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Airbumps
Kael O

(5 posts)

Registered:
01/08/2017 03:05AM

Main British Car:


Performance difference between EFI and Carby - Rover V8
Posted by: Airbumps
Date: January 08, 2017 07:02AM

Hi all,

I've got a stock standard Rover 3.5 (8.13:1) motor in my MGB. It's running on a Edelbrock 1404 (500cfm) 4 barrel carb. This setup at the moment does just under 130hp at the rear wheels. Which given the original 3.5 motors where only supposed to put out 135hp at the flywheel is pretty good.

I'm in the process of drawing up plans for a new motor. Looking to appropriate a 3.9 and having some work done to the heads and a slightly livelier cam. Its a street car so I don't need/want to go overboard but am looking for something with more torque and power output.

My question at this time is weather to run EFI or keep the Edelbrock. I've read a lot about the benefits of EFI and it sure seems that they run smoother and will achieve better MPG. What I'd like to know is what sort of tangible performance improvement the EFI would likely give me over the Edelbrock? I'd be looking at using Hotwire.

I'm partial to keeping the carby as the change over is simpler and I don't particularly want to go through the process of adding the fuel lines, sensors and messing around with the computer. That said, if the performance benefits were going to high I'd look into it.

I realise that the stock SU carbs would be well out performed by the EFI, but I'm not sure what the difference would be between the Edelbrock and EFI?

Any advice/input?

Cheers,


tr8todd
Todd Kishbach

(315 posts)

Registered:
12/04/2009 07:42AM

Main British Car:


Re: Performance difference between EFI and Carby - Rover V8
Posted by: tr8todd
Date: January 08, 2017 04:43PM

A buddy of mine has a built stroker Rover that made 327 on a very well tuned carb. He ditched the carb and installed a FAST throttle body injection system. He made 327 again. Throughout the torque curve he consistently made 10 to 15 FT/pounds more torque except at the peak, where it was the same. He has a cam with a broad power band. If I remember right he made 300FT/pounds from 2700 to around 5500 rpms. Startups are much easier and once its started, you just drive away. No sitting around waiting for it to warm up. No more unburnt fuel smell either. I just built a 4.6 and I'm going with one of the new aftermarket FI systems because I'm tired of smelling like gas when I get home from a ride.


Moderator
Curtis Jacobson
Portland Oregon
(4290 posts)

Registered:
10/12/2007 02:16AM

Main British Car:
71 MGBGT, Buick 215

authors avatar
Re: Performance difference between EFI and Carby - Rover V8
Posted by: Moderator
Date: January 08, 2017 07:24PM

It sounds like maybe you should run your carb for awhile whilst breaking in your new engine... but you'll never regret upgrading to EFI. It's a big upgrade. It was certainly one of the best things I ever did for my Buick 215 powered MGB. (I ran an Edelbrock 1404 for way too long!)

I can't say EFI gave me a 10bhp improvement, or whatever... because I didn't do before/after dyno runs. I'm confident there was some gain. Todd correctly pointed out the bigger difference. "The area under the curve" is larger whether peak horsepower has changed much or not. As you said: it's smoother power. Another big motivator for me was that EFI adopts to altitude changes. When I lived in Colorado, that was a big deal.

I knew I'd enjoy the whole process of engineering an EFI installation and tuning it. I also wanted an upgrade path. (Batch injection to sequential. Integration of crank-triggered multi-coil ignition. That's all detailed here.)

IMHO, putting a throttle body system on a 4-barrel manifold is a pretty big compromise. When was the last time any OEM offered throttle body injection? The Rover (multipoint injection) manifolds were designed for torque output. That's why they have such long runners. And, I expect it's no mistake that they have a relatively large plenum volume too.


Airbumps
Kael O

(5 posts)

Registered:
01/08/2017 03:05AM

Main British Car:


Re: Performance difference between EFI and Carby - Rover V8
Posted by: Airbumps
Date: January 08, 2017 08:04PM

Thanks for the feedback guys, appreciate it.

Happy to hear anybody elses input! :)


88v8
Ivor Duarte
Gloucestershire UK
(459 posts)

Registered:
02/11/2010 04:29AM

Main British Car:
TR6 74 2.5 injection six

Re: Performance difference between EFI and Carby - Rover V8
Posted by: 88v8
Date: January 09, 2017 06:25AM

A stock SU engine with 9.5 cr - like the one I have - gave 165hp flywheel.

I never have to wait for it to warm up. Perhaps that's a 4-barrel thing. The choke and the fast idle are interlinked, as soon as I start I can drive off.

And it doesn't smell of petrol. Sounds like some overfuelling going on.

When I look at the complexification of a 4bbl versus the SUs, for a stock engine really what's the point.
If you need to tune the carb that's another matter, selecting different needles for an SU is not easy, even over here in the UK.

Perhaps the easiest upgrade would be the higher compression pistons, and a high-torque cam like the Real Steel Stump Puller.

As regards efi, I admire those who can get their heads around it, I'm afraid I just regard efi as a pile of stuff waiting to go wrong.

Ivor


Airbumps
Kael O

(5 posts)

Registered:
01/08/2017 03:05AM

Main British Car:


Re: Performance difference between EFI and Carby - Rover V8
Posted by: Airbumps
Date: January 09, 2017 07:44AM

Thanks Ivor,

I'm partial to keeping the carby because I, like you, have never had any issues with it. It doesn't run rich, it starts first go, there's no fuel smell and I have no issues with driveability.

Which brings me back to my first point regarding performance improvement. Thats the part thats of interest to me. If I was going to see a >10% increase in performance by running EFI over a 500cfm Edelbrock carby I'd be on the side of the EFI. If it's just about driveability etc then I must say I don't really have any issues with the Carby setup in place at the moment.

Cheers,


mstemp
Mike Stemp
Calgary, Canada
(167 posts)

Registered:
11/25/2009 07:18AM

Main British Car:
1980 MGB Rover 4.6L

Re: Performance difference between EFI and Carby - Rover V8
Posted by: mstemp
Date: January 09, 2017 08:04AM

Having just changed from the Edelbrock to EFI I would say it's more than worth it. Easy 5 mpg improvement. As for the smell of fuel, that will have more to do with the cam shaft than anything. I too was hoping any smell would be gone but it was not the case fully. While I don't smell raw fuel in the garage anymore I still smell after driving the car. I am running o2 sensors with my Rover Hotwire setup as well as a wideband o2 sensor. Mixture is bang on but I still smel of an old car with out polución control, not to be confused with raw fuel. If you have a stock cam I bet this will not be an issue but something like a Crower 50232, unless you add a converter I think you will still smell of emissions.



BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5197 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: Performance difference between EFI and Carby - Rover V8
Posted by: BlownMGB-V8
Date: January 09, 2017 12:54PM

Your location makes a difference. Fuel will vaporize more readily in a warmer climate and unless you keep the stock vapor recovery system or an effective equivalent, just sitting in the garage it will leak fumes. How many fumes depend on how warm it is. EFI is a sealed system that will function fine under vapor pressure, meaning no fumes will escape. As for fumes from the exhaust, that will vary as per Todd.

SU carbs are good but have limitations. Throttle opening is limited by the vacuum signal (diaphragm) so you will always have a restriction at that point in the inlet. 4bbl carbs also require vacuum to pull the fuel over the lip of the float bowl, as does the SU. EFI has no such limitation as the throttle is mechanical and the fuel is under pressure. So if the injectors, the throttle body and the intake are sized to take advantage of these features and all else is equal, an efi engine is always going to produce more power. However, we are generally limited to the physical parts that are available. With efi on Rover engines this generally means either the stock hot-wire intake or throttle body injection. The hotwire intake is designed to enhance the midrange. For most people that is going to be the best. But if you are after top end power, a single plane intake such as a Wilpower or Huffaker and a modern TBI in about the 1000 cfm range will give you noticeably better results because of increased airflow. Just make sure your cam, CR, and exhaust are all up to the task.

You mention 165hp with SU carbs. Since the trouser intake was used on an engine that produced 137 hp I suppose this means you are using one of the independent runner intakes, but that low of an output with that 8 carb setup would seem to indicate something else about the engine is seriously off. That intake should easily support around 250 hp. As should any good, properly set up 4 bbl intake or a properly tuned port injection system. If you *are* using the trouser intake, any change you make will give you an easily noticeable improvement as that is the single most restrictive intake system ever devised for the BOPR engine.

But wait, you could be using the Rover twin SU setup, which makes a little more power than the trouser intake. Does it stick through your hood (bonnet)? That by itself is reason enough to replace it. Unlike a 4bbl with it's big round air cleaner just screaming "Performance" there's no wow factor in that Rover intake. If that's where you are, then yes, Yes,YES! Change the induction system. You stand to gain 50 hp at the bare minimum just with that one change, 4bbl and EFI alike.

Jim


Airbumps
Kael O

(5 posts)

Registered:
01/08/2017 03:05AM

Main British Car:


Re: Performance difference between EFI and Carby - Rover V8
Posted by: Airbumps
Date: January 10, 2017 01:44AM

Jim

Thanks for the input. Looking at your cars profile on here I must say its ...impressive...what you've done to it. Hardly looks like a B at all! Never seen anything like it! Well done.

I'm hunting around for a motor now. I think if I can find a complete 3.9 with the complete Hotwire setup I'll stick with it.


88v8
Ivor Duarte
Gloucestershire UK
(459 posts)

Registered:
02/11/2010 04:29AM

Main British Car:
TR6 74 2.5 injection six

Re: Performance difference between EFI and Carby - Rover V8
Posted by: 88v8
Date: January 10, 2017 05:11AM

As Jim says the standard SU setup with that pent roof intake or the Costello version, is not sexy. But the 9.35 (not my 9.5 typo) in the SD1 with twin SUs made 165hp flywheel.
Quite a stepup from the 135hp of the 8.15cr they put in the RangeRover.

Interesting point about fumes. I never had any fumes from my SU setup, in the garage or otherwise, but the Holley 2300 on my 63 AMC 327 which is sitting in the garage right now, that does have a whiff about it, which I guess in the summer will only get worse.

I wonder if that's why American cars favour plastic upholstery? Plastic doesn't absorb fumes as cloth or leather would.

Ivor


MGBV8
Carl Floyd
Kingsport, TN
(3106 posts)

Registered:
10/23/2007 11:32PM

Main British Car:
79 MGB, Buick 215

authors avatar
Re: Performance difference between EFI and Carby - Rover V8
Posted by: MGBV8
Date: January 10, 2017 12:03PM

Peak horsepower, a well tuned carb is right there with the best of them. The "area under the curve" as mentioned above, has more potential with the EFI. Fuel mileage? The EFI system will win that one.


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5197 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: Performance difference between EFI and Carby - Rover V8
Posted by: BlownMGB-V8
Date: January 10, 2017 12:04PM

No Ivor, it was strictly a money thing. Plus we were big into plastic in those years.

Kael, thanks for the compliments. Sorry to say the car isn't very driveable right now but I have hope. If you found the "340" thread that has the updates.

Now, if you could scour the countryside and come up with a 300 Buick engine it would be a better upgrade than any Rover you are likely to find. Should be plenty of info here about it. I believe the stock horsepower rating is 265, a bit less with the 2bbl. It can be used with the iron heads and intake, those can be swapped out for lighter parts later. The iron block is only 50-80 lbs heavier than the Rover, 50 lbs heavier than the 1800. The car will handle the extra weight without complaint. Worth looking into.

Jim


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