This is a question I got ask on another forum. I don't want seem like a knowitall, but I have never heard that before so I thought I would ask here first before I reply.

Here is the quote:"Don't you have to watch the boost levels on a stroker engine?
I've heard they get a little sensitive if you over boost 'em."

Now my engine is a Ford/Dart 363 with billet, splayed mains, all forged internals with H-beam rods, Weisco blower pistons {forged} at 8.5:1 with a Cometic head gasket set. Twin T4 turbo's.

Right now the limit on this little Mazda B2200 will be the rear tires, or lack there of.

How about it, anyone hear the quote above?

 

Stroker cranks limit the amount you can reduce the static compression ratio due to the fact that you can only reduce the compression height of the piston so much and the length of the rod so much before the piston gets too thin and the rod ratio sucks. The really aggressive stroker cranks (more than 3.4 stroke like yours) don't allow low compression. I can see someone easily incorrectly drawing the conclusion that a stroker engine always has high compression.

 

Plus a larger capacity engine is going to pump more air..
Longer stroke makes stronger exhaust pulses which assist turbo spool...

 

My compression height is .005, and the Cometic head gasket compressed was .040, so I'm loosing what your trying to say about limiting comp height.

Actually, I don't really understand what the guy meant by saying a stroker engine is more sensitive to boost. Sensitive as in spooling up too quick?

Looks like if that was the case one is running turbo's that are too small for that combo, if so then even that can be controlled by opening the waste gate sooner.

 

I am referring to the thickness of the piston that is often reffered to as the piston's compression height. You've only got so much deck height in the block and you can only dish the piston so much so longer strokes make it more difficult to keep the compression ratio down where you need it for forced induction.

Your making me feel silly because I am trying to play devil's advocate and justify someone's misconception.

 

Don't feel silly, I understand what your saying.

I would paraphrase it, but I think I would muddy up the water even worse.

The guy who asked that question is thinking of something else, or has it mixed up with something else.


Thanks.

 

i think he's confusing stroked motors with the theory that long rod motors are more detonation sensitive with their extended stay at tdc. never heard of a stroke increase causing "overboost" sensitivity. if you add stroke, you're going to have to replan your whole piston/rod combo, so a change in compression height and dish should be a given to keep compression where it's wanted. I'd say he either really knows something with years of experience to back his claims, or he's got a "theory".

 

It's true, following this theory longer stroke and same rod length = lower rod to stroke ratio = less dwell at tdc = less detonation sensitive

 

this one is simple for the simple minded

in a perfect world
302= 200 hp
302+15lbs boost = @400 hp

mild 347 = 300hp
same 347 + 15lbs boost = split block

 

Compression height is the distance from the connecting rod pin center to the top of the piston crown. That measurement should be ~1.100" Im basing that guess on a 3.4 stroke, 5.4 rod length, 8.200 block.

Depending on the forum you are talking about, plenty of guys get really hung up on "piston rock". Sure it actually happens but its my opinion that people let that get way out of proportion with reality. There is one forum in particular that has practically hundreds of posts about it in reference to Boss block strokers, so if you are posting there I would expect lots of of references to that.

Philip