Odd Dyno results
 

Put my motor back on the dyno today, mainly to check Air/fuel ratio and to test some carb spacers.
I built this Demon carburated 410 ci. SBC last year and dyno'd it last year with dyno headers: 496HP.@5400, 526 TQ@4500. A/F ratio 14.7 @WOT (yeah a bit lean) and the motor had some "run on" when we killed it. This "run on" would only last for about a second, but usually would result in backward engine spin. I went up on main jets 4 sizes from the 78 primary and 86 secondary, but did this off the Dyno. I regularly monitor plugs, and the motor has never had any "run on" in the boat.

So now to my results today, best of 487HP@5400, 517TQ@4400. A/F ratio 14.2 and the same old dyno "run on"
I went up 2 more sizes on jets, this helped the run on a little a bit and brought A/F down to the mid 13's.
I swapped my 1" four hole spacer (used in all previous tests) for a 1" open spacer. This lost about 5-8 HP and TQ across the board except at 5300-5400, gained 1hp and 1ftp, but no "run on". Next I tried no spacer, same result HP and TQ down, but no "run on". Put the 4-hole back on, power was back up and so was the "run on".
So am I still too lean? What's the deal with the spacers? I realize that my wet exhaust will fatten up the A/F, I'm just puzzled about this on the Dyno.

Re: Odd Dyno results
 

Run on can be from simple things like too high idle or shutting off at too high rpm , also.

List engine specs / parts used / timing / fuel used, etc.

Re: Odd Dyno results
 

Is this an actual A/F ratio from a WBO2 sensor, or a calculated number from the dyno?

Also, how much timing are you running at idle, and total?

Re: Odd Dyno results
 

How big is your carb (cfm) Maybe to big , giving poor signal to the booster ? THats why it likes the carb spacer.

Re: Odd Dyno results
 

Air flow calculated from dyno. Timing 21 degrees initial, 33 total.
750 Marine demon mechanical sec. After each pull, engine would idle down to 875 RPM and a/f would stabilize in the low 14's.
Like I said in the boat, even after a hard run, it will shut down smoothly.

4.00 stroke
4.04 bore
228/[email protected] 112 LSA setup on 110 ICL
10.3 static CR.
RPM Air Gap
91 octane

Without recurving the dist. I pulled total down to 30 which put initial @18 really no difference in run on, but a substantial difference in power.

Re: Odd Dyno results
 

Your Air Fuel Ratio numbers are WRONG! You may be able to idle properly at that kind A/F but you’re not going to run properly there. What are you running for an ignition system to get that kind of curve? 21 degrees would be extremely high for a combination like this; it should probably be closer to 15 or 16 degrees. If it doesn’t run on in the boat it may be due to the way your dyno operating is loading the engine. A 4-hole carburetor spacer usually is going to draw more fuel through the carburetor. As far as your tuning goes I would go with what runs the best in the boat, not on the pump.

Re: Odd Dyno results
 

I'm guessing that with your cylinder pressure, higher water temps of dyno, fuel octane, and possibility of some fuel still dripping out of boosters, is causing your run on.

What was water temp when this happened ?

The colder lake/ocean water and cyl head temps probably are keeping this from happening.

Can't guess if there is some other issue.

If no WB 02 the dyno's use air flow readings and fuel flow readings to determine A/F ratio's. Not accurate this way.

Re: Odd Dyno results
 

162 water temp. Mallory Dist., sloted adjustable plate. I can set as little or as much advance as I want within it's parameters. This motor likes 20 degrees initial without stumbling when blipping the throttle. I realize the caculated a/f isn't exact, and I ran this motor all of last year without any problems and it ran STRONG. I believe that my setup is fine for this application.

So maybe the 4-hole, unlike the open spacer, is creating a stronger signal and trying to pull fuel out of the boosters?
This dyno session was mainly to see the difference in power after a year and to also test spacers to see if any difference.
It looks like power was down about 2% from last year.

Re: Odd Dyno results
 

At Idle....doesent a carb pull fuel from the idle transfer slots that not regulated by the main jets ????????

Re: Odd Dyno results
 

Yup.

But at close to 900rpm if just using primary throttle blades for idle speed they may be open just enough to uncover them.........Also, a little too high float would dribble some thru boosters also.

Having one spacer do it vs another spacer would lead to possible chance this is happening.

Speaking of which - that cid's, rpm, and hp the open spacer should have made some more power. A few possible reasons why it didn't is #1 intake manifold too much of a restriction and/or #2 carb calibration is off.

A dual plane intake on top of an engine like this is going to have a 'killer draw' on the boosters and thus pull mucho fuel from them. A 500hp 410cid SBC is moving quite some air.

Re: Odd Dyno results
 

Float levels are good, idle transfer slots are "square".
I have thought about a single plane intake, I guess I am afraid of killing some torque on the bottom, and I don't want to raise the RPM.

Re: Odd Dyno results
 

The coupler I use on my dyno weighs a good 20 lbs. So, the rotating mass is quite a bit heavier when on the dyno. This may be contributing to a run on problem, just like idling too fast. Plus in the boat you have added drag from the drive. This could explain why it has runon on the dyno and not in the boat. I like to run my natually aspirated marine engines around 12.5-12.8 at WOT. You need to install an 02 sensor and measure it in full marine trim. That can effect the A/F a lot.

Re: Odd Dyno results
 

Not knowing how high you pulled the engine it would be hard to say for certain, but most likely the open spacer would have shown a little more power up higher (outside of where you're using this engine).

Most likely it's just the way the combination is running on the dyno.

Here's some information about spacers:

Carburetor Spacers:

Carburetors spacers can be a very useful tuning aid when working on your streetcar, or racecar. A spacer can be used to move the torque and power-band where it is more usable in your application, or they can be used to help work out inefficiencies in your combination.

4-Hole Spacers. As a rule of thumb a 4-hole designed spacer (4 individual holes one under each barrel of your carburetor) will increase your throttle response, and acceleration. They can also move the torque and power-band down in the RPM range. This is accomplished by keeping the air and fuel flowing in more of a column, which increases the air velocity. This can be a perfect addition if your vehicles throttle response is not as good as you’d like, or you’re getting passed when you pick up the throttle coming off of the corning. A 4-hole spacer can also help make up for something in the intake tract being larger than optimal (too large of a carburetor, cam, intake, etc.)

Open Spacers. As a rule of thumb an open designed spacer (1 big hole underneath your carburetor) will decrease your throttle response, and acceleration. They can also move the torque and power-band up in the RPM range. This is accomplished by increasing the plenum area, which will help in the higher RPM’s. This can be a perfect addition if your vehicle has traction problems when accelerating, or coming off of the corner. A 4-hole spacer can also help make up for something in the intake tract being smaller than optimal (too small of a carburetor, cam, intake, etc.)

Combination Spacers. A combination spacer (half 4-hole, and half open) can give you the best of both worlds. Increasing your throttle response, and acceleration over not using a spacer, and increasing or broadening the torque and power-band.

Plenum Dividers. A Plenum divider does as the name implies divides the plenum in an open plenum intake manifold from side to side. These are generally used to help prevent fuel slosh from side to side in high G load Oval-Track, or Road-Race applications. It is common on certain engines to have lean cylinders do to fuel slosh. A SBC oval track engine running on methanol can run lean on cylinders 3 & 5 while cylinders 4 & 6 will run rich. A plenum divider can help eliminate this.

Spacer thickness. Varying the thickness of your spacer will affect how it affects your engine. Normally the thicker the spacer the more of an affect if will have on your combination. Meaning if a ½” thick spacer helps you a little a 2” thick spacer can give you more of the same affect.

Spacer Material. There are many different types of materials used for manufacturing spacers. They all have pro’s and con’s. Wood for example is a great material as far as thermo efficiency, but can wick fuel, which is not safe. Plastic, or composite spacers are also very good at not transferring heat, but are not as strong, and can be harder to modify. Generally Phenolic fiber, or Aluminum is preferred. Phenolic is very good at not transferring heat, but can be hard to modify. Aluminum is not as good at heat dissipation, but can be ported or modified easily to work on specific applications.

Spacer Tuning. Since each spacer will react differently on each combination there is not a right or wrong type. Spacers are a great tool to have to help dial in a new combination, or tune your racecar for varying track conditions. Swapping out a spacer is a very simple change that can have great impact on the drivability of your streetcar, or racecar or even your boat. Having a couple types, and thickness of spacers around is always a good investment.

Re: Odd Dyno results
 

Doug,

Great Information

Re: Odd Dyno results
 

Thanks Doug,
That is a good read.
We limited the pulls to 5400r's (my choice) and the motor was still making power, so it's possible I might have seen additional hp at a higher RPM.

Re: Odd Dyno results
 

The rotational mass theory makes sense. I'm probably on the edge of detonation with the octane, compression and a/f. Occasionally I will mix 10 percent 110 octane with 91, and according to my calculator it yeilds 93.
How would a guy install an 02 in the riser of my Stainless marine manifolds?

Re: Odd Dyno results
 

If the power hadn't rolled over (or peaked) where you stopped the pulls you most likely would have seen more gain, but making power outside of your operating range doesn't really do you any good.

Re: Odd Dyno results
 

I sent one to SSM and had them do it. Cost was around $100. But any welding shop that can weld stainless can weld a bung in.

Re: Odd Dyno results
 

I can weld stainless. So the sensor would pass through the water jacket, maybe through a sleeve? And the bung is welded to the inner(exhaust pipe)?
Would you happen to have a picture?

Re: Odd Dyno results
 

post 25
http://www.offshoreonly.com/forums/s...highlight=bung

Re: Odd Dyno results
 

Lance, here is a pic of the spacers I had made.

http://www.crowniehq.com/forum/attac...5&d=1146522848

http://www.crowniehq.com/forum/attac...6&d=1146522848

Re: Odd Dyno results
 

Hey Tom,
That looks good, except I can't use a spacer on my manifolds, the risers clamp on.
On my risers, there is a gap between the inner and outer tubes anywhere from 1/8 to 1/4". The bung would have to be welded to both to create a seal. I'm not sure I could get a bead all the way around it on the inside.

Re: Odd Dyno results
 

Is that bung through a "wet" part of the exhaust? I can't really tell from the inside pic.
I just got to studying the picture of my manifold (above) and there may be enough room on the riser, just above the clamp. I believe that is a "dry area", I'll have to pull them apart to find out.

Re: Odd Dyno results
 

LMAC, I didn't realize this was you Lance. Thought those numbers sounded familiar. I've got a SSM riser with bung attached you can borrow. Just pay shipping. Are you near Brett in Kansas? He's coming here today, I can send it with him. Call me 830 6935591.

Bob

Re: Odd Dyno results
 

I'm in between you guys, OKC.
Good luck to Brett getting there and back, we are getting hammered with freezing rain and ice. It's supposed to stop sometime Sunday.
Thanks for the offer Bob, I may take you up on that when I get this thing completed. Actually I was thinking of installing a permanent A/F monitor. I've been doing a little research looking for a stand alone system, prices are all over the board. In your opinion, what would be the best system for what I'm wanting to do?

Re: Odd Dyno results
 

The Innovate LM-1 is what I use. Very good product at a reasonable price.

Re: Odd Dyno results
 

The Innovate stuff, or the F.A.S.T. systems are probably the best out there for the money.

Re: Odd Dyno results
 

Thanks guys,
I'll do a little searching for the best deal.

Re: Odd Dyno results
 

The Innovate stuff has some nice features, and you can always add LC-1's and add more than 1 WBO2.

Re: Odd Dyno results
 

Thanks for the input guys,
I purchased this:
http://www.innovatemotorsports.com/x...bf867f628aa2c8

Come on WARM weather!

Re: Odd Dyno results
 

Alot of the guys I see running this one, it will record

http://www.innovatemotorsports.com/x...cat=261&page=1