Well, I attended the Tampa Dyno Day here on Sunday (3/23) and had high hopes that the following improvements would yield some stellar results:

DART Iron Eagle Heads (180cc intake runner)
Hedman Jet-Hot headers
rebuilt carb and re-jetted

The last dyno run before these changes produced an impressive, flat torque curve and steady hp curve with maximums of 241.9 and 190.5 respectively.

The good news, I beat the max torque number, producing 308.1 ft lbs of torque and improved on the max hp, producing 210.5hp.

The bad news, max torque came in right at 2000 rpm and trailed off. The horsepower curve was comparable to my prior run.

Worth noting, my carb was running rich. I had some engine behavior problems (read: vacuum leaks) that I attempted to correct by richening the main jet and primary metering rods. Later, I corrected the vac leaks with a fresh set of carb gaskets around a metal spacer that came from Bow-Tie overdrives with a new TVS system. I probably should have re-installed the leaner jets/metering rods. a/f ratio on my prior dyno run were about 13.5 under WOT. This time, a/f ratio was 11.1 to 12.0; probably a bit on the rich side.

Question: could the rich condition have resulted in the lousy torque performance? The torque really trailed off after 2000rpm to the point where I actually produced far less torque overall compared to the 882 heads, cast iron exhaust manifolds and leaky carb.

BTW, I didn't notice until I returned home that the DynoSheet reading along the horizontal axis showed a reading in elapsed seconds vs. RPM. I can guess at the approximate RPM points as I performed the run from 2000 to 5500rpm. Sort of added to the overall disappointment of the day.

Bummer... :banghead: :banghead: :banghead:

DynoDay 2002:


DynoDay 2003:



[Modified by TedH, 9:13 AM 3/24/2003]

 

Sounds like you need a different cam to take advantage of the heads and headers.

 

The cam is a crane energizer, 270H with max lift of .454/.454. It is comparable to the Comp Cams High Energy 268H. Per the engine builder, the cam and heads are a good match.

I'm suspecting carb and/or ignition.

 

The graph you posted shows you running LEAN, not rich. AFR in the mid 13's to high 13's. You should aim for AFR in the 12.8-13.0 range. It's better to be slightly rich than lean. 12.5 will loose maybe 1-2 hp. 13.5 will drop 20-30.

Also check the timing curve. MAke sure you get 36 degrees above 3000 rpm with no vacuum.

 

So, which is leaner:

11.3 A/F Ratio

or

12.5-13.2 A/F Ratio

My understanding is that 11.3 is RICHER than 12.5 as there are fewer parts of air to fuel. Correct?

What is the recommended A/F ratio for a Carb'd engine under WOT?

 

Just repeating what zwede said above, the higher the number, the leaner. The lower, the richer. 11 is richer than 12, 13 is leaner than 12.

Zwede said 12.8-13.0 is about optimal. I think stoich is 12.5, but if everything were perfect, we wouldn't have to worry about AF ratio. :)

-Steve

 

Just think in gallons. One gallon fuel to 11 gallons air (11 to 1) or one gallon fuel to 13 gallons air (13 to 1). 13:1 is much leaner then 11:1. :)

tom...

 

Yes, running rich will kill performance. Usually noted on the dyno sheet. As soon as the gas kicks in the power drops. Your engine still builds power, so I don't think it is resulting in a huge power lose. Was there any black smoke coming out the back?

 

No noticable smoke.

 

One thing I did differently from the prior dyno pull was to attaching the distributor vacuum advance hose to a different port on the carb. Per Lars' instructions, I attached the vac advance hose to the 'ported' vacuum source on the right front corner of the carb base. Previously, it was attached to 'direct manifold vacuum' at the port on the left front corner of the carb. Since this is more an idle consideration (prevents vac advance at idle), it should not have impacted WOT performance.

 

I dunno, I think gaining 30 hp and 65 lb/ft torque is nothing to be dissapointed about for a head and header upgrade.

As far as the A/F issue, it looks like in the mid to upper RPM (>3500), the A/F is almost exactly the same as the old A/F, but I may be missing something.

 

The torque gain of 65+ was all at 2000rpm and trailed off after that (wasn't sustained). I would have expected to see it sustained at that level longer than just at 2000rpm. I'm suspecting a problem with either fuel or ignition as it appears I hit a brick wall on torque at 2000rpm.

The a/f ratio spiked over 13 after I took my foot off of the gas. Prior to that, it hovered around 11.8-12.0. Old a/f hovered between 13.2 and 13.5 right up to 5200rpm.

 

Something is definetely wrong... The power is too low for your setup...

 

:withstupid:

 

Ted:
What is your compression ratio? That cam is really small, I ran a cam similar to that (as you pointed out) when I ran the 268H in my stock L48 350. I would step the cam up if you have the compression ratio to support it.

As far as running lean. 75% of all muscle cars are run too rich, the difficult part is leaning a motor out. Of course you don't want it running way too lean, but a lean motor builds more power. Did you know that grand national stock car qualifying engines were run extra lean, alot of advance and run hot to get the most power. It is now no longer allowed but that's what they used to do. Rich engines are safer but are missing out on power because of running rich.

 

I am wondering if this is what the heads are supposed to do ? On the surface it does not look right but that might be in line with the runner size etc. WHy don't you give Dart a call ? Your torque is good. :D


[Modified by MotorHead, 6:28 PM 3/24/2003]

 

There was one other thing that I changed: rocker arms. I had wolverine stamped steel rockers (1.5 ratio) with the 882 heads and switched to Summit stamped rockers (1.5 ratio). If the rockers have an effective ratio that is significantly lower than 1.5, I'm wondering if they could be making my cam look smaller than it is. I still have the wolverine rockers. I went with the Summit because they also had the anti-gall pivot *****, I needed a fresh set of locking nuts and the price was right for the complete set; approx $50. Now, I'm wondering if I shot myself in the foot with that decision.

Any experience with Summit stamped rockers (good or bad)?

 

What Intake are you running? could be restictive...
I think you are on to the problem with the rockers/cam questions.. Probably just Not flowing enough...

 

You could probably bump it up to 1.6:1 roller tip rockers for a little more lift and help get a little more air into the motor.


-Aaron.

 

I may have found the problem. My air cleaner is the OEM version, dual snorkel with Thermal actuators on each snorkel. I have found that under most conditions the passenger side 'flap' stays closed regardless of air flow and temperature. What happens if the front snorkel's 'flap' also closed under hard acceleration? My suspicion is that for whatever reason, that is my problem. The flaps are closing on me and causing the air cleaner to pull through a 2" metal hot air tube that is attached to my left header. My suspicion tells me that is why my torque stops at 2000rpm although hp climbs to about 210ph. Both should climb much higher.

My thoughts are that I have an air restriction ahead of the heads, valves, rockers and intake manifold and its name is the air cleaner's thermal actuators. One way to test this theory would be to run the engine on a dyno with an open element air cleaner or w/out an air cleaner at all (one or two pulls should tell the tale). If that proves to be the problem, that should also resolve my rich condition under WOT; more air...

wish me luck! :seeya