Author Topic: Dyno time...what to expect  (Read 3648 times)

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BOutlaw

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Dyno time...what to expect
« on: August 26, 2019, 03:45:25 PM »
I'm taking the Ranchero to a chassis dyno this week for the first time. Ive never been on a dyno before and am asking for guidance on what to expect and maybe some things to Do or Not Do. The car has been doing well but I cant seem to improve on 6.80, 1.50 60 ft, 100 mph. Ive recently changed the carb and have run with the new carb but the times are still 680s. What kind of A/F numbers should I be looking for and any other guidance is appreciated.
My engine data was posted on the Drag Strip results thread but Ill post again here.

445 cu in
Comp 306S solid lifter camshaft, stock rockers, Smith Bros pushrods
BBM heads by Blair
FE power intake adapter and Victor 351 Yates intake
4200 convertor
4:81 spool
current carb is a Gary Williams 1020

Any guidance is appreciated. Ill post the results of the Dyno pulls …

Thanks in advance
Brad Outlaw

machoneman

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BOutlaw

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Re: Dyno time...what to expect
« Reply #2 on: August 26, 2019, 05:26:58 PM »
Thanks , Ill sure check that out.

Brad Outlaw

My427stang

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Re: Dyno time...what to expect
« Reply #3 on: August 26, 2019, 05:40:02 PM »
Follow instructions and don’t use the brakes, you will just smoke them up lol

Check for WOT using your foot the way you drive, and maybe take a few degrees of timing out and work up to it, safer

If the bowls haven’t been off in a while may want to put fresh gaskets in now
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Royce

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Re: Dyno time...what to expect
« Reply #4 on: August 26, 2019, 07:41:27 PM »
Chassis dyno is a tuning tool more than a way to measure actual horsepower.. There are so many variables on a chassis dyno it is hard to get any numbers that would correspond to what the engine would make on an engine dyno.. What you can do is look for improvements and try different things.  Hopefully your operator is not one who is carburetor challenged.  I am finding VERY few guys who can help tune a carb.  They all work with boost and EFI these days.. The last one I went to made the pulls gave me the numbers and told me  me make any tuning decisions.. You are going to work on timing and air fuel mostly.  You should get a vacuum reading at WOT which will tell you if your carb is a restriction, and the  machine should print out horsepower and torque curve and fuel curve for the test rpm..Your air fuel should be in the mid 11s to mid 12s  at WOT. At cruise in the 13s   , but those are guesses.  Your engine will tell you what it wants as you try richer and leaner settings.  Look at the fuel curve for anomalies.. It should be smooth across the rpm range  If it bounces around you may have to get deeper into the carb than jets. One thing you should consider doing is welding a bung in the header collector for an oxygen sensor.. The dyno will probably have a probe that slips onto the exhaust but I don't trust those.  Exhaust pulses can pull air back into the pipe and skew the readings..  Good luck and hope you can find some hidden horsepower
1955 Thunderbird Competition Coupe Altered Chassis "War Bird" 383 Lincoln Y block 520 hp
1955 Thunderbird 292 275 hp Y Block
1956 Ford Victoria 292 Y block

1957 Mercury 2dr Wagon "Battle Wagon" drag car 
1957 Thunderbird Glass body Tube Chassis drag car 333 cu in 500 hp Ford Y block
1961 Starliner 390/375 clone
1965 GT40 tribute w/FE
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Joe-JDC

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Re: Dyno time...what to expect
« Reply #5 on: August 26, 2019, 08:29:05 PM »
Do you use carb spacers, take some different ones, and different thicknesses.  Ram air?  Filter or not?  Make sure the tire pressures are even and the tie downs are positioning you on the roller correctly--owner should do this.  If the operator will let you, start your pulls at different launch rpm to see how the torque and hp react at those different rpm.  Check your time to accelerate for changes.   Joe-JDC
Joe-JDC '70GT-500

BOutlaw

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Re: Dyno time...what to expect
« Reply #6 on: August 26, 2019, 09:42:39 PM »
Thank you Joe, Royce and My427. Ive already read your posts numerous times to try and make sure I understand. Im glad you brought up about tuner being a carb guy. I talked to my buddy today whose taking his car as well, and he said the tuner guy not there Thursday as wife is having surgery but the computer guy is there. The tuner guy is a carb guy and apparently is actively running a dragster now. After reading your posts Im thinking we might better put off till Friday. I sure as hell cant make judgements on the data provided and apparently the computer guy is only that. If I do this I want to benefit not guess, soooooo, Im back to re reading your posts and will call tomorrow to try and postpone till Friday. thanks so much you guys.
Brad Outlaw

jayb

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Re: Dyno time...what to expect
« Reply #7 on: August 26, 2019, 11:45:26 PM »
When I dyno an engine I start with a conservative timing setting and run the first pull to gauge air/fuel ratio.  For peak power look for A/F numbers in the 12.5:1 to 13:1 range.  Since you will be at wide open throttle during the dyno pull, changing the main jets up or down will affect those A/F numbers.  If you start out really fat, like numbers around 11.5:1, I would go down 3-4 jet sizes to get into the right range. Otherwise, maybe 2 jet sizes per change, and maybe just primary or secondary, not both. Change jets, and retest.  If you start out lean, go up in size.  Do you have a jet box, or are jets something that the dyno shop provides?  You can't tune if you don't have a selection of jet sizes.

After you get the A/F numbers in the ballpark, start bumping the timing to see if you get an improvement.  With those heads you shouldn't need a lot of timing, so if for example you were starting with 28 degrees total, I'd bump in 2 degree increments and then retest.  Once you find that further increases do not improve the power, go back to the point where it stopped improving and leave the timing there.  By the way, running race gas at the dyno is always recommended, because if you go a little too far in timing advance, you won't hurt the engine when running race gas.

From there, I'd be looking at carb spacer changes or any other changes you want to make.  Sometimes a carb spacer will make no difference, and sometimes it will make a huge difference; I've seen a 25 HP improvement with a carb spacer.  No way to predict what the engine wants, you have to test. 

Dyno day can be a lot of fun; good luck and be sure to let us know how your results pan out - Jay
Jay Brown
- 1969 Mach 1, Drag Week 2005 Winner NA/BB, 511" FE (10.60s @ 129); Drag Week 2007 Runner-Up PA/BB, 490" Supercharged FE (9.35 @ 151)
- 1964 Ford Galaxie, Drag Week 2009 Winner Modified NA (9.50s @ 143), 585" SOHC
- 1969 Shelby Clone, Drag Week 2015 Winner Modified NA (Average 8.98 @ 149), 585" SOHC

   

6667fan

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Re: Dyno time...what to expect
« Reply #8 on: August 27, 2019, 09:44:17 AM »
Ask whoever is responsible if there is confidence in the A/F readings that they will collect. If there is any waffling on their perception of its accuracy I would shop elsewhere.
As mentioned above having your own A/F measuring is advisable if you really want to tune.
Also you could compare your system to the shop readings.
 Some shops focus on BSFC as a measure of efficiency which is nice if you are all about that. However sometimes that puts the engine into a tune state that is too lean for max power.

Have some reusable metering block gaskets on hand.

JB
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BOutlaw

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Re: Dyno time...what to expect
« Reply #9 on: August 27, 2019, 11:00:58 AM »
Thanks so much Jay and 6667fan, and everyone else, all comments help me to better understand what to expect. I feel pretty good about the tuner guy as he is an active racer and carb experienced from what I understand. I want the experience to mean something and will be prepared with jets and a couple spacers. I have a 1/2 in to 1/4 in wedge spacer on the carb now to level the carb, but also have a flat 1/2 inch spacer and a 2 inch spacer available, all three open. I do have a jet box to use. Right now Im running 33 total on the BBM heads and the new carb has 85 primary and 90 secondary jets. Ive reread the posts provided and really appreciate the insight. I will be running 100 VP. I do plan to purchase a good A/F ratio monitoring system but it wont be installed by the time I use the dyno. Im open to recommendations on the A/F system as it is in my plan for updates over the winter. Thanks again to everyone for all the assistance.
Brad Outlaw

blykins

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Re: Dyno time...what to expect
« Reply #10 on: August 27, 2019, 11:12:22 AM »
Take some air bleeds with you.  If the tuner is good, he will be able to see which part of the fuel curve needs to be changed.  Sometimes you need jets, sometimes you need to manipulate the high speed air bleeds.

My SOP is to make a short pull first to see where the AF ratio is.  No need in going whole hog on it if the ratio is way off. 

I would also aim to make your water and oil temps similar to what they are when you're racing, as those will make differences in horsepower. 

Make sure the car is ran with the air cleaner setup that you use as well, as that will affect the AF ratio. 
Brent Lykins
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BOutlaw

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Re: Dyno time...what to expect
« Reply #11 on: August 27, 2019, 12:26:37 PM »
Thanks blykins, sure didn't think of air bleeds either. Don't have any but will check to see if he does. May have to pick some up beforehand. Good idea on temps as well. Its great to have this forum and access to the vast experience available here. Drag racing again after so many years is just as fun as ever but things have changed so much since the 60s 70s. I remember being happy to get 5 runs on a set of Autolites, today there are better ignition systems, carb/intake systems, tires, and equipment to help with tuning. Thank you for your input.
Brad Outlaw

RJP

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Re: Dyno time...what to expect
« Reply #12 on: August 27, 2019, 12:35:58 PM »
BOutlaw, You have a P/M

Drew Pojedinec

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Re: Dyno time...what to expect
« Reply #13 on: August 27, 2019, 12:54:11 PM »
Not to disagree with You Jay, obviously you have a ton of dyno experience.
But why would you take an a/f reading without the timing set?
Seems like ratio will change with timing changes.

jayb

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Re: Dyno time...what to expect
« Reply #14 on: August 27, 2019, 05:03:18 PM »
Drew, I didn't mean to imply that you don't want to set the timing, just to set it at a conservative value to start.  My experience has been that A/F does not change much with timing changes, because usually you start out within 3-4 degrees of where you end up with timing.  I can't recall ever having to make a jet change after bumping the timing to the optimum level.  The other thing is if you do A/F first, you minimize the risk of a lean condition.  Lean A/F plus timing too far advanced can equate to engine damage, especially on pump fuel.

Also, Brent pointed out something I didn't mention, which is to go up the RPM range just a little at first.  I usually start with a pull from 2500 to 4000 RPM for most engines, and look at the A/F curve, adjust jetting (or VE map in an EFI system), and then go again.  When I'm happy at that RPM range, I'll increase it by 1000, usually going from 3000 to 5000 RPM.  Tune A/F, and repeat, move higher in the speed range, etc.  You get the idea...
Jay Brown
- 1969 Mach 1, Drag Week 2005 Winner NA/BB, 511" FE (10.60s @ 129); Drag Week 2007 Runner-Up PA/BB, 490" Supercharged FE (9.35 @ 151)
- 1964 Ford Galaxie, Drag Week 2009 Winner Modified NA (9.50s @ 143), 585" SOHC
- 1969 Shelby Clone, Drag Week 2015 Winner Modified NA (Average 8.98 @ 149), 585" SOHC