Author Topic: 7040207  (Read 2249 times)

Offline boat196

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7040207
« on: April 16, 2018, 09:52:49 PM »
1970 350/350hp, you rebuilt the carb, ran motor on engine dyno. BCFS was .501 at 3000 rpm and .571 at 5800 rpm. The operator noted the motor was running rich. Your thoughts.
Thanks Bob

Offline 77cruiser

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Re: 7040207
« Reply #1 on: April 17, 2018, 10:19:22 AM »
Did it have a wide band on it on the dyno? Either rich or inefficient. Or malfunction of the fuel flow meter.
Jim

Offline boat196

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Re: 7040207
« Reply #2 on: April 17, 2018, 03:21:55 PM »
No it didn't have a wide band. What's the fuel pressure range for a quadrajet.

Offline Cliff Ruggles

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Re: 7040207
« Reply #3 on: April 18, 2018, 04:24:22 AM »
Fuel pressure should be around 6-7 psi for dyno testing.   How much power did it make?

Was the engine stock, or modified anyplace?....

Offline boat196

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Re: 7040207
« Reply #4 on: April 18, 2018, 06:35:36 AM »
The motor is basically stock, except for cylinder head and intake porting the motor made 336 hp @ 5500 rpm and 364 lb ft of torque @ 4200.
Bob

Offline 77cruiser

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Re: 7040207
« Reply #5 on: April 18, 2018, 09:02:00 AM »
Did you pull the plugs after it was dynoed? If so how did they look?
Jim

Offline Cliff Ruggles

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Re: 7040207
« Reply #6 on: April 24, 2018, 02:16:04 AM »
Who ported the heads?  What were the flow numbers before and after the porting?.....Cliff

Offline boat196

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Re: 7040207
« Reply #7 on: April 24, 2018, 02:40:04 PM »
Brzezinski, stock flow are in the range of 180 int/150 exh. Now there 234 int/163 exh @ .450 lift.
Bob

Offline Cliff Ruggles

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Re: 7040207
« Reply #8 on: April 25, 2018, 05:57:33 AM »
Power numbers seem a little low for the combination of parts, but different dyno's come up with different results.  The operator should know if it close to what it should be making on his dyno based on similar builds they have had on there.

We have done a good many 350 builds here, and most come in around 380-420hp with similar parts.  I don't port any of those heads however, that deal doesn't always yield the results one is hoping for without other changes. 

Larger ports and better flow numbers just don't always make more power, especially if the heads had adequate flow for the CID/compression/cam right to start with.

When we dyno tune here I have a full set of custom machined secondary metering rods to dial the A/F in for best power.  The 350/350 carbs are a little "fat" at full throttle as most used AX, DA, or BG metering rods with small/long tips on them.  The emulsion tubes are also pretty small, so at WOT there is typically plenty of fuel being delivered to the engine.

Even with that said chasing A/F on the dyno doesn't typically result in big gains, and it's also a static test and one would need to be using the factory air cleaner and filter element to get it dialed in pretty close.

Things will still change when the engine is put in place, so I don't worry too much about the dyno tuning, we just get them close and do the final tuning once the engine is placed in service.........Cliff

Offline boat196

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Re: 7040207
« Reply #9 on: April 25, 2018, 07:03:39 AM »
Thanks Cliff, for the information, this was explained by you when I sent you the carburetor for rebuild/restoration. The porting was based on the motor needs, My goal was 350hp, the Dyno owner stated too me that his Dyno results are conservative. Next I

Offline Cliff Ruggles

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Re: 7040207
« Reply #10 on: April 26, 2018, 04:16:44 AM »
Without touching the heads other than good valve/seat work the 041 or 186 castings will EASILY make 1hp/CID with the stock cam.  The stock heads runner cross section and flow are very well designed and very well matched to a 350cid engine with the 350hp camshafts in them.  I doubt if the head porting really brought anything to the table for power improvements and can actually hurt power as larger ports tend to slow down the air velocity some.

There are quite a few other "players" in making power.  For SBC's in particular establishing very tight quench is one of them.  I shoot for .025-.035" here for quench distance decking and squaring the block so the pistons are right at the top of the block at TDC and using thin head gaskets........Cliff

Offline boat196

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Re: 7040207
« Reply #11 on: April 28, 2018, 06:57:59 AM »
The quench was set at .030

Offline Cliff Ruggles

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Re: 7040207
« Reply #12 on: May 02, 2018, 03:24:06 AM »
Very good place to be with a well thought out SBC build.  This will make the engine tend to run cooler, take less timing and less fuel (improved combustion efficiency), and it will make more power than a similar engine with more quench in it......Cliff