[rtanner]

Originally Posted by lust4speed

More stroke, more RPM's, and more cam is the way to go. Otherwise all you are doing with a bigger stroke is moving the same air at a lower RPM and will be producing the same horsepower maybe 500 RPM lower. Most of our combinations are flow limited depending on our heads, and the bigger engine is simply going to max out our heads at a lower RPM. So while much of this thread seemed to imply that the engine was mechanically limited on RPM, it might be better to say that the larger stroke will be flow limited if using the same intake system.

what he said!

[Steve C.]

Comments from similar topic made quite some time ago. Not all may apply here, but it provides some thought and conversation....


First, increasing the stroke greatly changes the angular relationship of the rod and cylinder. The rod is at a much sharper angle in relationship to the angle of the cylinder, generating enormous amounts of friction between the piston rings and cylinder walls, causing both friction and ring sealing problems. At lower RPM ranges this friction is easily overcome, but as RPMs increase, the friction reaches intolerable levels, to the point where the engine will not make enough power to even run itself! Most strokers have horrible fuel economy, and it's not just because of the extra performance equipment.
The second factor is directly related to the first. The increased rod.cylinder angularity also increases the piston velocity. That is, the piston will move up or down within the cylinder bore at a far greater rate of speed than a shorter stroke engine. Also, the piston "dwell time", that is the amount of time that the piston remains at TDC, is decreased. These factors have the effect of making the engine extremely sensitive to detonation, as well as making the engine sensitive to under-flowing heads. To illustrate, grab a bicycle tire pump sometime, and first try to operate it as quickly as you can. Then, slow down the pumping action. You will notice that it is far easier to move the pump handle slowly. Your engine is no different- slow down the piston, and the engine has less work to do. Again this condition is aggravated by high RPM conditions. The important thing to remember is that no matter how fast or slow the piston goes, the engine moves exactly the same amount of gasses during the same number of crank degrees. This situation could be improved by using the longest rods possible, which would increase the rod ratio and somewhat alleviate the angularity problem.
(remember, 6.8 rod with the 4.250 strokers)



Here's an interesting tid bit from Car Craft.....

"Think about rpm for a minute. That's revolutions per minute, referring to an engine's crankshaft speed. At 6,000 rpm, that's 100 revolutions per second, or one revolution every hundredth of a second. If you've got a 4.250-inch stroke, each piston is traveling 70,8333 feet per second at 6,000 rpm, which is about 48 mph, and it has to change direction twice every hundredth of a second. And you wonder why stuff breaks."

With a 4.500-inch stroke a piston will be traveling 75 feet per second at 6000 rpm.

And yes.... your 5500 rpm combo will probably push towards 6000 rpm on occasions !




"Long Armed and Dangerous" *

With the high piston speeds involved it will obviously require much better than production reciprocating parts. Good quality light 6.700" rods and lightweight pistons. Also it's more sensitive to detonation, as well as sensitive to under-flowing heads so watch compression with the iron heads, and they will certainly benefit from good quality port work.

(Concerning the math. If using a 4.250 stroke use a 6.8" rod for a better 1.6 R/S ratio. And results in a nice 1.305" compression height on the piston)


*Ray T. Bohacz
Article title
June '02 HPP



.

[HWYSTR455]

Yup yup Steve, engine parameters. I do think though the writer of the comments in the first example are a little on the harsh side, it's not that absolute. Rod/stroke, bore/stroke, are probably the most understood, and misunderstood. What little I know keeps me within 'popular' areas/parameters which generally work. But certainly, longer rods 'slow' the pistons' turn-around at TDC.

The longer the stroke, the more chance of block/crank stability issues, so IMO, over 4.250 stroke makes sense only in aftermarket blocks.

A 4.250 stroker combo can produce 500-700+HP, and, we are in the street section. What reasons would you want/argue to go more stroke?

.

[RocktimusPryme]

Originally Posted by HWYSTR455

A 4.250 stroker combo can produce 500-700+HP, and, we are in the street section. What reasons would you want/argue to go more stroke?

.

Just playing devils advocate here because I generally agree with you. Easier to go with what works and not worry about it.

But isnt adding displacement one of the easiest, and most reliable ways to add power to a street engine? Thus why you go 383 instead of 350? and 461 instead of 400? There are certainly those who know more on here than me. But it would seem its is generally accepted its much easier to make a reliable 500 hp 455 with good street manners than it its to me a 350 with the same attributes.

[Hooter]

I've also got a 4.75 Ohio forged crank in a MR1 block in my street car. Ran it on Drag Week last year. 6.7 rods. Mine made 858 hp at 6400 on pump gas. Detuning it a bit this year, but the piston skirts looked pretty good when I had it apart this winter. I'd have no reservations whatsoever running a 4.5 in a stock block.

[HWYSTR455]

I dunno, maybe I'm being a stick in the mud, but understand where some are coming from.

My understanding is stock blocks are reaching their' limits around 700hp, just doesn't make that much sense to me, but maybe I'm missing something. Not saying it can't be done, but you start pushing the risk window with little payoff, and at an added cost.

If you want to target more than 700hp, and you weigh the factors between a stock block and an aftermarket block, what would your choice be? If you don't mind the risk of lunching some high dollar rotating assembly, then sure, go with a factory block. And if you're doing a 4.5 throw, you need to be concerned with rods and pistons, your generic scat or other parts ain't gonna cut it. Why after all the other parts would you skimp on a block?

Have to take head flow into consideration too, your typical 290-315cfm heads on a large displacement engine will just be a bottleneck. So you're dumping all this into a factory block, which many have proven let go at levels the finished assembly will make.

Maybe I'm doing the math wrong on my logic, but I am listening if someone can convince me otherwise.

.

[Formulajones]

When talking about making 700 HP in a street car that's drivable, you automatically start getting into the larger engine sizes.
My approach to making the most "streetable" naturally aspirated power you can is to build the biggest engine you can afford to build. CI is king.

That means the biggest bore and stroke you can get away with. If your goal is 700 "streetable" horsepower, (since 700 was given as an earlier example) a larger CI engine doesn't have to be as radical to reach that level.

Reaching that goal with a smaller engine pretty much takes it out of the "streetable" scenario in most peoples eyes, unless you like alot of rpm, buying race gas, and routine valvetrain maintanance.

You're only going to get so far with a pontiac street engine if you limit the build to a 474 cubed (4.250 crank). 700 HP in an engine this size is starting to get pretty doggon' radical with compression and camshaft, excellent cylinder heads and likely a decent amount of rpm.

For streetability, I'd much rather build the bigger engine, keep compression lower, milder camshaft, not have to spin it so tight to make power, and enjoy the extra boat load of torque it's going to make along the way with that long arm in it. In the end, less gear, converter, less tempermental, less maintanance, and all around a much more enjoyable street engine.

Otherwise, if larger CI isn't something you care for but you want big horsepower in a streetable package, then go for the smaller engine and toss a ProCharger on it.

[gtome]

Wow some really great information coming out of this. I think im actually learning something! Exactly what I was hoping for; from both directions.

[HWYSTR455]

Actually, the 700 I mentioned was a theoretical block limitation, but has been experienced by a number of folks. Going from a 474 to a 501 is roughly the difference between a 4.250 and a 4.50 stroke, not that big of a jump, so I wouldn't really call it a 'smaller engine'. Sure, it makes a difference, but 100hp or so? And you can make a totally streetable 461 at @600+hp.

Totally understand the theory, and I am a bigger is better kind of guy, but there are limitations and considerations, all I'm trying to point out.

Now, once you remove the limitation of a factory block, then you can go 535 or bigger, and THAT makes a considerable difference.

.

[Formulajones]

Your point is why I wonder so many people jump on the 4.250 band wagon when a stocker is 4.210 to begin with. You aren't gaining much in the CI department that way either. Alot less than you gain with a 4.50 crank.

I can understand if you need a crank, then okay why not, but if I had a perfectly servicable 4.210 crank, I'd use it.

600hp isn't too hard to do with ~450 cubes or so, in any brand engine. Aftermarket parts make that pretty simple, and dozens of crate engines ready to rock that top the 600 mark. Although I have to say it's a little harder with a stock cubed Pontiac engine using heads with the standard valve/port arrangement. They lean more on the torque side than HP with the longer stroke and smaller bore setup compared to other brand engines of similar size.

But lets face it, anything under 500 cubes nowadays is pretty small when it comes to big block stuff. SBC's are 450+ cubes now. Aftermarket support makes it easy. But like anything else, speed costs money.

[JSPONT]

I just bought a 4.250 stroke. The reason I did not use the stock 455 crank was it was not forged. A forged 4.250 crank kit with pistons and rods is cheap. If you go with the 4.500 stroke you might have to clearence the block also.(extra cost or labor)
It was simple for me to buy that kit have it balanced to make big power. I also have a turbo charger though. It was cost effective.

[rohrt]

Originally Posted by HWYSTR455

Actually, the 700 I mentioned was a theoretical block limitation, but has been experienced by a number of folks. Going from a 474 to a 501 is roughly the difference between a 4.250 and a 4.50 stroke, not that big of a jump, so I wouldn't really call it a 'smaller engine'. Sure, it makes a difference, but 100hp or so? And you can make a totally streetable 461 at @600+hp.

Totally understand the theory, and I am a bigger is better kind of guy, but there are limitations and considerations, all I'm trying to point out.

Now, once you remove the limitation of a factory block, then you can go 535 or bigger, and THAT makes a considerable difference.

.

Great discussion on the 4.5 crank.

I read too about the 700hp limitation a long time ago. I didn't think it was so much theory as a test that was conducted. Would that have been in the old HO manual?. I seem to recall a test done with a blower where they kept increasing the pressure and cracked the block down the mains past the 700 hp mark.

I don't know what motor it was tested but if it was a 455 it has me wondering if a 400 stroker would take more abuse with the smaller main journals?

It also has me wondering if 700hp is all the same. Meaning if it made at lower RPM or Higher RPM, Nitros, turbo ect. Is it all the same to the block?

[JSPONT]

Originally Posted by rohrt

Great discussion on the 4.5 crank.

I read too about the 700hp limitation a long time ago. I didn't think it was so much theory as a test that was conducted. Would that have been in the old HO manual?. I seem to recall a test done with a blower where they kept increasing the pressure and cracked the block down the mains past the 700 hp mark.

I don't know what motor it was tested but if it was a 455 it has me wondering if a 400 stroker would take more abuse with the smaller main journals?

It also has me wondering if 700hp is all the same. Meaning if it made at lower RPM or Higher RPM, Nitros, turbo ect. Is it all the same to the block?

I know many guys making way more than 700, turbo and nitrous stock blocks, some been together more than 5 years and have been getting beatings all the time!! I think balance is very important, and of course a good tune.

[RocktimusPryme]

Using stock parts in super high performance applications is always going to involve outliers in either direction. As stated I am sure there are quite a few high horsepower stock blocks out there. And just as many that have been torpedoed. I see the same thing when 8.2 Bop rear strength comes up. People come in saying its best not to invest in them, to go to an 8.5 or 12 bolt. And inevitably there will be several who say "Ive been running mine for a decade behind 500 hp"

[Formulajones]

Originally Posted by JSPONT

I know many guys making way more than 700, turbo and nitrous stock blocks, some been together more than 5 years and have been getting beatings all the time!! I think balance is very important, and of course a good tune.

Yep, didn't seem to bother Tony at BES when my father first approached him about his goals with the car and presented a stock 455 block to do it with. At a 4,000 lbs. race weight, my father wanted to take his street car down into the 10's on pump gas. Knowing he was going to need something close to the neighborhood of 700 HP and alot of torque.

The recipe was going to be a 4.5" crank. Tony said not a problem. I know he planned to hard block it, at least half way, and I think that's a must with most stock block builds of any brand if you want to push it. Seems to be the norm with most high end builders. They were also going to use a lifter bore brace knowing pontiacs are weak there, and Tony was going to need to push the camshaft specs to make a 490something CI engine produce those numbers.

Unfortunately the block was badly cracked throughout the main webbing from spinning nearly every bearing in the block, snapped an oil pump shaft, excess heat and lack of oil. It ruined everything.

If it weren't for that, he'd have a 455 block with a 4.5" crank in the car as we speak. Instead that led down the path of new MR1 block, bigger crank, and it's just a domino affect from there. I think it turned out better anyway and my father is extremely happy with it. In the end it was a much bigger engine that didn't need to be as radical, easily made the numbers on pump gas, and there is another easy 100 HP in it if they changed a few things around.

[Formulajones]

Originally Posted by JSPONT

I just bought a 4.250 stroke. The reason I did not use the stock 455 crank was it was not forged. A forged 4.250 crank kit with pistons and rods is cheap. If you go with the 4.500 stroke you might have to clearence the block also.(extra cost or labor)
It was simple for me to buy that kit have it balanced to make big power. I also have a turbo charger though. It was cost effective.

Another excellent example why the aftermarket can be the way to go.

[Formulajones]

Originally Posted by RocktimusPryme

Using stock parts in super high performance applications is always going to involve outliers in either direction. As stated I am sure there are quite a few high horsepower stock blocks out there. And just as many that have been torpedoed. I see the same thing when 8.2 Bop rear strength comes up. People come in saying its best not to invest in them, to go to an 8.5 or 12 bolt. And inevitably there will be several who say "Ive been running mine for a decade behind 500 hp"

Kind of off subject a little bit.....The problem with that, being the internet, is that you have all types. They likely won't admit it, but when you get to know some of these people that say this rear or that rear will survive 500+ HP, you quickly find out these people either don't drive it like they stole it, they don't go to the drag strip that often, they don't use sticky tires, 99% of them have a slush box behind the engine, or the car just isn't setup well enough to hook and use the power effectively and it just spins. Sometimes it's all of the above.
I run into these people quite often owning and working on 4th gen Fbodies with their whimpy 7.5" rears. Guys push them till they break all the time. With a 6 speed in front it just makes me cringe. Auto's are easier on parts, sticks not so much. After a while, they break. I've seen them break so severly they take the transmission out with it. Becomes an expensive repair. We run a Strange 12 bolt in ours so I don't have to worry about it, and it's just a daily driver that only sees the track once every other year or so.

[RocktimusPryme]

Originally Posted by Formulajones

Kind of off subject a little bit.....The problem with that, being the internet, is that you have all types. They likely won't admit it, but when you get to know some of these people that say this rear or that rear will survive 500+ HP, you quickly find out these people either don't drive it like they stole it, they don't go to the drag strip that often, they don't use sticky tires, 99% of them have a slush box behind the engine, or the car just isn't setup well enough to hook and use the power effectively and it just spins. Sometimes it's all of the above.
I run into these people quite often owning and working on 4th gen Fbodies with their whimpy 7.5" rears. Guys push them till they break all the time. With a 6 speed in front it just makes me cringe. Auto's are easier on parts, sticks not so much. After a while, they break. I've seen them break so severly they take the transmission out with it. Becomes an expensive repair. We run a Strange 12 bolt in ours so I don't have to worry about it, and it's just a daily driver that only sees the track once every other year or so.

I was just relating it to the ongoing debate about the use of stock blocks in this thread. Wasnt trying to get off topic. But yeah I used to be a 3rd gen guy. So I know what you mean about the 7.5s. I shred one up pretty good behind a 350 hp or so small block. Got my hands on one of the Australian 9 bolts and didnt have another problem.

[Tom Vaught]

Originally Posted by Hooter

I've also got a 4.75 Ohio forged crank in a MR1 block in my street car. Ran it on Drag Week last year. 6.7 rods. Mine made 858 hp at 6400 on pump gas. Detuning it a bit this year, but the piston skirts looked pretty good when I had it apart this winter. I'd have no reservations whatsoever running a 4.5 in a stock block.

Didn't you quit after the first day of Drag Week? Thought someone told me you had troubles? If you only ran one day of the event not really "apples to apples" with the other Drag Week guys. If I am mistaken, I apologize for my error.

Tom V.

[Formulajones]

Originally Posted by RocktimusPryme

I was just relating it to the ongoing debate about the use of stock blocks in this thread. Wasnt trying to get off topic. But yeah I used to be a 3rd gen guy. So I know what you mean about the 7.5s. I shred one up pretty good behind a 350 hp or so small block. Got my hands on one of the Australian 9 bolts and didnt have another problem.

Sorry I didn't mean you were off subject, I understood how that related to this thread, I meant I was going to get off subject with my rambling