Ken Thompson":26hcn45a said:
I am having a C5 head rebuilt with new 1.75/1.50 valves, springs, adding a 350cfm holley direct bolt on adapter, 6 to 1 header and shaving the .060. The short block is a stock 250cid engine. I have been told I will loose power with this setup. Why? I am lost.
Thanks,
Ken
Nope, that's not true. But I'll tell you some very imprtant points since this is the Hardocre tech zone.
My wife and I drove a modified automatic 250 engined Falcon from 1995 to 2003. I had 500 Holley, +30 pistons, 256 degree cam, headers and K&N filter. We then used a stock 5 speed 200 Falcon for a week. Same 1984 body, different engines. My wife wouldn't have anything other than the 250. It may not have had lots more power, but in general drivabilty and appeal, she loved the bigger engine. My mate had a 1983 250 Falcon tow car, and then sold it for a 1983 200. He gained 5 mpg on the open road, and lost it all around town, and it was thirstier when towing.
So a 250 wins. Okay, we drive engines in the real world, so don't worry about what is said from here on in.
Now lets get analytical for a moment, and then ask, does it really matter?
Firstly, evidence is that a 250 has less latent power potential than a 200. If you add the same gear on a 200 as you do a 250, the 200 will respond much better for power tha the 250. This is proven by analysing the the facts from performance reports since 1969 and factory net power ratings after 1972 to the last 250's made in Australia after 1988.
Secondly, specifically relating to the US 250, the use of any stock 250 block comes with a major Ford design stuff up...a 100 to 110 thou block mismatch where the geometric edge of each of the six pistons fall short from the top of the block. This is a real problem allowing detonation to occur. Any 250 engine should have the 255 '4.2' V8 or 2500 HSC Taurus/ Topaz piston and rod combination to correct this problem. Its very hard and costly to correct, but there is probably 10 to 15 hp hiding in the 100 thou that Ford missed when paterning up thse engines at the factory. They never, ever fixed the problem.
The modern engine is detonation limited, and you never see a 25% improvement in power in a similar specification 200 because of it. Remember, a 250 is 25% bigger than a 200, and, all else being equal, the power
should go up proportinaly. This is not the case. So any mods to a 250 which don't include a block mod are automatically loosing 10 to 15% of its peak power.
Forget all of that now. What a 250 does have is 25% more torque than a 200. It has boat loads of tire smoking torque. This is the real plus for any modifed 250, you'll see an improvement in torque, but not a great deal of increase in power.
In Australia, our log and 2V 250's had the same 25 thou short fall as 144's, 170's, 188's 200's and 221's, and in each engine, the larger didn't lose out on the horsepower per cubic inches equation. So gross power ratings of 85, 95, 115, 125, 135, 155 hp respectively proved the engines just got tougher and tougher because the heads, carbs and compression ratio when up with each version. The modified 2V had 170 hp. Each engine gained extra power with its capacity increase, and more. Each engine had complimetary changes to suit it, just like your 250 does.
Interestingly, with the more efficient X-flow engine, the 200's were almost as powerfull as the 250's, and this was because the little engine had a better piston surface than the bigger 250.
I am therefore convinced by the evidence from 200 verse 250 comparisons from 1970 to 1984, that a 250 is lucky to see a 9% power boost from a 25% capacity increase EVEN IF it has a 25 thou recesed piston. When you factor in the 4% overall weight the US 250 has over the Us 200, the 250 really loose out in the hp per cubic inch rating.
What 250's have in there favour is torque which exceeds that of any carb 302 V8 from the 650 rpm idle to about 2800 rpm. Your using those revs all the time. And Compared to a 200, there is always 25% more torque at the rear wheels.
. If they did, I'm not going to be happy :roll: .
