To stroke or not to stroke?

[72hemi]

Alright I am sure this answer exists but I haven't found it yet, so I pose the question; how much additional power can one expect from a small block (340) by stroking it?

[Oldschool]

One way to get in the ballpark is to take the current HP at 340 CI and figure how many HP per cubic inch that comes out to. Let's use 400 HP out of 340 CI. That means that you divide the 400 HP by the 340 CI and you get 1.176 HP per CI. Take that same factor and multiply the 1.176 by the new CI. We'll use 416 CI. 416 CI X 1.176 HP/CI = 489.2 HP. That assumes that you upgrade the camshaft to take advantage of the longer stroke and that the heads will flow the extra air/fuel mixture to support the extra HP. I also assumed that the Compression Ratio will remain the same. Anyway - you get the idea. This little formula will get you in the ballpark and there are LOTS of variable to consider in order to go above/below the 489 HP figure....

[cudabob496]

https://www.youtube.com/watch?v=LS-oyLm-_fg

[72hemi]

Thanks that is exactly what I was looking for!

[rUNCHARGER]

I think heads are the key to a stroker. Stroking a 426 Hemi with their great heads is a natural. I wouldn't stroke a 360 with stock heads though or for that matter a 440 with stock heads. It's the whole package that counts.

Sheldon

[Chryco Psycho]

I disagree to a point  , stock heads will limit the performance of the package but it will still make a lot of torque in the midrange & with most strokers it hardly costs anymore to have all new parts over rebuilding the old parts , so it is still a win

[rUNCHARGER]

It's a win for future mods maybe. A stock 440 head is about as good as a 350 Chevy head in stock form. I see so many 14 and 15 second stroker motors it hurts. Guys build them so they can brag about them, that's about it. They don't have heads that can complement the extra inches and of course they have wrong combinations and don't know how to tune them anyway Stock Mopar engines were very well balanced  for overall torque, driveability and longevity. I know several guys with stock stroke 360 and 440 engines built on very low budgets that have embarrassed many higher dollar stroker engines. I have a couple of steel crank 440's downstairs and if I build one for my Challenger I'll spend the money on better heads before a stroker crankshaft. I agree though if you need to work the crank/rods/pistons it may be the same cost to spend the $2k for a stroker kit that is almost ready to drop in.
A true street engine has to factor in fuel mileage as well. I built a 528 instead of a 572 for the green Challenger because I knew the 528 would make all the power I could use on the street anyway and I would be able to drive it further on a tank of fuel than with a 572.

Sheldon

[Chryco Psycho]

Well I dynoed a 440 / 512 with ported 915 heads with larger valves & made 400 HP / 460 ft lbs tq at the rear wheels on a mustang dyno with peak power @5600 rpm

[cudabob496]

I think the head choice is more critical when you are changing the cam.
A more aggressive cam with same head, will not make much more power, if anymore at all.

[AussieMark]

I wouldn't stroke a 340 they were designed for high rpm stroking the engine will increase the piston speed and create more stress on the bottom end. The 340 was a great engine for the same reason the 426 was it didn't make heaps of waisted energy at low rpm and run out of breath early this made both engines more suitable for cars rather then trucks as was the case with typical high powered engines of this era they produced huge amounts of wheel spinning torque off idle then ran out of breath at low rpm great for a loaded truck but not so good for a light weight muscle car. This is what makes a lot of more modern cars so effective especially turbo charged cars you have that little bit of lag from the start that helps reduce waisted wheel spin then as the rpm increases power comes on. Like Sheldon said unless you are prepared to invest in the total package you will just be building a truck engine.

[Oldschool]

Heads are the key to any build, stroker or not. Too much head for the rest of the combo and it will be a dog at low/midrange rpm. Not enough head for the combo and it will run out of breath way too early. Example: the heads on my 528" HEMI were CNC ported Indy 426-1R's. They will work great on the 572" that I am currently running because they were a tiny bit big for the 528 combo.

When building a stroker, in order to get the most out of the extra stroke, you must increase the duration of the camshaft and here is why.  If you add an additional 1/4 inch of stroke, the stroke is effectively an 1/8" longer at the top of the stroke and an 1/8" at the bottom of the stroke. If your original cam shaft is set for the original stroke combo, it will open and close the valves too soon to take advantage of the new the extra cubic inches of the stroker set up.

Here is a great Mopar head flow chart. More information as you scroll down the page. When you know what the head flows at a given valve lift, there are charts available at Wallace Racing Calculators that will give you the max HP available at that flow. Pretty cool stuff....

http://www.mopar1.us/flow2.html

.

 

[72hemi]

Wow! So much information, I'm in overload right now. Got lots of thinking to do and more research.

[Mopar Mitch]

I'm interested in all this... small block... wanting overall improved torque and HP, especially mid-range ~3000-5000, and hi-rpm reliability... road course racing/lapping sessions... occasional pylon racing (stock 340 did really well for past 30+ years!)... decision time coming soon.... have supply of cast iron older heads... maybe jump for the EDDY aluminum heads.   Also have one set of intake-ported T/A heads... too use or not is the question.

[Chryco Psycho]

The factory heads are worthless IMO
 The ported 308 casting netted us 41 RWHP over the best X/J castings so that is the head to use .
 Seriously ported T/A heads might kill the midrange , you can make the intake port massive .
Why Eddy heads , I have looked at numerous sets they do not look impressive at all with major core shift & I really cannot see much gain other than less weight ,, you want a closed chamber , heart shaped with true quench , there are far better places to put your $$ with cylinder heads if you are going to upgrade 

[72hemi]

Well to hijack my own thread, what are peoples thoughts on the new Indy LA X iron heads?