ajmclean

i hear rumors that chevy under-rated the announced horsepower for TPI engined 5.0 and 5.7
so i was wondering if any of u guys who tested ur stock
cars at a Dyno ,

did u find hp different from GM HP ratings?

mainly im interested in 1985 305 TPI rated at 215 hp

and the 350 TPI all years ranged from 220-245

firebirdjosh

iTrader: (1)

I highly doubt a 305 from 85 was pushing over 215hp stock.

ajmclean

but it's will known that they underrated

the TTA , but im not sure if that was the case with camaros

Fmandan

IF they are underrated it's not by much. (5-10hp max). Most TPI 350 cars make very low 200's on a rear wheel dyno in stock form.

Sonix

iTrader: (1)

I think it's that most people think it "feels" like it's got gobs of power, due to the low rpm torque, and the incredible throttle response. You take a 215HP second gen say, and drive it, then take an IROC with TPI, and yea, that IROC feels much faster. (then again you've got weight on your side with that comparison too...)

84z28350

It might just feel powerful with its loads of torque. I think it was a bit earlier in the game (60-70) that engines were way under rated.

Fast355

iTrader: (2)

Mine was 165 HP @ 3,800 and 250 ft/lbs @ 2,400 at the wheels bone stock. It was a 1983 LE9 though. Factory rated at 175 HP @ 3,800 and 275 ft/lbs @ 1,600. 9.2:1 compression, 52 cc 267 heads (1.84 & 1.50 valves), 70s style cast iorn log manifolds, stock 2" dual exhaust, factory air cleaner, stock 4* timing spec, etc. Less than $300.00 had me at 185 RWHP and 285 ft/lbs though. Opened up the intake with a later model air cleaner and snorkel, K&N filter, later style manifolds with 2 1/4" outlets, 2 1/4" duals with glasspacks and H-pipe, recurved distributer,went from K to a F-hanger on secondaries(already had DR rods), adjusted secondary air valve (slightly tighter than bog when mashed), and tune-up.

Red Devil

No.

BigWhiteGTP

Yes! My '91 5.0Tpi auto with 77K miles put down 187whp and 267wtq! Dyno-Jet proven. So multiply by 20% and you get roughly 230hp and 320tq. So that's 15hp more and 20lbs of torque more.

However, I plan on dynoing my car again with the cai installed and catback unbolted to see how much it gains. I hope to hit 200whp and 275tq. Then headers & ported TPI and dyno it again. And so on and so on.

rx7speed

now what happens if you put it on another dyno? like lets say a mustang dyno (again I'm playing devils advocate in a way)
also who knows how the tech had the dyno setup.
also the whole 20% thing is not the greatest way to guess drivetrain loss

but if nothing else you did at least setup a benchwork hopefully (again pending tech error) to test your settings against

firebirdjosh

iTrader: (1)

Especially since you can't do it backwards the way BigWhiteGTP did . The whole 20% is not interchangable. You have 100 engine horsepower, thats 80 to the wheels then. But you can't say you have 80 to the wheels and multiply 20%, giving you 96hp. Also, someone needs to clarify wheel and engine HP becuase obviously people are mixing them up and using whatever number supports their argument.

BigWhiteGTP

Sorry, I don't see any other way to tell crank horsepower & torque then. Please let me know. All it the 20% rule is guesstimate. My GTP put down 195hp and 265tq multiply by 1.20 and you get the factory hp rating of 240 and 325tq. This is another example of GM's underrating of power. GTP's are advertised to only have 280tq at the motor. LT1's if they have 275-285hp, with DT loss of "assumed" 12-15% for manual and 20% for automatic, then they should have 230hp at the wheels for a manual and 220whp for autos. Then why do the M6's put down 245-250whp and autos put around 235? Either GM trannies, which are already superior to everyone elses in terms of DT loss, are even more superior only giving up 5-10% DT loss - OR- GM underrates their cars for insurance and warranty sake. And we all know about the LS1 and TTA numbers don't we.

I think I'll go with the latter.

Also, Mustang Dynos are way to conservative. If a car is supposed to put down 240hp and it's ran on a Mustang it will only get 220hp. I don't trust Mustang Dynos. And I especially don't like wasting my time and $$ on them.

redbird_400

85 Z28
Trans Am A4 LB9 V8 9.5:1 5.0 (305) 215@4400 275@3200 TPI ---- ---- 3.23

https://www.thirdgen.org/newdesign/tech/techdb.shtml


hmm... from the thirdgen page, does this mean that all of these posts are at the flywheel

rx7speed

mustang dynos are way too conservative you say right? but then agian put the same car on a dynojet and now it comes out to GM underrates their cars? and they put out more power then what the factory says?
maybe the mustang is being a little more realistic and GM isn't underrating their cars it's just the dynojet reads a little higher and makes ppl think oh hey GM underrated me I really have more power then what they claim

and I never heard that GM trannies where superior to everyone else in terms of drivetrain loss. not playing devils here I actually never heard that.

and what is underrating your car going to do for warrenty sake?

BigWhiteGTP

My point is that Mustang dynos are notorious for giving lower numbers, be it conservative or realistic. IF Mustang dynos were realistic then there would be lawsuits against every automanufacturer for false advertisement and all that crap.

Red Devil

Mustang dynos have been shown to be more accurate dyno to dyno amd dyno to track than dynojets.

Why the lawsuits? Import cars just had to 'fix' their computations recently, and none of the advertised HP numbers actually equate to real world numbers. I don't see any lawsuits with regard to either. Hell the advertised mpg formula is under fire and getting 'fixed' as well.

Dynojets are also shunned by quite a few power added cars because they don't load properly and the drums are a tad too large as compared to the Mustang dynos... unless your car actually is near the 5,000 lb mark or whatever the dynojets have as roller weight.

This is of course n0owithstanding the fact that the mustang dynos can typically convert over to 'dynojet' numbers rather accurately to boot.

Fast355

iTrader: (2)

Mustang IMO is the far superior dyno. You can accurately load your engine at part throttle with a wideband attached and do tuning on your engine. You can then reprogram it and make HP pulls while tweaking timing and fuel mixture. Then you can put it into the simulated 1/8 or 1/4 mile and change shift points and get an accurate reading. No ?s asked on the correct tune. Worked very well for me.

My 305 made 245 RWHP on the mustang. It is around 300 at the crank on fairly accurate programs and other similar builds. On a dynojet it would be higher.

rx7speed

forgot about that part of a mustang dyno

dynojets only allow full throttle tuning don't they?
and to my opinion being able to tune at partial throttle and full throttle is much more important then only full throttle tuning.

onebad84z28

Factory horsepower ratings are done with all accessories installed and operating,and are measured at rear of the transmission.This is from chiltons repair manual. also says it may vary from model to model.

Fast355

iTrader: (2)

Exactly, that is why with the A/C off you typically see close to the rated HP at the wheels.

DarthD

I know this topic is a little old but I just read it and I hate when false information is given as if it is a fact, so I have to make a few corrections.


quote:
--------------------------------------------------------------------------------
Originally posted by onebad84z28
Factory horsepower ratings are done with all accessories installed and operating, and are measured at rear of the transmission. This is from Chilton’s repair manual. also says it may vary from model to model.
--------------------------------------------------------------------------------

Factory horsepower ratings are NOT measured at the rear of the transmission. Chilton’s is dead wrong. They are measured at the flywheel. If you do not wish to believe me then you can go to www.SAE.org search for J1349 and purchase the paper from them. This is the standard that all OEMs follow for dyno testing engines.



You do not lose power with A/C on when under full throttle. The A/C cuts off during this time. Have you ever noticed during full throttle acceleration, with the A/C on, the air will become warm?



Mustang dynos are not more accurate than Dyno Jets. Don't take my word for it, go to http://www.mustangdyne.com/. They state that both styles of dyno are equally accurate.

The Mustang dyno shows lower numbers because they calculate more losses than the Dyno Jet. The Mustang Dyno takes into consideration the weight, and the aero dynamics of the car. The Mustang Dyno basically dynos the whole car while a Dyno Jet only dynos the drive train. The Mustang Dyno shows how much power is left over to accelerate the vehicle after all losses have been subtracted.

THEORY-
Let's say you dyno a small car on a Dyno Jet and it shows 300 RWHP. Then, you dyno it on a Mustang Dyno and it shows 275 RWHP. Next, you pull the entire drive train and install it in a big heavy car and dyno it on both dynos. The dynojet should still show about 300 hp, but the Mustang dyno may show only 250 hp because the big car weighs more and has more aero drag, so it will consume more power driving down the road.

Due to these extra inputs that the Mustang dyno uses, it does add an extra degree of potential human error to end result, but a Mustang dyno will function without the extra information and should be very close to a Dyno Jet.

I hope this clears up any confusion.

Fast355

iTrader: (2)

Not to argue to much but I have some 1994 chevy truck literature right in front of me. Okay, on the NET HP somebody should have told GM, why does GM literature of this time say that they are rating at the output shaft with all accessories installed and operating as installed in a vehicle, as well.

What makes you think that ALL vehicles have a WOT A/C cutout. They don't!!! I have towed @ WOT and 3,000 RPM many times, for several miles at a time with ice cold A/C. You can't tell me that the A6 compressor that was on my G20 to begin with didn't suck HP @ WOT during passing accelerations. It did big time, like 20+ off a 180 HP 305. Definately something you could feel. That is why I found a WOT A/C cutout switch for a 442 olds that mounted on the accelerator pedal bracket, like an old TH 400 passing gear switch. My 1988 GMC Jimmy didn't have a WOT A/C cutout either and the power sucked off the old stock 125HP 2.8 was even more noticeable. Hell, pedal to the floor, A/C on with the stock engine got you 80 MPH, A/C off got you close to 90. I always had to turn the A/C off prior to passing, even then I had to give it 100%.

As far as the dynos, I am after the power available to drive the car, not just the drivetrain power. For what I am doing I have found the Mustang superior in most aspects. Pretty simple, for bragging rights go to a Dynojet for the right tune go to a Mustang. They maybe both as accurate, but for realistic go to a Mustang.

Also on your theory part, lets take an extreme example, say we pull my 300 RWHP 312 out of my G20 which is taking 30 HP to go 60 MPH and weighs 5,300 lbs (#s put in the Mustang). What would it make in a Camaro that weighs 3,500 lbs and only takes 18 HP to go 60? Do we simply take and add 12 HP back on my numbers? Then lets say we put the same 312 in a 1,700 lbs T-Bucket. Then what would it make on the DynoJet?

DarthD

I'm not sure about the GM literature. What output shaft are they talking about? Could they be calling the end of the crank an output shaft? Those pamphlets do not always have the most accurate information. They are probably put together by marketing people who do not know a connecting rod from a push rod.

The engines are rated at the flywheel with all accessories installed. This is a fact. SAE J1349 is the standard that all the OEM's use.

I never said all cars have an A/C cut off. I'm sure some do not.
I was thinking of F body's as this is what ajmclean was asking about.

Both dynos work well for testing power gains but the Mustang dyno does have the advantage of being able to simulate a 1/4 mile run, and they can be used for part throttle tuning as well. So, I agree that the Mustang is probably the best choice tuning.

As for the G20 engine going into the Camaro, yes I believe it will show more power on a Mustang Dyno, and the T bucket would show even more.
The Dynojet should read about the same power for all three vehicles as long as you are transferring the entire drive train. (Including tires)

This is just my theory based on what I have learned about the dynos. If someone knows why this would not be true please let me know.

rx7speed

gm might rate their cars with net hp. actually I think just about everyone does anymore.
but what does that have to do with flywheel vs wheels for horsepower?

Air_Adam

GM started measuring net HP in 1973.

Realmac4

iTrader: (2)

My stock '91 350 TPI, 6 speed, headers, cat-back, 3.73 rear pulled 245 hp at the wheels, which shocked everyone. Those are dyno numbers, too.
Mike

AJ_92RS

But you can divide it by 80% (0.8) and get 100 hp.

What part of math class did you miss?

Take 300 hp x 80% (20% loss) = 240 hp

Now take 240 ÷ 80% (or .8) = 300 hp

Regardless, "20% drivetrain loss" is the most vague way of guessing and highly inaccurate. The only true way to find out the drivetrain loss is to do an engine dyno run, then a chassis dyno run. But even then you're relying on the accuracy of two different machines, two different operators, two different environments, etc...

Look at the average '98+ LS1 in the Camaro. Many have made 310+ HP at the rear wheels with the 6 speed, and they're rated at 305-310 HP from the factory. 310 HP puts them at 364.7 HP with a 15% drivetrain loss.

That puts them ~ 20 HP higher than the 'Vette's HP rating, and we all know that's not possible. Corvette engines are the Godsend of engines.

dimented24x7

iTrader: (2)

Depends on the year and options. I know some of teh early 90's trucks had the A/C cutoff and my daily driver has it as well. Its probably there more to prevent abuse to the compressor more then anything else. AFAIK, most of the earlier V8 cars/trucks just ahve it come on when the HVAC head calls for A/C.

Damon

LS-1s are underrated, no doubt.

GM originally planned on putting a milder cam in the f-body version of the LS-1 but that never happened- they're near identical motors except for the different intake/exhaust systems. The marketing literature, however, couldn't possibly show a lowly Camaro getting the same HP as the mighty Vette, so they just arbitrarily rated it at a lower HP number in the brochures.

LS-1 Corvettes usually put down almost identical HP as their F-body cousins (around 300). Their intake and exhaust are slightly less restrictive than the F-body but the added HP is used up spinning all those extra u-joints and driveshafts in the Vette's independent rear end.

This wouldn't be the first time GM underrated an engine. There's been many a debate on THIS BOARD about the cams the factory put in 305 TPI engines in automatic trans cars. IN THEORY they all got the "peanut cam" and the lower 190-195HP rating if you beleive the literature. Reality, from the experience of many board members here, is that sometime around 1990 GM started shoving the hotter "good guy" cam into ALL 305 TPIs- regardless of whether it was automatic or manual trans. Factory still rated the automatic 305 TPIs about 20HP less, but the reality seems to be they put out as much power as their 5-speed brothers. Easier to change a brochure than to change the engine.

Last one...... GM uses SAE horsepower and torque standards. Your local dyno shop uses a different standard (perhaps someone could chime in on what that standard is- it's on the tip of my tongue). SAE numbers are more conservative than the numbers used at your local dyno or in the magazines. I don't know by how much, but I'd say maybe as high as 10%. Magazines regularly get significantly higher HP out of factory crate motors than GM rates them. I've seen a few articles where an LS-1 crate motor tested by a magazine put 380HP+ on an engine dyno- right out of the box. That's not just being conservative, that's a different ratings standard at work there, IMHO.

Damon

...... as as for TPI engines being "underrated," I don't think so.

Ask anyone who lined up their TPI Camaro against a 5-speed 5.0 Mustang sometime around the mid-late 1980s and they'll tell you that more power would have been very much appreciated. The 5.0 Mustangs used to kick sand in the face of TPI cars back then all the time.

DarthD

I agree that they were not underrated, but power is not why the Mustang was quicker. The Mustang was lighter and had a lower overall 1st gear. However, they were not that much quicker. People seem to remember Mustangs just wasting Camaros. This may have been true overall, but it had more to do with the fact that most Camaros on the road were not TPI cars. Most had the lower hp engines. But, people did not see that. They just saw a 5.0 smoke another Camaro. I hated Camaros when I was in High School, because it seemed that anyone that had one thought they had a quick car, no matter which engine it had. I used to beat them in my truck all the time. It ran high 15's at best. I never raced a TPI car though, and I have seen the error of my ways and love all Camaros now.

I think some of it may be that there was and still is a LOT more performance parts available for the 5.0 than the 3rd gen Camaro. You never know who is stock and who is modded.
Stock for stock, they were pretty close in reality.


I have been collecting hundreds of stock dyno tests and averaging the results. All are from Dyno Jets. With the exception of the cars that are KNOWN to be underrated, a 12% drivetrain loss fits almost perfectly with what the rated power is and what the average RWHP is. I do not have a large enough sample size for automatics yet to come to a conclusion for drivetrain loss.

I am planning to put this data on my web site, but I'm still working on it. (the web site)

Air_Adam

Almost all of GM's crate engines actually are under-rated... GM has even said so. They under rate them intentionally, because then any **** that buys the engine can get the rated HP out of it.

- Example -

383sbc crate engine, GM tunes and dynos it to make about 450hp (just picking numbers here).

Now... get some guy off the street who buys the engine, doesn't really know what he's doing, and can't get more than 400hp out of it after he installs it and breaks it it, but does a poor tuning job on it.

Anyone smell a 'false advertising' claim here?

...Thats why GM under rates their crate engines intentionally. So that anyone off the street can get the advertised numbers out of it, whether they are pros or not.