SU vs Throttle body
Turbo Mini Forums

Forgetting issues of cost and complexities of installation.
Assuming the installation is fitted to an engine of very high power.
Would an SU carb outperform a Throttle body (Wet manifold) in terms of out and out power?
I have read the old posts and I can't seem to find a definitive answer.
Regards
Dave

well 95bhp and 101lbft torque with an SPi set up will pass an MOT with 0.098% Co and 155ppm HC

100bhp and 87lbft torque with a standard ECU on the same set up and doubtfull it would pass and MOT

try that with a carb

Carbs are history!

Glad you are back!!
Understand what you are saying but say for a 180+ bhp turbo motor would there be any drawbacks using a Throttle body instead of an SU?
Regards
Dave

Hi,
Can't see any drawbacks myself.
You'll obviously need to size the injectors for your engine spec, but that's about it. For tunablity / drivability / economy I don't think you'll better an electronic setup with an SU. For outright power there maybe some gains, these will come from the fact you have more precise control with the electronic setup.
Cheers,
Gavin :)

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Please bear with me here but I need to ask, Why do all the 200BHP whizz kids still run SU's? Is it for the simplicity of installation?
Regards
Dave

Id say simplicity

Bonus features of full engine management is Launch control, Mapped boost control (depending on what ECU, VEMS ), Anti Lag System, as well as simple features as overboost fuel cut hard and soft rev limiters, the list goes on.

It would have to be a wet manifold set up and Jenvy throttle boddies look the ticket

Oh and not forgetting that VmaxScart supper charger kits run wet manifold with two MJY100460 injectors, staged, when the duty cycle gets to a predetrmined point. They state 140bhp but then thats only because these injectors max out

Edited by Sprocket on 31st Jul, 2007.

So just leading gently on from this, and,assuming that charge robbing is an issue how much richer than optimum would you have to run to keep your engine safe? Ie the robbed cylinders at the correct AF ratio how rich would the other cylinders have to be 9:1,10:1,11:1,12:1?
I appreciate all the esoteric points that come from using an ecu but somewhere in the background I here too many negative suggestions when trying to do a 5 port on injection.
Surely a TB can outperform an old SU on a turbo motor.
I hope it can.
The deafening silence from all the big guns is apparent.
Regards
Dave

With a wet manifold i doubt very much you would get any more charge robbing than you would with a carb. Thats why wet manifold is still the way to go.

I would be using a reasonalbly small, single injector for idle and crusing, with a reasonably large injector for the higher loads thus keeping a good idle, yet treating the whole set up as a sort of single point system (very different from the SPi) that way you can configure the injectors to fire every engine event (twice per cycle) and avoid possible dead spots in the fuel supply. Its baisicaly a carb.

Forget the MPi manifold, its pants, its design was by far the worst rover came up with, may be it was intentional. Good results as you say have been had with the SU, so dont see the need for a fancy manifold, the Jenvy throttle body on an SU manifold should give the same results, the bend of the port runners giving good fuel mixing.

For now, forget port injection. TBH i really dont see the benifit of going to all the trouble of getting it working, What is gained other than neat packaging and slightly better emissions, not really a problem if you run a carb anyway.

I agree that a wet manifold should be pretty good and that it should not be worse than a carb for charge robbing. However, I think you mean you need to inject twice per rev and not per cycle (2 revs). And using 2 injectors is a must in my opinion: either one small and one large for the reasons mentioned or 2 medium ones. The 2 medium injectors would still allow a reasonable idle and would share the load equally which means they're always used the same. I don't know if that is really an issue but it's something to think about.

As for port injection, the code is there. There is some more testing needed but it's not as if everything needs to be done. I'm also working on the next version based on the latest version of MS2extra which will allow individual trim for each cylinder and separate injection timing for inner and outer cylinders. This will have the potential to eliminate any issue with charge robbing and take into consideration any difference in VE between the cylinders. So, in theory, it should allow to extract every last HP the engine is capable of producing by optimising AFR for each cylinder.

Also, this code will not be limited to siamese-port engines but will allow sequential injection for any 4 cylinder engine with individual cylinder trim. With the little response I've had about the siamese-port code, I assume that this part of the code will see much more use.

Jean

http://www.jbperf.com/

Oopsie, yes, twice per rev.

Thinking about about what you were saying, an injector of around 600cc would still give a decent idle with good emissions, i know, i run one, so two 600cc injectors staged would be adequate for danboy's 180bhp

As for the port robbing, i intend to use the Kent 274SP cam. The scatter timing reducing the charge robbing by mechanical means and the Inlet timing of 248 and exhaust timing of 274, keeping the valve overlap to a minimum giving a very good cam without the issues of long duration cams in forced induction aplications. Valve lift is a little low, but nothing high lift rockers wont sort.

Watch this space

I agree that the cam is probably a good choice. However, that would not completely prevent a difference in VE between inner and outer cylinders just from the fact that the conditions are different when their intake valves open.

For the inner cylinders, the port has been without any valve open for about a complete rev while for the outer cylinders, the inner cylinder valve has just closed which means that the air is far from laying still. So this, in my opinion, would mean a change in VE between the inner and outer cylinders which will probably change with RPM depending on port geometry and valve timing. However, this is just speculation on my part but would be interesting to verify and would benefit from port injection with per cylinder trim, if I'm right.

Having said that, I look forward to see what results you can get with your setup.

Jean

http://www.jbperf.com/

Sprocket and Jean ... welcome back!!!

Jean, can you PM me your e-mail again please as I want to discuss code testign again. After a very difficult few months life is slowly getting back on track and I really want to crack on with this now!!!

Every day is a school day ...........

How fast and how expensive ...... the same question...

Hey Roger, Wondered where you were, Did you miss the floods?
Regards
Dave

I've been super busy, bit of a crisis at work.

Luckly I was not hit too badly by the floods and neither was my mother in the other house. Just got water back on .... crazy how much you can look forward to flushing a toilet!!!!!

By the way, I'm coming down strongly on the side of a throttle body!!!!

Every day is a school day ...........

How fast and how expensive ...... the same question...

Anyone looked at these injectors by Siemens?

http://www.lingenfelter.com/store/ln10070.html

High impedence and over 600cc if the fuel pressure line is raised.

Andy

me too roger... me too.

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

Hi,
I'm on the bandwagon already :)
Cheers,
Gavin :)

VEMs Authorised Installer / Re-seller. K head kits now available!

WB/EGT gauges. Click here for customers write-up

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