The compression test is being done today. The plugs looked good and dry. The headers are the same as my hooker sidepipes, It's pretty much open at their shop. I'm thinking the Shogun breathers aren't breathing at all either, hence the blown out rear intake gasket and new timing cover seal leaking. I'm setting it up to suck into the base of the carb which I don't like but will improve the pressure/vacuum differences inside the block. The temp of the engine is below 190, he says it can't go above that. They are going to have to pressure wash this whole dyno room now....coated in oil.

 

Do you feel any pressure coming out of the breathers? Open breathers will do fine to vent the crankcase. Setting up a PCV will do little at WOT. They close off with low vacuum during WOT. You will still need good open breathers.

Good luck!


JIM

 

Which demon do you actual have? Down at my friends race shop they also have the throttle and engine loading handles. It takes some practice to not overload the motor before full throttle. Or else the motor will never hit peak power.

did you get some print outs on the A/f ratio and the specific ratio numbers?

 

did you get some print outs on the A/f ratio and the specific ratio numbers?[/QUOTE]

Good question George.......one of us should have thought of that sooner in the post. :o

 

Please see post on page 2: "Well the good news is it stayed together! With your runs, were you able to get A/F, BSFC and cylinder temps? These would give indication of how good your fuel curve is. These normally aspirated engines typically make best power in the 12.7 – 13.0 A/F range."

 

Well, today is another day and the saga continues. Got the intake gasket changed so the dyno room isn't in a mist of oil, changed jets and shooter cams, you couldn't see because of stinging eyes it was so bad. Started the motor up today and ... a loud exhaust leak, not a good one. A couple of the guys mentioned yesterday that they heard a miss, I did hear a small one but just chocked it up to an extra loud dyno room, nothing I considered serious. Well, today it reared it's ugly head in the way of a dead #7 cylinder. We had everything hooked up including hooking up the A/F ratio moniter . Fired it up and there it was. It's torn down right now, the head is off and the valve, head and intake gaskets are on the way. It looks like it was my mistake for not having #7 exhaust valve adjusted right. I went through it all but I'm wondering if the pushrod wasn't in the right place when it was tightened down and on opening stroke it just jammed open a little more than it should. Maybe the lifter didn't pump up all the way . Anyhow, the new stuff is ordered and I'm going to swap lifter pairs at 7 and 5 to eliminate the lifter issue, unless the problem goes to 5... These guys at the shop are great, I said...Ok, unbolt it, I'll take it home and get her done and the manager or owner of the shop says..."just tear it down and leave it there, your doing the work, it's ok there". Wow...it pays to buy you stuff and have them do the bottom end stuff at this shop. I've know the one guy there for over 20 years but just recently got acquainted with the rest of the guys. Good bunch of guys. I'm hoping thats the reason for only 420hp. I'm crossing my fingers. Wish me luck. I forgot to mention....#7 exhaust was bent. There was a perfect black circle on the top of the piston but it didn't even scratch the piston either. While the head was off I noticed a perfect burn, nothing on the outside, just a little black on the peaks of the pistins

 

I bought this Demon off of a guy on here. He said it was a Demon 850 but flows 950. Don't ask, I don't know. Regarding overloading, one pull he had the motor loaded right down at just around 2500 and took a few seconds to start revving up to overcome the load. I'm really not sure how it works so I couldn't tell you if he's doing it right or not.

 

Sounds like you're onto some HP there. Keep after it..it's all going to pay off soon!


JIM

 

Yes the Demon 850 flows allot more than the rated. I was just looking at their site for the base line jetting.

I recently did a small block stroker 396 ci on the dyno. We had to fab up the front pull throttle linkage to get full open throttle. We got up to exhaust gas temps of 1370 degrees and had a temp variation of 1224 on the lowest.

Your cam is small, but it should have TQ way up in the high 500's or low 600 in the 4400 t0 4900 range.

I've seen some oval port BBC iron heads on the dyno and they got the best power with 36 degrees total timing all in at 3000. So run the motor with no load and set the timing at 36 max without any vac advance.

I could never get my out of the box demon to run right. So I had a race carb shop dial in the air bleeds.............................. on a dyno test mule motor.

 

link to my last dyno day on a rear wheel

http://forums.corvetteforum.com/show...highlight=dyno

 

Well, I hope this cylinder is the reason for a low reading. Otherwise I'm thinking the dyno is not calibrated right. In the end though, its getting all the bugs out and the timing and carb set up right. I can always change heads if I don't like it. Maybe when it's all done a good chassis dyno will have the right numbers.

 

Well here's the results of the tear down. The shuffling valve...sorry, forgot to switch off video for the rocker...this was probably my fault . I'm thinking the pushrod wasn't sitting correctly when I tightened it down. Damn rookie...

 

Here's the video before the new dyno run. Clearly a smoother more responsive motor.



Now for a few dyno runs.This is the first one after the valve changeout.No jetting change, timing at 34 degrees.


And a few F-UP's


Here's the final run...




I'm happy with this outcome. 507hp is good enough for me. With a bit of timing adjustments and jetting it should go a little higher.

 

Also to add, this had 8 inches of vacuum at 800 RPM, hence the reason for the killer headlight mod and hydroboost. Average BSFC was .300. We completely forgot to hook up the A/F sensor. I was in a rush to get out of here. I didn't want to have the motor sit another day in this shop. It cost me $667. That includes one head gasket, two sets of intake gaskets and one valve. Not to mention these guys helped with the setup and trouble shooting a few times and it sat on the dyno for 4 days. I think I did well.

 

Looks like good progress, as it was. IMHO, you got off light considering the damage and all the time spent, but I sure wish you could have done more fine tuning rather than being sidetracked by the major debugging, tho. (Cool souvenir, BTW. )

Are you going to post the charts, or at least let us know your peak torque & hp figures w/rpms? ...and interested in knowing if your peak intake vacuum on top end was more than about 1.4-1.5 Hg, also.

 

Sorry guys...One pull I got 507hp at 5300 RPMS and 548ft/lbs at 3900. The printout is of the last run, slightly lower.I had 500ft/lbs from 3000 rpms to about 5300. I'm sure there's more in there somewhere. I will be posting the dyno charts tonight. Wifes scanning them at work. As for the vacuum, it dropped down but I couldn't see the gauge very well, I should have gotten a longer hose.

 

Didn't the dyno guys know that the BSFC should be numbers like .44 - .54 from 2500 - max rpm tested?

Here is an article.

What do dynamometer BSFC #'s tell me?

Brake Specific Fuel Consumption (or BSFC) is the ratio between the engine's fuel mass consumption and the crankshaft power it is producing. This makes it both a valuable fuel efficiency indicator and one more useful tool in gauging an engine's state-of-tune.

In the USA, the fuel flow for BSFC calculations is normally expressed in pounds per hour (lb/hr) while the output units, of course, are in horsepower (Hp). So, our standard formula for BSFC becomes: lb/Hp-hr . For an engine producing 200 horsepower, while guzzling 100 pounds of gasoline per hour, the equation would yield 100/200 = 0.50 BSFC. Unlike AFR (Air/Fuel ratio) readings which only reveal the mixture, BSFC data represents the power provided per fuel unit. AFR and BSFC are not equivalent!

The beauty of BSFC #'s are that they remain similar over a wide range of engine sizes (assuming both are of similar mechanical design and compression ratio). For example, a tiny one cylinder 50cc four-stroke and a 454ci V8 might both have a BSFC ratio of 0.45 lb/Hp-hr (when optimally tuned) at their respective peak torque points. Thus, if either of these engine's were overly richened, its BSFC might climb into the 0.55 to 0.65 range (because the fuel flow in our equation will be going up as the power is going down.

Consider the above example on a dyno that only displays horsepower. Without the BSFC data, it is harder to know that a rich mixture engine is the reason for sub-par output. But, when you also have the BSFC numbers in front of you, it aims you at the cause.

BSFC values all follow a hooked curve. At idle they run much higher - due primarily to the closed throttle pumping losses and excessive camshaft overlap. Minimum BSFC #'s occur at about the peak torque operating rage - the most fuel efficient (per Hp) operating point for an engine. As RPM increases towards peak power, the BSFC rises again, since more fuel energy is consumed just overcoming the speed induced friction and breathing restrictions.

Below are sample BSFC ranges for several typical engine types. Note, these are provided to illustrate relative BSFC behavior only. Realize that any change that improves the mechanical efficiency of the engine (e.g. a dry sump oil pan, electric water pump, low tension rings, lighter oil, etc.) will also reduce its BSFC values!


Engine @ 1,000 @ Peak @ Peak
Type RPM Torque Hp
4-stroke (low compression, carburetor) 0.62 0.47 0.52
4-stroke (high compression, carburetor) 0.60 0.42 0.47
4-stroke (high compression, closed loop) 0.52 0.35 0.42
4-stroke (supercharged, carburetor) 0.75 0.50 0.55
4-stroke (turbocharged, closed loop) 0.57 0.45 0.50
2-stroke (low compression, carburetor) 0.85 0.55 0.60
2-stroke (high compression, carburetor) 0.80 0.50 0.55
Diesel 4-stroke 0.35 0.25 0.30
Diesel 2-stroke 0.40 0.29 0.34

To find the optimum fuel curve for an engine running on the dyno, you should experiment with richer and leaner air fuel mixtures at incremental steady state test points (e.g. every 250 RPM). Starting with a known safe AFR value (rich fuel map, jet, or mixture needle setting) record the Hp, temperature, and BSFC values. Lean down slightly and retest – you are looking for improved power.

Keep in mind that you can easily go too far and end up sticking a piston, etc. This is why you must listen for knocking while monitoring the EGTs, AFR, and BSFC values. Experienced tuners will push the envelope a bit to get a flash Hp reading – but then back off for a cooling period - before the thermal heat sink protection is lost.

Once the peak safe power mixture is determined for each RPM point you can plot a target BSFC curve for the engine combination. Actually duplicating that shape is easy with a mapped fuel injection system. For carburetor equipped applications you normally need to work out air emulsion tube air bleed sizes, tweak boost venturis, etc. and even then some compromises must be accepted.

Back on the road, dynamometer optimized curves often prove to be a bit too lean for a good driving feel. This is because during transient conditions, like moving the throttle or accelerating, mixture requirements change. Since a slightly richer mixture only depresses power a tiny amount, whereas a slightly lean mixture can cause a very noticeable miss-fire and bog, the best drivability compromise is usually to richen up a tiny bit. That way, objectionable lean bogs are avoided at only a small expense of power and fuel economy.

The overall dynamometer verified fuel curve is still valid; it’s just been made more tolerant with a little fattening. As you gain tuning experience with various engine and induction system combinations, you will be able to hit an acceptable derivability mixture with little or no road test time. Compare that with blindly flogging the engine to death on the track – trying to optimize the best power curve mixture.

 

Hmmm... now I have a four stroke diesel. So correct me if I'm wrong but after reading that I take it that my BSFC being low means that the carb is running too lean?!

Great article BTW.

 

That is how I figured also...which means by jetting a bit richer you get more HP

 

What it is saying is that you are very lean. The 1000 rpm idle BSCF is rich at @60 to get a good smooth idle. Then it shows you that peak TQ is reached at a lower .47 BSFC Where peak power is found at a richer .52

I saw this on that 396 I built. To get max hp the TQ number went down. But like the article pointed out that slightly richer runs better on the street.

It is only in this past couple of years that I have been working at a shop with an engine dyno that I have started to understand the finer points