A Little Carb vs EFI info
12-04-2014, 11:05 AM
#11
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Funny thing about dinasours:
That is (the time period) what made our gas today.
They could not be stopped by anything in our time period, maybe minus nuclear weapons and, of course, as history dictated, mother nature.
That is (the time period) what made our gas today.
They could not be stopped by anything in our time period, maybe minus nuclear weapons and, of course, as history dictated, mother nature.
12-04-2014, 11:30 AM
#12
12-04-2014, 02:14 PM
#14
Fast Singles Club
Gold Member
iTrader: (8)
12-04-2014, 03:28 PM
#15
Have built a lot of engines with dual quads as well as fuel injected. Back in the day 50s 60s dual quads were used in some production engines and aftermarket as well as other multible carb setups. This was because of the size availibilty back then. They often produced amazing power over a wide power band. My duall quad 312 ford 375HP+. Why they out perform a EFI setup is having 8 smaller throats compaired to 1 or 2 large throats. Just think if a carb only had a single throat 750 CFM. Thats a similar comparison to to a HP SEFI system today. So you nail the throttle on a typ SEFI system air speed dropps sgnificantly compaired to 8 venturies. To make up for the SEFIs big drop it quickly nails the A/F ratio from 14.7ish to 12.5ish to cover the big hole that just opened up. Carbs on the other hand open up from 14.7ish and rather slowly in compairison AF would go to 14 to 13 to 12.7 as engine speed increases and need for fuel increases. So think about 1bbl 750 or 4 bbl 750 or 8 bbl 750.
So my last engine build was based on this. A 302 with ported DOOE (1969 351W heads) 235 CFM @ .500 lift, dual quad intake ported to flow 215 CFM bolted to the head, 2 small 4 bbl carbs modified to flow a total of 1040 compaired to a Victor 5.0 with a 75 mm TB. A mild 220 @.050 .500 lift cam. The SEFI set up took 6 months or so to realy data log and tune. Sent the carbs to Nickerson for stage 5 mods which could be done myself but wanted to make the carbs exactly matched in flow fuel and air. The dual quads out performed the SEFI including MPG 20 SEFI, 24 dual quads.
I would consider a SEFI set up with 8 stracks such as HILBORN would out perform the dual quad set up though.
So my last engine build was based on this. A 302 with ported DOOE (1969 351W heads) 235 CFM @ .500 lift, dual quad intake ported to flow 215 CFM bolted to the head, 2 small 4 bbl carbs modified to flow a total of 1040 compaired to a Victor 5.0 with a 75 mm TB. A mild 220 @.050 .500 lift cam. The SEFI set up took 6 months or so to realy data log and tune. Sent the carbs to Nickerson for stage 5 mods which could be done myself but wanted to make the carbs exactly matched in flow fuel and air. The dual quads out performed the SEFI including MPG 20 SEFI, 24 dual quads.
I would consider a SEFI set up with 8 stracks such as HILBORN would out perform the dual quad set up though.
12-04-2014, 03:29 PM
#16
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Wonder what the power would have been with two throttle bodies in the exact same location as the carbs where.
Also, with EFI you can usually use a little larger throttle body than you can with carbs because you do not worry about airspeed + direction going thru boosters with a throttle body.
PS: I'm totally fine with having carbs and EFI.
12-04-2014, 03:36 PM
#17
Registered
First if you look at that dyno graph the efi and carb are nearly identical under 4500 rpm. Second they did not address efficincy as in BSCFM (hope I got that acronym right) as in power produced per pound of fuel used. I suspect the EFI will be better.
But a lot of this is due to the LS engine cylinder heads causing so much swirl and tumble. They are just very efficient engines.
Wannabe
But a lot of this is due to the LS engine cylinder heads causing so much swirl and tumble. They are just very efficient engines.
Wannabe
12-04-2014, 08:52 PM
#19
PF Marine
Platinum Member
Interesting thread BUP.
IMO, the air gets a much straighter shot at the runners with carbs (much greater air velocity in the runners for more turbulence in the combustion chamber) vs having to turn extra corners with the TB setup. Would also like to see fuel curves, BSFC, egt's, and even 8 02's.
IMO, the air gets a much straighter shot at the runners with carbs (much greater air velocity in the runners for more turbulence in the combustion chamber) vs having to turn extra corners with the TB setup. Would also like to see fuel curves, BSFC, egt's, and even 8 02's.
