69CSHC

Guys I was watching this vid recently and something Bud Lindemann (Car and Track) said was a bit of an eye opener. He was reviewing a 1971 Chevy Camaro 350 2BBL and said that the factory HP rating could be off as much as 15 HP between 2 engines built on the same day according to engineers. ( from 0:40 to 0:50 seconds )

Was this common among all manufacturers or more of a Chevy thing considering they were more bargain buy orientated ?

joe_padavano

This is called manufacturing variance, and yes it is common with mass-produced engines, especially in that time frame. As emissions and CAFE laws got more strict, automakers have significantly reduced variability from one engine to the next, but in the 60s and early 70s, manufacturing tolerances were somewhat looser. That's why when you read a number on something like flow rate of an OEM head, or chamber volume, take it with a grain of salt. Production variability was greater than the precision on the measurement. This is why you blueprint a motor.

OLDSter Ralph

One clarification I would make. I think you mean factory horsepower OUTPUT, not factory horsepower rating. As Joe P pointed out, thats why you blueprint an engine.

Andy

Back in the day someone always had what we called a factory freak..Car that was stock and quicker than others..they just happened to buy the car were all the tolerances were right.. buddy of mine had a 68 gto 3 speed manual trans that was one of these cars .out ran any other gto, and many other higher horse rated cars, one being a boss 351 mustang another friend had..that boss should have easily outran that goat.

BangScreech4-4-2

Not sure I'm clear on the difference, Ralph. What about rated output? Can you elaborate?

VORTECPRO

Sure it could, I build Chevies constantly, the crankshaft stroke can vary .010 from throw to throw, the heads can have horrible core shift, the blocks can have crazy core shift, connecting rod length will always vary, all these things can have an effect on compression and flow through the intake tract.

joe_padavano

Actual output is what you get at the flywheel from a specific engine. "Rated" output is what the marketing department said to put in the ads. Once again I'll point out that the AT version of the 1970 W-30 came with the 285/287 deg cam used in every other non-W 442 with automatic that year (as well as the W-33 Delta and W-34 Toro). The MT version of the 1970 W-30 came with the 328/328 cam that wouldn't generate enough vacuum to operate power brakes or even the power piston in the Qjet. Both of these motors were rated at the same 370 HP output. Do you really think they ACTUALLY made the same HP? And this doesn't even begin to account for manufacturing tolerances as we've been talking about.

VORTECPRO

Your opinion on what factory stock 1970 W-30 would make on the dyno with headers?

OLDSter Ralph

Thanks Joe P, thats a better description.

69CSHC

Sorry guys my mistake, I misworded my post. Bud Lindemann actually says "delivering somewhere around 245 horsepower". Delivering being the operative word. What the engine actual produces not what its said to produce.

Natural born ringers. Your right, have come across those seemingly special cars. Built on the right day of the week...


As a kid I always remember hearing "you want to buy a car that's not built on Monday or Friday" or something to that effect. Meaning people are just getting back into the work routine at beginning of the week and people are just going through the motions eagerly waiting to get out of work at end of week ?

If that has any merit, I wonder if that is contributing factor to some of these variances. Or does that speak to lemons ? Or is all that just malarkey and its just a case of, it is what it is ?

P.S. thanks for the responses one and all.

OLDSter Ralph

"Delivering" is the keyword. "Natural born ringers" is more elusive to explain. Those can be a product of random occurrence of the right parts coming together on the same engine. Or engine tuning. Or both. Not everyone tuned to factory tune up specs. Bumping the time a few extra degrees can make a difference.
Since I have worked in factories and near assembly lines in my past life, I can give you my observation on the "Monday or Friday" theory. I think alertness is sharpest and attitude is better after the first "coffee break" on any shift. The first two hours on Monday and last two hours on Friday could be different, assuming No Saturday O.T. shifts or Sunday night "Startup shifts". I am sure that "Behavioral psychologists" could spin a different tale.
On the subject of "random occurrence of the right parts", let me suggest this. In the case of machining cylinder heads and engine blocks Large milling cutters with carbide inserts are used. In the case of cylinder heads, some machine operators would set the machine to mill to the "low side" (minimum combustion chamber volume) of the tolerance range, and as the carbide inserts wore down, the amount of material removed would decrease and would machine them toward the middle of the tolerance range. If the machine operator set the machine to the middle, it would wear to the high end of the tolerance range. Typically the machine operator would run the machine til the surface finish deteriorated or parts would go out of tolerance. Parts would be checked at prescribed intervals, such as every 25 parts. In the case of engine block machining, this scenario would also explain the differences in deck heights.
Assemble an engine block milled to the "low side" of deck heights (in the hole measurement} and cylinder heads machined to the "low side" (smaller combustion chamber volume) and you have an engine with more compression and more horsepower than another engine. Assuming this batch engines coming down the "line" were similar, they would hit the assembly line and be installed consecutively in cars that were dispersed to all parts of the country.
........Just me two cents worth.

joe_padavano

Well, to add one more layer of confusion here, there's the whole gross vs net horsepower rating thing. 1971 was the only year that Olds published both numbers.

android 211

Joe Oldham said something to the effect that if you build 3 identical motors one will be a stone, one will perform as you expect and one will be a screamer.

Koda

Nowadays, as I sit in a car factory on my lunch break writing this, I don't think that the Monday or Friday thing holds water in this manner. It's more of a "we forgot this part" or something did not get torqued down. By this I mean that the machinery is so automated, with the programs locked in, that it either goes together right, or something is forgotten, or something, like a socket, broke. There is very little decision making left to a line guy.

I worked on a short block sub assembly line in the Toyota WV plant at the beginning of my career. We were putting in the new GR engine line, of which the 2-GR powers the majority of the medium and kinda large Toyotas. As I recall, the blocks came from the machining lines (and these were all CNC mills doing the cutting on the blocks) with main caps on, and, after they went through the block washer, they would get one of four sets of bearings based on measurements that had been taken by a machine previously while it was still fixtured. These would address block main journal tolerance. I also recall the cranks just came to us as a part from Louisville Forge, and the pistons were assembled on piston sub line, but I don't think there was any variance to be selected in rings, or con rod bearings, or piston diameter.

They used to run for a lot every engine in the test rooms, but now I think they only do like every 6 or so and just fire up the rest briefly. All engines get spun by the crank nut for correct rotational force and some other checks. At the vehicle plants, like the one I am in now, there are two chassis dynos, one for checking power, and one for checking braking, that the cars go through on their way to the sales door. Flunk those, and it gets sent to confirmation area to be fixed. Those are function and vibration checks, not pulling HP or torque.

69CSHC

Joe I consider this information one of my favorites. Downloaded it from one of your postings a while back. Kept at the ready on my desktop. It helps provide some clarity were there was none.

I believe I may of heard that before and it falls right in line with this discussion.

Ralph, Koda, I really appreciate the insight. I took it all in, every bit of it.

Thanks again guys, one and all.