[blkfrd]

I've shy'd away from stroking my 302 because of cost, but after doing some research i've come up with a way to build a 331 stroker for very little more than it would have cost to build my 302. I've finished mocking it up and have confered with a local Hi Po engine builder so now i'll share it with all the VMFr's.

The stroker revolves around using slightly longer 289 rods and a piston that does not a really short skirt and the pin in the oil ring land. I've never been very fond of the idea that the 331 and 347 stroker pistons have very short compression heights. 289 rods are 5.155 in length vs 302 rods that are 5.090.
Next I had to find a piston with the right compression height. The KB322 hyper piston came in just .015" short with a 1.405 compression height...just right for decking the block to zero deck or so. The KB322 is a 351W stroker piston with two valve reliefs and the pin is BELOW the oil ring. The compression ratio came in at 9.9:1 with a 61 cc head (351W ported heads are going to be used in this case)...it was almost too good to be true!

The rod length to stroke ratio comes out to 1.59...same as a 347 stroker with 5.400 rods. Rod length is not the end all to beat all anyhow especially for a street motor that won't see more than 400 HP and 6500 rpm.

So how does this keep cost down? 289 rods are cheap and plentiful and for about a $250 investment to put better bolts in, resize, shotpeen, hone the small end out for a .927 pin, and polish the beams, their ready to go for a mild street motor. The rod bolts clear the cylinders too. The crank was $200 from speedomotive (high nodularity 3.25" stroker crank). The pistons were about $275 but I would have needed pistons whether I did a 302 or 331 anyhow.

I actually found a set of H beam 289 rods for $299 (really good price for H beams) and notched the cylinders to clear the rod bolts. I got the rods from The Mustang Depot on .

I mocked up the engine and the counterweights just touched the bottom pin boss of the piston. I called speedomotive and they said that they routinely grind the counterweights and a lot of material can be removed from them and the crank will still balance out. The crank comes from speedomotive with plenty of material on the counterweights. I ground the counterweights down .065 where needed and the clearance is set.

So there you go...a 331 stroker for about the price of a regular 302. I'll keep you posted on how it runs when I get it put together in a month or so.

 

[Arto65FB]

That is interesting. I have had similar doubts about stroker cost efficiency. I might rebuild my 289 next winter, I was thinking about doing 302 with 289 rods, but your combo would come up with more cid at about same price.

 

[mrgem]

Very cool solution. Please keep us posted on the development of the new "Blackford 331".

 

[mike65]

/forums/images/icons/cool.gif Sounds great, keep us posted.

 

[roadracer]

I wouldn't reccomend have grinding down the counterweights. They are rotating mass and removing any material way out there on the tip of the crank where velocity is high is bound to upset the balance of the motor. Have you considered re-balancing? Sure, a vendor who SOLD you the crank is going to reccomend a little filing and grinding. It's your motor anyway isn't it!

Many people remove a small amount from the pin boss of the piston for clearance in this situation. I have done it myself on a previously balanced motor with no adverse effects. In fact, that motor is in my 66' right now. Pistons are reciprocating mass and aluminum has a lower density than steel/iron so you're not upsetting things much. You also just remove it in one spot on the piston vs. all the way around the perimeter of the counterweight. You can then match weigh your pistons to keep the reciprocating masses equal.

Good luck!

 

[CAponyboy]

Yes, this is the alternative way to stroke your engine......you will still have to spin this motor to get the HP out of it.....due to the smaller rods and higher comp height of the pistons.

It is a streetable alternative and 400 hp is an attainable number for this.

If cost is the main issue, this is the way to go.

I like to however, use quality parts.....Eagle is the rotating assembly of choice for me. A crank can be had for $500
rods for $300 and pistons (I don't like KB pistons) go with either JE or Ross $900 with rings. $1700 for a complete rotating assembly.

then there's machining and build time.

I had my 3.4" crank shaved down by a guy in Tennesee. It is a 2 week turnaround but he takes about 20lbs off a 55 lb crank. He knived down the weights and made them straight instead of that heavy wedge shape.....less rotating mass means your engine can spool up to its power band quicker.


then it needs balancing anyway so....go for it!!!

you get what you pay for

 

[GypsyR]

You didn't mention if you had the rotating assembly dynamically balanced or not. With all the mix+match stuff I would consider balancing an absolute necessity.

 

[blkfrd]

If your implying that I am using cheap parts...I beg to differ. No one said anything about using inferior parts. I could spend more but why? There are many who swear by KB pistons. There are many that swear by Ross pistons. I have a good understanding of what parts are necessary for a reliable strong street motor. The other side of the coin is that there are those out there who overspend for what is really required and they get caught up in all the hype about super parts (no implication but an observation that I see all too often). In my opinion, if it is not cost effective or necessary, why pay so much for something that is not warranted.

The mock up was done to verify the feasibility of the design. Now it can be machined, balanced and assembled. I enjoy the thought of trying something different and the anticipation of the final outcome. I never intended to compromise. See ya at the drags.

 

[roadracer]

Thanks for clarifying

"a lot of material can be removed from them and the crank will still balance out. "

Knowing you intend to rebalance is reassuring!