78mm Stroke?

[bowagen]

I think I'm wanting to build a stroker motor and leaning towards a 78 stoke. Is there any real downside to this stoke? I've searched, a lot, and found some interesting stuff. But, mostly I run across threads that push people towards the 82-84 stroke. The thing is, I like engines that like to rev and have a higher power band so that's why I'm leaning this way. In fact, that's why I didn't build a stroker motor originally.

I'm currently running a well built 1776 that surprises people and runs much faster than most people think it should. It keeps up well with lager displacement engines but it's time to either freshen that engine up or build something new, which leads me here...

Thoughts, opinions or just bashing is all fine

[jfats808]

Do it. 78.4 & 82 mm strokes are my favorites. Once you start going 84 and up , u will run into extra details and requirements. Youre going to find after building a bigger stroked motor that power will be available at much lower rpms. This why a lot of guys build it bigger. 78.4 is a fine choice.
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[Alstrup]

[bugguy076]

The 78mm stroke has been the middle ground for a long time. I use a 76mm for drag racing. It works well for what i want it to do. Stroking makes bottom end torque.
If you are looking for high end power, take a look at the heads, carbs, exhaust, and cam.
It sounds like your engine needs freshening, and now is a good time to go over the combo. What you already have may just need tweeking to gain a lot.
Only you can decide how far to go.
Remember to upgrade the tranny if you add a lot of power.

[bowagen]

Tranny is good and was built to take more than I have behind it now. Herald Carter put it together for me years ago when I first put the car together. SB mainshaft, threaded super diff, etc...

I see where the 78 stroke is stuck in the middle ground and I can't really get a feel on here what the consensus is on that stoke. Like I said, most people seem to really push for the 82mm. Maybe the 82 is just the s**t and I'm missing out, don't really know because I haven't ever driven one.

[vwracerdave]

With the parts available today the 82 is the way to go. 2110 is an awesome street engine and can live 80K-100K miles with quality parts. Use 5.4 VW journal rods and a pre clearance cam.

Herald Carter built my transaxle
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[bowagen]

With everything else being equal (cam, carbs, heads, compression, exhaust, cylinder size, etc) how would the 82mm rev and what would the power band be compared to a 78mm?

I get torque and appreciate it but don't want to totally kill the fun of wringing out an nicely built, higher revving engine. That's what is the hesitation in going any bigger on the stroke. Reliability is more important than longevity. The car is driven about 3000 miles a year and for fun only but is still a street car.

[75smith]

[modok]

78 stroke rare? heck no. I think they are more common than 82.
I bet if you were to survey Bob Demello and DPR and the Bergs you'll find 78 is the most popular size stroker in the history of the hobby.
Made popular partly because it's the general accepted limit for how much you should stroke a crossdrilled crank, and how big you should go with stock rods, but also just a good size too.

Last five years or so maybe there are less popular. Why?

"today" we have disposable chinese cranks, ok aluminum engine cases, and aftermarket heads so big you have to go 82 stroke just to match............
But if that's not the kind of engine your putting together then sure 78 is a great stroke.

[Quokka42]

Mostly the ranting is just from people who won't be building the engine themselves. 78 stroke is a real stroker but needs much less clearancing, or you can use stock type rods for a mild build, 82 is, well, a bit bigger
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[rustybusjef]

82mm stroke with 5.4" rods make a fairly narrow motor and you get more power for the same money.What is it going to be put in ? Are you looking for a low RPM torquer or a high strung peaky powerhouse ? Will you be needing to run a heater ?

[bowagen]

It's a '67 sedan, no heater and I like high strung peaky powerhouses. Car is a 3000 mile a year fun car. It's a street car that might see some strip time just for the hell of it but that's not it's purpose. It would be cool if it was able to run in the 13's in it's street trim.

I know that larger engine parts are about the same relative cost as their smaller counterparts so it's not a budget thing. I'm trying to put together a combination that I know I would enjoy driving based on my personal driving preferences.

So, my real question here is; if someone has a well built, higher horsepower engine with well built high flowing big valve heads, appropriate compression, exhaust, cam, carbs, etc what does an 82mm stoke do to the usable power band compared to a 78mm if everything else is identical? And, short of some clearance work that needs to be done, is there any real negatives to running a 78mm stroke?

I don't necessarily subscribe to the bigger is better thing. I know big displacement has it's place and it easier to make power with but I won't be just slapping this thing together. My goal is to put some good research and thought into it so I'm not looking to upgrade it right away.

[modok]

Changes the powerband verses what? If it was perfect to begin with then any change will make it worse, but it rarely is perfect.
Longer stroke will always lower the powerband and broaden it somewhat, all else equal, but all else isn't.
You'll be better off to choose the stroke to work best with all else, whatever those constraints happen to be.
the carbs and heads will be either too big or too small and what agout gearing? Will you be revving it high 5% of the time and driving like grandma the remainder or something more sporting? Which is better will depend on that. it may make more power with bigger or smaller.........who knows?


Look at it this way, what is the ideal rod ratio for most things?
Some will say 1.6, some will say 1.75
78 stroke will give you about 1.75, and if you like "higher revving" engines then that's probably the way to go in that respect.

[mark tucker]

with the right parts the 84 stroke will rev faster as it will make more power. do it right do it once be done and go have fun.

[rustybusjef]

An 82mm crank can broaden your torque curve slightly but I doubt you could notice it if built it right , like high compression , good heads , correct cam , etc
Dont forget the old saying "There's no replacement for displacement"

[bowagen]

What about rod ratio? The rod ratio of a 78 vs 82 stroke is better (higher) which creates less wear and more efficiency and in theory a snappier engine with better throttle response.

To me it's more about the butt dyno and the overall feeling when driving as opposed to the most of something (HP/torque).

I know your can get more power (HP/torque) with more displacement but how much power does a 47 year old 1800 pound street car really need before it becomes unusable?

The goal is to have something thats quicker than most things on the street, fun to drive and reliable without getting carried away.

[Quokka42]

The difference in rod ratio between 78 and 82 is SFA, and if you apply the trig as to what effect on the operation of the engine it is more like a BCH, or 3/5ths of 5/8s of F all.
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