RWHP on a factory '68 327/300 engine??
09-01-2015, 12:33 PM
#1
Team Owner
Thread Starter
RWHP on a factory '68 327/300 engine??
Has anyone here ever dyno'd (chassis dyno) a factory 327/300 powered '68 Vette with 4 speed transmission? I wonder what kind of RWHP a stock 300 HP 327 produced as I might have my car dyno'd just to see if the mods on the engine and exhaust made a noticeable difference..
My 327 has a performance cam (relatively mild - don't have the specs as it was in the car when I bought it), a Team G intake and a Holley 750 w/ vacuum secondaries and side pipes with maxflow inserts.. I'm curious on what HP difference those mods could be worth??
My 327 has a performance cam (relatively mild - don't have the specs as it was in the car when I bought it), a Team G intake and a Holley 750 w/ vacuum secondaries and side pipes with maxflow inserts.. I'm curious on what HP difference those mods could be worth??
09-01-2015, 01:04 PM
#3
Team Owner
Thread Starter
That sounds about right based on the standard calculation.. I'm not sure.. HP was rated differently until 1970.. I believe that the HP rating on pre 1971 cars was engine HP less accessories and from 1971 and later, the accessories were considered in the rating. So, a 300 HP engine in 1968 would have been rated about 270 engine HP rating in 1971. So, if you subtract 15% drivetrain loss from 300 HP, you get to 255 HP which is more or less what you suggested but if your starting point is 270 HP which is the way HP has been rated since 1971, you will get to 229.5 HP.
I believe that DRIVETRAIN loss is about 15% but then you also have to add accessory loss for another 5 to 10% I believe.. So, I would "expect" a stock 327 from '68 to dyno around 230 HP or less but I'm not sure. I'd like to see actual dyno numbers for stock '68 base cars.
I believe that DRIVETRAIN loss is about 15% but then you also have to add accessory loss for another 5 to 10% I believe.. So, I would "expect" a stock 327 from '68 to dyno around 230 HP or less but I'm not sure. I'd like to see actual dyno numbers for stock '68 base cars.
09-01-2015, 01:12 PM
#4
It would be interesting to see the numbers. IF it had an automatic I would think closer to 20% loss or more. The 4 speed helps you there a little I think. Although the factory I don't think ever rated the HP different from AT to MT...I assume we are talking PS as well? Stock fan?
I thought the HP rating change came in 1972...I could be wrong.
I have also read that motors will lose HP over the years due to wear. Something in the 1 to 2 HP per year which at best is a guess. So a 30 years old motor could naturally lose 30 to 60 HP just to age and wear.
I thought the HP rating change came in 1972...I could be wrong.
I have also read that motors will lose HP over the years due to wear. Something in the 1 to 2 HP per year which at best is a guess. So a 30 years old motor could naturally lose 30 to 60 HP just to age and wear.
Last edited by Dean_Fuller; 09-01-2015 at 01:15 PM.
09-01-2015, 01:28 PM
#5
Team Owner
Thread Starter
It would be interesting to see the numbers. IF it had an automatic I would think closer to 20% loss or more. The 4 speed helps you there a little I think. Although the factory I don't think ever rated the HP different from AT to MT...I assume we are talking PS as well? Stock fan?
I thought the HP rating change came in 1972...I could be wrong.
I have also read that motors will lose HP over the years due to wear. Something in the 1 to 2 HP per year which at best is a guess. So a 30 years old motor could naturally lose 30 to 60 HP just to age and wear.
I thought the HP rating change came in 1972...I could be wrong.
I have also read that motors will lose HP over the years due to wear. Something in the 1 to 2 HP per year which at best is a guess. So a 30 years old motor could naturally lose 30 to 60 HP just to age and wear.
09-01-2015, 01:31 PM
#6
Team Owner
I think it will be a bit lower. The 1971 base engine was rated at 270 gross hp. The 1972 engine was rated at 200 net hp. I don't think there was much difference in the engines.
The 1968 300 gross rating was probably around 225 net. That would be at most 200 hp at the rear wheels on a dyno.
The 1968 300 gross rating was probably around 225 net. That would be at most 200 hp at the rear wheels on a dyno.
09-01-2015, 01:36 PM
#7
Team Owner
Thread Starter
I think it will be a bit lower. The 1971 base engine was rated at 270 gross hp. The 1972 engine was rated at 200 net hp. I don't think there was much difference in the engines.
The 1968 300 gross rating was probably around 225 net. That would be at most 200 hp at the rear wheels on a dyno.
The 1968 300 gross rating was probably around 225 net. That would be at most 200 hp at the rear wheels on a dyno.
My understanding is that the HP rating until 1970 was engine dyno numbers WITHOUT accessories (no alternator, no fan, no mufflers (open headers) and starting in 1971, they would use engine dyno numbers with all the factory accessories and factory exhaust. That reduced the power by 10%. Add another 12 to 15% for drivetrain loss with manual or 20 to 25% for TH400 and you will see a total loss..
It all depends on what accessories were used on the engine dyno. If it was dyno'd with all factory accessories, 12 to 15% drivetrain loss (with manual transmission) sounds reasonable but if it was dyno'd without accessories, you have to expect AT LEAST 20%, more likely 25% with MT and 30% with AT.. At least, my personal dyno experiences seem to indicate that.
Modern cars are all rated with engine dyno numbers with all factory accessories.. That's why C5's C6's and C7's usually only have about 12.5% drivetrain loss as accessory loss is already part of the engine dyno numbers for those cars.
Last edited by GrandSportC3; 09-01-2015 at 01:39 PM.
09-01-2015, 01:44 PM
#8
Drifting
I'm curious too, mine is a completely stock base car, 327/300hp, 3spd auto, 3:08 rear axle, with 67,000 on it. Motor was verified as original to car- block, heads, carb. If I had to guess, I would say 200 horse, I'm embarrassed to say a Honda will beat it. I does drive beautifully though.
09-01-2015, 01:59 PM
#9
Team Owner
Actually, the reason why the 1972 had less HP than the 1971 was due to the dropped compression ratio. The HP rating was done the same way.. However, compression went from over 10:1 in 1971 to 8.5:1 in 1972 for emission reasons.. There was no difference in the way the HP were rated between 1971 and 1972. A 1971 350/270 HP had exactly the same RWHP as a 1970 350/300, they were just rated differently.
My understanding is that the HP rating until 1970 was engine dyno numbers WITHOUT accessories (no alternator, no fan, no mufflers (open headers) and starting in 1971, they would use engine dyno numbers with all the factory accessories and factory exhaust. That reduced the power by 10%. Add another 12 to 15% for drivetrain loss with manual or 20 to 25% for TH400 and you will see a total loss..
It all depends on what accessories were used on the engine dyno. If it was dyno'd with all factory accessories, 12 to 15% drivetrain loss (with manual transmission) sounds reasonable but if it was dyno'd without accessories, you have to expect AT LEAST 20%, more likely 25% with MT and 30% with AT.. At least, my personal dyno experiences seem to indicate that.
My understanding is that the HP rating until 1970 was engine dyno numbers WITHOUT accessories (no alternator, no fan, no mufflers (open headers) and starting in 1971, they would use engine dyno numbers with all the factory accessories and factory exhaust. That reduced the power by 10%. Add another 12 to 15% for drivetrain loss with manual or 20 to 25% for TH400 and you will see a total loss..
It all depends on what accessories were used on the engine dyno. If it was dyno'd with all factory accessories, 12 to 15% drivetrain loss (with manual transmission) sounds reasonable but if it was dyno'd without accessories, you have to expect AT LEAST 20%, more likely 25% with MT and 30% with AT.. At least, my personal dyno experiences seem to indicate that.
Didn't they provide both gross and net hp ratings for 1971?
09-01-2015, 02:00 PM
#10
Race Director
1971: SAE gross as well as SAE NET rating. Low compression
1972: SAE NET rating
My '71 LS-5 454 had 8.5:1 compression. SAE Gross was 365hp, SAE NET 280hp.
1972 saw some further drop in compression, but nothing like the drop from 1970 to 1971.
As for the OP: I'd be surprised if an all stock '68 327/300 dynoed over 200 rwhp. I'd expect somewhere in the 170 rwhp range.
09-01-2015, 02:05 PM
#11
Team Owner
Thread Starter
09-01-2015, 02:07 PM
#12
Team Owner
Thread Starter
I'm curious too, mine is a completely stock base car, 327/300hp, 3spd auto, 3:08 rear axle, with 67,000 on it. Motor was verified as original to car- block, heads, carb. If I had to guess, I would say 200 horse, I'm embarrassed to say a Honda will beat it. I does drive beautifully though.
09-01-2015, 02:08 PM
#13
Team Owner
Thread Starter
1970: SAE gross rating. High compression
1971: SAE gross as well as SAE NET rating. Low compression
1972: SAE NET rating
My '71 LS-5 454 had 8.5:1 compression. SAE Gross was 365hp, SAE NET 280hp.
1972 saw some further drop in compression, but nothing like the drop from 1970 to 1971.
As for the OP: I'd be surprised if an all stock '68 327/300 dynoed over 200 rwhp. I'd expect somewhere in the 170 rwhp range.
1971: SAE gross as well as SAE NET rating. Low compression
1972: SAE NET rating
My '71 LS-5 454 had 8.5:1 compression. SAE Gross was 365hp, SAE NET 280hp.
1972 saw some further drop in compression, but nothing like the drop from 1970 to 1971.
As for the OP: I'd be surprised if an all stock '68 327/300 dynoed over 200 rwhp. I'd expect somewhere in the 170 rwhp range.
09-01-2015, 10:19 PM
#14
Race Director
09-01-2015, 10:55 PM
#15
Team Owner
Member Since: Jul 2004
Location: Redondo Beach, California
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Thanks for all the interesting information.
If I had a NCRS 68, I'd cheat..I'd rebuild the engine as a 350 or 383 and have installed the tungsten weights on the crank to show a neutral balanced crank!!!
If I had a NCRS 68, I'd cheat..I'd rebuild the engine as a 350 or 383 and have installed the tungsten weights on the crank to show a neutral balanced crank!!!
09-02-2015, 06:49 AM
#16
Drifting
Now I'm curious, I read answers that a stock 327 would have less than 200hp, what would a 427, 390-435hp be than, 250-300 at the wheels 
Oh the humanity!
Oh the humanity!
09-02-2015, 09:12 AM
#18
Team Owner
Thread Starter
09-02-2015, 09:32 AM
#19
Race Director
Remember the 365 hp was SAE Gross. In other words: Fantasy numbers.
SAE Net was 285 hp. 285 flywheel and ~245 rwhp is pretty good, less than 15% loss.
Most crate motors are rated SAE Gross because it produces big numbers. The new LS crate motors are SAE Net.
SAE Net was 285 hp. 285 flywheel and ~245 rwhp is pretty good, less than 15% loss.
Most crate motors are rated SAE Gross because it produces big numbers. The new LS crate motors are SAE Net.
Last edited by zwede; 09-02-2015 at 09:34 AM.
