Vacuum CFM for 2.8L V6

[Rockonp04]

Deciding what EFI to buy for my Sunbeam V6. What CFM can I expect on these engines? This is important because of the injector size and duty cycle.

 

[Barry]

Deciding what EFI to buy for my Sunbeam V6. What CFM can I expect on these engines? This is important because of the injector size and duty cycle.

An old and pretty accurate rule-of-thumb for automotive gasoline engines is 2 CFM per HP. Getting 200 real world HP from a naturally aspirated Ford 2.8 V6 is probably optimistic, so 400 CFM should be plenty. The bottom line is that all of the mainstream aftermarket throttle body EFI systems are technically too big for a naturally aspirated Ford 2.8 V6. An oversized (350-400 HP) TBI-EFI setup should still be an improvement over an equally oversized carburetor.

Note that MAP based EFI systems do not always work well with "hot" cams and low idle vacuum.

 

[Rockonp04]

Yea. I spoke with MSD and Holley and essentially it's a 1000 cfm carb. Thinking about the 2 barrel alternative for the Holley Sniper but I would have to swap out my 4 barrel Offy intake, which in my opinion is a step backward. I could use an adapter to change the 4 barrel to a 2 barrel but it would raise the efi 1" higher which with this engine leaves almost no clearance.

 

[britbeam]

Just curious why do you not want to use the four bl Holley 390cfm. I havent been following you so Im not sure what your building.

 

[Rockonp04]

I would like to use a 4 barrel efi for my build. Not sure it has been done before but just getting all of the information to see if it is even worth it or can even be used.

 

[Bill Blue]

You might use a Holley 390 as a throttle body. Install injectors either in the intake manifold or concealed inside the Holley. Control it with MegaSquirt.

Bill

 

[DanR]

Getting 200 real world HP from a naturally aspirated Ford 2.8 V6 is probably optimistic, so 400 CFM should be plenty.

As Barry stated above, 400 should be plenty!!

The 390 has been utilized most effectively. The 2.8 at best is maxing up to 200HP unless you are building an all out racing engine.

When I first got the bug for the V6, I went with the flow and got the cam recommended only to find it produced little to no vacuum at or around 900-1000 RPM per the Delta Rep I spoke with.

I will probably go with something like what Bill Blue and 260 and Barry recommend next time. Maybe even a 4.0 would go well too

 

[Bill Blue]

Most 2.8 builds seem to end up at about 150 hp. So 300 cfm would be realistic.

Bill

 

[Barry]

I will believe 200 net HP from a naturally aspirated Ford 2.8 V6 street engine on pump gas when I see the verifiable results from a real / reputable engine dynamometer (or 175 HP on a real / reputable chassis dyno).

 

[DanR]

The 2.8 at best is maxing up to 200HP unless you are building an all out racing engine.

Guys, I did not word this too well! What I meant to say is UNLESS you are building an all out race engine you will not get 200 or better.

My Blue Boy is about 175-180 from what Jim Nichols (Alpine 260) has said if I am correct. I have no plans for a Dynamometer test. I have nothing to prove to my self. It is a most enjoyable ride set up as I now have it")

I am running a COMP (a rather nice street) cam, 2.9 Valves, port and polished (not to an extreme - The Comp 36 241 4 ) with 8.5 compression, 390 Holley 4bbl on an Ofy intake, hooked up to my Straight back Headers. 1 & 1/2" tubes with 2 & 1/2" Collector 11" in length. Most of what Sven Pruett recommended.

I would highly recommend you (Rockonp04) listen to these Guys! They have been an inspiration to me!

 

[260Alpine]

Dan, That is flywheel HP. Probably around 140 HP at the wheels. Which is a guess due to simulation, but I'm more conservative and compare to real Dyno charts pretty close. The stock V6 is around 120HP at the flywheel and you add cam, Offy intake , 390 Holley and headers. The mild port job helps a little too. For those on a budget I like Mike Armstrong's setup with stock intake and Holley 2 barrel. I think the Holley Sniper 2 barrel EFI would work good too.

 

[Rockonp04]

Just an update. I did some digging and the Atomic EFI won't work with the cam setup I have. It can't go past 250 degrees on the intake. My cam has 252 degrees. Kind of a bummer because now I would have to use the 2 barrel Sniper EFI which in my opinion is a step backward in terms of airflow. The 4 barrel EFI just doesn't work with this engine since the vacuum is minimal and the injector size is geared at the V8 crowd.

All said and done, I think we are going to go with the Holley 390 after all. We are going to run all this by a hot rod shop who does our engine work just to confirm my suspicions but the only alternative is a 2 barrel EFI with a custom adapter. We would also have to get the engine ported and polished again which is extra money for the build.

I'll keep all of you posted. Thanks for all the advice.

 

[Barry]

I don't think 2 extra degrees of duration is a deal breaker; the real problem with the Atomic EFI is that it is way too big (about 3 times too much CFM and injector size) for the Ford 2.8 V6. The 2-barrel Sniper EFI is also too big (about 2 times too much CFM and injector size) for the Ford 2.8 V6, so airflow is not an issue.

IIRC, there was a 2-barrel version of the Offy intake that might mount the 2-barrel Sniper EFI without needing a custom adapter.

It would not be nearly as "macho" as the Offy intake, but I suspect that the 2-barrel Sniper EFI on the stock 2-barrel intake would work fine.

 

[260Alpine]

Mike Armstrong modifed the stock 2 barrel intake for the Holley 350 2 barrel. Barry is right, even the 2 barrel EFI is way bigger than necessary but the Fitech and Sniper have been successfully used on much smaller motors. VW beetles and 4 cylinder Toyota's. We used a 1000cfm 4 barrel throttle body on the 300 Stroker Buick V8. The computer control seem to adjust/learn the fuel management just fine. You can buy a 2 barrel to 4 barrel intake adapter from Holley/Mr. Gasket but the height is about 2". No problem if you have a scoop.

https://www.amazon.com/Mr-Gasket-2-...=2025&creative=165953&creativeASIN=B00068OS2W

 

[Rockonp04]

I have had long conversations with all of the EFI techs and all seem to say the same thing, it will work but the injectors won't be optimized. It would not be in the duty cycle the injectors were designed for. They stop just short of saying it won't work. Technically it will work but how well? All have said the injectors would be spraying at a fraction of what they are designed for.

In my opinion, the 2 barrel would be a restriction. As Jose puts it, it would be sucking through a straw. So even though the 2 barrel EFI has the right injectors, the restrictive nature of the 2 barrel manifold restricts the engine.

I have researched high and low for a solution and the adapter plate from 4 barrel to 2 would simply restrict the engine and raise the height another 1". We are not about to install some gaudy intake scoop to experiment with the EFI setup.

I called Jose and he confirmed all of my suspicions. This would be an expensive endeavor if I was purchasing EFIs and left and right and trying different intake manifolds when I already have my Offenhauser ported and polished.

I did my research and homework and an EFI in the four-barrel configuration doesn't quite exist for this motor. A four-barrel EFi with smaller injectors simply doesn't exist... yet.

I bought a Holley 390 today. Learned a lot. If I had 5k to throw around I would do it, but it doesn't fit into my budget.

 

[DanR]

I believe you will be happy with the 390 Holley 4 bbl on the OFY.... Get it together and enjoy the ride I certainly do!

 

[Bill Blue]

Two bbl is restrictive, what is your hp target?

Bill

 

[Barry]

Facts:

The Holley 390 4-barrel carburetor is rated at 390 CFM.​

The Holley Sniper EFI 2-barrel is rated at 580 CFM.​

Conclusions:

The Holley Sniper EFI 2-barrel "would be a restriction" and "sucking through a straw."


​

 

[Rockonp04]

It's not the 2 barrel, its the intake manifold.

 

[260Alpine]

I think you would be surprised at what the stock intake would flow. If ported like the OFFY with a 1"adapter and 350cfm Holley 2 barrel I think it would show very little loss compared to the OFFY and 390cfm four barrel.