first off a 5.315 stroke 347 is in fact uses the same piston as a 331..

you can not provide any proof that a 331 will last longer than a 347..


btw a longer rod stroker puts less stress on cylinder wallson a 347 than a 331 or even a damn 289/302...

everybody runs to the 347 is bad wagon because of engine failure...want to know why?...because a moron screwed it up and the first damn thing they blame is the rod stroke or wrist pin is in the ring land...

give me a credible engine builder that saysa 347 won't last or consumes oil ect?...... not dss or some cracker jack builder hell ask the people at fordstrokers.com

 

i will check in when i order the parts on whether or not i will go with the 331 or 347 price will be the deciding factor. And i can notch the cylinder walls myself i just wanted to avoid that. I have to convice my friend into going that route as well. I need to find a set of long tube headers for that to fit into the 67 and will flow for lets say that 347 and also would like to get a cam big enough for that. The cam is going to have to work with the d80e full ported heads but work better with the other heads down the road.


thanks,
kevin

 

Strokers use shorter rods relative to stroke length, not longer. So strokers have smaller rod ratios(shorter rod / longer stroke = smaller ratio). Physics is physics and geometry is geometry, shorter rods mean more severe rod angle. The issue is whether or not it's enough in strokers to shorten life. Well, yes and no. Theoretically yes at least, all things being equal, the engine with the shorter rods will wear faster, even engines with the exact same bore/stroke. In reality though, there's a lot more contributing to wear in an engine than just rod ratio, and those other factors may lead to engine failure long before the rod ratio ever becomes a factor in longevity. One thing to consider on engine life with rod ratios though, is GM's LS7 in the Z06 Vettes has a small rod ratio, only like 1.58 iirc? It's pretty much getting down towards as short as is practical in an engine, obviously they weren't too concerned about excessive wear from the rod angle. Also factors dealing with wear vs rod ratio are going to get into the internal configuration and where the piston is in the bore relative to cylinder presure. In an engine with a short rod, if combustion is basically over before the rod angle ever becomes steep, or compression doesn't begin until after the rod angle shllows out, then it won't even matter.

In the end the biggest factors when dealing with rod ratio are going to be piston velocity and piston dwell time, effecting maximum sustainable rpm and combustion efficiency respectively. It tends to go hand in hand, the lower piston velocity at TDC from longer rods allow greater rpm(and a longer rod for the same stroke length will have a shorter and lighter piston usually), and the increased dwell allows time for the fuel charge to burn at higher rpm. In an engine with a shorter rod ratio such as a stroker, there's less rpm potential but also because the longer stroke allows power to be made at lower engine speeds, the longer dwell time isn't needed, since piston velocity(rpm) is lower, allowing more time for combustion to occur. Rod ratio also affects breathing to a degree, since it's changing piston velocity and position in the bore relative to crankshaft position/cam timing, so it changes the strength of the induction pulse and the pumping effect on exhaust gas. Longer rod ratios favor breathing at higher rpm generally speaking, and shorter rod ratios favor breathing at lower rpm generally speaking.

The rod's angle to the crankshaft relative to combustion pressure will effect where power is made as well. A shorter rod setup tends to favor producing peak torque at a lower rpm, since when the rod's angle is perpendicular to the crank(where best mechanical energy transfer takes place) the piston tends to be higher in the bore, earlier in the combustion cycle when it's more effective, where cylinder pressure is higher. Shorter rods tend to exert more force on the crankshaft. However, at higher engine speeds where there is less time for combustion to exert pressure on the piston, the longer rod holds the piston higher in the bore for a longer period of time on account of reduced piston velocity in the upper half of the bore. Remember that at higher rpm the velocity of the piston moving away from the combustion process causes the cylinder volume to increase rapidly, and when the volume increase occurs fast enough that combustion pressure can't keep up, cylinder pressure drops off and power along with it. Whereas the shorter rod accelerates away from TDC faster but creates the 90deg angle to the crank sooner and with the piston higher in the bore, and makes more torque at a lower rpm, the longer rod keeps the piston in the upper portion of the bore - where most of the combustion takes place - for a longer period of time, allowing more effective combustion pressure to be exerted on the piston at higher rpm than with a shorter rod, on account of the time factor. So a longer rod setup creates a 90deg crank angle later in the combustion cycle when overall pressure is lower, and makes less peak torque, but allows more time for combustion to exert force on the piston at higher rpm, so peak torque though lower, occurs at a higher rpm, and produces better high rpm horsepower. This is all assuming the same bore/stroke. When getting into strokers, the shorter rod engine also has a longer stroke so the effects of the short rod become increased, along with displacement. This is part of the reason why strokers make more power at lower rpm, not only is stroke length and displacement increased, but the rod angle becomes shorter causing the engine to favor producing low rpm power even more.

It all comes down to how much power you want to make and where. Shorter rod setups favor more torque at lower rpm, and longer rod setups favor more hp at higher rpm, all things being equal. When dealing with strokers, the engine with the longer stroke always has the displacement advantage. A longer rod 331 could make more top end power than a shorter rod 347, which will make more bottom end torque, provided there were enough difference in rod ratio and each engine were optimized to take advantage of it. One could argue that the increased rod angle of the 347 will decrease life, which may be true, but the increased rpm on a 331 will also work to decrease life. Which again brings it back to where you want to make power.


The best reason though to use the loger rod setup, is the higher up you can get the wrist pin on the piston, the lighter the piston will be and it'll have shorter skirts, so less friction with the cylinder wall. There's a lot of energy contained in those pistons with inertia, the lighter they can be, and the less friction with the cylinder wall, the better. Most strokers have very short c/h pistons.

 

I am not sure i understand this ? The strokers i have seen use longer rods with more stroke on the crank .
If they did not do this the long stroke crank with short rod would pull the piston to far down in the cyl. and not push it high enough up in the cyl. without a very high comp.height piston and very heavy piston.




Again i dont get it ??
Longer stroke+ longer rods = more tq. and less rpm needed.
And i dont see a longer rod 331 making more power than a 347 .
They both use the same 5.4 rod if you have a good shop build it.
If the shop is not so good then use th 5.315 rod.
But all parts being equal the 347 will make more power everywhere in the rpm band.


Also the stroker kits 331 and 347 cost the same.
fordstrokers.com

 

I would throw out the fordged crank unless you r are 100% sure you will upgrade to an aftermarket block later. A cast crank will out last your stock block. For a budget cam, the X is just fine. there are better, but that cam in a stroker, with 185's will be easy 11's, all day long.

 

Strokers have shorter rods RELATIVE to stroke length. IE 5.09/3 (302) is a longer rod ratio(~1.7) then 5.4/3.4 (347, ~1.58). With a stroker you may use a longer rod, but you increase the stroke length as well, so the overall ratio in a longer stroke engine tends to be lower, not higher, for the same deck height. Generally speaking though, it's going to depend on the internal configuration of the engine, the amount of extra stroke and the rod length chosen.

My example was that a shorter stroke, longer rod RATIO(not neccessarily longer overall rod, sorry if I was not clear about that) 331 would be able to turn more rpm safely, and potentially produce better horsepower in the upper rpm range(we'd be talking pretty high rpm though given that both a 331 and a 347 can tolerate pretty high rpm if both are built well), whereas the 347 would favor producing more power at lower rpm. If you look at engines like IRL, F1 and Pro Stock, they all run majorly oversquare setups, try to fit the longest rod they can just to cut down on the rod angle and piston weight, but have large bores and short strokes(in some cases the bore is around 2x the stroke). Smaller displacement shorter stroke engines tolerate higher rpm better, so you don't suck in as much air on each induction pulse, but turn more rpm and have more induction pulses, trading displacement(in the case of a stroker it comes from increased stroke length) for rpm. Strokers are great for street cars because they basically turn low rpm most of the time, so the longer the stroke the better.

Ultimately when it comes down to rod ratio, the biggest impact from changing it comes from the ability to run a shorter compression height, and therefore lighter, piston. Realistically, rod ratio should be determined by other factors, rather than other factors being determined by rod ratio. Like in Pro Stock cars, the rod ratio is limited by shorter deck height blocks, which they run to keep pushrods shorter and have a more stable valvetrain. The more stable valvetrain contributes FAR more to making high rpm horsepower than the rod ratio ever will.

 

Okay so i've done a little more research and depsite peoples opinions I am going to take the professional advice and go with the 347. I would like to know which 347 stroker kit to go with. As in which rod length 5.4 or the 5.315?. The longer or shorter stroker crank. I think the shorter rod kit use the same piston as the 331. Correct if i am wrong but I would just like the one that would the best setup.

I also need to know which cam will work for this 347, I would like to go with a comp and stay around $300 give or take 50.

I know these heads are not going to flow enough, but they will suffice and choke it out for now. What springs, retainers, and locks from comp should i go with as well.

 

I'd go with the piston/rod setup that has the lighter piston, which is generally going to be the longer rod/shorter compression height piston. All 347 kits have a 3.4" stroke crankshaft. The lighter the internals the better, but there's no need to get high dollar h beam rods, most i beam rods will take more than the block will. Ultimately that'll be determined by what's in the kit, if it has h beams and is a good price, go for it. As far as cams, Comp makes some cams for stroker EFI setups(they'll work with carb as well, just won't have a radical idle), the smallest one is like a 2,000-6,200rpm range I think? It's an OTS(off the shelf) grind, so it should be around $250-350. Get whatever springs/locks/retainers they recomend, and I'd go with the 10 degree locks/retainers. You can also check out Crane, or call one of the manufacturers to inquire about a custom grind. A lot of people on this forum like Jay Allen's cams, from Camshaft Innovations.

 

Im going to run a comp 250 cam in my car. Just got it exchanged today on warranty fo an Edelbrock cam (long story). It will be hear Wednesday. Im really looking forward to getting the engine built, its gonna sound/run awesome!!!

 

i think im going to have to go with the ford x303 cam due to the cost

so the stroker kit i want is going to be 3.4 stroke, and 5.4 rods or the 3.25 stroke?