e use's a 5.315" rod, vs the standard 5.4" rod and the cam is the E cam (smog legal). If you look at my post on page 1, I put a pic of the pistons I use in my 347 and there is NO intersec issue. That piston is made by Probe, it's the SRS series Flat Top design. I use the 5.4" rod.

Take Care,
Scott

 

[90Notch]

Scott full aware of the 347e kit but there's no need for it, my 331 interected oil ring groove and consumed no more oil than the 306 it replaced. Its marketing crap, as for the physics of it (since people like to use this) a shorter rod will yeild more stress on wall so in addition to the "added" stress a 347 kit puts on wall you just compounded the issue . Not to mention that the kits that do intersect the oil groove come with support rails.

 

[Gearbanger 101]

Its marketing crap, as for the physics of it (since people like to use this) a shorter rod will yeild more stress on wall so in addition to the "added" stress a 347 kit puts on wall you just compounded the issue .

Incorrect, the 347's longer rod/stroke ratio intersects the bores from a more exaggerated angle and creates more sidewall load on the bore than the 331 and therefore increasing wear over time. Or were you just guessing when you said that and hoped nobody noticed? Maybe you should have paid a little more attention to the physics aspect while in math class? Either way, it's not as relevant considering neither side seems to want to budge on their reasons for choosing their preferred combo.

 

[93cobra12]

thats why 331 last longer.. A B stuff people..

 

[DavidF]

If I’m not mistaken CHP offset the pin location to help this side load problem.

 

[CobraGT87]

Scott full aware of the 347e kit but there's no need for it, my 331 interected oil ring groove and consumed no more oil than the 306 it replaced. Its marketing crap, as for the physics of it (since people like to use this) a shorter rod will yeild more stress on wall so in addition to the "added" stress a 347 kit puts on wall you just compounded the issue . Not to mention that the kits that do intersect the oil groove come with support rails.

oh ok. I saw in your sig that you were going with the 347e. I guess I mis understood your sig. sorry bout that.

theres so many threads now about the 331 or 347 issue, side loads, rod ratio etc. For a N/A street motor, the life expectancy is the same. If I was building a blower motor setup, I would of gone 331 as well, simply because it's more rev happy. I built mine for N/A TQ for street driving, no 1/4 stuff..

Take Care,
Scott