331,347 or 363 strocker?
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87coupe50
Member
if you plan on putting a blower on it, do it right the first time so it will hold up to what you're gonna throw at it. aftermarket block! I would personally recommend calling FordStrokers. a 363 should be the same price as a 331 or 347 and customer service is second to none... be advised that it will take them a while but they do have sort of a "layaway" plan.
Go as big as your budget allows! 347 if you go with a stock block, 363 if you go with an aftermarket block. You're actually probably going to want to go the aftermarket block route if you're planning boost.
This is completely false. Engine size has nothing to do with what RPMs the engine peaks at. It's all in the heads/cam/intake/exhaust etc.
This is completely false. Engine size has nothing to do with what RPMs the engine peaks at. It's all in the heads/cam/intake/exhaust etc.
skunk21
Active Member
just about everyone hit on the head ( don't get the whole block size, rpm response..like NikwoaC stated engine size has nothing to do with revs or peak hp) a 331 is basically the same money has the 347 so i would go with the bigger displacement. what are your hp goals? keep in mind ( if you already didn't know) the stock block is good for around 500-520ish rwhp has a rule of thumb, although a big killer of the stock block is high rpms and poor balance. If big power or a 363 is your goal go aftermarket block like stated, dart & world are solid bets.
if you put the same parts on a 331 and a 363, the 363 will peak lower in the RPMs. im speaking from experience.
Your post said nothing of using the same parts on the different sized engines. In that case, of course the bigger engine is going to run out of breath at a lower RPM than the smaller engine using the same parts.
But then, why would you use the same parts on two different sized engines?
87coupe50
Member
Yea, sorry was in a hurry on the first post. quick question: should you run a larger intake/cam combo if you have a larger bore motor? i personally like to have something that performs from lower RPMs, but my car is mainly a street car.
Generally speaking, yes. The increase in displacement will demand more airflow. However, be aware that a 0.030" "cleanup" overbore is really an insignificant change, where as a 0.125" overbore (in the case of an aftermarket block) is more of a significant difference. Of course, a .125" overbore on a 8.2" deck motor is only a ~15-20ci difference...
On that note, if the stroke does not change, increasing the bore can actually help the same cylinder heads breathe better, because you are unshrouding the valves. Some cylinder head manufacturers *cough*AFR*cough* take advantage of this by advertising their flow numbers using an oversized bore, which is misleading to most folks who will probably never run those heads on anything bigger than a 4.030" bore.
Not really. You run a higher piston velocity with a greater stroke. More distance (greater stroke) in the same amount of time (rpms) requires more speed. The greater the velocity the greater the inertia to overcome and the greater stress against the rod and crank (that missle called the piston at 6000 rpms needs to actually *stop* at TDC and start going the other way after all
). Greater stroke also means greater rod angles (for a rod the same length). At larger rod angles cylinder pressures are less effectively translated to torque at the crank. For these reasons stroking has diminishing returns.Ultimately the more stroke you use to gain displacement the lower your rpm ceiling drops before the motor comes apart from the increased forces. Without using exotic metals, you can only make your pistons so light to compensate. You can only make your rods so much stronger (and subsequently heavier) to compensate.
So does any of this stuff come in to play with a 331 or a 347? I honestly have no idea, and the answer may very well be no. But it is true that you can't just stroke to infinity without it affecting your rpm ceiling.
that was alot of big words in your post. the simple 331/347 rpm answer is no, it dosent come into play. If you have the right rotating assembly and heads that will breath you can make a 347/363 rev to 8500+rpms.
Shaolin Crane
Banned
Not really. You run a higher piston velocity with a greater stroke. More distance (greater stroke) in the same amount of time (rpms) requires more speed. The greater the velocity the greater the inertia to overcome and the greater stress against the rod and crank (that missle called the piston at 6000 rpms needs to actually *stop* at TDC and start going the other way after all
Ultimately the more stroke you use to gain displacement the lower your rpm ceiling drops before the motor comes apart from the increased forces. Without using exotic metals, you can only make your pistons so light to compensate. You can only make your rods so much stronger (and subsequently heavier) to compensate.
So does any of this stuff come in to play with a 331 or a 347? I honestly have no idea, and the answer may very well be no. But it is true that you can't just stroke to infinity without it affecting your rpm ceiling.
While I agree with the inertia argument to an extent, you still can't say that it seriously affects RPM capability in any sort of blanket statement. You can build a 363 to easily withstand 8000rpm with non-exotic off-the-shelf parts, while a stock short block 302 would explode long before it ever got to that RPM. Like anything else, it's all in the combo and the parts used.
Also, about the rod angularity thing... I've heard some argue that greater rod angles actually increase available torque, all else equal. If you look at it from a geometrical standpoint, a greater rod angle scenario reaches the point of maximum torque production - when the rod is perpendicular to the crank - sooner in crank degrees.
I'd also like to point out that a stock pushrod 302 has a ~1.7 rod ratio, while the 7000rpm 5.0 Coyote has a "less ideal" 1.63 rod ratio...
But I think a rod angularity argument is over the scope of this thread... And also best left to the pros, haha.
Really? I didn't know the stock ratio was 1.7 on a pushrod 5.0, for some reason I always thought it was 1.6, but maybe that's just because that's the ratio I see more often.
I've always wondered if it's better to try to get your lift at the cam lobe or through the rocker ratio. I'm thinking that with the lift at the lobe, you have the problem of moving the lifter and rod that much further to cause float. Where on the flip side with more ratio, you're putting that much more stress on the lifter and rod.
I have zero clue which method is preferred, and I don't have enough money to blow up the motors to find out.
Hey that's a good point about the degrees of rotation to a 90 degree angle between the crank arm and the rod. I had never thought about that. You're right, with a longer crank arm, you reach that point sooner, which means you reach it at a higher cylinder pressure. I would think that would mean more torque and if you can spin the rpms it would mean more power too. That gives me some stuff to chew on, thanks for sharing!
You're right though I don't mean to threadjack.
Really? I didn't know the stock ratio was 1.7 on a pushrod 5.0, for some reason I always thought it was 1.6, but maybe that's just because that's the ratio I see more often.
I've always wondered if it's better to try to get your lift at the cam lobe or through the rocker ratio. I'm thinking that with the lift at the lobe, you have the problem of moving the lifter and rod that much further to cause float. Where on the flip side with more ratio, you're putting that much more stress on the lifter and rod.
I have zero clue which method is preferred, and I don't have enough money to blow up the motors to find out.
I said rod ratio, not rocker ratio.
