Has anyone had a dyno tune on their small block carb engine. A hot rod shop in the area was very impressive in showing me their dyno set up. The Dyno Guy said "with a pocket full of jets I will get 30 more HP" Is that an accurate statement? I am seriously thinking of going this route.

 

it depends on how well tuned the car is now....

you can find 100 horses on the dyno if the baseline is terrible, the sky is the limit, if your car is real close, he might find 10, but really that would be nominal because he wold be tuning for that peticular day's air density, humitity, and tempature

as soon as the sun rises tomorrow, the world is a different place.

 

But, you'd at least find out the condition of your tune, and you'd likely leave there with the tune optimized to the point that you'd know you didn't need to mess with timing and jets anymore.

 

Good points, the carb would be dialed in so it would only be a matter of the timining, plugs, etc from then on.

 

I'm with Donny here, I had my engine dyno tuned after it was rebuilt and it ran great. But the fine tuning came later after doing some highway & city driving, hot & cold starting & driving etc.. Real life driving has many different conditions, the dyno room has one preset condition.

Dave

 

I would ask beforehand if they have the springs, weights and vac cans to optimize the timing curve, not just set base timing...

This takes more time, and as we know time=money

 

My 63 had been sitting for a couple of years while I was deployed overseas. When I got back I was having a tough time getting it running right, not to mention moving to Colorado with a significant change in altitude. I ended up taking it to a speed shop that specialized in Corvettes and Camaro's to be Dyno tuned. I was very happy with the results.

They jetted the carb for the altitude change and set timing to maximize power, torque, and air/fuel mixture. Gave me several nice graphs, so I have a good baseline for future adjustments. Dyno time ran me about $220/hr, so make sure easy stuff (new plugs, good spark plug wires, etc) is done in advance, so they can focus on adjustments and get you off the Dyno as soon as possible.

 

We spent two days tuning and modifying my 64. I consider it time well spent. The car has never run so well or been so easy to drive. As Mikem350 says you need someone who has all the bits to modify the distributor and carb and knows what he/she is doing. Also I should have done as PRTSkipper suggested and have all the new stuff already installed, like blocking the heat riser ports.

 

Also with all the changes in gas formulations going on, varying from season to season, etc, prob best to use your normal brand, and tell the dyno operator

 

Timing is straightforward. Max WOT advance should be 36-38 degrees. Initial should be as much advance as the engine will tolerate without detonation. Advance should come in as fast as possible without detonation. Vacuum advance should add another 16 degrees to the total at idle and steady state cruise.

The 327/350 has the laziest centrifugal advance map of all the 1965 smallblocks. For best results, start with slightly rich jetting to stave off detonation, and aim for the fastest advance that the engine can handle. If your engine is a stock build using the 151 cam, then if it will tolerate 16 degrees initial and another 20 centrifugal, all in by about 3000, then you will have an excellent performer. This will mean doing some modifications to the advance slot in the distributor's advance mechanism. Remove and do not use the advance slot bushing, and weld up the slot so as to limit max centrifugal to 20 degrees. Mix and match springs to bring in advance as quickly as possible without detonation. It is perfectly acceptable to use 2 different springs on the 2 flyweights.

Once the spark advance, both vacuum and mechanical are set, then decrease jet size until onset of detonation at tip in during cruising...........this is the point of max spark advance and also near max cylinder pressure if the cruise RPM is around 3500 RPM. Step up one jet size from this point. Remember to be consistent with your gasoline. I use Sunoco Ultra 93 since it's the highest octane available in my area, and priced equally with competitors' Tier One gasolines.

As a final check, you can get the car to cruise speed and keep it there for at least 15 minutes. Shut it off while at speed and pull over to a safe spot. Remove and record the color of all 8 plugs. On a 2 plane manifold, the high half of the plenum (passenger side) feeds cylinders 2-3-5-8 and is normally richer than the opposite side. The lower half (driver's side) feeds 1-4-6-7 and is usually leaner than the opposite half. If the spark plugs agree with this, then you can stagger jet the carburetor by one jet size. Of course, you should also compensate with the idle mixture screws to balance them accordingly, as well.

Obviously, all of this takes a lot of time. At $220.00 an hour dyno time, it is not feasible to do this kind of thorough tuning. Computer controlled powertrains are a completely different animal, and dyno tuning for them is a very valuable tool. For pre emissions controlled engines, dyno tuning is not economically feasible unless you own the dyno.

 

Nice description Triple Black

 

Thanks, Tripple Black, That is good information. FYI, I am running a MSD distributor with adjustable advance stops and several sets of springs. I have a stock build with the 151 cam except for flat top pistons. Right now my "all in" advance is 36 @ 3000 RPM. However, the vacume advance is plugged. Also, I have a set of Trick Flo 62cc combustion chamber heads that I was going to install b/4 I do the dyno tune. I would be interested in your thoughts.

 

If he could get 30 more hp out of my engine with a pocket full of jets, I would gladly pay his price.

But the last dyno run, after Lars tuned the car, was at 12.9:1 A/F ratio and I don't think he can get 30 hp by changing the A/F ratio a couple tenths of a point one way or the other.

Depends on what you drive in with.

 

Too bad you have flat top pistons installed......the 151 really runs better with the 5.3cc domed L2166NF pistons, or equivalent.

Questions:

1. Can you tell me the part number of your pistons? If they are the most common replacements for the weaker engines, then they are plain cast aluminum, have 4 valve reliefs and the dome volume is -5.3cc as opposed to the L2166NF forged domed aluminum whose volumes are +5.3cc. There are also 2 valve relief hypereutectics from Speed Pro whose dome volume is -5.0cc.

2. Were the decks or heads ever milled, to your knowledge?

3. What is the overbore, if known?

4. What is the head gasket used on your build. Need compressed thickness and bore diameter.

These will give us an accurate starting point for the engine's static compression ratio. I assume that your heads are 2.02/1.60 461's; if they have not been surface ground then their combustion chamber volume is 66cc. The "small valve" 461's are 64cc. The 62cc heads will gain you some more much needed static compression, but not enough to make the head swap worth the effort..................unless.......... ............you have anything other than steel shim head gaskets in place now. I normally would NOT recommend them, but in your case, the better sealing MLS or composite gaskets are .036", minimum and you need ALL THE static compression you can get.

Because of the SCR deficit, I recommend advancing the cam timing by 4 additional degrees beyond the stock 4 degree recommendation, for a total of eight degrees. Of course, there are better ways to build SCR, the best way by far would be to ACCURATELY deck the block to zero or probably negative deck clearance. Doing this will give you the required 10.75 - 11.0 SCR and, equally important, square up those woefully lopsided decks that were hewn with that monstrous contraption known as a broaching machine. The inaccuracy of that Rube Goldberg device is in the neighborhood of .030", which can leave the nominal deck height of your block at 9.025" plus/minus .020"/.010".

Assuming a .030 overbore, a .019" steel shim head gasket whose bore is 4.100, and 9.025 decks with 4 eyebrow flattops (-5.3cc), 3.25 stroke, 2.02/1.60 461's, and virgin decks and head surfaces.....................your calculated SCR is 9.42:1..............1.25 points below the minimum ideal required for a 151 cam whose timing is 4 degrees advanced.

Having said all of this, I can safely say that if you do nothing to fix your engine's SCR deficit, then you should set your initial timing to 20 degrees, set the stop on the mechanical advance to 18 degrees, use the lightest advance springs possible so as to have your advance come all-in by 2300, and have your vacuum advance function as original and delivering a full 16.5 degrees crankshaft advance at 8.2 in-hg, as original when connected to full manifold vacuum. Any more spark advance than this (even though the engine will still not experience detonation because of your pathetically low cylinder pressure) will kill torque and power.

If you do these things, then try to run the car on mid grade, or even regular fuel. There is a better than even chance that it will run detonation free on regular, and almost a certainty to run detonation free on mid grade.

 

Tripple Black,
I know, I have regretted not installing domed pistons almost since the motor was rebuilt.

-The bore is .030 over

-Don't know what piston but I don't think is is a hyper

-the deck was milled I think .010

-I am pretty sure the heads were also milled as I had them completely reworked

-I think the head gaskets are Fel Pro. not sure of the p/n

Thanks for your input. I appreciate it.

 

Put the 62cc heads on and use a 0.019" steel shim gasket. Advance the cam like I said, and give it all the timing it can handle by following my directions above. We now know that this engine will take all the advance you can throw at it, so why pay someone to arrive at a conclusion that you already know? Just remember...............NO MORE THAN 34 DEGREES MAX WITH THE NEW HEADS (IF THEY HAVE COMPACT, KIDNEY SHAPED CHAMBERS) AND NO MORE THAN 38 WITH THE OLD WEDGE CHAMBERS.

Jet the carb the way I recommended earlier and save your money on the "tune" session. Fill the tank with regular gas and enjoy your Corvette. Curious about power output on the finished product? Pay the usual $100.00 for three pulls and run one in 4th gear and the other two in third gear. Make sure that the pulls start out at 2000-2500 RPM, air cleaner base installed, cover and filter removed, hood open, brand new spark plugs.

Of course, you can always shave those new heads and bring your chambers down to 58cc. If you decide to do that, then we'll have to rework the timing and upgrade to premium fuel.