Stock rod length or 6.200 for 393 stroker?
 

I see that CHP offers a standard 351W rod length and a longer 6.200 rod for the 393W. Any advantages for the longer rod?
Planning on a rebuild for my 351W. Cheapest way would be to go 393,since I have the good Eagle 3D rods already in the engine. Bore is .030 but will go to .040 to get it fresh.
Other option would be to go 408,only diff. being new rods.
Just wanted some info on the longer rod 393 setup.
Heads are the Bennett Stage 2 TFS Highports.

longer rod will put the pin further up into the piston, making for a smaller/lighter/quicker accelerating combination.

more cubic inch is always easy hp, just have to figure the price difference.

What I have heard over the years..

Less side loading on the piston/cylinder wall. It also slows the process of the piston changing direction holding the piston at TDC for a few degrees more crankshaft rotation allowing more A/F mixture to enter the chamber. And weight of the piston as mentioned.

Some argue to put the longest rod you can fit into an engine. I think there is a point that it becomes pointless and the gains arent measurable.

Rod length is, basically, irrelevant.

As far as the CHP kits...the reason I did that (originally) was because the only 5.956 rod that was available was stock. Using the 6.200 allowed a decent piston and a lot of options for upgrading the rod.

Probably the best reason for using it now is the comparative weights of the 1.350 C/H piston and the 1.600 C/H piston.

If you already have the crank and rods....changing the piston is probably the way to go if you wish to save money.

It's what I'd do. You can always build a different short block for the future, especially since the heads will outperform the combination.

because the piston is lighter and the rod angle in relation to the bore wall is is less acute the motor will be able to rev higher than the shorter rods. The angle is the same reference as the Rod/Stroke Ratio ..Rod Ratio.If you are going to use a cam that is not making power above 6000 the shorter rod will be OK.... So it all depends on the cam you are going to use.
John:JEKYLHYDE

The correct rod to crank ratio is 8:1. Eight rods....one crank.

Unless there is an rather severe imbalance between cubic inches and cylinder head size rod ratio is irrelevant.

The ratio between the crank stroke and the rod length is ,my friend, very important.
If the angle of the rod is to acute the rod will go through the cylinder wall at great speed and leave you on the side of the road!!!...

Oh horse poop, my friend.

If you carry any argument to the ridiculous extreme you can prove anything.

This, I think, is a reality based board. No one in the industry has a piston forging long enough to allow that scenario.....so I won't sweat it.

Rod ratio is not a consideration when designing a combination unless there is a serious mismatch between the engine and cylinder head sizes.

351C and BB Chevy have short rods....big head, little motor. BB Chrysler has a long rod.......big motor, little head.

I doesn't really matter even then but the rest of the time, pick a rod, it's all good.

Rod ratio is the least important piece of folklore to consider when building an engine.

If anyone really cares about this...here is a pretty good thread you can read.

http://www.460ford.com/forum/showthr...ight=rod+angle

Since the original poster stated he already has the good Eagle rods, I would say stay with the standard length rods at this point. With a 393, rod angle is probably pretty meaningless since it is a minimal increase in stroke. There seem to be plenty of good pistons available these days to go with the shorter standard rods, so why not go that route?

As far as strokers though, it may or may not be folklore, but without a compelling reason and/or a Dart block, I will stay away from the big 427W stroker in the stock blocks. Plenty of horsepower to be made in the 393 and 408 stokers without the issues.

Man, you guys need to back off on the caffeine a bit. You're wound way too tight..... ;)

Bob

That's because people say silly things like this:


I've done somewhere around 600 of these a year...since 1995 (or so) and have never seen any reason to not use them. While the 427 is not my personal preference there is no reason to avoid them.

....then again...other than the original low cost of the 393, which was great for the consumer, I don't much see the point in that either.

Mark... If you are going to build an engine that is not going to rev very high and use a cam that will make power low down on the rpms by all means build an engine with a rod /stroke ratio of less than 1.6:1 .
If on the other hand you are a driver who likes to rev your engine at higher rpm's then a better than 1.6 ratio is desirable . As you may know.. the current F1 engines use a ratio around 2.5:1 which allows them to rev to 20,000 rpms for hours on end. I would hazard a guess that the rod ratio had a lot to do with the design of these engines, but being an engineer I would imagine that I do not have a clue as to what I am talking about. A low Ratio may hold up on the street for a period of time, but if you are building an engine for longevity a better ratio is desirable. Of course if you are building engines for others and don't really care how long it will last ........then it does'nt matter at all.
I am also a little confused as to what the head size has to do with Rod/Stroke ratio???%/%/

How the heck do you find time to post on this forum with that work rate, thats about 1.6 motors a day without weekends or holidays:JEKYLHYDE or have you got a few slaves doing the hard yards for you!

30.......rather well paid "slaves"

As to the RPM/Rod ratio.....any Big Block Chevrolet. There's a ton of 6.385 rod x 4.250 stroke high rpm engine out in the world. (1.50:1)



AS to head size and rod ratio look at the Big 3 (well.....you know....)

Most stock engines have a rod to stroke ratio of about 1.7:1. The differences are the 351C....Big Block Chevy...(too much head) and BB Chrysler, 455 Pontiac, 455 Olds (not enough head).

The slower the head, the earlier you need to get air moving. The faster the head, the more you need to slow it down in the higher RPM range. (speed relating to the velocity/capacity of the intake port.

Rod ratio is the last thing one should worry about when designing an engine. There are exception...when using a Boss Block, for example. The cylinder length is so short (stupid short) that you have to futz around with rods to keep the piston in the hole at BDC.

You really should read that link to 460.com that I posted.

Incidentally...that 650 number is all 427s combined...kits, shorts, longs, and completes.

We do around 400 assemblies a year.

I did read every word on that link and some, well a lot contradicts what you are saying. The "too much head too little head" thing would be compensated by camshaft profile. I think that you are trying to argue a mute point in so much that, Yes the big block chev does have a Rod ratio of 1.5:1 as a stock ratio that was initially designed as a truck engine intended for low rpm use. This does not mean that the motor will not hold up for a decent period of time, which is what they do . The thing is, if you decide to hotrod that engine and look at all the different offerings they all seem to try to improve on the Stroke /rod ratio with in the space constraints that are available.
Hey ..Mark!!! I am really just arguing for the sake of it.........I guess that is what boredom does to you...me!!!
The Ratio mattered to me when I built my motor but the best I could get was 1.6:1 and with that it revs to 8000rpm....I don't know if it would do it all day..but it does it long enough for me to kick as much a$$ as I like with my car....Loving it!!!!

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.

Stock rod length or...............
 

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.

Ant, I think the 'Wing' would have to be ' right way up' to help induce wheelspin :), or are you refering to my 'infamous, legal but how can we outlaw it' muffler design? Havent tried that on the TVR, probably wouldnt get past the committee that controls it!!!:) Much more fun when I can do as I please.