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how much HP loss from crank to rear axle

 
Old 06-05-2019, 06:49 PM
  #41  
glass slipper
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Originally Posted by Rescue Rogers View Post
You may want to reword this section. In a muncie 4 speed which is very common in our vehicles all the gears are turning all the time,even if they arent locked in, the cluster gear is slaved to the input shaft and is never disconnected so I would assume a higher loss for that particular transmission. A super T 10 may be similar
I'm talking about the power flow. All modern synchromesh transmissions have all gears "meshed" at all times. However, HP loss occurs through the gears that power flows...there are no gears for 4th gear in your Muncie 4-speed, the input shaft and output shafts are "locked" together for a straight through power flow.
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Old 06-05-2019, 06:55 PM
  #42  
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I think I follow your logic
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Old 06-05-2019, 06:58 PM
  #43  
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Originally Posted by Rescue Rogers View Post
I think you guys are not presenting your sides well, Any loss of anything can be presented as a %. IF you give a range of percentages then you are covering your self for any changes in given values. If you have engine A with x number of HP then increase the HP and the set value of a given pump doesn't change,Your percentage will still be in a small range. And if that value stays within the given percentage it is obviously true. I could also say 10% to 25% and that covers a huge amount of loss. So yes starting with 350hp and loosing 5.7% gives you a loss of 20 hp. And gaining 100 HP from a cam change and losing 20 hp is still only a 4.4% change so you are arguing over a 1% difference that falls into his percentage range......

I've got a Dyno day this weekend and I asked the tuner what they normally see in their motors from crank to wheel differences on average, He asked me make amodel engine and tranny questions and said 13% to 15% is normal. I would say a professional that does it all the time would have a good idea since its his job, and his reputation. I hope I stay in that range.

My desktop dyno says I should have an easy 420 hp athe the crank gross, Hotrod says they got 450 hp gross with my setup. lets average that to 435HP, then take 15% of that for accessories 378.26 and another 15% for driveline and I should see 329HP at the wheels. I hope to get up to 350HP , but 329HP at the wheels would be pretty good for a stock bore 327.

Also remember that these lossses arent exponential. You cant add the 15% of the net lose and the 15% of the driveline loss and say you will loss 30% total because then I would end up down in the 315HP range. The output at the crankshaft is the amount you will loose the driveline percentage from.

Good luck...I and others would be really curious what the RWHP is after the dyno runs, assuming your 435 Gross HP is close to reality which I am sure it is if you know what the parts can produce in a SBC.....25% loss from Gross HP 435 would put you right at 326 RWHP...you are probably going to be in the range of 315-330 RWHP.....5-10 RWHP either way up or down would be pretty darn impressive for a calculated estimate based on the range percentages......

Edit-Either way there is no way that Gross HP to RWHP in these cars with these engines is 10-15% which was the original misinformation statement (and quoted often erroneously) that started all of this discussion.

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Old 06-05-2019, 07:00 PM
  #44  
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Originally Posted by Rescue Rogers View Post
I think you guys are not presenting your sides well, Any loss of anything can be presented as a %. IF you give a range of percentages then you are covering your self for any changes in given values. If you have engine A with x number of HP then increase the HP and the set value of a given pump doesn't change,Your percentage will still be in a small range. And if that value stays within the given percentage it is obviously true. I could also say 10% to 25% and that covers a huge amount of loss. So yes starting with 350hp and loosing 5.7% gives you a loss of 20 hp. And gaining 100 HP from a cam change and losing 20 hp is still only a 4.4% change so you are arguing over a 1% difference that falls into his percentage range......

I've got a Dyno day this weekend and I asked the tuner what they normally see in their motors from crank to wheel differences on average, He asked me make amodel engine and tranny questions and said 13% to 15% is normal. I would say a professional that does it all the time would have a good idea since its his job, and his reputation. I hope I stay in that range.

My desktop dyno says I should have an easy 420 hp athe the crank gross, Hotrod says they got 450 hp gross with my setup. lets average that to 435HP, then take 15% of that for accessories 378.26 and another 15% for driveline and I should see 329HP at the wheels. I hope to get up to 350HP , but 329HP at the wheels would be pretty good for a stock bore 327.
Why not just say HP loss in the range of 50-100 HP stated as a constant and ignore the linear/exponential components?

Anybody can buy a dyno and become a professional dyno operator, it doesn't mean they understand what's going on where the tire meets the roller.

I think the thing I'm missing here is you guys aren't concerned with accuracy and I apologize for trying to shed some light on the technical side, I was seriously trying to help you guys understand about HP loss from the crank to the rear axle as the thread title states. Please continue and ignore my posts.
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Old 06-05-2019, 07:15 PM
  #45  
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The thing is, regardless of it being 'constant' or not....nobody cares. Once its established its always reported in %.

And once the loss is determined isnt it always the same % as you add hp? For instance, my C5 A4 with the 2.73 rear gear dynoed at 290 and was rated at 350net. Thats a 60hp loss or 17%/ If I were to do the usual 'bolt-on' intake/exhaust/tune or whatever the loss would still be 17%...not 60rwhp. Thats most like to report %
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Old 06-05-2019, 07:16 PM
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Thanks to all that responded to my question.
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Old 06-05-2019, 07:18 PM
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Originally Posted by jb78L-82 View Post
Good luck...I and others would be really curious what the RWHP is after the dyno runs, assuming your 435 Gross HP is close to reality which I am sure it is if you know what the parts can produce in a SBC.....25% loss from Gross HP 435 would put you right at 326 RWHP...you are probably going to be in the range of 315-330 RWHP.....5-10 RWHP either way up or down what be pretty darn impressive for a calculated estimate based on the range percentages......
We'll find out this weekend if all goes well.
stock block, forged crank, KB domed 11:1 pistons, total seal rings, Comp Cams .501/.510 274/284 duration solid mechanical lifter, 16lb flywheel, scat I beam rods, Hekkemian racing aluminum heads, RPM intake and quadrajet, K&N filter, fuel cooler, electric fan, 7 quart pan, MSD dizzy and 6AL limitied to 6800 rpm. I'm very curious, and I would love to be able to pull it and get a gross HP rating .

Either way the seat of the pants Dyno is really impressive, I cant wait to to get it up to Epping for the friday nite 1/4 mile

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Old 06-05-2019, 09:23 PM
  #48  
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Originally Posted by glass slipper View Post
Why not just say HP loss in the range of 50-100 HP stated as a constant and ignore the linear/exponential components?

Anybody can buy a dyno and become a professional dyno operator, it doesn't mean they understand what's going on where the tire meets the roller.

I think the thing I'm missing here is you guys aren't concerned with accuracy and I apologize for trying to shed some light on the technical side, I was seriously trying to help you guys understand about HP loss from the crank to the rear axle as the thread title states. Please continue and ignore my posts.
While I understand what you're saying, and I agree that there's a mixture of constant, linear, and exponential components, I still think that a percentage value is more accurate in practice than a constant, just from numbers achieved in a variety of cars and engines across the board. Quoting a 50-100hp loss would mean that (for example) if I were to install a 50hp BMC A Series engine in a Corvette then it would not be able to move at all... I am quite certain that is not the case? The modified engine built for my MG made 121hp on the engine dyno with no accessories, and just over 90hp to the wheels through a 5 speed gearbox and rear axle, right around that 25% number again. Now, certainly the losses (as a percentage) tend to decrease as horsepower increases, but adding 50hp at the engine never (in my experience anyway) results in an additional 50hp at the wheels. Generally it would result in a gain of 40-45hp at the wheels, again coming back to that % loss idea. I agree fundamentally with the logic of what you are describing, but in practice a % loss seems to be a more accurate guesstimate than a constant.

Last edited by Metalhead140; 06-05-2019 at 09:25 PM.
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Old 06-05-2019, 10:28 PM
  #49  
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Its proof once again that numbers are fine on paper but dont translate to the real world perfectly. Theres always a percentage in there somewhere.
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Old 06-05-2019, 10:34 PM
  #50  
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its normally in the 17% mark . But does it matter .
As most road vehicle don't have enough grip o the road to handle high torque anyway.
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Old 06-06-2019, 01:02 AM
  #51  
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Originally Posted by glass slipper View Post

An example of exponential losses is inertia like the wheel/tire and any other rotating driveline component. On a chassis dyno that controls the rate of RPM increase, the amount of HP going to inertia is small and any increase in HP from one run to another results in zero increase in HP going to inertia.
This part is dead wrong. An inertia dyno like Dynojet measures how fast the drums the wheels drive accelerate. Lower power vehicles will accelerate the drum at a slower rate. High power will accelerate it at a much quicker rate. The thing is a more powerful vehicle not only accelerates the drums at a quicker rate but also its own crankshaft, flywheel clutch/torque convertor, and the rest of the drivetrain all the way back to the tires and wheels and of course any accessories the engine is driving. Even accelerating the pump in an automatic transmission will affect the power because higher power will accelerate the rate of increase in fluid pressure. So yes, inertia is a very big deal on inertia chassis dynos. This is also why lower gearing at the differential affects power numbers as everything in front of the differential now accelerates at a faster rate. The only way to figure the losses in power is by percentage because of this.

The only type of dyno that you can control the rate of acceleration is a computer controlled brake dyno like a Superflow. The vast majority of chassis dynos in local shops across the country are inertia type dynos.

Mike

Last edited by v2racing; 06-06-2019 at 05:34 PM.
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Old 06-07-2019, 08:21 AM
  #52  
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Originally Posted by jim2527 View Post
The thing is, regardless of it being 'constant' or not....nobody cares. Once its established its always reported in %.

And once the loss is determined isnt it always the same % as you add hp? For instance, my C5 A4 with the 2.73 rear gear dynoed at 290 and was rated at 350net. Thats a 60hp loss or 17%/ If I were to do the usual 'bolt-on' intake/exhaust/tune or whatever the loss would still be 17%...not 60rwhp. Thats most like to report %
It seems quite a few people here care about insisting it's only a percentage in spite of the overwhelming evidence to the contrary. Let's look at your example above where you did bolt-ons and say you got an increase of 50 HP for a total of 400 Net. Using the 17% method puts the guess at 332 RWHP. If you've read my posts, I've never said it was purely a constant but that you would be closer using a constant. I also identified the gear losses in the differential through the hypoid gear set as a percentage loss, it's about 4-5%. So let's apply 4% to the 50 HP gain and 2 HP of it goes to gear loss making the total loss 62 HP resulting in 338 RWHP. The real irony is if only a constant of 60 HP had been applied leaving us at 340 RWHP, it's still closer than using a percentage.

But let's take your example and expound on it a little. Instead of bolt on equipment, let's look at a max effort build with any choice of power adder and displacement on your C5. You now have 1000 HP net but applying the 17% across the board loss leaves you with 830 RWHP and 170 HP going to the drivetrain. The extra 110 HP would have to be going to the transmission or differential but 1 HP=746 Watts which means 82,060 Watts of heat to be dissipated...ever grabbed a 60 Watt light bulb??? 82,060 Watts is a LOT of heat...the transmission, differential, or both will literally have a melt down. The 650 extra HP going through the differential (assuming zero loss through the transmission to make a worst case scenario) results in an extra 26 HP loss through the gear set which can be managed on a short term power application like drag racing but would require a differential cooler for road racing.

I've already said I'm ok with you guys guessing at RWHP using percentages based on the brown hand theory, I'm just trying to shed a few technical facts on drivetrain losses. I'm just wondering why go through all of the gyrations when you already know a 430 HP engine in a certain drivetrain results is 330 RWHP, there are plenty of posts above that say exactly that. Everything in between those two numbers is just a bunch of hocus-pocus.
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Old 06-07-2019, 08:25 AM
  #53  
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Originally Posted by Metalhead140 View Post
While I understand what you're saying, and I agree that there's a mixture of constant, linear, and exponential components, I still think that a percentage value is more accurate in practice than a constant, just from numbers achieved in a variety of cars and engines across the board. Quoting a 50-100hp loss would mean that (for example) if I were to install a 50hp BMC A Series engine in a Corvette then it would not be able to move at all... I am quite certain that is not the case? The modified engine built for my MG made 121hp on the engine dyno with no accessories, and just over 90hp to the wheels through a 5 speed gearbox and rear axle, right around that 25% number again. Now, certainly the losses (as a percentage) tend to decrease as horsepower increases, but adding 50hp at the engine never (in my experience anyway) results in an additional 50hp at the wheels. Generally it would result in a gain of 40-45hp at the wheels, again coming back to that % loss idea. I agree fundamentally with the logic of what you are describing, but in practice a % loss seems to be a more accurate guesstimate than a constant.
My 50-100 HP range was for his specific engine in his specific car as has been stated many times before my post. You took a specific statement I made and turned it into a general statement in an attempt to make a red herring deflection. Please keep things in context.
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Old 06-07-2019, 08:58 AM
  #54  
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Originally Posted by glass slipper View Post
An example of exponential losses is inertia like the wheel/tire and any other rotating driveline component. On a chassis dyno that controls the rate of RPM increase, the amount of HP going to inertia is small and any increase in HP from one run to another results in zero increase in HP going to inertia.
Originally Posted by v2racing View Post
This part is dead wrong. An inertia dyno like Dynojet measures how fast the drums the wheels drive accelerate. Lower power vehicles will accelerate the drum at a slower rate. High power will accelerate it at a much quicker rate. The thing is a more powerful vehicle not only accelerates the drums at a quicker rate but also its own crankshaft, flywheel clutch/torque convertor, and the rest of the drivetrain all the way back to the tires and wheels and of course any accessories the engine is driving. Even accelerating the pump in an automatic transmission will affect the power because higher power will accelerate the rate of increase in fluid pressure. So yes, inertia is a very big deal on inertia chassis dynos. This is also why lower gearing at the differential affects power numbers as everything in front of the differential now accelerates at a faster rate. The only way to figure the losses in power is by percentage because of this.

The only type of dyno that you can control the rate of acceleration is a computer controlled brake dyno like a Superflow. The vast majority of chassis dynos in local shops across the country are inertia type dynos.

Mike
That part is dead right. Look at the bolded red part in my post you quoted, I specifically said "On a chassis dyno that controls the rate of RPM increase". Most modern dynos sold today are capable of controlling the sweep rate of the engine which means the time required to perform the dyno run is exactly the same every time regardless of the HP the engine makes which means inertia losses are exactly the same from one run to another.

There are three general types of chassis dynos:
1. Pure Inertia
2. Pure Absorption
3. Combination Inertia and Absorption

Numbers 2 and 3 can control the sweep rate of an engine, Superflow is far from the only one selling them. Even Dyno-Jet sells the combination inertia/absorption and have been for several years. There are many dyno manufacturers that sell dynos capable of controlling the sweep rate. If your tuner has an inertia only chassis dyno, it may be time to find a more modern tuner.

Look guys, I get it. You're not interested in facts that don't agree with your perceptions and I'm really ok with it. Either spend a little time trying to understand my posts or just ignore them. At least present them factually when trying to discuss them.

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Old 06-07-2019, 12:03 PM
  #55  
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REAL WORLD EXAMPLE:I’ve been following this thread for a while … it’s always interesting hearing debates about losses, brands or types of dyno’s and peoples’ assumptions about their builds prior to testing a motor.I’ve run multiple motors on engine dyno’s over the past 20 years, and continue to believe that it’s the best $300 investment after completing a new build.You end up with a safe tune, and knowing what you actually have.



Last year I completed a 355 build for my 1970 L46 (original block, Dart SHP heads, retro-roller, stock clutch fan & water pump, original rebuilt Quadrajet, completely rebuilt original points-type ignition, long-tube headers, 9.9 compression).I ran it on an engine dyno for break-in and basic tune-up, followed by (for the first time) chassis dyno after 800 miles.

The motor made 394hp @ 5600rpm and 413 lbft on a Superflow engine dyno.At 800 miles I ran it on a Dynocom chassis dyno.After checking for optimum timing (in my case 35-36 degrees – no difference), a hanger and pair of rods for the carb (it was lean + stumble on acceleration under load) and tweak of the secondary spring tension, the car picked up a lot of power vs. coming in the door, and finally made 326hp at the wheels and 360 lbft of torque.This means HP loss of 17% and TQ loss of 13% through the drivetrain in my case.I am running the original Muncie M20 and a 3.73 rear.

After this, I think I’ll always run a car on the chassis to insure a good tune-up.In my case it was actually running lean for the first couple months once it was in the real world, even though the engine dyno tune-up showed good A/F across the board.
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Old 06-07-2019, 02:46 PM
  #56  
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Originally Posted by JoeMinnesota View Post
REAL WORLD EXAMPLE:I’ve been following this thread for a while … it’s always interesting hearing debates about losses, brands or types of dyno’s and peoples’ assumptions about their builds prior to testing a motor.I’ve run multiple motors on engine dyno’s over the past 20 years, and continue to believe that it’s the best $300 investment after completing a new build.You end up with a safe tune, and knowing what you actually have.



Last year I completed a 355 build for my 1970 L46 (original block, Dart SHP heads, retro-roller, stock clutch fan & water pump, original rebuilt Quadrajet, completely rebuilt original points-type ignition, long-tube headers, 9.9 compression).I ran it on an engine dyno for break-in and basic tune-up, followed by (for the first time) chassis dyno after 800 miles.

The motor made 394hp @ 5600rpm and 413 lbft on a Superflow engine dyno.At 800 miles I ran it on a Dynocom chassis dyno.After checking for optimum timing (in my case 35-36 degrees – no difference), a hanger and pair of rods for the carb (it was lean + stumble on acceleration under load) and tweak of the secondary spring tension, the car picked up a lot of power vs. coming in the door, and finally made 326hp at the wheels and 360 lbft of torque.This means HP loss of 17% and TQ loss of 13% through the drivetrain in my case.I am running the original Muncie M20 and a 3.73 rear.

After this, I think I’ll always run a car on the chassis to insure a good tune-up.In my case it was actually running lean for the first couple months once it was in the real world, even though the engine dyno tune-up showed good A/F across the board.
What was the HP/TQ on the first Dynocom pull? Also curious what shop you used (you're near me)

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Old 06-07-2019, 03:26 PM
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Hi Suprspooky - On the first pull(s) he wouldn't run the car up over 4000 rpm as it showed very lean. I'll have to look back at the sheets (at home) to see what we started with, but what I can tell you is that it was somewhere in the 250-260 range I think for HP. I figure that the chassis tune got me a solid 50-70hp and 30+ lbft once we were finished. It was hugely noticeable.

I used SharaDon performance in Hugo, MN (mainly because we have friends who are related). You can PM me if you want for details, but let's say things started off a little rocky when I arrived, mainly due to some disorganization & lack of communication in the shop, and like most shops they are more comfortable with Holley's and computers vs. Quadrajets. Thank goodness The Carburetor Shop just 10 minutes up the road in Forest Lake (Pat) knows carbs - and Quadrajets - extremely well, so I was able to run up and get some advice and the parts I needed on the fly. In the end, I was happy with the tune-up and experience. If I were to do it again I might possibly look at other options.

I had my engine originally dyno'd at R&R in Spring Lake Park (NEVER again) ... and then re-dyno'd by G&S Dyno & Chassis in Shafer, MN ... another scary, messy shop but lots of know-how and in the end (Gary) got me sorted.
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Old 06-07-2019, 03:41 PM
  #58  
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With regard to this entire conversation and thread - What I finally figured out (which many already know) is that dyno numbers are cool and all, but the real reason for the engine and chassis dyno time and expense (for us normal guys at least) is to optimize the tune-up and get the best performance and drivability out of the combination you put together.

There will ALWAYS be someone at the event or in the next lane with potentially more power. Stupid amounts of power driving around - what a cool time to be in the hobby. I really wanted 400+ hp when I went to the dyno - and fell a little short - but when I started the build really wanted a uber-dependable SB that sounded healthy and was fun to drive, with good manners. I started this one with a leaky, asthmatic 80K mile 350 but ended up with a really, really nice driver. It's not 500 hp, but it's snappy and it is tuned to it's best potential. I went to my dyno day alone, with an appointment, and they took their time because I was paying for it. I'll probably never strap down at a dyno day, just because it becomes a game of the number more than the real purpose of tuning.

To the original question by the OP, in my case the drivetrain losses were 17% on the hp side and 13% on the tq side. Probably would have lost a bit more with an automatic, I am told.
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Old 06-07-2019, 04:31 PM
  #59  
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My real world experience.... my former 427 small block was dynoed at 628 hp on the engine dyno before installation. Afterward, in the car in street trim (full exhaust, all accessories) on the DynoJet it produced 490 rwhp. If my math is correct, total loss was 22%. This is with aTH400 auto trans, 4.11 rear gears, and a 4000 flash rpm converter. I use the numbers to tune the car...best air fuel ratio, timing, and jetting; a baseline for future improvements. With a high stall converter, don't count on a real accurate rear torque reading. It multiplies torque big time when it flashes, throwing the graph all over the place.
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Old 06-10-2019, 07:41 PM
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Originally Posted by JoeMinnesota View Post
Hi Suprspooky - On the first pull(s) he wouldn't run the car up over 4000 rpm as it showed very lean. I'll have to look back at the sheets (at home) to see what we started with, but what I can tell you is that it was somewhere in the 250-260 range I think for HP. I figure that the chassis tune got me a solid 50-70hp and 30+ lbft once we were finished. It was hugely noticeable.

I used SharaDon performance in Hugo, MN (mainly because we have friends who are related). You can PM me if you want for details, but let's say things started off a little rocky when I arrived, mainly due to some disorganization & lack of communication in the shop, and like most shops they are more comfortable with Holley's and computers vs. Quadrajets. Thank goodness The Carburetor Shop just 10 minutes up the road in Forest Lake (Pat) knows carbs - and Quadrajets - extremely well, so I was able to run up and get some advice and the parts I needed on the fly. In the end, I was happy with the tune-up and experience. If I were to do it again I might possibly look at other options.

I had my engine originally dyno'd at R&R in Spring Lake Park (NEVER again) ... and then re-dyno'd by G&S Dyno & Chassis in Shafer, MN ... another scary, messy shop but lots of know-how and in the end (Gary) got me sorted.
Thanks for the info, my RWHP numbers are from Sharadon last fall (no tune, I'll be tweaking with a AFR meter soon, but wanted a baseline), Pat is the man for Carbs period, I get most of my Holley parts from him. It sounds like we could trade horror stories, I went with Wheeler for my Block work and Engine Dyno, due to mis-communication my Motor got started/idled for a few seconds with no oil.
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