At minimum you should look at exhaust temps. I have not been impressed with the older methods of airflow and fuel flow since both are hard to calibrate over a wide range. You may want to invest in an air/fuel meter that uses a wideband O2 sensor.

Yeah, I'd pop it in the car break it in and then get it all tuned up. A lot changes to the tune when under a load (a Dynojet is roughly 2800 lbs). What people call "rolling road" dyno is the best for all around tuning. But honestly, so is reading the plugs  

Don’t let the dyno naysayers get you down. 

Have you talked to the local dyno operators about what their opinion is?  Just a seat of the pants guess but by knowing displacement, RPM and fuel comsumption it seems like one could come up with an approximation of air fuel ratio.

I have spent a lot of long days in a dyno cell. More were joyous occasions some were not. I have pretty much decided that the biggest value of those days was to get everything  to about 90 percent. There are so many more dynamic things to consider when you get things all together in the car. Vehicle dynamic loading is a lot different than a water brake or eddy current load. Unless you just want the experience or you are going to race the thing, I would spend the money on a good air fuel ratio gauge and put the motor in the car. I can't ever remember running an engine on road or track the way it came off the dyno. At least I had to change mixture. The air/fuel ratio meter makes that a breeze.

If you are knowledgeable and experienced, firing off a brand new engine in your car may seem like no big deal.

But, if you are like me, and do not possess black magic plug reading skills, carburetor ouija board for jetting, chicken bones to set the timing and distributor curve, plus nerves of steel to break in a flat tappet cam spending $300-$600 to get someone to do it on a dyno and make a few pulls may actually be a smart investment.

Could be even more of a challenge in the car if you have to run reduced rate valve springs for cam break-in.  Even with a quality AFR gauge sometimes taking that info and correctly applying it is difficult for someone who does not have their masters in vacuum and Carburetor magic.

Plus the value of finding a leak before you very carefully install the engine and all accoutrements.

All this being said, my car will have an AFR gage, and it will get tuned while on the road.

Last edited by Bentworker (10/15/2018 7:43 PM)

Honestly, reading plugs doesn't work anymore.  It may with points ignition, but once you go to anything high energy the spark is so hot they don't foul out anymore and come out looking like its got a good mixture unless its WAAAAY off. 

I've never tuned an engine by reading plugs that wasn't a two stroke.  Tuning to me is as follows:

Tuning fuel delivery on a carbueted system is somewhat intuitive with a properly sized carb.  One reason I really like the Edelbrock carbs is that they are easy to tune.  If you limit yourself to making one change at a time and observing the impact on drivability you can tell if the change was positive or negative and then make further changes from there.  Once you have that dialed in you can make strip passes until the car is consistent and then try making further changes in the quest for more power and lower ET, though you may also find you lose some drivability.  I take a pass on a fast car at the strip that's no fun to drive on the street.

Timing is a bit more cryptic.  I always start timing an engine based on compression ratio and efficiency.  A modern chamber in a high compression engine is going to need less timing.  An old chamber design on a low compression engine will want a lot of timing.  I would start with no more than 32 degrees total on a higher performance engine, and start around 36 on a low performance one.  Typically you want light springs and all the advance in by 3,000 RPM.  You can try the old bump base timing 2 degrees till it pings then back off, but some engines just won't ping and you have to tune it by feel and drivability.  Once you get that set you can monkey with vacuum advance if you want.  You won't be able to do any of this effectively on a dyno.  You can tune for max power; that's it.  Those same settings may well cause detonation in the car.  Timing on the ragged edge is heavily load dependent. 

One thing to consider about a dyno is that IMO its not a great way to break in an engine, because of the load applied you are really more wearing it in than breaking it in.  On a race engine that's going to live a short life anyway its not a big deal; its going to be under load all its life.  On a street engine you're giving up some longevity starting it off this way. 

So, in summation, for the experience of it?  By all means go for it.  Under the auspices that it will be better tuned?  Either you can tune an engine or you can't.  A dyno is just another tool, but its no substitute for fundamental understanding of how engines work and how changes affect the system.  If you're going by A/F ratio an in car gauge is going to tell you more in the long run than one on a dyno, because the engine is under dynamic loading. 

I paid to have the engine dyno’d and thought it was money well spent. It’s been years since I tried to tune anything and I probable wasn’t that good back then. I got the sheet for bragging rights, the tune was good enough, not perfect, I got to hear it run, and I found out where it was leaking oil and water before it went into the car and corrected that on the engine stand.

If they have a set of dyno headers available, use them. My headers were new with no runtime till the dyno. The ceramic coating was dulled a good bit during the dyno time. I have read that the dulling is a common thing during dyno time due to the heat generated. Does that happen all the time or just to me, I have no idea. Just putting it out there as food for thought.

If the headers aren't glowing you aren't dialed in yet

The old saying is lean is mean, and its 100% true, but it does make some heat. 

Read the plugs or not?  Hey man, whatever works for you.  I'm just saying its never worked for me once we topped 50,000 volts on the ignition, which was first gen GM HEIs and any Fox body or later Mustang I worked on.  Now, electrode erosion from preigniton is a different matter, BUT you have to be careful that what you are really seeing is preignition and not a plug with the incorrect heat range.  Plugs that are too hot will lose the electrode from overheating.  Its harder to pinpoint on thicker electrodes, but on thin wire platinum or iridium plugs I've literally seen them disappear.  A colder plug solved the issue I was having on that particular car, but it was a different set of circumstances that led me to consider heat range as opposed to preignition first, SO it all comes down to experience and unfortunately for the novice there's no magic fix for that. 

The good news is that the more you tune the better you tend to get at it.  You'll figure out a particular car/engine and know what it likes and doesn't and when.  My biggest advice while learning is WRITE STUFF DOWN.  I bounce back and forth from late model EFI to Diesel to old school carb on my various vehicles and I can't remember what the last setup was, what it did, etc.  So I've found taking good notes to be an absolute necessity.  I can tell exactly what my setup is by just looking at the notes, and I can see what I already tried, so I know it either worked better or worse, or made no difference and continue on from there. 

Ok, here are the general specs.

347”
3.25” stroke
4.125” bore
5.4”’ rod
Internally balanced
10.25:1 compression
AFR 185 heads
Edelbrock Air Gap manifold
Quickfuel based 680 VS card
Cam is a relatively mild custom ground Comp roller. 218/224 duration, lift is 550 and lsa is 114.
1.6 rockers
Distributor and ignition is Pertronix Ignitor III

I think that covers the important bits!

So is this like the Price is Right?

Whomever gets closer without going over wins a free bottle of air?

I’ll guess 365... pretty sure 6sally6 is right on.

Bentworker wrote:

So is this like the Price is Right?

Whomever gets closer without going over wins a free bottle of air?

I’ll guess 365... pretty sure 6sally6 is right on.

And yes, Price is Right rules apply! 😀
 

371