I am wondering if stroking affects compression, and how. I would think it would somewhat, however something in my mind thinks that the only difference would be the duration of the cam (if it closes sooner with a larger stroke, that can build way higher compression, correct?). The block in question is concerning building a 496 engine, so I'm wondering. Thanks.

Yes, the stroke is a major factor in compression. As displacement increases the CR rises given the combustion chamber size and other factors remain the same. That is because the CR is calculated using the volume of the cylinder compared to the combustion chamber. As the volume of the cylinder (bore area times the stroke) increases the CR goes up given the same chamber size.

The cam affects the dynamic CR by using the piston position at intake closing to calculate the cyl volume instead of the actual stroke of the crank. The displacement of the engine is not changed.

So is it possible with the right parts to easily run 89 (you know how I am, always want to make these good engines but want to afford gas mileage graemlins/clonk.gif ) or even 87 with a stroked engine just as with any other, or does compression get bumped up too much when a 454 is stroked to 496?

low compression strokers still make some good power. ive heard of some really nice 383 combos with relatively low compression.

Originally posted by soccerguy045:
So is it possible with the right parts to easily run 89 (you know how I am, always want to make these good engines but want to afford gas mileage graemlins/clonk.gif ) or even 87 with a stroked engine just as with any other, or does compression get bumped up too much when a 454 is stroked to 496? Yes it is.
You just raise the total chamber volume by using less piston dome volume or more dish depending on applicaton & you can end up with the same static compression.
You will need to adjust the cam accordingly as the dynamic compression will go up with the same cam because you are closing the valve earlier in relation to where the piston is in the bore with the longer stroke.

That makes some sense, thanks. I know I'm asking too general of questions, but would a mild (89 octane running 496 with good heads) make as good/more power with a 454 running the edge of 93 octane with good heads? I know there are so many factors, but is there a general rule? It seems to be that way with a 383/350, so am wondering. I also have the idea in my head, for some reason, that if big blocks don't have the right compression and setup, they are total slugs. I guess that goes for any engine though.

It will work just like the 350/383.
For the street the torque of the larger engine will rule.
Might be a tossup in a race deal but that's not what we are talking about, if it were you just add compression to the 496 & still rule :D

Stroke and rod length govern where the piston top is with respect to being down in the cylinder when the intake valve closes..

A longer stroke crank with a stock length rod allows the piston to be down in the hole a schosh more then a shorter stroke crank with the same rod.

This is what makes a big cam seem slightly smaller in a stroked motor using the same rod b/c the dynamic compression ratio is increased due to trapping a slight amount more charge in the cylinder when the intake valve closes!!

pdq67

Taylor,
in your situation a 454 is plenty, you dont need to add cost to the situation.
As i've mentioned you can also build a 350 that will hit your goals.

You'll be able to build the 454 with a milder/cam and less compression to hit the same goal, but an engine with much more torque is going to be borderline daily driveable unless you have alot of experience driving a powerful engine in situations where too much throttle can put you into danger.

Just saying, you can build a quick motor, without going over-board and building something that is too powerful for your driving ability at the moment.

Start with a SBC 350, and get used to how powerful a strong 350 is before moving up to a 454" motor.
You can get that car into the mid 12's with a 350 if you build it to suite the car.

Keep in mind, fast cars are cool, as well a radical idle, ect, but your primary concern should be streetability.

BTW, its a bit presumptuous to know if "it's enough" for someone else? Isn't it?

Tay, your logic is spot on. If you want to run this engine on 87 octane, by God, build it as BIG as you can. If you can't build torque through compression, then you have one other major system variable to work with , DISPLACEMENT. If you don't already own a 4" crank, then a 4.25" one isn't all that much more.

Put it another way, if you hold "streetability" constant, how do you make more power. DISPLACEMENT.

Unfortunately, as clear as the math is this way, it is also the other way, to wit, gas milage. More displacement = more fuel. Pure and simple. And I presume that even a small 427 will move the car at nearly the same throttle opening as a 496. So given equal rpms/throttle opening = fuel consumption will be more. How much? It probably linear, ie. 454/496 = .915, or maybe around 5-10% less mpg at worst.

It'll get circular here, because then you ask, oh, can't I build a high compression street 454 that make the same power and also gets better mpg?

Yes. graemlins/clonk.gif

BTW, you can make a 496 as street docile as a 325hp/396 and still pump out north of 550 lbs ft ( my plan).

And yeah, you can't punch it unless you're pointing in a straight line!

What piston you use is also going to make a difference in your compression as is deck height. Stroker pistons have the wrist pin in a different location than 350 pistons. The bottom line is, the right combination of parts will let you build an engine that runs on 87 oct.

I've driven a mopar with a 440" engine, mildly built with 10" converter, at 50mph giving it too much throttle would easily get sideways or spin the car around.

I'm not comfortable talking a young driver into building something that he would be easily capable of getting hurt with.

I've spoken to Taylor off this board, and i know what his plans are.

I made a promiss to Al that i would do my best to keep things civil, so i would Much Appreciate it, Gene, if you'd can the low blows, which i have ignored in another post.

Thanks for your help and everything. I know we've talked about small blocks and stuff, but I am also just kind of at the stage where I like to toy with different ideas to learn and such. Next week I'll probably want a supercharged nitroused 283 or something, lol.

Feel free to IM me when you need help with the next question.

But to answer your question, making NO other changes except for stroke and compression height (dimension from the pin center to the top of the piston), you would see an Increase in compression with more stroke and a Decrease in compression with Less stroke

Asolutely, its squeezes more mixture into the same space. More mixture = less mpg as well.

AND what I said is why it does like it does when you change stuff!!!!!!

Took it a long time ta soak into my "pointy little head"..

Heck, I even had ta draw pictures on a board using a T-square and triangle, just like the old days..!!

pdq67

too much stroking can also cause you to go blind! tongue.gif

Originally posted by pdq67:
AND what I said is why it does like it does when you change stuff!!!!!!

Took it a long time ta soak into my "pointy little head"..

Heck, I even had ta draw pictures on a board using a T-square and triangle, just like the old days..!!

pdq67 =
Hey PDQ,,,,
You didn't need to draw all them pictures, all you had to do was read my post about two above your first post. graemlins/clonk.gif :D
:D

He, He!! Wasn't there a song out years ago called "Strokin" or something like that?? "Strokin' ta the right and strokin' ta the left"..

Right on Mike, but this was years and years ago when I found the info. in a copy of "Circle Track" roundy-round mag.

Don't know about going blind but have heard you won't grow any hair on the palms of your hands!! OR so the older guy's always told us young-un's... He, He!!

pdq67