Firm Conclusions on an Endless Depate. "Rod to stroke r

[Anonymous]

In Australia through the use of a shorter ACL piston one is able to fit longer 200ci conrods in a 250. For those who dont know, this is done to correct was is considered to be a poor rod to stroke ratio in a 250ci.
Although the the rod to stroke ratio is a point of contention amoung many who know this subject better than myself. I have spent endless hours trying to find if there is any common oppinion on the subject.
There is an awful amount of conjecture and where real extremes are involved there is no doupt the the Rod to Stroke ratio does have a big effect. So Ill try and keep what is said as it relates to a ford 250.
It appears that almost all agree on one thing that a poor ratio does effect the wear of an engine. This is something that can be measured and a poor ratio is harder on the pistons due to the fact that it tends to drive the piston into the sidewall. (mind you some of the high reving Hondas have about the same ratio as a 250 and are known for durability as is a Ford 250)
the effect on HP is a bit less certain but it seem if it does have some effect its only very small. An article called "Great Myths I have Known and Loved" says that an article in 2001 National dragster magazine conducted test altering the Rod ratio on a 500 inch Chevy Pro Stock engine and Dyno tested the results apparently long rod short rod it didnt seem to matter he says that there was not much if any HP differences recordered. Other tests can bare this out.
Wear, HP, what about revability and the effect of any additional strain the rod ratio might have on and engines bottom end. There is a good article called Rod ratio Kinematics although not done on a Dyno its computer program findings show clearly the effect of an increase of a rod of about 1cm in an S 14 engine with an Evo 111 crank. this is about the same increase of fitting an aussie 200 rod into a 250.
The results are that there was an increase in the engines red line. But guess by how much, wait for it. 123 rpm thats right a staggering, mind boggling 123 rpm. And at what revs I hear you ask only about 8323 rpm up from a previous 8200 rpm with a 1.5 % decrease in piston acceleration. In the article it says that this should not be considered inconsequentual. Well maybe not for a dragster on the strip wanting to blast to the moon, but for me and my 250 2V its inconsequentual.
At a rough guess it would amount to maybe about a 60 rpm increase on my 250 2V 4600 redline. Wow I can hardly wait to get those 200 rods in there. mind you Ill have to get a much more accurate Tacho, its kinda hard to pick a half a hundred rpm increments on my tacho. The wear factor must also be dirrectly linked to revability.
Perhaps the argument in all of the rod ratio debate should not, "if it makes a difference" but "how much of a difference is it going it make". But For me the 200ci rods I got for this will be staying on the wall in the garage for a very very long time. Oh by the way the effect of a so called poor ratio is improved by a longer stroke. A good example a this is a 250 Ford. Oh and just one other thing, my mate accidentally reved his 250 2V to 7000 rpm the other day (and yes, it still runs)

 

[rbohm]

8) one thing tech writers tend to overlook when doing comparisons like this are the bsfc numbers, and the fact that cam timing, intake and exhaust tuning, head ports, etc. all have an effect as well. this was born out many years ago when an early long rod offenhauser engine was rebuilt using shorter rods. the result was a loss in power and fuel economy. is this proof positive that long rods are better? no, but then when you tune engines to take advantage of either a long or short rod, and then compare the two, you have an apples to oranges comparison. personally i will take the long rod engine anytime.

 

[xctasy]

I've done some posts before on this. David Vizard has done control testing, and the results conclude that better rod ratios in the 1.8 to 1.5:1 zone improve top end power. I made some quotes on his 1988 Mini article on A-series engines before on this forum, and it looks like the frictional losses provide more power on an ever increasing measure as revs rise. Thus in the area below 1.8:1, going to a longer rod is of benifit, but above 1.8:1, the wieght of the engine and other factors (including expenses) cancel out the advantages. Ex Repco Phil Irving in his book tuning for Speed also underscores the fact that 1.8:1 is the sweet ratio, below it, you're overloading the engine, above it, weight increases. Although his 2.5 liter Formula One Braham design had 6.25 inch Diamler majestic rods on a very shrt stroke engine...a 2.2:1 or so stroke to rod ratio!

XR 500, StrangeRanger and some others contributed a huge amount to the debate. The link for the general discussion was http://fordsix.com/forum/viewtopic.php?t=1658&start=0&postdays=0&postorder=asc&highlight=

The ex Repco, ex Ford Australia engineer who helped develope the Aussie 250 quoted some interesting things on a link I started. I'll see if I can find it soon...within next two days. (I've run out of internet time! :nono: :fume: :duh: )

 

[Anonymous]

Tim, you are correct that opinions vary on this subject. But I for one would go ahead and use the long rods. I think any improvement of the 1.50 r/s ratio would be worth it if you can use off the shelf parts.The problem with the 250 is there's just not alot of room for long rods unless it's de-stroked or custom pistons are ordered. Right now I'm thinking about chrysler 2.5 rods (6.180) and KB 305 chevy pistons, but that's still a 1.58 r/s ratio small improvement. I could offset grind and improve the ratio but lose cubes.
What to do, what to do?
Do you know what compression hts. those ACL pistons are available in?

Thanks

 

[Anonymous]

In Australia through the use of a shorter ACL piston one is able to fit longer 200ci conrods in a 250. For those who dont know, this is done to correct was is considered to be a poor rod to stroke ratio in a 250ci.
Although the the rod to stroke ratio is a point of contention amoung many who know this subject better than myself. I have spent endless hours trying to find if there is any common oppinion on the subject.
There is an awful amount of conjecture and where real extremes are involved there is no doupt the the Rod to Stroke ratio does have a big effect. So Ill try and keep what is said as it relates to a ford 250.
It appears that almost all agree on one thing that a poor ratio does effect the wear of an engine. This is something that can be measured and a poor ratio is harder on the pistons due to the fact that it tends to drive the piston into the sidewall. (mind you some of the high reving Hondas have about the same ratio as a 250 and are known for durability as is a Ford 250)
the effect on HP is a bit less certain but it seem if it does have some effect its only very small. An article called "Great Myths I have Known and Loved" says that an article in 2001 National dragster magazine conducted test altering the Rod ratio on a 500 inch Chevy Pro Stock engine and Dyno tested the results apparently long rod short rod it didnt seem to matter he says that there was not much if any HP differences recordered. Other tests can bare this out.
Wear, HP, what about revability and the effect of any additional strain the rod ratio might have on and engines bottom end. There is a good article called Rod ratio Kinematics although not done on a Dyno its computer program findings show clearly the effect of an increase of a rod of about 1cm in an S 14 engine with an Evo 111 crank. this is about the same increase of fitting an aussie 200 rod into a 250.
The results are that there was an increase in the engines red line. But guess by how much, wait for it. 123 rpm thats right a staggering, mind boggling 123 rpm. And at what revs I hear you ask only about 8323 rpm up from a previous 8200 rpm with a 1.5 % decrease in piston acceleration. In the article it says that this should not be considered inconsequentual. Well maybe not for a dragster on the strip wanting to blast to the moon, but for me and my 250 2V its inconsequentual.
At a rough guess it would amount to maybe about a 60 rpm increase on my 250 2V 4600 redline. Wow I can hardly wait to get those 200 rods in there. mind you Ill have to get a much more accurate Tacho, its kinda hard to pick a half a hundred rpm increments on my tacho. The wear factor must also be dirrectly linked to revability.
Perhaps the argument in all of the rod ratio debate should not, "if it makes a difference" but "how much of a difference is it going it make". But For me the 200ci rods I got for this will be staying on the wall in the garage for a very very long time. Oh by the way the effect of a so called poor ratio is improved by a longer stroke. A good example a this is a 250 Ford. Oh and just one other thing, my mate to 7000 rpm the other day (and yes, it still runs)

accidentally reved his 250 2V

 

[Anonymous]

Damm this key board
nice two see your knowlegde is increased so much tim.
when i got to 7k on the taco the car has never been the same ;I just cant get rid of the tapping noise.
ive replaced the push rods lifters evrything has been adjusted right ,i drive the car around do about 100km and the noise is back again repeat process and the same result Does anyone have any idears tim if you dont mine asks phil for us
cheers G/Spack

 

[addo]

Hexhead, I think the long rod pistons are in one height, with three or four dish choices. Alloydave is the man to ask on this.

 

[Anonymous]

Because the rod ratio is considered to be as bad as it is in a 250 in may be just worth putting 200 rods in it to get a half reasonable ratio. But I expect the difference is still only going to be minimal.

Oh and GSPack.
Revin to seven isnt a good idea in a 250. at 4600 rpm a 250 has a piston speed of 2990 fps. 3000 fps is considered the safe limit for an engine under "normal circumstances". anything above this and wear and risk factors start to increase and multiply rapidly the further the revs increase. You dont have to rev a 250 to extract its maximun performance (even with youre cam).
I hope you fix youre problem.
Cheers Tim.

 

[xctasy]

heXhead said

I think any improvement of the 1.50 r/s ratio would be worth it if you can use off the shelf parts.The problem with the 250 is there's just not alot of room for long rods unless it's de-stroked or custom pistons are ordered.

The 1998-2002AU/2002- date BA Falcon Intech SOHC/DOHC have rods which are six inches long that will interchange if you just deck the piston to ensure you don't hit the head or valves at full flight. A less-than 58 thou piston skim should work on a US engine. Ford Australia spent bulk dollars on adding just 118 thou to the length of Aussie Falcon I6 con-rods, which used to be a blueprint 5.885 inches until 1998. They are just the same as US 250 rods, and the rod ratio is improved only from 1.505:1 to a meger 1.535:1, which is the same as the US 200 (1.529:1). They spent millions doing it, so it must have been worth it!

Only thing is, make sure you have sufficient budget. Take it from me, my 3.46 stroke, 6.275 200 X-flow rod engine with its technically ideal 1.81:1 ratio has only cost me $3000 dollars to loose 22 cubic inches.

To get a 200X-flow rod in a US 250, and get a 1.605:1 ratio, you'll need to look at GM 4200 i6 +20 thou pistons (3.66 inch) and a stock 3.68 inch bore block. Or pay $$$ for custom 200/221/250 Falcon or Chevy 229/305 forged pistons, or track down a piston manual for foregin cars, like BMWs, Porches, or some thing with pistons around the 93.5 to 95 mm (3.681 to 3.740 inch).

All our Aussie post 250/4.1 X-flow sixes, like the 3.2/3.9 and 4.0's use either 3.612 or (Factory+20 thou) 3.632 inch pistons. You could sleave a 250 block bown to 3.652 [you over bore, and use a liner like a diesel or GM Gen III alloy block], and use import +20 ACL AU pistons, and save big money on forged pistons, and go for stock AU Falcon Rods and pistons. They handle 5900 rpm!

Talking bench dynos here. If a 250 six can rev to 5300 rpm, you could get 260 hp net flywheel and up to 275 lb-ft from a streetable 280 camed six with a 465 Holley with a 2V or Argie head, or maybee a log with triples Carters or Webers. A stock log, but with a great carb like a throated out Holley / Weber , 38 DGAS or 500 cfm 2-bbl #2300 Holley, would trip the 200 hp net flywheel figure at 5300 rpm with a 264 to 280 cam with enough net lift. That would give over 220 foot pounds, maybee more, and would drive really nicely in traffic or on the highways. Push the envelope on cams, carbs, and exhasts. If you have to rebuild, consider cost-effective mods. Custom rods and pistons are not a good first port of call.

 

[Anonymous]

Just find it hard to belive that Ford would spent millions to increase the rod this much (600 inch rods). perhaps they were going to spend the millions anyway and the 6 rods jusy happened to fit as an added bonus??

Tim

 

[xctasy]

Yes, it make me wonder when Ford America has 1.17 inch deck Zolner pistons in its 5.4 V8 engines why Ford wouldn't invest in shoving 6.275 inch long rods and 1.25 or so deck pistons to make there 4.0 I6 a real screamer. Perhaps the next Falcon?