Disappointing day on the dyno

[Brewzer67]

For anyone following this post I am happy to report that I pulled the trigger today on a new carb since the 850 Demon was so undersized. I talked to Dom at Thumpercarbs today and ordered a BLP BX4 that will flow 1050. It uses their 4150 base but has a dominator top so I don't have to buy a new manifold. Once I get the rear end in and the carb set all I need to do is get the battery disconnect switch in and I'm ready to race come spring.

 

[65Fury440]

My 526 with a Demon 850 pulls no vacuum at 7k rpms.

It will be interesting to see if the new carb helps, since on paper, the venturis in the BLP are smaller than the Demon.

You have to wonder if the original dyno was off, combined with the converter.

After seeing the compression and leak down are good, you have to feel better.

I don't remember, but you did degree the cam didn't you?

Here are the carb specs.

Wishing you the best!

http://blp.com/cart/index.php?main_page=product_info&cPath=72_123_400_403&products_id=1629

https://www.holley.com/products/fuel_systems/carburetors/demon/mighty_demon/parts/MAD-850-MS

 

[68 HEMI GTS]

My 526 with a Demon 850 pulls no vacuum at 7k rpms.

It will be interesting to see if the new carb helps, since on paper, the venturis in the BLP are smaller than the Demon.

You have to wonder if the original dyno was off, combined with the converter.

After seeing the compression and leak down are good, you have to feel better.

I don't remember, but you did degree the cam didn't you?

Here are the carb specs.

Wishing you the best!

http://blp.com/cart/index.php?main_page=product_info&cPath=72_123_400_403&products_id=1629

https://www.holley.com/products/fuel_systems/carburetors/demon/mighty_demon/parts/MAD-850-MS

I was actually surprised to see the demon has a 1.56 Venturi. It’s the same as an old Holley 850 which actually flow more than the rating. I gotta imagine the BLP specs are wrong. A 1.40 Venturi is small for that cfm rating. My 1050/4150 is a 1.59

 

[65Fury440]

I was actually surprised to see the demon has a 1.56 Venturi. It’s the same as an old Holley 850 which actually flow more than the rating. I gotta imagine the BLP specs are wrong. A 1.40 Venturi is small for that cfm rating. My 1050/4150 is a 1.59

It does say you can order different venturi sizes so who knows.
What surprises me is when I spoke to BLP a couple weeks ago they did not mention a carb with a 4500 top. I have a ported 337 intake I'm fond of.
20-30 hp between a 1050 cfm 4150 and 4500 are numbers I have heard thrown around, because the 4500 has a better pattern, will be interesting to see how this new setup works.

 

[Brewzer67]

My 526 with a Demon 850 pulls no vacuum at 7k rpms.

It will be interesting to see if the new carb helps, since on paper, the venturis in the BLP are smaller than the Demon.

You have to wonder if the original dyno was off, combined with the converter.

After seeing the compression and leak down are good, you have to feel better.

I don't remember, but you did degree the cam didn't you?

Here are the carb specs.

Wishing you the best!

http://blp.com/cart/index.php?main_page=product_info&cPath=72_123_400_403&products_id=1629

https://www.holley.com/products/fuel_systems/carburetors/demon/mighty_demon/parts/MAD-850-MS

Thanks. I am not sure what venturi size the carb will come with but that is an interesting point. I would assume Dom will specify a larger size to get to the 1050 (and actually BLP says 1060) rating. It does say on BLP site that bigger are available so that would be my guess. I know the total flow is also largely dictated by the boosters used as well so we'll see what boosters he uses. Before choosing the BLP I asked Dom about just working over the Demon but he said there was no way he could get it to flow those numbers.
I did degree the cam. I was off by a half degree (installed at 106.5 instead of 107) but I was also using a smaller wheel so it could be 107 but for sure is definitely close enough. The cranking compression numbers are also right where they should be so that pretty much confirms cam location.

 

[Brewzer67]

It does say you can order different venturi sizes so who knows.
What surprises me is when I spoke to BLP a couple weeks ago they did not mention a carb with a 4500 top. I have a ported 337 intake I'm fond of.
20-30 hp between a 1050 cfm 4150 and 4500 are numbers I have heard thrown around, because the 4500 has a better pattern, will be interesting to see how this new setup works.

I don't have a 337 manifold but I really like the tuning potential they represent. Since they sit significantly lower than the Indy it opens up the possibility of using some spacers to tune with. The Indy is so tall I barely have clearance even with the scoop. I would like the ability to be able to test with 4-hole, open, shear plate, and merge spacers but can't. I had really good luck on my last combo with a 1-1/2" merge spacer with a 1/2" phenolic 4-hole on top of that. It was what the combo wanted plenum-size wise and really helped fuel percolation issues. Depending how things shake out I may see if I can find a 337 and send it Larry to port match and work the plenum so I can get some of that ability back.

 

[68 HEMI GTS]

I don’t know what your issue is with a spacer on the Indy, mine looks to be plenty compact with a 2” spacer..

 

[biomedtechguy]

I don’t know what your issue is with a spacer on the Indy, mine looks to be plenty compact with a 2” spacer..

Holy cow! That picture reminds me of this:

 

[Brewzer67]

I don’t know what your issue is with a spacer on the Indy, mine looks to be plenty compact with a 2” spacer..

View attachment 554049

Any taller and you'll need one of those red flashing lights to alert the planes! Actually, I've seen worse. There used to be a guy that ran at the track by us years ago that had two 2" 4-hole spaces on top of a 2" open spacer on a Weiand Accelerator single plane. He had a crazy large cam and claimed it kept the low rpm reversion issues from over fattening his idle mixture. I don't know that I bought it and his ET's definitely didn't back it up.

 

[PRHeads]

I’m just going through some old posts and this one caught my eye........

This one finished up last December, so I expect some updates might have occurred this past summer.

New carb?
Another dyno session perhaps, or a trip to the track?

I kind of find it amusing how many people dismiss the value of getting an engine tested on the dyno before it goes in the car.
As long as the numbers are at least reasonably legit...... it gives you an indicator of what kind of performance to expect.

While it’s true there are many cars running down the drag strip where the performance isn’t as good as the dyno numbers would indicate.
What you very rarely see is cars running way quicker than than the dyno numbers indicate.

Another thing you don’t see is too many engine builders with high success rates building motor combinations based around specific rules packages getting rid of their dynos.

 

[Cranky]

I agree that a dyno is a great tuning tool but not all of us have the extra dollars to use or have easy access to one. If an engine builder has one, I can't see that builder getting rid of it either. Imo, a dyno will put you into deep into the middle of the ball park and then it's up to the racer to find tune the combination. You can also research what combination works well for your location and do pretty good too. It just depends on what you are looking for your car to do. If you're looking for every ounce counts and have deep pockets, the dyno can be your friend.

 

[BSB67]

Dyno - #1) its tuning tool, #2) it's a cover your a** tool for the engine builder.

The differences in dyno results based on tuning changes is meaningful. The actual numbers by themselves mean little to me, but might mean something to the dyno owner/operator.

To me, a guy that has his motor run on a dyno after a build, makes minor timing and jet changes and 3 or 4 pulls is about worthless IMO.

 

[PRHeads]

I didn’t really mean for this to turn into a pros/cons list of dyno testing, but rather was looking for updates as to what progress the OP has made with his ride, since it seemed like he was pretty disappointed with how it was when the updates ended last December.

That being said, I’m going to respond to Russ’ comments about making 3 or 4 pulls on the dyno.
While that’s not how it usually goes when I test a motor, IMO..... even if that’s all you did..... on a new build that’s still going to provide worthwhile info.

If the motor has a flat tappet cam, it’s a good way to beak in the cam and seat the rings.

If it’s a combo with dual springs, it’s much easier to swap out the springs on the dyno than leaning over the fender of your car.

Even with only a few pulls, at a minimum you get to verify the carb calibration is such that it won’t wash down the rings, or burn a piston.

You can verify the valvetrain has no issues up to the limit you intend to run the motor. I feel this is pretty important with hyd cams, since the lifters tend to give up at a lower rpm than what most people expect, and if you know what rpm that occurs at, you can keep from trying to rev it to an rpm where you could be doing some damage.

See where the tq and hp peaks occur to help with converter and/or gear selection.

See that there are no major leaks to deal with before installing the motor in the car.

And..... you get to see if your planning paid off with the engine making the power and torque you were expecting.

With most street/strip and bracket race builds, it’s rarely about finding every last horsepower.
It’s more of a systems check/verification to make sure all the components are working as expected.

 

[BSB67]

I didn’t really mean for this to turn into a pros/cons list of dyno testing, but rather was looking for updates as to what progress the OP has made with his ride, since it seemed like he was pretty disappointed with how it was when the updates ended last December.

That being said, I’m going to respond to Russ’ comments about making 3 or 4 pulls on the dyno.
While that’s not how it usually goes when I test a motor, IMO..... even if that’s all you did..... on a new build that’s still going to provide worthwhile info.

If the motor has a flat tappet cam, it’s a good way to beak in the cam and seat the rings.

If it’s a combo with dual springs, it’s much easier to swap out the springs on the dyno than leaning over the fender of your car.

Even with only a few pulls, at a minimum you get to verify the carb calibration is such that it won’t wash down the rings, or burn a piston.

You can verify the valvetrain has no issues up to the limit you intend to run the motor. I feel this is pretty important with hyd cams, since the lifters tend to give up at a lower rpm than what most people expect, and if you know what rpm that occurs at, you can keep from trying to rev it to an rpm where you could be doing some damage.

See where the tq and hp peaks occur to help with converter and/or gear selection.

See that there are no major leaks to deal with before installing the motor in the car.

And..... you get to see if your planning paid off with the engine making the power and torque you were expecting.

With most street/strip and bracket race builds, it’s rarely about finding every last horsepower.
It’s more of a systems check/verification to make sure all the components are working as expected.

And that is likely perfect for many of today's enthusiasts. I was speaking for myself. And the reality is I have little in common with today's enthusiasts. So your point is well taken.

 

[Bigfoots N Mopars]

I’m late to this thread, we Dyno’d my 512 last March. My main selling point was to break in the solid lifter cam and the engine. As far as tuning the timing was best at the first set up and the Quick Fuel 850 was almost perfect out of the box. (Maybe a little small??) We did find an oil leak wich was fixed post Dyno. I was very happy to not find that after the drive train was in the car. I am proud of my “numbers” but agree they mean nothing until I get to a track.

Would also like to hear more from the OP, I’m running TF 270s with a smaller cam .650 lift non roller cam.

I would like to do a rwhp Dyno session when my car is done, but just to see how the engine stall converter and 4:10 gears work together. But will probably do the Track instead

 

[65Fury440]

I’m late to this thread, we Dyno’d my 512 last March. My main selling point was to break in the solid lifter cam and the engine. As far as tuning the timing was best at the first set up and the Quick Fuel 850 was almost perfect out of the box. (Maybe a little small??) We did find an oil leak wich was fixed post Dyno. I was very happy to not find that after the drive train was in the car. I am proud of my “numbers” but agree they mean nothing until I get to a track.

Would also like to hear more from the OP, I’m running TF 270s with a smaller cam .650 lift non roller cam.

I would like to do a rwhp Dyno session when my car is done, but just to see how the engine stall converter and 4:10 gears work together. But will probably do the Track instead

Not to derail the thread, for comparison sake, what numbers did your engine pull?

 

[Challenger340]

IMO, Engine Dyno's are a beautiful thing, not "just" for the invaluable Break-in/Tuning/Proof of Patent product etc. before the Engine goes in the Car..... but when used longer term ? even with basically the same engine builds over & over again ? the things that commonly are taken as "gospel" in Engine Building that get dis-proven !
I will leave it at that.

 

[BlooDSMeaR]

I have never done a dyno session until my last engine build. I did it so I know where the numbers sit what RPM range is so on and so forth. This is my first hot rod engine built for strip then street. My first engine ran on the dyno and made great power, Brought it home and installed it a few days later it developed a miss. Found the cam took its time to wipe the lobe.
On my second time around I had a HYD roller cam installed so I wouldn't have to worry about the cam again. On start up she ran great, but on the 3rd or 4th pull, one of the lifters failed. I was lucky I didn't just bring it home and install it. This machine shop does not give a warranty on race builds. He had to eat the cost of the new roller cam and lifter, and all the other materials he had to use. That's why I paid the extra $300 to have it ran.

On a side note, What is the OP doing with the Demon 850 carb he took off? I could use a bigger carb, if he wants to sell it.

 

[Hemirunner]

As a drag racer, I like the info to correctly convey the right information to the converter guy...

 

[moper]

First off - Don't worry. It's not broke. It's more than likely the combination of the Mustang dyno (how it takes and plots the power points and the calibration), and the convertor. If you want to really know, as was said earlier - go run the car, get the mph, and then weigh it at the track. Dynos are at best tools. Not god. Not fact. Not empirical numbers. So my advice is, if it's mechanically good, go run it. It is much easier to get power that way, and it rules out all the BS numbers others may have seen.