Dyno results, before and after!
Thread Starter
Burning Brakes
Joined: Dec 2017
Posts: 1,043
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2023 C3 of the Year Finalist - Modified
Dyno results, before and after!
Hey guys, thought y’all would find this interesting.
1975 L48 TH400 3.55 gears, all stock EXCEPT edelbrock performer intake and edelbrock 600 carb.
Made a sad 153rwhp and 202rwtq.
I rebuilt the engine with all new internals, performance mods being:
flat top pistons, 2 valve relief
edelbrock e street 64cc heads
torker plus cam
Performer EPS intake manifold
thunder series 650 carb
summit brand headers, true duals with H-pipe and cutouts.
Just got back from the dyno anddddddd
276RWHP and 326RWTQ
assuming a 20% loss that’s 345hp and 407tq at the crank. Overall I’m happy with it as those were about the target numbers for the build. I also thought the stock L48 numbers were good considering it supposedly came from the factory at 165hp.
just posting this for info/discussion.
1975 L48 TH400 3.55 gears, all stock EXCEPT edelbrock performer intake and edelbrock 600 carb.
Made a sad 153rwhp and 202rwtq.
I rebuilt the engine with all new internals, performance mods being:
flat top pistons, 2 valve relief
edelbrock e street 64cc heads
torker plus cam
Performer EPS intake manifold
thunder series 650 carb
summit brand headers, true duals with H-pipe and cutouts.
Just got back from the dyno anddddddd
276RWHP and 326RWTQ
assuming a 20% loss that’s 345hp and 407tq at the crank. Overall I’m happy with it as those were about the target numbers for the build. I also thought the stock L48 numbers were good considering it supposedly came from the factory at 165hp.
just posting this for info/discussion.
Last edited by randallsteel; Dec 29, 2020 at 05:15 PM.
Popular Reply
Dec 29, 2020, 06:24 PM
Thread Starter
Burning Brakes
Joined: Dec 2017
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2023 C3 of the Year Finalist - Modified
Most importantly I put 4 stickers on the back window, each an easy 25 hp
Le Mans Master
Joined: May 2002
Posts: 5,084
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From: Lebanon Township New Jersey
I'm glad you're happy with the results of your build. Just for discussion purposes, that first dyno test of a nearly stock, 45 year old L48 engine, rated at 165 flywheel HP, yielded a rear wheel HP number of 153. Using your 20% loss figure, you might have expected 132 HP, at most. This makes me question the accuracy of the dyno numbers.
Le Mans Master
Joined: Jun 2019
Posts: 7,624
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From: Indiana
I'm glad you're happy with the results of your build. Just for discussion purposes, that first dyno test of a nearly stock, 45 year old L48 engine, rated at 165 flywheel HP, yielded a rear wheel HP number of 153. Using your 20% loss figure, you might have expected 132 HP, at most. This makes me question the accuracy of the dyno numbers.
Le Mans Master
Joined: May 2002
Posts: 5,084
Likes: 786
From: Lebanon Township New Jersey
Thread Starter
Burning Brakes
Joined: Dec 2017
Posts: 1,043
Likes: 414
2023 C3 of the Year Finalist - Modified
I'm glad you're happy with the results of your build. Just for discussion purposes, that first dyno test of a nearly stock, 45 year old L48 engine, rated at 165 flywheel HP, yielded a rear wheel HP number of 153. Using your 20% loss figure, you might have expected 132 HP, at most. This makes me question the accuracy of the dyno numbers.
Race Director
Joined: Sep 1999
Posts: 11,358
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From: Plano TX
I'm glad you're happy with the results of your build. Just for discussion purposes, that first dyno test of a nearly stock, 45 year old L48 engine, rated at 165 flywheel HP, yielded a rear wheel HP number of 153. Using your 20% loss figure, you might have expected 132 HP, at most. This makes me question the accuracy of the dyno numbers.
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Old Pro Solo Guy
Joined: Dec 2017
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From: Marlton NJ
Le Mans Master
Joined: May 2002
Posts: 5,084
Likes: 786
From: Lebanon Township New Jersey
A 30 HP improvement, a 60 - 80 HP improvement on a 165 HP engine by changing a new catalytic converter to a different type??? OK, I'll defer to you experts.
Last edited by BKbroiler; Dec 29, 2020 at 07:25 PM.
Thread Starter
Burning Brakes
Joined: Dec 2017
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2023 C3 of the Year Finalist - Modified
What I could tell by looking under it, it appeared to be the factory GM one. Now there is a chance it was emptied out at some point. I didn’t look at it when I got the exhaust done.
Had a 1976 L-82, 4-sp
Joined: Mar 2011
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From: Some days your the dog and some days your the hydrant.
Royal Canadian Navy
I think the L-48 was underrated at 165 hp just like the L-88 and hemi were underrated. 
Last edited by resdoggie; Dec 29, 2020 at 07:22 PM.
Old Pro Solo Guy
Joined: Dec 2017
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From: Marlton NJ
The 1974 L48 was the last year for true dual exhaust and was rated at 195hp. The same engine in the 1975 was only rated at 165. Those cat convertors that year were truly awful. Pancake shaped cans with pellets inside. So 30 HP for that one change alone and a few more for the headers and better mufflers (20). So let's call it 50+HP shall we. (Ok maybe not 60) But 215 vs 165 is a 30% increase, and it does indeed feel like a different engine once you remove that "cork"
Then he did heads, and cam etc.etc. and got more out of it.
Great job!
I'll bet it runs like a different car!
Then he did heads, and cam etc.etc. and got more out of it.
Great job!
I'll bet it runs like a different car!
Is my vette stock?? HAHA
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From: Im not allowed to tell you
2020 C3 of the Year Finalist - Modified
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The drivetrain is a set number of loss not a true percentage. If it absorbs 30 hp to turn it it doesnt matter what amount is in front of it to turn it, it will never change. So if a 195hp motor gets 165 to the wheels, then it needs 30 hp to turn all those gears and thats it, but that low a number is hard to believe if just a mechanical fan can eat 20 hp.... So a 276 rwhp would be a 306 hp motor? So without getting an actual dyno number for the original motor it would be just a guessing game. But I agree, a 350 cu motor only making 195hp would be a really low performer. I would think it takes closer to 60 to 75 hp (Maybe more, I'll have to go see if a more realistic number has been posted) to turn all those gears so that would be a more reasonable number which would get you closer to the predicted number and make the original motor a more believable 235hp base motor and this new one closer to 346hp.
Is my vette stock?? HAHA
Joined: Oct 2015
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From: Im not allowed to tell you
2020 C3 of the Year Finalist - Modified
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just a quick check, one comparison story with different motors and different drivetrains I found was a drive train with an Auto trans in it lost 100hp. A manual trans lost only 40hp. So its definitely drive train and accessory driven. So if you have a manual and a clutch fan I would say an easy 60 plus hp was lost so you are right in where you though you would be!!! good job
Tech Contributor
Joined: Jun 2004
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From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
The drivetrain is a set number of loss not a true percentage. If it absorbs 30 hp to turn it it doesnt matter what amount is in front of it to turn it, it will never change. So if a 195hp motor gets 165 to the wheels, then it needs 30 hp to turn all those gears and thats it, but that low a number is hard to believe if just a mechanical fan can eat 20 hp.... So a 276 rwhp would be a 306 hp motor? So without getting an actual dyno number for the original motor it would be just a guessing game. But I agree, a 350 cu motor only making 195hp would be a really low performer. I would think it takes closer to 60 to 75 hp (Maybe more, I'll have to go see if a more realistic number has been posted) to turn all those gears so that would be a more reasonable number which would get you closer to the predicted number and make the original motor a more believable 235hp base motor and this new one closer to 346hp.
At a constant speed down the highway, there's going to be modest losses due to gear mesh friction, bearing friction, and fluid/gear-oil "pumping". Increase or decrease the speed, and the load/loss changes accordingly.
During acceleration, losses really show up. The gear mesh friction goes up due to the higher load/forces at the teeth, and losses due to rotational inertia go up as well. All the gears and shafts in the drivetrain are acting like multiple flywheels, consuming power during their rotational acceleration. The faster they are accelerated, the more power they had to first drain off of the engine.
There's no free lunch in this world. If you want to go faster, it takes more power to overcome the drag/resistance/inertia in the equipment environment.
Is my vette stock?? HAHA
Joined: Oct 2015
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From: Im not allowed to tell you
2020 C3 of the Year Finalist - Modified
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Respectfully, I gotta disagree. The drivetrain losses are going to be speed and acceleration dependent, so they're always changing.
At a constant speed down the highway, there's going to be modest losses due to gear mesh friction, bearing friction, and fluid/gear-oil "pumping". Increase or decrease the speed, and the load/loss changes accordingly.
During acceleration, losses really show up. The gear mesh friction goes up due to the higher load/forces at the teeth, and losses due to rotational inertia go up as well. All the gears and shafts in the drivetrain are acting like multiple flywheels, consuming power during their rotational acceleration. The faster they are accelerated, the more power they had to first drain off of the engine.
There's no free lunch in this world. If you want to go faster, it takes more power to overcome the drag/resistance/inertia in the equipment environment.
At a constant speed down the highway, there's going to be modest losses due to gear mesh friction, bearing friction, and fluid/gear-oil "pumping". Increase or decrease the speed, and the load/loss changes accordingly.
During acceleration, losses really show up. The gear mesh friction goes up due to the higher load/forces at the teeth, and losses due to rotational inertia go up as well. All the gears and shafts in the drivetrain are acting like multiple flywheels, consuming power during their rotational acceleration. The faster they are accelerated, the more power they had to first drain off of the engine.
There's no free lunch in this world. If you want to go faster, it takes more power to overcome the drag/resistance/inertia in the equipment environment.
You can't use % unless you just want to guess. My point is his new motor is making less horsepower at the crank or the original motor was losing a lot more horsepower through the drivetrain than he thought which is probably what is happening. It's a lot more loss through the older AT trannys than the old manuals
Had a 1976 L-82, 4-sp
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From: Some days your the dog and some days your the hydrant.
Royal Canadian Navy
Look at it another way. If the 165 hp engine goes down the road at 60 mph, it takes say 70 hp. Drive train loss is say 20%. So 14 hp loss in drivetrain. Now throw in a 500 hp or 700 hp or 1000 hp engine in there. Go back and drive it again at 60 mph. It still only takes 70 hp to do 60 mph and the drivetrain loss is still 20% i.e. 14 hp. Now do 80 mph with the 165 hp engine. It now takes 110 hp to go 80 mph. It's not a linear relationship of hp to speed but an exponential relationship. So now the 1000 hp engine at 80 mph. It's still only takes 110 hp to move down the road at 80 mph. Drivetrain loss is still the same at 80 mph - 20% of 110 hp is 22 hp.
Tech Contributor
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From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
yes but his number is at a given rpm or speed. Not across the range. For example, let's suppose At 6800 he is making 165 hp at the rear wheel and that is 20% loss from 206.25 hp which is 41.25hp. So if he throws a 500hp motor in there the same drive train is now sucking up 100hp. Lets try 1000 hp, it now takes 200 hp to move that same car.
You can't use % unless you just want to guess. My point is his new motor is making less horsepower at the crank or the original motor was losing a lot more horsepower through the drivetrain than he thought which is probably what is happening. It's a lot more loss through the older AT trannys than the old manuals
You can't use % unless you just want to guess. My point is his new motor is making less horsepower at the crank or the original motor was losing a lot more horsepower through the drivetrain than he thought which is probably what is happening. It's a lot more loss through the older AT trannys than the old manuals
I have a particular dislike/distrust for inertial dynos. They're fine for doing relative measurements, but not absolute measurements. There's too many unmeasured masses/unknowns in the "equation" for a chassis dyno to give you any reliable or accurate "measurement" of the driveline losses.
Tech Contributor
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From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
Look at it another way. If the 165 hp engine goes down the road at 60 mph, it takes say 70 hp. Drive train loss is say 20%. So 14 hp loss in drivetrain. Now throw in a 500 hp or 700 hp or 1000 hp engine in there. Go back and drive it again at 60 mph. It still only takes 70 hp to do 60 mph and the drivetrain loss is still 20% i.e. 14 hp. Now do 80 mph with the 165 hp engine. It now takes 110 hp to go 80 mph. It's not a linear relationship of hp to speed but an exponential relationship. So now the 1000 hp engine at 80 mph. It's still only takes 110 hp to move down the road at 80 mph. Drivetrain loss is still the same at 80 mph - 20% of 110 hp is 22 hp.
We both agree that the drivetrain loss (at steady state speed) is independent of what engine is under the hood. But I don't agree with you that the drivetrain loss curve/percentage (20% in your example) is constant over speed. I suspect, and I welcome correction, that the horsepower needed to overcome the aero drag at increasing speeds rises much faster than the increased horsepower needed to spin the drivetrain at increasing speeds.