Stock rod length or 6.200 for 393 stroker?

[Jac Mac]

I must be bored as well, Im afraid I go with the 'long as possible' rod club as well. Mainly from three totally different applications that convinced me
1. Was involved with a 'budget' race class down here with Ford/Holden inline six cyls--
Holden 202ci, 3.625 bore x 3.25 stroke-5.250" rod (1.61/1 Rod Ratio) single barrel carb, no porting polishing, 3angle valve seats, regulated cam profile/grind, headers & compression free.
Ford 200ci, 3.68 bore x 3.13 stroke-6.250 rod (2.03/1 rod Ratio) Same cam & other rules as Holden, & Ford had intake cast in head-lovely.

Holden idled rough/lumpy-Ford was so smooth you would swear it was a sunday church car- slightly down on power to Holden-- Cure... same lobe profile, but open up lobe centers by 4°-- parity between makes restored!!

2. 351w in marathon type Jet Boat-- cam grind profile that provided excellent results from 350 chev (5.7 rod--3.5" stroke). In the Windsor 351 (6.025 rod--3.5" stroke--*** Aussie 302c rod ) Now with that cam EGT's were very high & did not respond to jet & timing changes, yet plug colours etc were fine. Did same trick & had another cam ground on wider Lobe centers, EGT's dropped by around 200° , & picked up 400RPM in the process.

3. 351w block fitted with 400c Crank & 6.580" 400c rods & a very special set of pistons. SVO C3 heads. Man did this thing do the numbers. The owner/driver still reckons to this day that it made more power than later Nascar 355 combos he has used ( Dynoed in USA at over 800hp ). Other 392/427 combos seem to run out of breath around 6000/6500--that 'Thing' for want of a better name simply kept on pulling--you gotta be doing something right when the wheelspin starts again on the 3rd/4th shift @ around 140mph with 15" wide slicks.

To put it simply, since a longer rod increases the pistons dwell time at TDC/BDC increased duration or wider lobe center is needed to take advantage of piston movement when it does start to happen. Now for any given lobe center there is a limit to how much duration you can stand before you need to open the LC angle up, yet from the examples above its obvious that the short rod motor wont appreciate this as much as the long rod version.

[Ant]

Jac Mac

The car that had the wheelspin on the 3rd/4th shift @ around 140mph with 15" wide slicks, did it have a huge upside down plane wing attached to it, or are the rear springs too stiff...............!
Just joking, .... its going to be interesting with my little 675 bhp US dynoed engine behaves, I dont think sudden flicks of the steering under full power are advised.

Originally Posted by Jac Mac

I must be bored as well, Im afraid I go with the 'long as possible' rod club as well. Mainly from three totally different applications that convinced me
1. Was involved with a 'budget' race class down here with Ford/Holden inline six cyls--
Holden 202ci, 3.625 bore x 3.25 stroke-5.250" rod (1.61/1 Rod Ratio) single barrel carb, no porting polishing, 3angle valve seats, regulated cam profile/grind, headers & compression free.
Ford 200ci, 3.68 bore x 3.13 stroke-6.250 rod (2.03/1 rod Ratio) Same cam & other rules as Holden, & Ford had intake cast in head-lovely.

Holden idled rough/lumpy-Ford was so smooth you would swear it was a sunday church car- slightly down on power to Holden-- Cure... same lobe profile, but open up lobe centers by 4°-- parity between makes restored!!

2. 351w in marathon type Jet Boat-- cam grind profile that provided excellent results from 350 chev (5.7 rod--3.5" stroke). In the Windsor 351 (6.025 rod--3.5" stroke--*** Aussie 302c rod ) Now with that cam EGT's were very high & did not respond to jet & timing changes, yet plug colours etc were fine. Did same trick & had another cam ground on wider Lobe centers, EGT's dropped by around 200° , & picked up 400RPM in the process.

3. 351w block fitted with 400c Crank & 6.580" 400c rods & a very special set of pistons. SVO C3 heads. Man did this thing do the numbers. The owner/driver still reckons to this day that it made more power than later Nascar 355 combos he has used ( Dynoed in USA at over 800hp ). Other 392/427 combos seem to run out of breath around 6000/6500--that 'Thing' for want of a better name simply kept on pulling--you gotta be doing something right when the wheelspin starts again on the 3rd/4th shift @ around 140mph with 15" wide slicks.

To put it simply, since a longer rod increases the pistons dwell time at TDC/BDC increased duration or wider lobe center is needed to take advantage of piston movement when it does start to happen. Now for any given lobe center there is a limit to how much duration you can stand before you need to open the LC angle up, yet from the examples above its obvious that the short rod motor wont appreciate this as much as the long rod version.

[Mark O'Neal]

Originally Posted by Jac Mac

Im afraid I go with the 'long as possible' rod club as well.

So am I, sort of.

First I decide how much power I want to make. Then I decide what engine I want to use. Then I pick the longest rod I can comfortably use in that combination.

But it's still irrelevant...and, even after 35 years of doing this...I don't have a good reason.

[Mus408]

I just researched,one of the most successfull current production engines,made today...the Corvette's LS-7.
It has the 4.125 bore and 4.000 stroke coupled with a 6.067 rod length,which gives a 1.51 rod/stroke ratio. So,if it works for them for a long life,should be fine.
Would it not be great,to have off the shelf heads,like those of the LS-7,for the smallblock Ford! 2.20 intake valves and 360 cfm stock from the factory!
And we think that a 225 cc intake runner size is big doings,on the Ford 427 strokers.

[Jac Mac]

Flow rates are fine, but one thing that bugs me when people start talking port volumes; Its only relevant when comparing say one BBC intake port to another BBC intake. Take an FE head for example- valve stem centerline to intake port face is considerably shorter and port volume lower than most other designs since pushrods go thru intake manifold.. Also if you look at many of the newer heads with raised inlet porting the volumes are larger than stock due mainly to increased runner length, but cross sectional area is quite often smaller. In this case it is Flow Quality, not Quantity that gets the job done.

[Mark O'Neal]

What really frosts my cookies is when they start spouting off about average cross section......

What crap.