Power increase

[plee4139]

The 289 in my Skyhawk has been over bored from 0.030 to 0.060 and has quite a bit more power. It hasn't been modified in any other way. The original HP was rated at 210. What would the rating be now?

[PackardV8]

Peter, the increased compression and ten more cubic inches should be worth 6 - 8 horsepower more. Chances are, you're just feeling it develop the rated 210 horsepower of a new engine versus the lower power of the previously worn-out.

jack vines

[thunderations]

You would need to dyno the engine to get that info. You were probably way low on HP before the rebuild, so just getting close to the original HP would seem like a vast improvement. I would expect less then 10 HP over new.

[Dick Steinkamp]

Your .030 over motor had 294 cubic inches. At .060 over it has 299 cubic inches. If the stock 289 had 210 gross HP and if the overbore was the only change, you could probably expect the 294 to have 214 HP and the 299 to have 217.

(210/289 X 294 or 299)

As Jack says, the increased compression due to the overbore (and maybe a little higher CR if the deck and heads were trued up and/or thinner head gaskets used) might give you a couple more HP.

[swvalcon]

What Jack and Dick said. What your feeling is the difference you feel in a new car and your old one on it's last leg trade in.

[Mike Van Veghten]

One more power adder..!

The fact that you spent a hand full of money on your new engine, your mind is telling you...that it was all worth it..!

Mike

[jclary]

Well, the added power is great when appreciated and handled with reason and care. Back in my hell raising days, an Air Force buddy of mine bought a great little 56 Chevy coupe. Supposedly, it had a freshly souped up (whatever that meant) 283 engine. One weekend (1966) we drove the 250 miles to my home. I was driving it when we encountered one of my hometown buddies driving his Buick. He challenged us to a little street race, while I was driving the Chevy. My Air Force pal (the owner) kept telling me to floor it...and I did...till the engine came apart!

The bib overall wearing country mechanic who fixed the damage, gave us a lecture about how much pressure was on the crank journals in that 283 when it was factory stock. Then, like a school principal scolding two little boys, he explained how much the extra power from the overbore was way more pressure than the undersized crank could handle from it being turned and oversize bearings installed. It was an expensive lesson for both of us. I offered to pay a share of the repair, but my friend manned up and took responsibility for urging me to keep flooring the gas when I wanted to back off.

Bottom line is that if you overhaul an engine and it results in more power...make sure you understand that more power does not mean all the components are up to the task of handling the power. There is a huge difference in an overhauled/rebuilt engine...and building a "performance" engine.

[64Avanti]

Well back then that 283 couldn't have been souped up enough to cause an engine failure. In fact the bearing sizes should have supported more than 500 hp without anything else wrong. The mechanic was just giving an excuse for why the engine failed!

[Jerry Forrester]

extra power from the overbore was way more pressure than the undersized crank could handle from it being turned and oversize bearings installed.

bs bs bs bs

[sals54]

When I did the overbore, R2 cam, .125 milling off the head with thin gasket to boost compression, over sized valves, Z28 dual valve springs, ported and gasket matched on intake, exhaust and carb, hogged out the bowl area above the valves, gasket matched and hogged out the exhaust manifolds, ran 2-1/2" exhaust, it didn't seem to bother the stock bottom end of the engine at all. Even after 10 years of beating it like I stole it.
It's more likely that you did something else to hurt the bottom end than just an oversized bearing. Or else why would they continue selling the bearings for 50 years. Folks would be pretty sore by then.

[jclary]

bs bs bs bs

Well...I didn't own it...never knew who built it...and really didn't care. All I know is that Jim (the owner) and I had to hitchhike back to the base, be there on time to keep from being AWOL. The old mechanic that chided us about the engine repaired it, Jim paid for the repair and then sold the car. By the end of that year, he was reassigned to another base and I wound up at an AF base in Austin, Texas. I always felt bad 'bout blowing Jim's engine.

My thinking is that it had not really been properly rebuilt in the first place. Just another case of a young military kid away from home desperately wanting a car to drive and eager to accept the bull from a slick used car salesman. I had taken a part-time job off base and the best I could do was a little Honda Motorcycle and an old mid-'50's Cushman scooter.

Jim was a good New York kid a long way from home on the coast of South Carolina. We lost contact after getting assigned to duties at different bases. I hope he's had a good life.

[jrlemke]

I wouldn't worry about the bottom end, the 4 bbl 289 was rated at 225 hp from the factory. As far as I know, the only difference was the 4 bbl carb. I think the "Chicken Hawk" and the"Stude Tomato" and the supercharged Studes have stock bottom ends. -Jim

[StudeNorm]

I am sure the bottom ends were all pretty much stock in the Granatelli Studes, Ron Hall's and all the rest that manage to pull 600+hp from the engine. I'm also sure someone will speak up if I am wrong.

[StudeRich]

Somehow after John's post, we got into Chevies and then back to Studes, all pretty much unrelated.

Everyone knows a short stroke Chev. bottom end, with small Rods, Mains and a weak thin wall Block cannot take what a Stude. V8 can!

[jclary]

Somehow after John's post, we got into Chevies and then back to Studes, all pretty much unrelated.

Everyone knows a short stroke Chev. bottom end, with small Rods, Mains and a weak thin wall Block cannot take what a Stude. V8 can!

Thanks, Rich...perhaps I just lack the ability to articulate, but you seem to have read and understood my point. I was not attacking either Studebaker or Chevy engine quality, but certainly just because someone repairs an engine and increases the power, does not necessarily mean that all the components can handle the power. My point was that apparently the Chevy engine was overbored, and the bottom end was undercut to the point that it had weakened the crank, and or rods, etc... Also, it is possible that the work was just plain sloppy.