Random answers --

The exhaust aft of the cats is not the best. I'd say it's the worst, but a potatoe in the tailpipe would be worse. So, yes, there is definitely exhaust work to be done and I can very easily imagine the engine is doing a lot of work trying to get rid of the exhaust gases. I'm not even going to bother having a back pressure test done because I know I'm going to replace everying from the cats on back. I'd consider just replacing the exhaust before putting it back on the dyno, but the engine behaved reasonably well below 4,400 RPM, so I'm going to get the A/F fixed via the carb jetting and the exhaust fixed, and then back on the dyno.

There is no air pump. There was a working air pump, but it went bye-bye when the headers were put on. Not only is there no belt, there is also ... no pump.

I have no clue what side the sensor was stuck up. Is this Really Really Important, or just kinda important?

The cats should be working very well -- they are brand new. Apparently they are new enough that they even smell brand new. They are also about a foot or two aft of where G-d intended them to go. And there's two of them -- one for each pipe. Would that make the A/F even more artificially lean since each cat is only servicing four cylinders?

Gerry made a comment about engine load and the 15:1 ratio. Remember -- this is supposed to be a 350HP engine. Assuming a 20% loss through the transmission and diff, I should have put down 280HP. So there was more lossage than what I'd have expected.

As regards various comments about jetting, thanks for all the input. QJets (and car carbs in general) are a mystery to me. Anyone have a nice new Goldwing they'd like to trade for a slightly used Corvette? Just kidding.

There are some questions in my mind about my throttle cable, so it's possible the secondary throttle plates aren't being opened completely. Replacing the throttle cable is item #3 on the list of "things to do before going back to Colvin".

 

Where did you get whatever it is you used and how much was it?

 

Not really. Once you know each side in a true dual exhaust registers the same readings, which side is not important as far as a power run. It only shows up as an anomaly when the engine is at idle and you can have a false high reading due to pulsing in the exhaust.

Nope. Only efficiency affects the ratio. If one in a single converter system or both in a dual converter system are operating efficiently, then the reading will reflect the same (again, unscientific) + .5 more oxygen than true.

Even though you are using a ZZ4, the factory rating is optimized. I don't know that I would use that as a scientific basis for comparison. After all, you screw up the carb calibration and/or the ignition and you won't get anywhere near the factory rating. You would have to do an engine to chassis dyno measurement to know what's true. And besides, comparing gross flywheel horsepower to an inertial dyno isn't usually relevant since the measurement techniques are vastly different. You use the dyno, chassis or engine, to tune the engine not as a basis for comparison.

My comment was that an AFR of 15:1 at WOT will make the engine breakup badly unless you have some sophisticated combustion chamber design that we are not privy to. Most carbureted engines are very sensitive to ratios above stoic even in cruise and if you can get this ratio in cruise with a carb and not have a lean surge, then you have one nice setup. Easy to do with EFI and electronic engine management, but so easy with a carb and mechanical ignition.

That's a very common problem when it comes to performance issues. Most dyno operators will make that their first check.

 

Julie
i've been working on an article
http://community.webtv.net/MATTGRU/Dyno

 

Matt,

Your article seems a bit tongue in cheek. How much of it is serious? I'm not interested in playing "my car dynoed better than your car", but must admit that I got a chuckle out of several of the suggestions.

 

it's all so serious, i added #21 for a laugh at the end.
everything doesn't apply to every car every time. u have to pick and choose depending on the car/owners' goals/use

 

Hmmm. Several others besides #21 looked not-so-serious. Like, the one about using ice to cool the intake and the other about removing the cooling fan.

 

1960....Cunningham Corvette....LeMans...finished 8th overall.....on ice...
Rich

 

Yeah, but I don't see driving around town with a block of ice under my hood. There's a name for ice in Texas -- temporarily solid water. There's also a name for cold air induction -- "slightly less unbearably hot air induction". Texas isn't actually Hell, but I suspect it was one of the early models that was later rejected as being not quite hot enough. Close, but not quite.

 

We also need to keep in mind that the humidity may be a factor. There's a lot of water molecules in Texas air. It would be like a Californian taking a spray bottle and maintaining a steady spray into the carb. Water isn't all that bad since it does indeed turn to steam which expands to create the mechanical force, and sometimes seperates into hydrogen and oxygen. Hmmm, I'm wondering if the high O2 reading is due to the later, and the H2 is recombining with loose Carbon to form some unburnt by-products instead of burning like it should. I do know that chemistry speaking if you throw in a tiny bit of platinum catalyst then 2H2 and O2 will burn...that's how the catalytic converters work...not sure if they still use platinum anymore. But, you might want to try some platinum spark plugs. I use Bosch because none of the american manufacturers make a plug that directly cross-references to the stock numbers. But, I think you might be surprised at how much of a difference a platinum plug will make if incomplete combustion is the problem. In brief...I had a Pinto which one exhaust valve that was 1/2 gone, and another that had about 1/8 of it gone...it could hardly get up to 50 miles an hour...actually started to die on me and was getting hard to start. I threw in some platinum plugs and it perked right up and did 70 easy, and ran nicely with quick starts.

 

Just a point of view that took years to notice.

Don't get too caught up in max numbers. They're nice to know but its your driving rpm range where any increases really pay for themselves.

Giving up a few max hp for an increase lower down is more streetable fun. This philosophy works for everyone, just notice what rpm range you normaly drive in, increases here are used much more than at say 6 grand. or even 4400.

I like Dyno run 1 better than 2 since your hp and torque are higher most of the time. This run actually produced more power.

mostly the 3200 - 3600 bump. compared to max value loss.
20 hp? increase vs a 6 hp max loss
20-30 ftlbs increase vs a 4 lb max loss!
Its a wide long gain VS a narrow loss.

Besides it looks like your cam is good to about the 4400 mark while its really meant for the mid range. Pretty flat curves with a break/loss at that rpm point, that also seems to follow your a/f ratio?

 

Rockn-Roll:
I once atomized(misted)water in my carb at 1500 RPM to get rid of a carbon knock.That was in 1982...no problem since,as I started a strict maintenance schedule.
Speaking of those Platiniums,which ones are you running ?
Tallgirl: Gila Bend,AZ is the original model for hell....

 

Wait a minute... the A/F sensor isn't downstream of the cats, is it? If so, I don't know what you're measuring....

 

I assume it was. The sensor was shoved up the tailpipe. It's quite a few feet from the cats to the tailpipe and the thingy didn't look =that= long.

 

Some of these Vettes have a sensing line to the cat itself....Calif version L-48, I think...

 

OK - I'm guessing that, since you have cats and the sensor is downstream of them, that the sensor is used by the dyno shop to tell the "total" condition of the exhaust stream including how effective the cat converters are. If they are newer, they will scrub out a lot of the fuel (hydrocarbons) and clean up the exhaust.
In any case, I'd do my tuning on the performance of the engine and wouldn't worry too much about what these A/F numbers are.

Good luck

 

Bosch 4206 Platinum Plugs...they pop up when parts stores look up replacement plugs.

I think Z-man has a good point Tallgirl. If you really are serious about fine tuning the carb to get the best A/F ratio then perhaps when you do the exhaust thing then get the bolt-on cats and remove them and bolt in a straight pipe before taking it to the dyno for testing & tuning.

 

I chatted with my mechanic long enough this morning (seems my left front fender had an interesting conversation with a brick wall and I need to get a swag on the cost of repairing my newly smashed up fender ...) that the engine cooled. We pulled the #3 plug and lo and behold it was perfectly fine -- nice tan color as far as the eye could see. So I'm guessing that y'all are probably right and the A/F is fine.

After chatting with him I headed over to Royal Muffler and made an appointment to have the mufflers and a mess of exhaust pipe replaced on Monday. Anyone have anything bad to say about Magnaflow's?

After the new mupplers are put on, it'll be off to someplace else to get the current oil changed (it's the second oil change after the motor was put in) and replaced with synthetic. Then back to the dyno and see if the mufflers did anything to move the knee at 4,400 RPM ...

 

HOW HOT does it get in Texas???

Well you can take a pitcher of ice water and spill it toward the ground, and the water will evaporate and ice melt before it ever get there....

GENE

 

You called your mechanic a "dork" several times, then you hit a brick wall with your vette.....hmmmm....Karma? lol...Yes, Tallgirl...this is your "Dork" mechanic saying I'll see you soon.....