Was talking to someone today who suggested putting a 302 crank in my 351w. Has anyone heard of this ? Not that I'm going to do it, hell I can't figure out my ignition, let alone messing with the internals. Just thought it was interesting. And if anybody would know about this, someone on this board would. Just curious, Darrel
Why would anybody do that? First of all the main bearings are much larger in a 351W, you would need some kind of bearing spacers. The 351W cylinders are an inch taller, not sure what kind of rods you would run. You'd have a tall block with a short 3.0" stroke.
Maybe they had it backwards and thought a 351W crank turned down on the journals would fit a 302 block making it a stroker. Seth
They used to do that back before stroker kits were available. Now you can just buy a stroker crank for less than half of what machining a bigger crank would cost.
Maybe, don't know a thing about it !! I just thought it was interesting and wondered what he was talking about ! Maybe he got his cranks and blocks switched. Said something about doing it in his "Tuxedo" Fairlane or something like that. I'll talk to him again soon and try to clarify.
He said it was a Formal not a Tuxedo as I previously stated. And he insist they used to put smaller cranks in bigger cubed engines. He is about 60 and hasn't messed with cars in ages. Maybe he's not remembering correctly. Oh well, thought it was an interesting subject. Thought maybe I'd stumbled on something I hadn't heard of.
It used to be (still is in my opinion) cool to put short throw cranks in small block chevys. Maybe that's what he's thinking of. Like a Z28 302 or a 327 vette. All of the Ford 302s were done on short deck blocks so I don't know what he's thinking. Even the Boss 302 was done on a short deck. A lot of people seem to equate short throws with high reving engines, when it's the rod angle that has more to do with your piston speed than anything.
Many high rpm forms of racing use short stroke cranks. It's been a long, long time since I have seen one, but they used to sell spacer kits to put a 302 crank in a 351W. I think they even have been modded and used in Clevelands back in the day. You can still find spacers to put a 350 crank in a 400 block... Chevy stuff. No matter what, it's not a good idea for street cars, too much rpm needed to make good power. Dave Useless trivia: Austrailia didn't have a W based 302. Their 302s were destroked Clevelands. Their 302 heads are what you get when you buy Aussie heads. Their 351 cube engines got the same open chambers that we had over here. That is why the ports and chambers are smaller on those heads... They were designed to support 302 cubes, not 351.
Someone posted on here a while back about a strong roundy-round SBF BECAUSE it had a short stroke (high rev engines obviously). :blank:
Having a short throw does not necessarily mean you will have a high RPM engine. For instance. You can have a 3" throw and a 4 inch rod and that will have a higher piston acceleration value than a 4 inch throw and a 6 inch rod. Sice Force is equal to Mass times acceleration, the long rod long stroke engine makes less force on the rod. The 4 inch stroke with the 6 inch rod will put let stress on the con rod at 6000 rpm than the 3" stroke and 4 inch rod because stress is basically equal to force divided by cross section area of the rod. Therefore the engine with the smaller stoke/rod ratio will be able to rev higher without breaking a rod. What a short throw gives you is more room to run a longer rod and push the pin up in the piston to make the piston lighter. This is what makes the short block capable of handling the high rpms. If you dont' take advantage of this, it does no good to run a short stroke. In a carbed engine, the small stroke/rod ratio gives you a smaller piston accleration which in turn gives you a less sharp vacuum signal to the carb, so it will idle like crap. But it also increases the dwel time at TDC, so you don't have to run as much timing, and can get a more complete burn, and more power. In a fuel injected engine, the idle problem is hardly noticable, but all the advantages are still there.
^What ATO said (that's my story and sticking to it).^ Is it also true that the torque band is 'wider' with a short stroke? I realize this has to do with the cam specs also, but in theory - because of the higher rpms, the "useful" torque is there during a wider range of rpms. ..or not.
Long rod engines have a longer piston dwell at TDC and tend to burn the fuel better and thus have a higher BMEP giving you a more broad torque curve. For instance... A piston that is within 2 degrees of TDC for a longer period of time at 6,000 RPM will burn the fuel at a higher pressure than an engine with a piston that spends less time within 2 degrees of TDC. The efficiency of the fuel burn has a lot to do with the pressure of the mixture during ignition. I don't know if that makes any sense or not. Basically a long rod engine lets you spend more time at or around TDC where the volume is the smallest and the pressure is the highest. More pressure means more torque and a better burn.
The ultimate question for us to ponder is: If you have a deck height of X", what do you do with that given deck height? No one in the hobby can agree... It is the eternal arguement among engine guys. You can use a short stroke and get the benefit of long rods dwelling longer, and therefore absorbing more potential energy and turning it into extra force on the crank. OR You can use that extra deck height to force more stroke into a given block, gaining more cubes... Everyone knows cubic inches is cubic power. Right? That is the debate. I wanted for a long time to build a long rod engine, just to prove a point, but the more I ponder it, the long stroke always wins the arguement in my head. How about you guys? Would you settle for a 1.45 rod ratio just to squeeze out that last cube, or would you forego some cubes to squeeze in that 1.9 rod ratio? Dave
Well.... The 4.6 I'm putting into my mav kind of made that decision for me. It's a fairly tall deck for such a small engine, but the piston is almost falling out of the bottom of the cylinder as it sits. There are some stroker kits out there, but I haven't heard a whole lot of good stuff about them. I think it's like a 3.55 stroke with a 5.7 or 6 inch rod. I'm just going off of what I can remember. I'm sure it's not very accurate. Personally I like to set an RPM limit for myself, decide on a rod ratio based on that, and then see how high I can push the pin up into the piston. You don't really need oil rings for race enignes anyway.
