Oz 250 I6/X-FLOW mods from Ford Engineer!


This is a piece of information from an August 1990 Australian Street Machine article on high performance sixes. It's from Bill Santuccione, a Ford Australia development engineer who worked on the Aussie 250 and Cleveland V8 engines during the 60's and 70's. It is worth a read to determine ways of making a six cylinder Aussie Cross flow Falcon engine produce big power.

"The 250 six is a good engine to modify in a mild sense - if you make the torque work for you. On an around - town street car, a strong 250 can be a lot quicker in the first 50 to 100 yards away from the lights than even a V8.

Bill says the biggest problem with the 250 is its design. "Almost across the board, I believe the 250 suffers because of its stroke/rod length ratio. Rod length verses stroke is a crucial factor when it comes to determining the optimum 'revability' or torque output of engines. The Falcon six has a bloody terriable ratio copared to the ideal formula.

"Back in the old days at the engine laboratory in Geelong, we did a lot of development work on cams for the 250. You know, aiming for driveability, torque - getting the best of all worlds if you like. And I remember then playing with compression ratios and valve sizes and all the things you do in research and development. It didn't matter what comp ratio. valve sizes or cams we evaluated., all wen were able to do was move the horsepower peak up or down in terms of horsepower out put but not in rpm.

"Mormally when you start to 'cam' an engine up, the horsepower goes up and the power peak moves up accordingly. On the Falcon six, due to what I believe was that rod lentgh ratio, it didn't matter what you did. It remained at around the 4800 rpm mark'. Bill reckons the Ford six can rev to around 7500 - which is prettydamned good for a stock Falcon six. It's just there's no point in doing it. Peak grunt happened 2700 rpm ago...

"What I'd be suggesting to anyone going for more horsepower is to be conscious of that characteristic and aim to fill the torque curve as much as possible, " Bill says. "Your horsepower will increase proportionally but not much further than that rpm point." Bill says that the 250 is agood street package. But for racing, he thinks you'd have to consider increasing the rod length. Okay.Fine. And you wonder why there aren't many killer 250's around! As it happens, Bill is curently planning a kit designed specifically to get around this problem...

Lets assume you want to get good power out of a 250. First port of call is, of course, the cam. "I'd think of someone like Crow Cams," Bill says. "They 've got a coputer so you can feed that kind of stroke/rod length data into it and come up with the best result."

The same torque characteristics come into play when you're talking about carb choices. " The fact that you're only revving to the 5000 rpm mark means big carburation isn't that critical. But the tripple Webers are probably the best package to go with because they lend themselves to 'pulse - tuning' (Timing the pulse to coincide with the next intake filling charge). That complements the fat torque curve situation." Bill says he's also done a lot of promising development on four barrel Holleys by altering the tune length of the intake runners.

Headwise, Bill reckons you just have to go for the better breathing crossflow head."In terms of making maximum torque and horsepower, it just breathes that much better - the port shapes and angles are very, very good. But with the Series II alloy head, I think, the combustion chamber shape was different to the earlier one. They changed to an almost kidney shaped chamber and I remeber they appeared to be a bit prone to pinging. That's a particularly critical thing if you start building a higher compression engine."

Bill says that apart from the torque curve and the possibly suspect later model alloy head - plus the fact that the water pump location tends to cause number one cylinder to run cooler than the rest - the 4.1 litre (sic)engine is a pretty srong engine. "I've never found any weaknesses in the bottom end, the bearings or any thing else." That means if you'd like to build one up, normal rules apply."We almost always up - rate the oil pump output - that's always good insurance. And the standard conrod bolts tend to be a bit on the plsticine side. Even if you're not reving the engine too high I'd still go to a set of high performance bolts."
This is great stuff. With the stock log, 2V or Crossflow this is the kind of info that will lend to building the 1hp to 1ci engine.

Please let us know if Bill publishes any numbers that we can apply before a rebuild.

Thanks, Ric.
Does the crossflow have the same stroke/rods as a US 250?

Can you use 300 rods? If you can find a piston with a compression height of 1.118 That would give you a ratio of 1.58 vs 1.50. Not alot but every little bit helps.

If there is such a piston a 302 rod could be used in a 200.
what if you spent the money for some custom pistons.....put a 200 crank in a 250 block and ran a real long rod? would that help the motor to rev up much?

I agree rod ratio is the weak point of these motors if you want to make big power. I've thought alot about this and one idea was to use 6.2" small block chevy small journal aftermarket rods, detsroke the crank .140 and use KB 1.43 comp. ht. 305 chevy pistons. You would then have a 241 cu. in. motor but more importantly a rod/stroke ratio of 1.69. Sound like an idea? Does anyone know the width of the big end of the rod? sbc is .940
Theres an easier mod to change the rod ratios on the xflows; Grab a set of 3.3 litre rods, and a set of ACL Race pistons. While the new ratio escapes me, it comes up with a near identical ratio thats found in the current 4.0 I6 in the New Falcon :)
Regarding 6.275 inch 3.3 rods in a 4.1 or 250 engine. The rod ratio ( called L/R by some engineers) is 1.605:1 with a 3.91 stroke, which is in fact much better than the 250 stroked 4.0 and 6 inch rodded AU/BA 4.0 Liter sixes.

An ideal rod ratio is 1.8:1...over that, the engine weight per horsepower starts getting excessive, due to the block deck being proportionally higher. Ford's factory 5.6 liter Winsdor 342/347 in the last T-series Falcons had a 1.588:1 ratio, and was over 156 pounds lighter than a factory XE Falcon 351 Cleveland. That's why Ford pursues this pragmatic habbit of scraping the maximum cubes out of its existing blocks. The poor L/R ratios are not an issue unless you are violently working them!

Ford only gained from a poor 1.505:1 ratio common to all 250's, (US and OZ) to a still fairly tragic 1.53:1 rod: stroke ratio of the current 3984 cc 6.00 inch rod DOHC sixes. The reason these engines are so much sweeter than earlier sixes is the crankshaft, head, cam and noise isolation work that Ford put into these 4 liter machines.

In my opinion, the only factory six cylinder Ford engines that had rod to stroke ratios any good were the tall deck Aussie 200/3.3 OHV I6's , the
3.2 liter Cammer I6 in the '88 EA Falcon, and the 144 four bearing crank I6 in the orginal 1960's Falcons. The 240 Big six is also ideal in its rod to stroke ratio. These engines were very smooth runners because so little side thrust was imparted on the cylinder walls during operation. Engineers have found a difference in L/R ratio of 12% (from 1.8:1 to 1.61:1) looses 4 hp on even 80 to 90 cube fours! On a 250 six, going from a 5.885 inch rod to a say, 6.275 inch Aussie 3.3 rod could theoretically yeild 5 to 6 horsepower by doing nothing other than a piston swap.

My project 228 Ford destroker runs 6.275 inch 3.3 liter rods with Chevy 305 forged pistons decked to 1.475 inches, and a modified 221 crank from an early 1969 Falcon. The crank is steel, not cast, and the stats are:

3.736 bore, 3.46 stroke, and 1.814:1 L/R ratio. I spent lots of time and money to get these components. In practice, I'll have an engine that loves revs and is smoother than a 250. But I'm sort of sad that a stock 240 Ford F150 truck engine would have better specs, cubes, and rod ratio than my one. Along with a Small block Ford bellhousing. If I had my time over again, I'd never go into improving rod ratios unless you can do it cheeply[/b]. Ford Australia's Bill Santuccione said make the 250 torque work for you. After spending $1000 New Zealand on forged 305 Chev pistons, $300 NZ on a steel 221 crank and $400 NZ on honed 3.3 rods to improve this ratio thing, I can only agree with him!
:shock: $300 for a crank???

Over here, you're NUTS to pay over $200 for the whole, virgin 221 motor.
Yeah...but over here were just NUTS!.

Actually, I picked the 221 engine up from the back of a panel shop in Dunedin for free. $300 for the balancing, grinding and minor welding to accomodate the 221 crank into the 250 block. It wasn't just a straight drop in! The 221 had a 8.425 inch deck, and 5.14 inch rods for a 1.48:1 rod ratio. Not a nice combination!

Enough to make anyone CRANKY.

The only thing I can say is I've spent over $1700 to loose 22 cubic inches. It doesn't make the sense I thought it did. And it's still not finished and running yet. I spent too much time making it perfect dynamicaly because a turbo was all part of the plan. It's now a short stroke, long rod mule. It made me feel better when my workmate had to spend the same amount when he broke the automatic on his Subaru SVX Turbo last year!