ROD RATIO IN A 200/250 HYBRID

O.K. I'VE ONLY RECENTLY BEEN ENLIGHTENED ON THE SUBJECT OF ROD RATIO.(THANKS FORUM) FROM WHAT I UNDERSTAND THE RATIO ON THE 200 IS NOT THE GREATEST. SO HERE'S WHAT I'M WANDERING,...
IF ONE WAS TO PUT A 200 CRANK IN A 250 WITH ITS HIGHER DECK, THERE WOULD BE ROOM FOR MUCH LONGER RODS.SO, IS THERE A ROD THAT WOULD WORK? PREFERABLY A BOLT ON WITH LITTLE MACHINING.
I THINK IT WOULD BE COOL TO JUST GO TO THE WRECKING YARD AND FIND A 250 BLOCK AND SOME LONGER RODS WITH THE RIGHT SIZE HOLES AND THROW IT ALL TOGETHER WITH SOME TEMPO (OR WHATEVER) PISTONS AND MY 200 CRANK AND HAVE AN ENGINE THAT WOULD REV ALL DAY. I'M SURE SOME BODY HAS THOUGHT ABOUT THIS BEFORE ME. DOES ANY ONE KNOW OF SUCH A ROD?

200 main journals 2.2486 250 main journals 2.3986

Simpleman, the problem is 250 blocks used larger crankshaft main journals so the 200 crank will not fit.

you can sort of do this on a auzzie cross flow .using 200 rods in the 250
either getting the ACL piston to do the job or and offset grind on the crank.

for only a .050" difference could you not have the block milled and aligned honed? either way you will prob be talking a custom rod/piston combo anyway. before someone mentions the cost of it just remember it isn't how fast do you wanna go it is how fast do you wanna spend.

nick

As fellow New Zealand countryman alloydave has said, the Aussie 200 I6's after 1970 had 250 blocks with there thicker seven bearing main journal bearings. They used 6.275 inch rods and were a much smoother engine than any US 200 or 250 in my experience. However, the extra 1.6 inches of windowed pure cast iron on the block costs a great deal of weight, and having done the same sort of destroking concept on my 250, I'd advise against using a heavier block to correct a problem US engieers purposely designed in to there engines. These guys in Windsor Canada, and Geelong, Australia, threw millions of bucks at these engines, if it was easy to correct rod ratio, they'd have done it from the foundary!

Regarding building a long rod 200 in the USA, I'm not sure if the Falcon crank in US 200 I6's are steel or not, but there is a long run downhand steel welding process which allows you to build up the main bearing diameter with weld. But only if it is steel, not nodular or cast iron. Yes, I know it sounds shocking , but the strength of a crank is in its finish, and seven bearings on a post 1966 crank are good enough to handle it. This way, you don't need to use an Australian 2.4 inch main bearing, post 1970 cast crank. Besides, the US and Oz thrust bearing widths are different according to Jack Collins.

The American saying " For straight line go, go cubic inches" is true. Revs kill engines, and I'm certain keeping the existing capacity and finding a good longer rod and shallower piston is the best bet. That note from a David Vizard article showed that a 12% improvement in rod to srke ratio can produce an extra 3 to 4 horsepower on a 80 to 90 cubic inch four. On a big 200 cubic inch six, there has to be more than 6 to 8 horsepower on a 12% improvement, and 3 to 4 horsepower on a 6% improvement. Doing crank swops and such aren't cost effective unless you are increasing the stroke. Then the rod ratio suffers again. Thats way Ford Australia spent millions in 1999 on changing from the US 250 5.885 inch rods to 6.00 inch rods, to yeild a piddly change from 1.505:1 to 1.535:1, a tiny 2% improvement. That ment they could use a shorted deck version of the exsiting pistons without much expense.

:idea: Here's an idea I've had for a long rod 200. I don't know if it would work (bearing width and cam clearance issues), but small block v8 fords share the same rod journal size with the 200, so how about using 289 rods (5.155") with custom pistons? This would give a rod/stroke ratio of 1.65:1. Just under a 15% increase. Pistons for this combo are available from modular v8 piston manufacturers in custom compression heights and are available dished, domed or flat topped. I found some with a 1.090" compression height which would work with the stock deck height of the 200. They would only require a .020" overbore.

So, what do you guys think? Would it be worth it? If it all will fit, I may try it.

It was discussed before the crash. There's a big difference in journal width between the 200 and the much narrower 289. which could cause problems with fore and aft location of the rods

How much narrower are we talking about? Narrow rods have been used in engines with wide journals before. All that's required is a bead welded on each side of the rod. just machine it down to the size required. As long as the difference isn't more than about .120" this will work just fine. if it will work for 500 cubic inch 500 hp big block v8's (at 7000 rpm too), it should work for a 200 hp inline.

Hey 82Inline here's an idea for a long rod 200. 5.205 rods from a 2.3 pinto engine. I can't remember the width of the big end but I'm sure its at least as wide as a 200 rod. These rods are long for the pistons you described but with a rod journal size of 2.05" you can offset grind the crank to a 3.00" stroke and have a rod ratio of 1.75. Where did you find those pistons? What Engine did they come in? Are they forged? I'd like to know because I want to do something like this on my 200 build-up.

Happy Holidays

so, does the 250 and 200 also have different size rod journals or is it just the mains?
also , what does it cost (roughly) to have a crank offset ground?
anybody had this done?

Hi, Hexhead:

The pistons I mentioned are made by Ross, but a few other companies make them also. They're available in bore sizes up to 3.800" and like I said, dished, domed or flat topped. Yes, they're forged. They're made for the Ford 4.6L Modular engine (Mustang GT engine) One website that has them is http://www.modmaxracing.com/

The 2.3L ford rod idea is a good one because those rods will be MUCH easier to find and, like you said, the engine will have an even better rod/stroke ratio. The pistons I mentioned will work just fine with an offset ground 200 crank. You can even get pistons short enough to use with the stock stroke. The ring stack will be a little tight with the short compression height and this may cause longevity problems if you're looking to get 100,000 miles out of your engine, but would be the way to go for a high revving race 200 (or a hot street motor).

I like this idea.

Anyone out there know the bearing width for the 2.3L 4 cylinder?

Yes the rod journals on the 200/250 are the same size. To offset grind a crank it should'nt cost any more if you're going to have the crank ground anyway. I've seen the 2.3 rod width listed somewhere as .990" or it may have been more than that. I can't remember. That's what happens when you get old.

hey heXhead. It seams obvious that a stroker crank and regrind should cost the same...but it aint brother. Wish it was!

I've looked at offset grinding, and I'm aware that it is a difficult and time consuming thing. The existing rod journal needs its throw (half the stroke) established before cleaning up any wear. For this reason, you often loose more than the 10 thou undersize you have to grind...often it ends up being a 25 thou loss off the existing stroke before you even start offset grinding! After the clean up calculation you can then add on the difference between the parent rod and the donar. The process is more difficult than straight resizing, and it unbalances the crank, needing another outlay of cash to correct it. Here are some things I've found:-

Eg 1. If you had a 351 Cleveland V8, and needed more cubes, you could throw in 300 I6 rods at 6.244 inches long....these are designed to run a 2.126 journal like the 302 Windsors. The stock jounal is 2.311, so normally you'd bank on 2.311-2.126 = 185 thou stroke increase ( from 3.5 inches to 3.685 inches). Problem is, the most expert machine shop cannnot verify a 3.5 inch stroke anyway, as the journals throw can vary more than 2.5 thou without blinking. Add into that normal wear, your potential 3.685 inch stroke ends up being about 25 thou less. So 3.685 becomes 3.66 inches.

Eg 2. I decided I'd get a rod ratio of 1.7:1 if I used a destroked crank and long rods for the 250 six engine I have. I went to a machine shop with some 6.5 inch Mitsubishi 2.6 Astron rods, and told them they could offset grind the 250 crank to reduce the stroke. The Mitsubishi journals were to be 2.047 inches. I told him that would give me 2.126-2.047 = 0.079, or 79 thou off my cranks 3.91 inch stroke. They guy then informed me I'd loose only 54 thou, not 79. That was the difference between being able to fit custom 1.075 inch deck pistons ( which were the thinest I could buy from my local machinest) and not being able to fit the pistons at all. If its 25 thou or half an inch, a miss is a miss. Even on a 9.47 inch tall block, the pistons would come out too far, and decking the piston was out of the question. My only other option was a thick copper gasket, but alloy heads don't like em, especially on a streeter! Oh, and it would have cost me three times the standard crank regrind after a rebalance.

A mans gotta know his limitations!