6-71 EFI question
Thread Starter
TECH Apprentice
Joined: Oct 2013
Posts: 350
Likes: 25
From: North Shore MA
6-71 EFI question So I have a Hampton 6-71 sitting on the shelf. When you have something like that hanging around, the wheels start turning.
Suppose I mounted it to my 5.3 using a carburetor style intake (no provisions for fuel injectors), and ran two 4150 style throttle bodies in place of carbs. For the fuel injectors, they would be mounted between the top of the blower and underneath the throttle bodies on a typical injector style spacer.
If I were to mount the injectors above the blower, can they still be operated by the stock ecu? I ask because they'd be firing depending on cylinder location, so would them firing at different times be a problem mounted above the blower?
Basically I'd be building a sort of homemade efi setup that runs off the factory computer and harness.
I'm just thinking out loud here, so if I'm way off let me know. lol
It probably be easiest to run the two 750DPs, or two efi units on top in place of the carbs.
Suppose I mounted it to my 5.3 using a carburetor style intake (no provisions for fuel injectors), and ran two 4150 style throttle bodies in place of carbs. For the fuel injectors, they would be mounted between the top of the blower and underneath the throttle bodies on a typical injector style spacer.
If I were to mount the injectors above the blower, can they still be operated by the stock ecu? I ask because they'd be firing depending on cylinder location, so would them firing at different times be a problem mounted above the blower?
Basically I'd be building a sort of homemade efi setup that runs off the factory computer and harness.
I'm just thinking out loud here, so if I'm way off let me know. lol
It probably be easiest to run the two 750DPs, or two efi units on top in place of the carbs.
TECH Resident
Joined: Sep 2013
Posts: 993
Likes: 119
From: Mechanicsburg, PA
I run dual 750's on a 6-71 blown SBC. If I had it to do over again, I'd go EFI. As far as sequentially firing the injector, I don't know if that would effect anything or not. Surprisingly, when I tried to run 2 corner idle mixture instead of 4 corner ( on each carb ), several cylinders ran lean. Even after setting the idle mixture. I mentioned it to Bruce Larson one time and he said they ran into the same thing on their old alcohol injected set-ups. With one injector disconnected it would run lean on a couple cylinders no matter how much fuel they added to the others. You would think those 2 big rotors would mix/distribute the fuel evenly, not so. I'd recommend a microsquirt and injectors above the blower with throttle bodies set-up like Dario did with his Mini Cooper. Make the throttle bodies big, these 6-71's like to eat. E85 would help cool the blower even more. Roots blowers are antiquated heat monsters, but sure make a statement when you pull in somewhere. Old guys think "Hell yeah a blower!". Young guys think "Tard should put a turbo on it and it'd be fast." lol
The only bad thing you can say about a roots blower is that it's not nearly as efficient as a turbo because it robs power from the crankshaft to make boost. My 408 made well over 900hp on the dyno in 15lbs, No doubt a turbo making the same boost would have made more power but the blower would make better torque down low.
As far as running one on the stock ecu, Unless you already the ecu/harness/ and tuning software I'd look at aftermarket. It should work, The blower doesn't really care if the injector is firing in a multiport configuration or batch fire as long as enough fuel is pumped into the blower.
Don Hampton, wow, haven't heard that name in a long time. Used to buy my blowers from
him back in the day. The thing that kind of scared me about running a roots on an LS engine,
esp. if the 3" belt, was how little crank/balancer engagement there really is. And how far out
from the engine the belt is. I ran a couple Procharger setups on the LS, one was the vette setup,
but the belt runs closer to the engine, and a setup like the SB/BB's used, the belt was farther
from the engine. I haven't heard of any snouts snapping, but was a concern. Back in the
day we snapped a couple small block ones-they made a brace and some ran BB snouts on
the SB's. I would think it would be a challenge running FI with a stock ECU. You could prob
setup an IAC with some tinkering. I have seen a couple setups with the injs. below the blower,
TB's above were just air valves. OK, too much coffee this morn, I started early, lol.
him back in the day. The thing that kind of scared me about running a roots on an LS engine,
esp. if the 3" belt, was how little crank/balancer engagement there really is. And how far out
from the engine the belt is. I ran a couple Procharger setups on the LS, one was the vette setup,
but the belt runs closer to the engine, and a setup like the SB/BB's used, the belt was farther
from the engine. I haven't heard of any snouts snapping, but was a concern. Back in the
day we snapped a couple small block ones-they made a brace and some ran BB snouts on
the SB's. I would think it would be a challenge running FI with a stock ECU. You could prob
setup an IAC with some tinkering. I have seen a couple setups with the injs. below the blower,
TB's above were just air valves. OK, too much coffee this morn, I started early, lol.
Teching In
Joined: Feb 2017
Posts: 12
Likes: 1
From: NB, Canada
My understanding was running injectors bellow the blower is less then ideal for both cooling and lubrication of the blower. I’ve discussed running a 6-71 on a microsquirt powered sbc with a friend and we thought that port injection would be ideal for fuel distribution and maybe you could run a single injector on top of the blower the reasons stated above. But you don’t have enough injector control on a micro to do that so it would have to be a pretty crude set up.
My understanding was running injectors bellow the blower is less then ideal for both cooling and lubrication of the blower. I’ve discussed running a 6-71 on a microsquirt powered sbc with a friend and we thought that port injection would be ideal for fuel distribution and maybe you could run a single injector on top of the blower the reasons stated above. But you don’t have enough injector control on a micro to do that so it would have to be a pretty crude set up.
There is no lubrication needed on a roots unless its a stripped blower but cooling is needed. The blower rotor clearance is set according to the fuel you intend to run so that when up to operating temperature it will make the most boost without being to tight causing damage. To loose and it's not going to make as much boost.
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Teching In
Joined: Feb 2017
Posts: 12
Likes: 1
From: NB, Canada
If you're going to run it on an aftermarket system then you can run a 16 injector setup, 8 above the blower and one per cylinder below the injector.
There is no lubrication needed on a roots unless its a stripped blower but cooling is needed. The blower rotor clearance is set according to the fuel you intend to run so that when up to operating temperature it will make the most boost without being to tight causing damage. To loose and it's not going to make as much boost.
There is no lubrication needed on a roots unless its a stripped blower but cooling is needed. The blower rotor clearance is set according to the fuel you intend to run so that when up to operating temperature it will make the most boost without being to tight causing damage. To loose and it's not going to make as much boost.
The blower we were looking at running was straight of a Detroit so maybe my friend was overstating the importance of the lubrication.
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Verdad Gallardo Many aftermarket ecu’s can run 16 injectors and even have them staged, but my understanding is a microsquirt which bad Apache mentioned above is maxed out at 8 injectors.
The blower we were looking at running was straight of a Detroit so maybe my friend was overstating the importance of the lubrication.
The blower we were looking at running was straight of a Detroit so maybe my friend was overstating the importance of the lubrication.
Thread Starter
TECH Apprentice
Joined: Oct 2013
Posts: 350
Likes: 25
From: North Shore MA
As far as running one on the stock ecu, Unless you already the ecu/harness/ and tuning software I'd look at aftermarket. It should work, The blower doesn't really care if the injector is firing in a multiport configuration or batch fire as long as enough fuel is pumped into the blower.
It be a cool little project this winter. I'm sure the injectors firing in a sequence isn't ideal, but I'm thinking with enough fuel flow it shouldn't matter? I like the idea of retaining efi due to the drivability, but I'm not totally opposed to running the old 750s if this idea doesn't pan out.
So are you saying to pump meth into it all the time, idle/part throttle/cruise?, You need something to spay the rotors constantly, Not just wide open throttle.
That's why I was toying with the idea. I already have the car setup and running on a stock harness and computer, and I have the ability to tune it.
It be a cool little project this winter. I'm sure the injectors firing in a sequence isn't ideal, but I'm thinking with enough fuel flow it shouldn't matter? I like the idea of retaining efi due to the drivability, but I'm not totally opposed to running the old 750s if this idea doesn't pan out.
It be a cool little project this winter. I'm sure the injectors firing in a sequence isn't ideal, but I'm thinking with enough fuel flow it shouldn't matter? I like the idea of retaining efi due to the drivability, but I'm not totally opposed to running the old 750s if this idea doesn't pan out.
Most people I talk to think the air/fuel is pulled down through the middle of the blower when it actually travels along the side of the case.
The only thing you have to be concerned about is getting an even distribution per cylinder, It can be an issue with carbs so efi won't be any different, Usually it's more of an intake issue than a blower or injector/throttle body issue. I would try it on a disposable engine first if possible. You wouldn't want to risk a high dollar engine unless someone else has shown it to work well.
Teching In
Joined: Feb 2017
Posts: 12
Likes: 1
From: NB, Canada
I had a think about this last night and I feel pretty dumb for falling for the lubrication fallacy. I’ve been around working 6 and 12v-71 diesels and the blowers run for years. They don’t receive any outside lubrications... Live and learn I guess.
Teching In
Joined: Feb 2017
Posts: 12
Likes: 1
From: NB, Canada
I’m sure that’s true on a new blower from any reputable go fast shop, but if I’m pulling one straight off of a 6v-71 Detroit and throwing it on top of something then I think it’s unnecessary.
Thread Starter
TECH Apprentice
Joined: Oct 2013
Posts: 350
Likes: 25
From: North Shore MA
I look at it this way, the engine needs X amount of fuel at idle all the way to wide open throttle, As long as it distributed even enough in the top of the blower you shouldn't have any one cylinder run lean enough to cause damage.
Most people I talk to think the air/fuel is pulled down through the middle of the blower when it actually travels along the side of the case.
The only thing you have to be concerned about is getting an even distribution per cylinder, It can be an issue with carbs so efi won't be any different, Usually it's more of an intake issue than a blower or injector/throttle body issue. I would try it on a disposable engine first if possible. You wouldn't want to risk a high dollar engine unless someone else has shown it to work well.
Most people I talk to think the air/fuel is pulled down through the middle of the blower when it actually travels along the side of the case.
The only thing you have to be concerned about is getting an even distribution per cylinder, It can be an issue with carbs so efi won't be any different, Usually it's more of an intake issue than a blower or injector/throttle body issue. I would try it on a disposable engine first if possible. You wouldn't want to risk a high dollar engine unless someone else has shown it to work well.
I figured since the fuel is entering from the top and compressed, it is probably pretty evenly distributed once it makes it to the manifold? I'm sure the overall design of the intake will be responsible for taking that mixture and distributing it evenly to the cylinders.
