Re: Rod length? Piston speed?
 

Look at all the used NASCAR stuff for sale on eBay...... Big bore, short stroke, long rod. Piston weight seems to be the priority. They spent a little money on research and development. So you know they've figured something out. Mind you, all of the secrets won't make it to ebay until it's common. So there could be a secret short rod combo... But I doubt it.
I could be comparing apples to oranges. But you can't ignore decades of homework.

Re: Rod length? Piston speed?
 

Well, you sure took the rod length at face value. There are "other" parameters in cup engines that have an affect on the "total" engine package. Just like in F-1. Yes, they are very well designed and tested for the purpose they are built for. If long rods are the answer then why did most of the 358 cu in PST engines (making well over 2.5 HP per cu in N/A) use very , very short rods and BB pins?

Re: Rod length? Piston speed?
 

That's the question I'd like to know the answer to. What is the advantage to a short deck block and short rods in a modified or comp engine? It has to do with the 9,000 to 11,000 rpm range...

Re: Rod length? Piston speed?
 

Intake manifold design

Re: Rod length? Piston speed?
 

I believe the thinking behind high rpm short rod motors is that the piston accelerates away from TDC faster which helps initiate intake flow plus you have the benefit of the lower piston / rod (rotating) weight. It appears to me this works well if you have adequate or more than adequate air flow but it’s my guess is that you need to keep these motors buzzing in a narrow RPM band.

Re: Rod length? Piston speed?
 

Adger, you mentioned intake design....Are you referring to mainly having a sheetmetal intake? Can you elaborate a little more? And at what RPM ranges do you think responds better to the short rod/short deck configuration?

Re: Rod length? Piston speed?
 

When you build an intake for a short deck engine you can stand the ports up.
You can also design the area under the carb better.. like tighten the runners up closer to the carb c/l. Then you can also build a port that enhances the short rod. The benefits go on and on......

Re: Rod length? Piston speed?
 

Let me ask this, If you do not have a short deck block, would there still be any advantage to having a shorter rod than a 5.7 for a stroke in the the 3.00 to 3.25 range running in the 8000-10000 rpm band?

Re: Rod length? Piston speed?
 

Maybe.. Depends on the head port/design.

Re: Rod length? Piston speed?
 

I thought the prevailing thought behind the long rod is to keep the piston at top dead center longer giving the fuel time to burn completely and create maximum cylinder pressure. The burn time for the fuel remains relatively constant even though the RPM increases, that is why you have to advance the timing as well.