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Dyno Outputs and Drive Train Parasitic Loss

J

Jason85GMC

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So, I just got my K5 on the dyno last week, and I must admit I'm a little underwhelmed with the numbers it posted. The truck itself is running great, but the actual numbers have made me curious how my stats stacks up to other similar build dyno's.

Short version is a fairly built .383 Stroker (built for Torque, not HP), headers, dyno-tuned Qjet and MSD distributor, 700R4 (stock T-case), 4.11 gears (with an Eaton Locker), all rolling 36's.

The dyno results were 280 RWHP (5k RPM), 318 RWTorque (3860 RPM).

A couple of questions.

1. How much parasitic drivetrain loss is there really in the 700R4 and transfer case?

(I didn't dyno the engine before I put it in, so I can only estimate, still if I assume a worst case 30% loss in the drive train, the numbers still don't add up to what I would expect from this .383 at the crank.)

2. Does anyone have dyno results for their K5, for comparison?

(Not what you think you're getting, but what the dyno tested!)

3. Is the 4.11 gear ratio to high for 36's?

4. Advice for number improvements? (More for torque, than HP.)

Thanks,
Jason
 
You lose about 15% through the running gear with an auto trans. Looks like your engine makes about 330hp at the crank and about 375tq at the crank.
 
Everything I've read so far in a few hours of googling has been on the order of:

Manual 2wd ~15%.
Automatic 2wd ~18 to 20%
Automatic 4wd ~25% to 30%

Jason
 
4X4HIGH said:
You lose about 15% through the running gear with an auto trans. Looks like your engine makes about 330hp at the crank and about 375tq at the crank.
Click to expand...


Your flywheel numbers are probably just in the 400's. Probably loosing 30% just from your running gear AND 36in tires on top of that. See if you can find some roller tires and go at it again.

4.10s are the right ratio for 36-38s with a stick... So I would say your quite under geared. 35s with a 700r4 is suppose to land ya at 4.56s some even say 4.88s.
 
Jason85GMC said:
So, I just got my K5 on the dyno last week, and I must admit I'm a little underwhelmed with the numbers it posted. The truck itself is running great, but the actual numbers have made me curious how my stats stacks up to other similar build dyno's.

Short version is a fairly built .383 Stroker (built for Torque, not HP), headers, dyno-tuned Qjet and MSD distributor, 700R4 (stock T-case), 4.11 gears (with an Eaton Locker), all rolling 36's.

The dyno results were 280 RWHP (5k RPM), 318 RWTorque (3860 RPM).

A couple of questions.

1. How much parasitic drivetrain loss is there really in the 700R4 and transfer case?

(I didn't dyno the engine before I put it in, so I can only estimate, still if I assume a worst case 30% loss in the drive train, the numbers still don't add up to what I would expect from this .383 at the crank.)

2. Does anyone have dyno results for their K5, for comparison?

(Not what you think you're getting, but what the dyno tested!)

3. Is the 4.11 gear ratio to high for 36's?

4. Advice for number improvements? (More for torque, than HP.)

Thanks,
Jason
Click to expand...


The amount of power an engine makes is from how much air it can move in and out. If you dont have much money in your heads with valves, springs, and porting with a decent cam, then you will never reach the potential of your engine. A good friend of mine just went from a 383 to a larger engine, and was making in the neighborhood of 600 rwhp with that 383, but the heads on that engine doubled the price it took to build it.


Having said that what heads do you have, and what kind of work has been done to them? If you have stock heads with a valve job, might want to look at swapping on the later model vortec iron heads, and having them ported out with new studs springs etc. They are some of the best flowing cast iron heads for the sbc engines.
 
Allright, here's some more details on the engine.

I was expecting about ~ 450 HP/tq at the flywheel, depending on what you believe for parasitic drive train loss, I'm barely breaking 400 if that.

383 Stroker with a 4 bolt main and ARP bolts.
o Block is balanced.
o Engine is bored .030 over.
o Scat Stroker crank.
- The head's are World Product Sportsman 2's with 2.02/1.60 inch valves, and 76 cc's.
- It has Crane Gold Roller Rockers. (it has hyd.lifters)
- SPS Pistons and the compression ratio is 9.25 to 1.
- The cam is a Isky with a 480 lift.
- The carburetor is a 780 cfm Quadrajet it has an Eledbrock Manifold, dual plane.

Oh and by the way, I'm new here just found this site a month ago, so Hi everybody, and thanks for the replies. I'll try to get some pic's of the rig up in a few days.

Jason
 
Jason85GMC said:
Allright, here's some more details on the engine.

I was expecting about ~ 450 HP/tq at the flywheel, depending on what you believe for parasitic drive train loss, I'm barely breaking 400 if that.

383 Stroker with a 4 bolt main and ARP bolts.
o Block is balanced.
o Engine is bored .030 over.
o Scat Stroker crank.
- The head's are World Product Sportsman 2's with 2.02/1.60 inch valves, and 76 cc's.
- It has Crane Gold Roller Rockers. (it has hyd.lifters)
- SPS Pistons and the compression ratio is 9.25 to 1.
- The cam is a Isky with a 480 lift.
- The carburetor is a 780 cfm Quadrajet it has an Eledbrock Manifold, dual plane.
Click to expand...

How do you know that the compression ratio is 9.25:1? What are ALL the actual specs on the cam IE: gross valve lift (at what rocker ratio), duration at .050", lobe separation angle? Was the block decked and if so what is the deck height (how far down the bore is the top of the piston)? What is the CC's of the valve reliefs in the piston and or dish or dome? What is the compressed thickness of the head gasket being used and also what is the head gasket bore diameter (this will be larger than actual cylinder bore diameter)? Were the combustion chambers in the head actually CC'd or are you only going by what the manufacturer says they are?
 
Don't think I'll be able to easily answer ALL of those questions, the machine shop did most of that work to a loose set of requirements after I spun a bearing on the previous 350 that was in there, and decided to bulk up to the 383, but digging out my build sheet.

Compression ratio, pretty sure it was measured and not calculated, number is from the machine shop engine build sheet, and is carried out to 3 digits. (9.251 to be exact)

Rocker arm ratio = 1.5.
At cam timing for .050:
Intake Duation = 224 (max lift 107 ATDC)
Exhaust Duration = 234 (max lift 117 BTDC)

Lift:
Intake @ cam .310 @ valve .465
Exhaust @ cam .325 @ valve .488

No decking.

Jason
 
Well, it's doubtful you have 9.25:1 compression. The shop that did the work should have provided you a DETAILED list of parts and clearances. I could build you an engine and tell you it is xx compression ratio and without giving you any detailed specs there is no way for you to tell otherwise. What piston number was used? You did say SPS pistons but i'm sure they make more than one piston for a chevy.
 
Desktop Dyno shows 364HP@5K and 460TQ@3500. 25% drivetrain loss 273HP and 345TQ. Took a guess at some of the parameters but with the info you posted, it's pretty close.
 
I'd say you're right in the ball park. You might, and most people do, have unrealistic expectations for your engine. The guys where I dyno call their dyno "The Dreamcrusher".
 
I think a guy needs to ask himself, "Does it perform?" Seat of the pants dyno is the only one you have to be satisified with.
 
Kjunky5 said:
Desktop Dyno shows 364HP@5K and 460TQ@3500. 25% drivetrain loss 273HP and 345TQ. Took a guess at some of the parameters but with the info you posted, it's pretty close.
Click to expand...
what do you use for the head type? i.e. street, stock ports, modified etc.? I have the dyno 2000 program, and that can make a big difference in the outcome.
 
76zimmer said:
what do you use for the head type? i.e. street, stock ports, modified etc.? I have the dyno 2000 program, and that can make a big difference in the outcome.
Click to expand...

I didn't save the sim but I think I did street. I could have probably found more info on the heads with a little searching to make an air flow file. But I just guessed to see what I'd come up with.
BTW I have 1102HP 1013TQ turbo 396 sim for the Camaro.:thumb: A guy can dream right?
 
Stomis said:
See if you can find some roller tires and go at it again.
Click to expand...


I know that guys do this all the time, but it doesn't make any sense to me....

Why bother running some little donuts to "make the number" when in reality you'll be doing all your driving on the big meats? All you're doing is creating a false perception of what your setup is really capable of.

:dunno:

Engine & chassis dynos are kind of like RTI ramps... they are fun to play with, but don't tell the whole story.



:usaflag:
 
4X4HIGH said:
Well, it's doubtful you have 9.25:1 compression.
Click to expand...
Really? Why? not to be a jerk, but . . .
If I remember right, the SRP's come in -16 and -24cc inverts. A 72cc chamber (One of the options of the sportsman II) and the -16cc with a 38 or so crush comes out right at 9.2 and change with the slug in the hole about 5thou or so. The -24cc slug and the other option of the sportsman II's, the 64CC zero decked with a 38 crush comes out right around that number again. I don't know his machinist, but I would definitely not doubt him in this. The math seems very do-able.

Sportsman II's are a good head. They are pretty lousy on the exhaust side, but make decent power and a good durable head. Especially if you are not spinning rpm's. They only have a 200cc runner as their small port, so you are losing some power down low. But not enough to go and switch out heads. The Sportsman II's have come in many different combinations over the years, but the 72 is the largest CC I remember. Did he CC the heads, or is the 76 a possible misprint? However, I could see this thing tuned perfectly, making 375-385 real horsepower on the dyno at 4900-5200, depending on valve train. (And that is 485 for everyone that just puts parts together and tells everyone at the local hang-out what it is making. There is a reason my dyno has "The bull stops here" right on it.)
And with a hydraulic cam with that profile on a 383, to think your horsepower will ever equal your peak torque number is a little misleading though. If you are happy with the performance of the truck, just go and have fun. Numbers don't mean crap! If you want more performance, look into really getting everything tuned in. Timing, fuel, etc. Numbers are just for bragging. Dynos are for finding more power when changing perameters and comparing, not some stupid final number. Performance is reality. If your truck kicks butt, forget what the numbers say.
 
There are a couple real numbers that do mean a lot, E.T. @ MPH! :wink1:

(but I think we have the wrong vehicles for that)
 
My real original goal here was to try to estimate the drive train parasitic loss to back calculate the engine perfomrance, and see if it was in the ballpark expected for this build. (It's the first time this trucks been on a dyno.)

I just got the truck to Colorado, and had it "tuned" for the altitude on the dyno, so a timing and valve adjustment, distributor recurve, carburetor jetting and metering rod adjustment. The posted numbers were the post tune (best) results.

So if you believe 25% loss through the drive train (seems reasonable from my research), that means the 318 RWTQ is about 397 TQ at the engine. (This engine is built for low end torque, so the high RPM horse power numbers aren't that important to me, though I will admit, I thought they were a bit low too.) Anyway, I was hoping for a "bit" more (> 430 TQ) torque out of this engine given it's build parameters, but the dyno is what it is. The torque plot itself is nice wide, and fairly flat across the RPM band, so that's good.

All that said, the trucks running great! I'll try to get some pictures of the truck up soon.

Jason

Note: I don't have it in front of me, but I think 76 cc came from the machinist build sheet, so either they mis-printed it, or they actually measured it, I'm not sure which. Your right though, I looked and the largest the Sportsman 2's come in is 72 cc spec, from the World Product web page.
 
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