I heard that a engine that is EFI doesn't breath as well as the same engine with a carb, talking longer runner efi intakes. I was wondering how much truth there is to this? It looks like the LSx engines are making better power then just about any carb motor I have seen. Edelbrock is coming out with a carb intake for those motors so that will be interesting. Also, a lot of the Ford guys would rather use a carb intake on a 351w then an EFI intake, but on a 302 they would keep the EFI instead of the carb.

thanks
Jeremy

 

I can't see that being true.

EFi would have an edge on intake runner tuning, as opposed to
an open plenum design with central carb positioning.

There is a thread in this forum which highlights flow testing.

Not a quote, but an EFI head/intake deals mostly with air mass
only (as opposed to air/fuel mass) which allows higher runner
velocities.

I think this is more a question of 'ease of tuning' between the two?

Maybe someone just got lucky with a better set of matched intake
/carb with the engine configuration over the stock EFi system?

 

I thought the same too. I have always said that if everything being equal on everything except the intake, the EFI will have better street manners bcuz of the long runner design. I recently saw an artical in Mustangs and Fords where they build a 351 that made ~427hp/410tq with:

9.5:1 cr with RPM heads
RPM intake with 670 Autolight carb
220/228 112 LSA hr with 1.6rrs
lt headers

I have a old HR artical where they built a 351 that made 400/458 with:

11:1 cr with TFS R heads
extruned honed 5.0 rpm upper and truck lower (said flowed 290/runner)
220 single pattern hr 112LSA with 1.6rrs
lt headers

I just found it weird that the carb motor made almost the same power with less head and cr, granted the EFI 351 made more AUC, but I thought is might back up my point.

 

Does it mention the RPM at which the power peak was made?

I bet most of the numbers will come down to valve timing.

Those are two entirely different engines to begin with.

At first I thought you meant simply swapping a manifold and carb
on an EFI engine.

 

In the EFI motor, it was 4k for tq and 5k for hp. For the carbed motor I think it was 55k for hp and ~4k for tq, somewhere around those numbers.

 

It would have to be at least 5252 RPM for HP peak on the EFI motor

 

EFI , makes it easier on the HeadPorter

you have more leeway with cross-sectional area with EFI

its going to be interesting to see how much and where in RPM range will LS-1 or LS-6 make its Peak TQ and HP points and how much Peak TQ and HP ?? with a Carb instead of EFI

the driveablility upon initial cold startup and colder climates
with EFI -vs- Carb will also be interesting on LS-x heads