Volkszone Forum banner

1 - 13 of 13 Posts

·
Registered
Joined
·
251 Posts
Discussion Starter · #1 ·
I'm in need of some guidance from anyone who has experience with turbo or supercharged engines. Here's the story...

I'm in the early planning stage of an engine. It will be built for a hard running street and strip car and include a supercharger I already have. OK...I know turbo is the accepted way to go but I've had the blower for some time and fully intend using it. Checking the supercharger spec, I will be looking to build an engine slightly under 2.0l (1915, 1929 etc etc).

Obviously there are a number of ways to get to this engine capacity via different stroke and bore combinations and, I am aware that on normally aspirated engines, bigger bore equates to more horsepower whilst bigger stroke equates to increased torque. Question...does running forced induction have much of an effect on this or does it largely still hold true?

If there is anyone out there already running turbo or supercharged cars around this capacity, what combination did you use? What boost are you running? How much horsepower and torque is your engine producing (dyno measured figures please, not guestimates as I like to work with fact based information where ever possible)?

Appreciate any input on this.

Cheers Paul
 

·
Registered
Joined
·
251 Posts
Discussion Starter · #3 ·
Thanks Mr Thumbs

I saw your disagreement with them on the other thread and don't really want it to run into this one. I am after some constructive information to help me in making quite a critical decision.

I know you have experience with blowers and, even if not directly with aircooled engines, I would appreciate your thoughts. After all where it can be backed up either in practice or theoretically (but based on real theory, not guesswork), sometimes you do need to go against convention to move things forward.

Cheers Paul :)
 

·
Registered
Joined
·
20,445 Posts
Mr PiL - sorry for the delay ......
Usually bore & stroke considerations are critical for normal non-forced induction motors as you are looking for good fill (mostly that is an induction tract issue) , swirl in the comb chamber and then flame front propagation.
Certainly the first two become negated on any positive pressure at the inlet valve. The flame front becomes important again if you are filling the combustion chamber as flame speed is highly proportional to the gas compression and the mixture quality. Surprisingly low octane fuels have a higher flame speed than high octane.
So if your boost is high such stuff as spark plug position, bore and piston acceleration influence the on set of 'pinking' - which I am certain you know is the gas exploding and not burning.

As you can't change the spark plug position - we return to your original question. If the bore/stroke ratio has any influence, I think a tendency to go for stroke over bore will help. All my work (experimentation, messing about etc) was with engines with a much longer stroke to bore ratio than the typical Beetle engine. The usual way we could enlarge the engine was by increasing the crank, and the one thing we always though was that the supercharger made changes in stroke length less critical to ultimate performance than if the stroke were lengthened on a normal non-forced motor. That is the stroke increase would require a lot of work to get the most out of it if no sícharger ñ with a sícharger ñ just turn up the boost and change the advance.

And IMHO, more importantly, s'charging reduced the effect that a 'brick on a stick' cam has on the engine - the forced induction tended to soften it. So you could have a wild cam that would be a bit lairy for the road ñ but when sícharged it would become a lot more tractable as low end had more torque. Not addressing the fuel consumption issue here. :D

Conclusion - I guess you should choose the bore/stroke to suit other parameters, and just let the pressure take care of itself by your setting up of the timing, and the vernier adjustment of the cam. (Can you do that on a Beetle engine?)

BTW - I like suck through and superchargers - that is what I always did. From a Shelsey Walsh hill climb specials through to FIAT twin cams.

Good Luck and enjoy the scream
 

·
Registered
Joined
·
693 Posts
metric_thumbs said:
Mr PiL - sorry for the delay ......
Usually bore & stroke considerations are critical for normal non-forced induction motors as you are looking for good fill (mostly that is an induction tract issue) , swirl in the comb chamber and then flame front propagation.
Certainly the first two become negated on any positive pressure at the inlet valve. The flame front becomes important again if you are filling the combustion chamber as flame speed is highly proportional to the gas compression and the mixture quality. Surprisingly low octane fuels have a higher flame speed than high octane.
So if your boost is high such stuff as spark plug position, bore and piston acceleration influence the on set of 'pinking' - which I am certain you know is the gas exploding and not burning.

As you can't change the spark plug position - we return to your original question. If the bore/stroke ratio has any influence, I think a tendency to go for stroke over bore will help. All my work (experimentation, messing about etc) was with engines with a much longer stroke to bore ratio than the typical Beetle engine. The usual way we could enlarge the engine was by increasing the crank, and the one thing we always though was that the supercharger made changes in stroke length less critical to ultimate performance than if the stroke were lengthened on a normal non-forced motor. That is the stroke increase would require a lot of work to get the most out of it if no sícharger ñ with a sícharger ñ just turn up the boost and change the advance.

And IMHO, more importantly, s'charging reduced the effect that a 'brick on a stick' cam has on the engine - the forced induction tended to soften it. So you could have a wild cam that would be a bit lairy for the road ñ but when sícharged it would become a lot more tractable as low end had more torque. Not addressing the fuel consumption issue here. :D

Conclusion - I guess you should choose the bore/stroke to suit other parameters, and just let the pressure take care of itself by your setting up of the timing, and the vernier adjustment of the cam. (Can you do that on a Beetle engine?)

BTW - I like suck through and superchargers - that is what I always did. From a Shelsey Walsh hill climb specials through to FIAT twin cams.

Good Luck and enjoy the scream
I have only had experiance with a blower that ran through a su carb on a alfa sud 12 years ago so I am not the best to comment and that came as a sharrock [not sure on the spelling] kit of parts so it was a simple bolt on,off you go no brainer

On reflection I did have a problem with the crank and I had it reground and balanced which certainly helped

The thing about turbos is you can get away with some mismatched parts and still get a decent bang for your buck

If I was going down the super charger route I would try the system on a few old 1600 twin ports and suck it and see as so to speak before spending big money on a race engine
 

·
Registered
Joined
·
251 Posts
Discussion Starter · #12 ·
Thanks for the input everyone, some good info to think about before going and spending any cash.

Some of the links make interesting reading too. Japeto looks like a really nice set up you have put together. I couldn't find what stroke your engine is running on that thread though? I would also be interested to hear what results you get on the Dyno once set up.

Cheers again everyone :D
 

·
Registered
Joined
·
378 Posts
My motor is 84mm x 94mm bore.

Passed the MOT (thanks beng) and finally taken it for a drive after nearly 3 years. :)
 
1 - 13 of 13 Posts
Top