I wish Engine Masters would post BSFC numbers too

[lil289]

Since this contest was designed around streetable motors - 2,500-6,500 RPM's, fuel economy might be a concern here. Not the primary one obviously but a concern nonetheless. What good is a street car if it makes big power but sucks so much gas that it winds up sitting in the garage most of the time? Besides, the competitors are coming out with such creative ideas that it would be interesting to see if some oddball design, while not making that few extra percentage points of power for the win, might be a lot more fuel effiecient. I'm sure the OEM's would be interested in this sort of data too. What do you think?

[OldSStroker]

Since this contest was designed around streetable motors - 2,500-6,500 RPM's, fuel economy might be a concern here. Not the primary one obviously but a concern nonetheless. What good is a street car if it makes big power but sucks so much gas that it winds up sitting in the garage most of the time? Besides, the competitors are coming out with such creative ideas that it would be interesting to see if some oddball design, while not making that few extra percentage points of power for the win, might be a lot more fuel effiecient. I'm sure the OEM's would be interested in this sort of data too. What do you think?

The BSFC numbers would be good only for wide open throttle (acceleration) operation. They would have very little to do with part throttle cruising. If the builder decided to jet a little rich to help keep from melting down the pistons, BSFC would be higher for similar power.

[rmcomprandy]

They don't post 'em because they're terrible; using extra fuel to squelch detonation with the 91 octane they're required to use...! The exhaust temps are way high with high compression ratios 'cause the gas is still burning in the pipe even with short duration cams.
This year they've limited the compression ratios to a maximum of 10.5/1 so, it will probably be different.

[automotive breath]

The BSFC numbers would be good only for wide open throttle (acceleration) operation. They would have very little to do with part throttle cruising. If the builder decided to jet a little rich to help keep from melting down the pistons, BSFC would be higher for similar power.

Very good point, what would be the correct way to determine the more efficient engine?

[Joe Mendelis]

They don't post 'em because they're terrible; using extra fuel to squelch detonation with the 91 octane they're required to use...! The exhaust temps are way high with high compression ratios 'cause the gas is still burning in the pipe even with short duration cams.
This year they've limited the compression ratios to a maximum of 10.5/1 so, it will probably be different.

Usually higher compression means lower exhaust temps, not higher. You are burning a higher mass of fuel by peak pressure, so there is less heat when the exhaust opens. You are operating at higher thermal efficiency. If you have more efficiency you have more heat energy against the piston instead of out the primary tubes.

[SStrokerAce]

I have the Superflow files for Shermans winning runs for 2002. I'm not sure how accurate Westechs stuff was but the BSFC was .273-.387 during the pull, with corresponding A/F ratios of 17.3-13.9:1

Bret

[RRBD]

I have some experience with the EMC, I think most of the engines that show up at the contest are dyno queens, not many good for the street in their respective dyno trim. That was the premise, street, pump gas engines, they are far from it now. Lets see them each drive 300 miles, highway/city in a 3400lb car and a 16lb radiator cap. How often do you see a street engine with .800"+ lift, roller and those hellacious springs?

Scott

[putztastics]

I have the Superflow files for Shermans winning runs for 2002. I'm not sure how accurate Westechs stuff was but the BSFC was .273-.387 during the pull, with corresponding A/F ratios of 17.3-13.9:1

Bret

Bret, anyone, do you believe the .273 BSFC and 17.3 A/F ratio are accurate?

[Gary Blair]

They are dyno queen's for sure. I think we will be able to run the af ratio's in a more realistic range this year. I think you will still see .800 lift cams because some cylinder heads are lagging in the mid lift area.

I like the concept of big blocks and small blocks at 434 CI. Should be quite interesting.

[BRENT FAY]

Just curious? When those dyno queens start detonating how bad do they kill the top ring? Is it the top ring dying (do they show blow by cfm?) or are they just not making HP due to the detonation? .......Idea, :............if it is just detonation and not ring DONT read any further.............. idea : how would a 4 ring package work? With such light weight rings could you make the top ring a sacraficial unit and still have a comp. ring in the 2nd groove with gas ports? I know it would cause a little more drag but after all the pulls it still might be a player! Ok, so I went outside the box............. When you start beating up on me for this idea ,just hit me where it doesnt show cause I bruise easy It was just a thought!!!! Brent

[SStrokerAce]

I have the Superflow files for Shermans winning runs for 2002. I'm not sure how accurate Westechs stuff was but the BSFC was .273-.387 during the pull, with corresponding A/F ratios of 17.3-13.9:1

Bret

Bret, anyone, do you believe the .273 BSFC and 17.3 A/F ratio are accurate?

I find it hard to believe. I mean they are super lean but it makes you wonder. You would need perfect distribution to do that.

Bret

[putztastics]

I don't believe them for a second.

To me those numbers are a classic result of fuel turbine and air turbine lag.

It might be more accurate to say fuel flow reading lag, to me the problem is in the lag between the carb's booster fuel flow and when the fuel fuel flow meter sees the changes in the carb booster fuel flow.

I would bet a steady state test would result in way different numbers. If you don't believe the dyno's BSFC and A/F ratio numbers are warped by sweep testing try both an up sweep and down sweep and compare them.

Where in the pull were the .273 BSFC and 17.3 A/F ratio numbers?

The .387 BSFC and 13.9 A/F ratio numbers are probably when the meters "caught up" and are far more believable for an up sweep. I would still bet they are leaner than what a wide band A/F meter would show.

One thing I have learned using a wideband is that the A/F ratio is usually pretty flat across a dyno pull, the wideband meter does not show the same A/F variance the dyno shows. So it might be a lot of the air bleed tuning (to get the A/F ratio even across the dyno pull) is in response to an A/F ratio curve that is not accurate.

I've come to the conclusion the only accurate BSFC numbers would be steady state ones. You might get repeatable sweep test BSFC numbers but I don't think they are accurate. And remember BsFC will change with the weather since it is based on brake hp.

[crosshatch]

Autoshop's dyno numbers were on display at the DTS booth in the PRI show last Dec. ,along with his engine.

His bsfc averaged .36 and A/F was in the 12.6-13.2 range.

[rmcomprandy]

Joe Mendelis - That's WHY I mentioned higher exhaust temps with higer compression BECAUSE it's not a normal thing. I'm NOT guessing here...! Is 1550* a normal exhaust temp for a high compression, (most were around 12.5/1), NA street engine.
AND, they multiply their actual observed torque & horsepower power numbers by 2% before they're corrected without changing any fuel numbers; they might look lean but, they're certainly NOT.
If you want to see what's really happening; go to the contest and see. What's written about in the magazine is kinda streached.

The top rings are usually about .325" down the piston so it's not affected much by a small amount of detonation.
The rules REQUIRE a three ring package of two compression and 1 oil ring.

[Motorman 407]

Rmcomprandy if you been there you should know that they don’t use exh.temp sensors in the contest. A/F is not involved in any corrections but shows what happens in real time. There has been NO rule requiring 3 rings, that is new for 2006. "Top rings are usually .325 down"? Did you measure everybody or do you base your information on what you hear and read in magazines?
If so look at the picture in PHR of the spark plug from Lennarts winning engine and tell us how terrible the fuel ratio was in his motor.
I’m sure that the top engines from the EMC could out run and out live most of the street stuff built with Chinese junk that seems to be the standard out there these days.