dtana

We all know that some stock engines produce more power than others. My question is..........Assuming factory fresh mass produced stock engines made within the last 25 or so years, what is the normal acceptable range in terms of horsepower for engines that are produced & approved for sale?

Pls. don't ask me where (as I can't remember), but I've "heard" that a range of 4% higher to 4% lower than official factory claims is considered within perfectly normal tolerances (I'm guessing I'm not using the correct terminology btw).................& that a range of 8% higher to 8% lower encompasses 95% of engines approved & sold in a given model year. Furthermore, any engine where power is more than 8% lower than advertised is rejected. So to put it in real terms, for a 300hp car, a 8% range would be from 276-324hp & that no advertised 300hp car should leave the factory if it doesn't produce at least 276.

Can anyone confirm that all (or any) of this is correct? If not, can someone speculate as to whether this would be accurate? Thanks.

C4in mesa

Friends of mine have told me that if you want the answer to this question for whatever car or truck you own, take it to a dyno shop and pay the $75-100 for 3-4 pulls and know for certain with paperwork to prove it. I can not answer you question directly as to if there is a discrepancy about factory claims.

dtana

Ok, just to clarify or reiterate............I am not asking about my horsepower numbers or horsepower for any specific car. My question is about what are considered acceptable tolerances within modern massed produced car engines of the same type produced in the same factory in the same year.

dtana

Where are all the engineers who could shed some light on this?

rocco16

I'd say that +/-4% should be about right...maybe a bit less.
I'd also say that this is a calculated number, since the factories do not normally dyno every engine they make so who knows what the actual range is. I doubt if the factory engineers know.

When developing an engine package, the factories do dyno the development engines, so they know what the output range is on a very small number of engines made with the same components.
I doubt if there are many engines that deviate from the nominal by very much. After all, what are the chances of one engine being the recipient of every component being on the "best" side of manufacturing tolerances for power production: have a cam with every lobe having the max allowable lift, every piston having the most clearance, every rod having the max length, every combustion chamber being the smallest in volume, every valve seat being perfectly, every injector orifice being perfect, etc.?
Every engine will have components that are on the good side of allowable tolerances, and components that are on the bad side of allowable tolerances.
It all evens out considering the components in an engine.

c4cruiser

Engine components today are manufactured to some very tight tolerances. That's smply because of the methods used to make the pieces. Computer designed to certain specs that are tight and the manufacturing equipment is designed to meet a very narrow spec range. And QC is done constantly so any component that is out of spec would be found and rejected. Same with engine assembly; a lot of the work is done by robots. And with computer controls for engine operation, I would expect that the +/- tolerances for performance figures would be very small.

Now for engines that are hand assembled (like the Z06 engines, you may see a difference or maybe not). Going back to the '90 C4 ZR-1 motors, it was possible to see as much as a 50HP difference from the advertised 375HP figures. That was in part because of the hand-built aspect of the motors. Cam timing and even how the vacuum actuators for the secondary butterflies were installed (some got installed upside down which resulted in a good 30HP or drop at WOT) were factors in having a wide sweep of performance in those particular engines.

But with the level of automation today, there's no reason why every production engine coming off an assembly line should not be within a very small range of power output.

dtana

C4cruiser & Rocco16..........Thx. for the thoughtful replies. They make a lot of sense. I was very surprised to hear about the wide variance in power with the ZR-1s. One would think that GM would have had a much better handle on that situation especially considering how much money the car cost new.

One last question. If it is correct to assume that (as a rule) modern mass produced engines have a small power output variance, then what about the case of the LT-4s? Is it just wishful thinking on the part of some owners on the internet............ or is there truth to the rumor that those cars were "conservatively" rated for HP as a matter of some policy ?

cv67

Look at most car forums so many want to believe thier car was underrated. Only a few purposely were way back in the day

My take right or wrong is there is a wide variance in dyno #s, an operator can make them read whatever he wants to a point the customer will never know the difference keeps them coming back.

Track times never lie though

dtana

Though I don't know enough about dynos to agree or disagree with your suggestion................I'd respectfully suggest that "track times" can indeed lie quite a bit as well. Or perhaps a better term than "lie" might be something like "mislead".

C4in mesa

I agree 100% track times NEVER lie. But with the LT-4 being rated at 330HP think about this , different heads, different cam, different intake and roller rocker arms. Seems to me that would all add up to more than 30 horsepower. The OP asked a question that definitely has cause to scratch your head. This reference that dyno shops will manipulate the data makes me second guess just taking it to ANY shop.

dtana

As for the suggestion that a dyno shop technician may be manipulating data for some nefarious purpose.............I can see that as a distinct possibility if the dyno shop also did the work for you. But in other situations I'm not sure if it's really that good business. Though I suppose that since most people yearn for positive reinforcement the temptation would always be under-report early & bump up the numbers as the modifications come in. BUT, my initial question had to do with "stock" vehicles..........not modified ones, if you guys recall.

I guess I'm not getting why some of you guys keep saying that track times NEVER lie. A dyno shop is a much more controlled environment than a track I would argue...........& that is what you would ideally want. Also, being .10 or .20 faster or slower on a track could come down to way more factors on a track compared to inside a shop. Besides, though I've "heard" people casually say that .10 faster equals 10hp more, I'm not sure if anyone has tried to prove or disprove that notion & whether that applies universally or only for Vettes.

9T3VETTE

I would say that is a safe assumption. Over the years (especially the last 20) QC has risen to a new level. With such tight tolerances on components and the added quality measures in factories for completed products, anything out of that spec is scrapped or reworked. On the same note, continuous improvement ideas and things like DFSS (design for six sigma) are hot topics to improve the quality of products produced. In turn this is related directly to the variance (engine HP in this case) in completed engines. The average Joe would be astonished to see the amount of work that is put towards having standards and quality products coming from OEM plants.

rocco16

There is a difference between factories giving conservative ratings and engines having wide variations in output.

While I believe that 330hp may be a slightly conservative rating by Chevy when the LT-4 was offered (340 may be more realistic), I don't believe that individual engines varied from 330 to 380hp as is sometimes claimed. That just is not likely (maybe not possible?) in today's modern manufacturing.

markKlein

[QUOTE=dtana;1586298496]We all know that some stock engines produce more power than others. My question is..........Assuming factory fresh mass produced stock engines made within the last 25 or so years, what is the normal acceptable range in terms of horsepower for engines that are produced & approved for sale?

Pls. don't ask me where (as I can't remember), but I've "heard" that a range of 4% higher to 4% lower than official factory claims is considered within perfectly normal tolerances (I'm guessing I'm not using the correct terminology btw).................& that a range of 8% higher to 8% lower encompasses 95% of engines approved & sold in a given model year. Furthermore, any engine where power is more than 8% lower than advertised is rejected. So to put it in real terms, for a 300hp car, a 8% range would be from 276-324hp & that no advertised 300hp car should leave the factory if it doesn't produce at least 276.

I don't think so, as stated above, they don't dyno every car coming off the line, so how would they ever know?

Black89Z51

There is a tolerance specified by the SAE engineers. I can't for the life of me find it though.

volkswagens-for-life

It's impossible for a track time to lie. It's very possible for different dyno's to lie.


If you have a car advertised @ 275hp but you run consistent high 12's... who's the real winner? 275hp or high 12'?

dtana

Define "consistent high 12's". Are you saying 12.7, 12.8, 12.9 or 12.95?? Or all of the above?
Because the difference in HP could be as much as 25-35 HP between the high & low numbers with a car of the Corvettes weight. To say nothing of the weather, temperature, track consistency, driver consistency etc etc. I suspect dynos of the same model operated honestly & under consistent parameters will not produce variances in the 25-35 HP range.

Also it is noteworthy to point out that quarter mile times are but one measure of performance just as HP numbers whether accurate or not are but one item in determining how fast a car can go from A to B.

volkswagens-for-life

If you've got 100hp but run 11 second 1/4 mile times, which one are you more concerned with

In all reality, a dyno doesn't do anything for me other than bragging rights. I'd rather have a 300whp c4 corvette that runs 12's or faster than a 450hp new charger that runs 13's.

1lndonr

Track times rarely are good indications of power. Track temperatures, humidity (dewpoint), tire composition, suspension condition, auto or manual transmission, and driver skill all affect track times. The only real test is a calibrated dyno and all testing done on the same dyno.

In the 1960's we paid huge premiums to blueprint a complete engine and even then tolerances were within .005 in. Today's engines having been manufactured with computer controlled machines which routinely hold tolerances to .0001 in. Completely unheard of in the '60's. This is why engines of recent manufacture commonly run 150,000 to 200,000 miles before teardown.

phoneman91

I believe that most published SAE net ratings are purposely low. And that there is as much as a 10 percent - + variation from SAE published net ratings . Especially after the 1999 Cobra issue,most engine SAE net ratings are low.

I also believe that how a new engine is broken in accounts for much of the stock variation in performance and power output.