TrimDrip

so you can put a 3.4 in. crank in an 8.2 inch deckheight stock 302 block and have a better piston to rod ratio than a 3.5 in. crank in a 9.5 inch 351 block?

Joel5.0

What is a "better" R:S ratio? ...... .... what is the importance of the R:S ratio? Does it take any precedence over the weight of the rotating assy. in the acceleration department? .... Would it markedly make a difference in reliability and endurance? The OEM cases mentioned previously, are typical examples how that generalization does not apply:

347: 5.4 rod 3.4 stroke = 1.59 R:S
347: 5.315 rod 3.4 stroke = 1.56 R:S

OEM
3TC: 123mm rod 78mm stroke = 1.57 R:S
300 I6: 6.210 rod 3.980 stroke = 1.56 R:S
454 BBC: 6.135 rod 4.00 stroke = 1.53 R:S

PJC Racing

Since Joel already explained it all, all I'm going to say is: FAIL.

TrimDrip

I would trust a 331 as far as reliability and durability at 500 hp to wheels more than I would a 347. Look at how much friction is going to be lost by running the same rod length with a 3.4 crank vs. a 3.25 crank. Less friction in a 331 is going to give more hp.
Now I understand that an engine isn't anything more than an air pump. The more air it takes in and gets out the more power it makes. The 347 obviously wins in that department. It is hard to believe though that DSS told my friend a myth when they sold him the 12:5:1 331 motor over the 347 for the reason of hp would be better in his lighter car and it would last longer. ya know?

Joel5.0

How much friction that is? How does it convert into a reliability problem? If a 347 is obviously a "bigger air pump" than a 331, how does that "friction increase" nullify its horsepower potential? Why did the 331 example shown below, needed some NOS to barely win over the N/A 347?

Grant+331+nos+Mustang+vs.+Dan+347+N%2fA+Mustang+Wi th

Why did DSS told your friend a myth to sell him a 331 over a 347? .... overstocking of 331's? .... The fact that "DSS said it".... doesn't mean it's less of a myth.

PJC Racing

The 2 primary magazine mail order short block companies are DSS and CHP. To compete with CHP's 347 (CHP's biggest seller) DSS pushed the 331 as a better engine based off of rod/stroke ratio and got alot of people to believe in the myth.

If you go back about 8 years and look at both companies adds you will see CHP primarily sold 347's, you could get a 331 from CHP but for a substantial increase in cost, DSS primarily sold 331's, you could get a 347 from DSS for a substantial increase in cost. It's marketing.

TrimDrip

that gray car was pulling away at the end and it looked like he let out of it like it was a time dialed in. I can't tell which one is which but, the grey one claimed a 10.83 @ 127 the week before.

TrimDrip

you know, I don't really doubt that at all. I read that in a magazine about that long ago.

I thought I read it in the one that had the 331 ways to outrun an ls1. I looked it up on the internet and didn't see it in the article. If I can find that magazine, I am going to see if it is a different write-up for the article. I know it was somewhere between 2002 and 2004. I built my 393 in 05 and quit buying magazines.

They did claim the 30 or 40 horse over the 20 lbs of torque.

Joel5.0

Here you go, here's the generalization article that started spreading all that myth........ to the "T"....



The addition of the "In some extreme cases, the poor rod ratio can even collapse cylinder walls as it side loads the piston in the cylinder really hard." comment really tops it all. I guess that doesn't apply to 351w strokers?..... or to Toyota 3TC engines running turbo with NOS for years?.... like the one used by the owner of the machine shop I take my business to..... = http://agracingvideo.com/p/videos/ponce/19feb09/15.wmv

Not bad for a setup overly side-loading those cylinders, causing a lot of friction + forced induction + NOS..... for years on a stock block.....

TrimDrip

that was a quick pass. Was that a true 1/8th mile?
reason I ask, we got a track around here that will make 7.20 cars run 6.50s.