"Obviously adiabatic expansion is the next question on the list. So if we take a good look at the carburetor we see its not only a perfect machine for atomizing fuel, it also has another advantage. The joule-thompson effect.

Tests performed using quartz plates and infra red sensors located in the plenum area beneath an NHRA Pro-Stock engine revealed an intake manifold temperature drop on a 85 degree day of almost 20 degrees as a result of the the carburetor creating this effect.

So when your neighbor with EFI is ingesting 85 degree air, your power-plant could be ingesting 65 degree air."

Could someone please explain this to me? The delta P (ambient/intake) in the example is relatively low, so it seems this would have a negligible (measurable, but not significant) effect. What I'm likely to suspect is that the cooling is much more a result of the gasoline absorbing the heat thus lowering the intake charge temps. Yes, a nice benefit to running a carb. BTW, this has been done before on EFI motors to help cool the intake charge in race applications.

Andy1

 

Yeah Andy... you are correct.

I guess actual working knowledge and understanding dont hold anything around here. Nor does the knowledge from working for Roger Penske, Dick Guldstrand and having around 2000 hours of dyno time with TRACO Engineering (the independant business behind GM's early EFI efforts), while working shoulder to shoulder with GM's engine development team... specifically the fuel injection engineers. Nor does it hold any water to have worked for PPI (along with TRD and TMS) on Ivan Stewarts SCORE efforts employing the development of the V8 power plant or having my hands in Fangio's Cart effort either. I bet growing up in the racing industry and cutting my feet on the salt at Bonneville wouldnt have anything to do with the knowledge I have retained over the years.

Ya know, its a shame I havent written down all the numbers from the tests and experience that form my opinion.

I could probably bet you that being an instrumentation engineer that works specifically in the theater of aero/thermodynamics, advanced heat transfer distribution and measurement and specializing in Liquid Crystal Thermography to desiminate results...... wouldnt support the theory to why the Joule-Thompson effect is an inthalpic process.

But then again, I'm not in my mid-20's and know everything. I just know and understand from what I have actually done in my life. But I think you are right.......

Engine power is related to air intake temperature. Lets use the easier math; an 11.11*C (20*F) change in the intake charge, works out to around 3.58% difference in power production. On a 500hp engine, that works out to be roughly +18hp.......... going to the carburetor.

Yes, the fuel does absorb some of the heat in this process. Afterall, anytime you pressurize a fluid (which a fluid can be defined as a liquid or a gas) there will be an increase in temperature. So specifically, in reference to the fuel going thru an injector, it does transfer heat into the fluid. The emulsification properties actuall help the carburetor in this manner even more. Not to mention that anytime you turn a "fluid" more than 12* in a direction, the restriction and resultant friction also build heat into the mixture.

Joules experiment alone..... and a little time in understanding isothermal compressibility and understanding the variables in the expansion coefficient..... will go along way in your search for real conclusive explaination.

 

Guys,
It just boils down to what turns your crank. Some like carbs, and some like EFI, it is just like red cars and blue cars, neither is the right color and neither is the wrong color. The argument can be made by the Carb guys that a properly tuned Carb will produce more power than an EFI, but the EFI guys can point to the fact that the EFI will automatically compensate when the temperature or barometric pressure change, while with the carb, you retune the carb when the weather changes. My personal opinion is that the EFI offers the best compromise betwen great power, good fuel economy, clean emissions, and good driveability. I drag raced form many years, and have had about all the jet changing I can stand for the rest of my life, and will probably never build another carbed car again except for the restorations that I do, and then only because it is necessary. For my hotrods, I am a solid convert to the LSX engine, and the GM designed EFI that comes with it. There are other electronics packages that appear to offer better performance and easier tuning than the GM PCM, but it does not offer some of the functions that I find necessary for a daily driven car, and the diagnostics that can be scanned when I am 500 miles from home, are an absolute necessity. As to the cost, I would guess that it costs more to convert a LSX engine to carb and MSD ignition, then you would ever spend on a harness and PCM programing. In regards to the complexity of the EFI, I would also disagree on that argument as well. The PCM and harness setups that are being sold now days are pretty much plug-and-play. When you move away from the race-only and theoretical engine and start talking about the real world of daily street driven cars ( where most of us really live), the EFI looks better and better.


Regards, John McGraw

 

Chicane,

Well, that's certainly an impressive resume, especially if you're the DT part of BTDT. Lots of guys in racing have only BT, but talk the DT part too.

I think you missed part of my question, but that's ok. Anyway, I agree that lowering the intake charge temp will increase power. To some point, all IC engines are liquid cooled from the fuel in the intake charge.

I would be willing to bet we have crossed path's sometime throughout the years. Seems you've been around SoCal some. Though I have never worked professionally in the racing business, I have been around it my entire life (and have raced). Bonneville; yup, been there and El Mirage too. Wrenched on all kinds of stuff. Lot's of two-stroke stuff. Did quite a bit of carb work as well. A business partner sublet our shop to CCR in the early Mazda days, which was next door to John Morton's shop and around the corner from Electomotive. A good friend worked close by at Fisher Eng'g. RIR, OMS, Lion's, Gardena. Boy, those were the days!! Anyway, not too many years left before retiring from medical device engineering, so thought I'd build one last hotrod. LS1 powered 914 with a Getrag 6 speed; which is why I'm here. Guess what I've learned, is what I don't know.

Andy1

 

No, but it's a good deal for those afraid of technology and I think a carb deal would be better for drag racing.

For a street car I will keep my EFI and besides, it's not like it saves you any money (to go the carb route)

 

If this is a shot at me, which it certainly seems it is, I never claimed I know everything. Far from it. I just disagree with your opinion on this subject to a degree, and as Andy stated, the finality of your conclusion that was written into it.

 

Just did my sons jeep 350sbc. Had very nice tpi,new injectors,new tps and iac,,etc,,etc. Swapped it out for a Q-jet I built and an hei that I recurved...Results?? easily out runs and out performs the tpi AND 3-4 mpg better. Cold here,,20 degrees. 3 pumps choke sets itself and fast idles then kick it down and drive away. good debate though. BTW, I actually remember reading that comment by Smokey.

 

Wow! Don't know if I've ever seen somebody dig up a 6 year old thread before, congrats on using the search feature I guess

 

Yeah, I wasted part of my night reading this thread & waiting/watching to see if ANY of the dates on the posts would get more recent than '06, & thinking "GEEZ, this entire freakin' thread is just a whole lot of , and "

Sure hope we don't see any more threads like THIS one for a while...

 

Go to the carb forum. There are a half dozen more threads on carb vs. EFI, many rehashing the same stuff. Only thing that seems to have changed is carb'd LS motors are pretty common now so there are a lot of people posting actual results.

I like my carb. I still don't have it quite right, but I like tinkering with it.

Oh, and I learned the other day that Purell hand sanitizer gets rid of the gas smell on your hands. Valuable knowledge.