does 30 cubes make a difference

[68pont455]

big block chevy 496 vs 466
4.31 bore 13-1 compression
stroke off 4.00 6.385 rod r/s of 1.596 vs. stroke of 4.25 6.385 rod 1.502 r/s

any thoughts on rod stroke ratio. i have seen reviews on this subject from it means nothing to it is one of the most critical things in a rotating assembly beside rod and crank quality steel and machining.

i would go with the better r/s ratio but it means 30 cubes and possibly 45+ horsies lost or the lesser r/s ratio and possibly have longevity issues? Will be looking for around 700 hp so what does anyone out there think of this subject.

zac

[johnjzjz]

Originally Posted by 68pont455

big block chevy 496 vs 466
4.31 bore 13-1 compression
stroke off 4.00 6.385 rod r/s of 1.596 vs. stroke of 4.25 6.385 rod 1.502 r/s

any thoughts on rod stroke ratio. i have seen reviews on this subject from it means nothing to it is one of the most critical things in a rotating assembly beside rod and crank quality steel and machining.

i would go with the better r/s ratio but it means 30 cubes and possibly 45+ horsies lost or the lesser r/s ratio and possibly have longevity issues? Will be looking for around 700 hp so what does anyone out there think of this subject.

zac

OK their are a few different ways to get those cube #s sooo i an not sure what combo you are thinking about, having said that this could be a great post, with lots of info but to those who dont get the differences wont get it > example > LIKE the short rod motor can extrap more power from the low # rod stroke ratio with the correct cam timing and make more power VERSES the longer roded motor with greater dwell time at top dead center can make greater power but what does it give up < SPEED of torque ??? - what combo were you looking at BTW - jz

[68pont455]

i could go with the 4 or 4.25 stroke at this point doesnt matter. block is at the 4.31 bore and done up for assemble. i have not obtained the rotating assemble yet so i figured i would check out opinions on the subject. if rod stroke ratio is not as critical to overall longevity and performance i will go with the 4.25 stroke and get the 496 cube motor vs the 4.00 stroke 467 cube motor. i have always heard "no replacemnt for displacement" but after reading some engine builders tech notes i thought i would get some more info on the subject before i make a decision. rod length will be 6.385 so its just a matter of stroke at this point.

[johnjzjz]

a std deck 10.2 BBC with that length rod and stroke ( 496 ) has the oil ring running through the wrist pin hole ( short piston compression height ) < its not really a thing its done all the time the only problem is the stroker has BIG torque leaving the line and requires lots of good parts dont cheap out on anything it will break it if you do - the right combo could be almost a second faster than a 461 BBC and controling the wheel standing is also a thing make sure the pan is above the cross member, the first few passes on a good track you will lift and it will crash down on to it ( the pan ) - MY choice is a 496 the side load with that rod is the same. type pressures as a stock 454 so its not as good as a 427 its actualy 2 up from it if you get what i mean 1050 dom carb, super victor , 725 roller , 12.7 to 1, 330cc heads, AFR or brodex, belt drive on cam , 750 + HP 3000 lb car 9 teens 8.90 possable in good air 2 speed with a 4.56 diff 14 32 tires 4500 conv use the torque not the rpm - jz

[68pont455]

block is a 9.8 standard deck. going with a .250 longer rod due to the .250 longer stroke. the piston pin should have to move that far as to put it in the oil ring should it. piston length should still be okay. dont want to go with a real short piston and have rocking issues. dont know if this would even be a concern. this looks to be a real popular combo to gain cubes.

[rscamaro73]

You should be good with the long rod/stroke. What manuf. are you looking to get the parts from ? As bad as they used to be, my friends say Speed O Motive's rotating assemblies are ok....but I know of some guys from Team Chevelle that deal with BBC's all day long for street/strip so I could pass their info to you (send me a PM if you want it). They made a 555cu running stock heads and a hyd cam and it ran 9.98. They also sell on ebay whole motors.

Also tons of sellers on ebay so prices are good.

Have you narrowed anything down as far as heads/cam/carb ??

BTW - where are you getting your machine work and how good are the prices ??

[Pampered-Z]

johnjzjz,

I have a question, if you can clearify, or enlighten me.

I was always under the impression that all things being equal, a shorter/longer rod has less effect on top end performance as opposed to mid range. Talking general terms, not full on race motor to squeeze out ever HP. Although I'd like to know which would be better.

Also dewell has less effect on a N/A engine then on an engine with a power adder. I assume that cam overlap would be a big factor?

How would overlap be effected on a N/A engine, I was always under the impression on a boosted engine, you want the dewell to help keep the piston up to keep the cylinder area small so that you use the cam overlap to help clear the cylinder and reduce bleeding off boost.

[johnjzjz]

Originally Posted by Pampered-Z

johnjzjz,

I have a question, if you can clearify, or enlighten me.

I was always under the impression that all things being equal, a shorter/longer rod has less effect on top end performance as opposed to mid range. Talking general terms, not full on race motor to squeeze out ever HP. Although I'd like to know which would be better.

Also dewell has less effect on a N/A engine then on an engine with a power adder. I assume that cam overlap would be a big factor?

How would overlap be effected on a N/A engine, I was always under the impression on a boosted engine, you want the dewell to help keep the piston up to keep the cylinder area small so that you use the cam overlap to help clear the cylinder and reduce bleeding off boost.

WOW someone who is thinking - it would take hours to go over all the different conceps that are around about the issue most only know what they read in a comic book ( super chevy and alike ) but it depends on what you need and how strong are the parts - stock block - with power adder you want a long rod < keeps the load off the cylinder wall and lenghtens the dwell time good for torque but not for speed of torque meaning it will be a bit slower winding up on a dyno with a thousanth second timer ploting the motors movement through its pull - and yes a longer dwell helps the motor burn the excess from an adder - and cam timing really comes into play - drag, road racing, boats and modifies all want different things - street play toy buy heavy stuff over kill it because of the reverse loads in play < ??? de acceralation has a greater affect on a motors stress loads than reving it up - NHRA Prostock is a classic example you hear the motor shift and when the shoot is deployed the motor is cut and free wheels because the de cell loads streach the rods bolts in the oposit direction and experence has shown they break in half - compression and over lap go hand in hand you can cut static compression and still have big power using lobe seperation angles as a guide to what your looking for many cam companys only sell to the masses what works with available parts especially today when very few people even know how or what cam degreeing does - i seen a comic book on a shelf one time said brutal power from cam degreeing hahahahahahahhahahahahahah what a crock its in most shops used as a tool to see just wheir the cam ends up with valve to piston clearence and how close is it to what the cam card said it was and in most cases its not even close - ploting an engine is not that hard if you know the place you are going - changing in mid streem is a pain you will never get it all remember that find what will fit the budget and what you plan to do with it most of the time and stay in that loop -- jz

[Pampered-Z]

Thanks.

I know the real answer is more then a 2 page mag article. Factors like force transferred down the rod length being absorbed wasted force being transferred via the side load, etc, etc, etc. More then I get out of just reading an article. Just wanted to validate that I at least understand the theories.

Nice point, I never gave a thought about forces applied during decelleration!

[LTb1ow]

So what are some good sources for someone that wants to learn about this stuff?

[johnjzjz]

The thing is today no shop if you work in it will teach you more than one or 2 things ( nascar garage concept ) and the reason is its all preparatory info so they say, when i came up in the racing bussness everyone in the shop could do it all because it was required to learn all of it, and we used all the different things ( machines ) and of course their was always a guy who could do majic with one or more pieces of equiptment, and so far for me anyway , NO book written by any of the experts i have read even comes close to what you should be taught - i dont have an answer all i can say is if its a hobby you wont retain what might be taught because you dont use it and if its your lifes work and you dont have a good job in a real shop < if any are left most have closed i dont believe their is anyplace to learn it -- jz

[LTb1ow]

That blows, it is a hobby for me, but I would like to learn more about the science behind it.