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Dual Purpose Engine Setup (Turbo And N/a)


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#1 nikollou

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Posted 03 November 2017 - 08:25 AM

Hi guys, I am in the process of building a 1975 mini that I will be using both for daily driving but also for the occasional track time and some historic racing. 

 

The thing is, I would like -if possible- to set up a car that will work primarily as N/A, but to which I will be able to selectively "bolt on" a mirage manifold with a turbo and get that extra umph that makes driving a turbo so much fun. Of course the other elements of a turbo setup (oil pump, fuel pump & reg, oil feed etc) will be sorted as well.

 

So I know that it is impossible to build a one-suits-all car and I am well aware of the compromises at hand and the fact the car will never reach peak performance as either of the two scenarios would on their own.

I just like the idea of having a dual-purpose car, IF that is possible.

 

So my question -apart from any other comments- would be mainly around CR & cam selection as these are choices I have to make now during the engine build phase and I cannot change afterwards.

  • Regarding CR: For a N/A car I would be looking at 10.5:1 ratio. If I set up the engine at this ratio, would I have issues when it operates with the turbo? I am not planning on running insane amounts of boost, just enough to keep the engine/gearbox safe but give that smile on your face when you get sucked in by your seat as the revs get higher.. Maybe I should shoot for something like 10:1?
  • For cam selection, obviously aggressive cams are not an option here, but what do people think would be the best "compromise" solution assuming the turbo will be running low boost so that when running the car as NA I get as much fun factor as possible. Could I go for say a Swiftune SW7 or a Kent 276 or a Calver RE13? I have had a discussion with Keith from Calver Racing who has been very helpful and his recommendation is somewhere in the Biper BP255 range and that the RE13 which I would choose if I was doing a purely NA car would not work well. I tend to trust his valued opinion, just curious to see what other people say/recommend.

I have done some research both here and on a couple more sites and haven't found someone looking to set up such a dual purpose car so I thought it would be interesting to start such a discussion and get people's opinions.

 

Has someone done this already? What do people think and how can I get some help on the specific questions around CR & cam selection I raised above?

 

Obviously I'll be happy to keep people posted on the build if you find it interesting... Or to see how much of a mess this will turn out to be!!

 

Thanks!



#2 Steve220

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Posted 04 November 2017 - 11:19 AM

Build a turbo engine, turn boost down and control your tempo by your right foot if you're after MPG. I used to find all my previous turbo cars a delight to run off boost and return good mileage from a tank full; however not as fun when the boost is wound up, granted.



#3 mini13

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Posted 04 November 2017 - 11:29 AM

As above thats the beaut of a turbo lump, you can wind the boost up or down, or its actually pretty easly to have a switchable set up of say 7 psi and 15psi boost.

 

in terms of economy, lost of people manage 40+ mpg on a turbo engine on a run, and they are very road drivable if the boost isnt set high,

 

the bigquestion IMO is how much power are you looking for? if its not a lot, say 130hp, then you can keep the compression ratio to about 9:1 and make it a bit nicer with the boost wound down, much above that your going to be looking at fitting a straight cut box and its going to be fairly noisy.

 

cam wise go for somthing short, SW5, MG metro/kent500, or a kent 274i all these will have little valve overlap which is important on a turbo, even somthing like a 266 would be a bit overlapy IMO



#4 Ethel

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Posted 04 November 2017 - 12:08 PM

All turbos are N/A until they spin up. Turbos were developed for economy on big diesels as they recover exhaust energy, that can work on road cars too if you pick gears to reduce the rpm and use the extra torque.

 

Compared to a tuned N/A engine,  the lower compression is offset against longer duration cams that reduce the dynamic compression (inlet valve shuts further up the compression stroke).



#5 nikollou

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Posted 06 November 2017 - 12:39 PM

Hi guys and thank you for the prompt replies! It's my first post in TMF and even though I am an avid follower and have read pretty much everything here to help my build, this is the first time I'm asking for specific help and I really appreciate the replies!

 

To answer mini13's question as far as desired BHP, yes I'm definitely more than happy with something in the 130 range or maybe even lower in order to keep my helical gears and noise levels down and also to help promote longevity of the gearbox (I believe the more BHP the more stress to the gears and other components of the gearbox that will require more frequent checks/replacement).

 

I also wanted to clarify something I realise wasn't clear in my initial post: The historic racing I would like to participate in will most likely require me to not have the turbo physically installed as it will not pass regulations, whereas daily driving and track days will more than welcome the addition of boost. SO that means that just running the engine with no boost would not be a viable solution for my case even though it sounds like a great all-around car.

 

So how does one go about building an engine that will work both with and without a turbo physically installed?

 

Are the above recommendations still suitable for what I need? (CR wise 9:1 and cam the milder options as per mini13's post..?)



#6 mini13

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Posted 06 November 2017 - 01:10 PM

ok, basically build it around what I have mentioned, 9:1 compression short cam etc and you will be able to run that on either setup, it may be a little lacking as NA due to lower compression, but will work ok. altenativly you could also swap heads which is not much more work, but it means buying a head gasket each time,

 

another dificulty is the change in "tune" probably the easiest thing is to swap carbs, keeping them set up for each system, for ignition if you are alowed to run programable ignition you can just upload the set up for each.

 

theres nothing particuarly clever about a turbo engine, it just needs to have a lower compression ratio, and a cam thats not too mad. Also you want decent pisons and a head that dosent have massive valves in it, but they both a given for a good fast road build anyway.



#7 nikollou

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Posted 09 November 2017 - 03:31 PM

Ok great stuff mini13 thank you for the continued support in developing this idea!

 

Head-wise I have a 12G940 with big valves to which I will be doing some "stage 1-2" porting myself using vizard's bible. No plans on replacing the valves with even larger ones, I just want to change valve seats to allow for unleaded fuel.

 

Carb-wise yes I was definitely planning on having a pair of hif44's bolted on their own manifold and setup for each purpose. 

 

Ignition-wise since I am a huge geek and gadget fan I have been very intrigued by 123's TUNE+ model with Bluetooth which allows for two maps that can be changed via an external switch (I picture having a "TURBO" switch on the dash and find the idea quite amusing) and it also allows you to make on-the-fly changes using your smartphone to more easily calibrate your exact curve. In theory, how would the two curves compare? I Assume the Turbo curve will require some further retardation to avoid detonation due to the higher effective compression.. Right?

 

Also fuel pressure-wise If I have a turbo fuel pump with the relevant regulator can just dial the reg all the way down to a level that works for the N/A setup or are we talking swapping out pumps with say a faucet solid state & its equivalent reg?

 

Finally this might be a stupid question but do I need a waste gate or can I go by without one? If yes, what is the simplest solution that will make the swapping process relatively easier, taking into account that I am not going to be running large amounts of boost?

 

So I was thinking for the sake of the project of making a "conversion checklist" that i will follow each time step by step so I thought I might start it up here and anyone that is willing might chime on on things I have either forgot or got wrong.

 

So the checklist would look something like (e.g. in the case of N/A to Turbo):

  1. Disconnect & remove existing carb/intake/exhaust manifold (LCB)
  2. Install turbo exhaust manifold (mirage type - no turbo box installed so possibly tilt engine slightly forward with adjustable top poly bar)
  3. Install turbo (GT17 I assume is the better choice)
  4. Hook up waste -gate? (Same question as earlier.) 
  5. Connect turbo to exhausts system (custom piping down to remaining Maniflow system minus the LCB?)
  6. Install Turbo set-up Carb
  7. Connect Turbo to Carb via MG Metro plenum (no intercooler planned) & silicone hose
  8. Hook up carb to control cables & fuel feed (Adjust regulator or swap out pumps/reg's? Same question as earlier.)
  9. Hook up turbo to oil system & water system (also will need to have a way of blanking the pickup for these for N/A but don't think it's gonna be that hard)
  10. FLICK TURBO SWITCH ON DASHBOARD
  11. Start engine and smile  :proud: 

 

Does this sound about right? What am I missing here and could someone help with the myriad of questions I have posted?

 

THANK YOUUUUU!!!!



#8 timmy850

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Posted 09 November 2017 - 10:17 PM

In regards to the ignition set up another option is getting a programmable setup that can retard the timing as boost increases. This Aldon unit is a good example, it has a MAP sensor and you can program the ignition in proportion to the boost levels. You can also set up a switch to go from one map to another.

 

http://www.aldonamethyst.co.uk

Instructions:

http://osneyconsulti...nstructions.pdf



#9 nikollou

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Posted 10 November 2017 - 07:50 AM

In regards to the ignition set up another option is getting a programmable setup that can retard the timing as boost increases. This Aldon unit is a good example, it has a MAP sensor and you can program the ignition in proportion to the boost levels. You can also set up a switch to go from one map to another.

 

http://www.aldonamethyst.co.uk

Instructions:

http://osneyconsulti...nstructions.pdf

 

Great recommendation timmy, thanks a lot! Wasn't aware of this option to be honest but seems interesting..



#10 mini13

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Posted 10 November 2017 - 09:57 AM

yep as mentioned, with a programable system you can map the advance, if your swapping carbs off then your going to end up with a slightly doifferent mixture so the advance should change, and exhaust setup but you would beable to get away with running it on the turbo mapand  it just wont be operating in the boost part of the map. basically the same as turning the turbo bost right down.



#11 Ethel

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Posted 10 November 2017 - 03:49 PM

Megajolt was popular for ignition on turbos, the (Ford) donor bits will be harder to find I guess. There are more options now, programmable ignition that can retard for boost is well worthwhile. Two carbs aren't needed, carbs can't directly sense boost anyway, that's what the fuel pressure regulator is for - with a restrictor to create a pressure differential for the carb, or some fancy electronic control. Turbo fuel pressure regulators work automatically, by sensing the boost pressure. Many turbos have a built in waste gate, did you mean dump valve? Both are pretty much essential in some form or other.

 

I'm not sure you've got the idea that all turbo engines function as normally aspirated engines much of the time. If you build a turbo engine, it'll only boost when you open the throttle far enough and for long enough to fill the cylinders and so push enough gas down the exhaust - i.e. when you demand more power. If you wanted to limit the power you only have to trick the waste gate in to opening, so the exhaust gases can bypass the turbo. This is what they did with the turbo Metro - actually they had it set to open with not much boost and "hid" extra boost from the waste gate actuator with a valve that leaked some of it away when they wanted more oomph.

 

I'll bet there's a "how it works" video on Youtube to help you.



#12 nikollou

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Posted 15 November 2017 - 08:46 AM

Great to see more incoming info, I'm starting to feel more optimistic about this build..!

 

So a couple answers to the above:

  • Ignition-wise I think I'll stick to the 123 programmable solution as it looks as "original" on the outside as possible, whereas megajolt would not pass regulations for historic racing.
  • Thanks for the clarification Ethel, to be honest my mechanical knowledge is fairly decent, but when it comes to forced induction I have relatively limited experience. I realise now that what I intended to ask was about the Dump Valve and not the Waste Gate which will be an internal part of the turbo. 

So as I get more details finalised around the setup a couple more questions remain.

I think I'm now looking at:

  • GT15 turbo @10psi or even 9psi boost hoping for 130-140BHP
  • 12G940 head with stage 1 porting
  • 9:1 compression ratio
  • Swiftune SW507-or-equivalent cam

My pending questions:

 

Would it be advisable to use 1:5 or 1:3 ratio rockers?

 

Could I get away with the Dump Valve?

I have been doing some reading on forums and there seem to be threads of people verifying they have been doing this with no issues. I'm only saying this to make the turbo setup as minimal as possible to facilitate a relatively easy swapping process. I understand that the purpose of the DV is to protect back pressure when lifting off the pedal but if its already relatively low boost maybe I will be OK? Also the Metro Turbo did not have a DV, right?

 

Can I get away with the Metro ECU?

So the purpose of the ECU was to regulate boost levels above and below 400RPM from 4 to 7 psi respectively as I understand to protect the gearbox. Assuming I'll be upgrading to the x-pin diff I just want to verify that I do not need the ECU and presumably I can just statically set up the actuator of the internal waste gate of the turbo to a specific boost level (10-9psi) and anything above that will be "wasted" out to the exhaust system? 

 

Can I use the turbo fuel pump & reg when removing the turbo and running the N/A setup?

Having done some research I was wondering if I could get away with adjusting the turbo fuel regulator down to 2psi (vs 3.5psi for turbo) via the nut on top and then leaving the boost sensing hose blank therefore getting a constant 2psi to the hif44 which should be just about fine for N/A. Sounds feasible? Maybe however there will be excessive wear on the reg as it will be constantly bypassing a lot of incoming pressure..?

 

Here is the updated swap to-do list:

  1. Disconnect & remove existing carb/intake/exhaust manifold (LCB)
  2. Install turbo exhaust manifold (mirage type - no turbo box installed so possibly tilt engine slightly forward with adjustable top poly bar)
  3. Install turbo (GT15)
  4. Install dump valve or not necessary?
  5. Connect turbo to exhausts system (custom piping down to remaining Maniflow system minus the LCB)
  6. Install Turbo set-up Carb
  7. Connect Turbo to Carb via MG Metro plenum (no intercooler planned) & silicone hose
  8. Hook up carb to control cables & fuel feed (Adjust regulator or swap out pumps/reg's? Same question as earlier.)
  9. Hook up turbo to oil system & water system (also will need to have a way of blanking the pickup for these for N/A but don't think it's gonna be that hard)
  10. FLICK TURBO SWITCH ON DASHBOARD
  11. Start engine and smile   :proud:

 

Thx again guys for all the help!



#13 Steve220

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Posted 15 November 2017 - 08:56 AM

for 9-10 psi, you will need a blow off/dump valve otherwise you'll get compressor stall. 



#14 Ethel

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Posted 15 November 2017 - 11:23 AM

1.5 rockers are good, but there are better things to spend the money on if you already have the potential to break the transmission.

 

There's a blow off valve built in to the Metro plenum, but it's not as fancy as the vacuum assisted aftermarket ones.

 

I think the electronic boost control was binned when they fitted the Metty engine to the ERA Minis. Production cars with warranties have different ideas about reliability and maintenance.

 

10psi with 9:1 compression sounds a bit ambitious without an intercooler.

 

The fuel system can be exactly the same - has to work without boost on a turbo engine anyway.

 

The regulator will always bypass lots of fuel pressure as it's really a bit of a work around to use a 30 odd psi pump to supply perhaps a 1/3rd of the pressure. If there's no boost then plenum just communicates atmospheric pressure to the regulator anyway. 

 

I'm still confused by 9 & 10. Unless you're planning on physically removing the turbo there's nothing to be gained and potential to damage the turbo if it's still hot or just windmills. If you want a switch, use it to limit the boost with a solenoid bleed off valve  - much like the Turbo Metro did. 



#15 Turbo Phil

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Posted 15 November 2017 - 12:02 PM

Are you restricted with what you can do to the head by regulations or budget ?

I would fit a dump valve. The old Metro T3 was a fairly robust unit and only ran 7psi anyway, but the smaller GT15 and 10psi warrants one IMO.
If you want it to be discrete use one of the plastic recirculating OEM ones as fitted to Saab's.

I wouldn't bother with the stock ECU.

Phil.




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