opinions sought re small 12cyl twin turbo

[jimbob82]

This is all theoretical ATM with the view of doing it for real in the near future.

Specs:
Bore 60mm
Stroke 60mm
Valve lift 10mm and using 1.5 ratio roller rockers
Inlet valves 2 - 24mm with 28mm diameter ports running approx 70mm in length - 1 port for EACH valve
Exhaust valves as above but 21mm valves and 25mm diameter ports

Im looking at running 1 turbo for each bank of 6 cylinders. Looking at data a gt25r would be nice for each bank.

Rpm redline is 13k and max power from those 2 gt25s is approx 640bhp @ 12000rpm.

The thing I'm considering is using slightly smaller turbos so they spool up quicker without sacrificing much on power.

Any recommendations? I much prefer garret turbos but willing to look at others if they fit the bill.

Also for the more knowledgeable, is there a way of calculating theoretical airflow through an open port? Given the diameter, length and atmospheric pressure? Just curious

Just looking for more input from a fresh brain looking at it. Maybe we can "debate" whether its worth running turbos aside from the fact everyone loves a turbo

[SuperchargedVR6]

Why a 2 litre V12 over a V6 or V8, or even a 4 pot?

I'm just thinking that's quite a lot of frictional and pumping losses for such a small capacity?

Just interested really

[jimbob82]

Sorry I should have said. Its not a v12 its a boxer.

I don't like v engines

Plus 12 cylinders would be smooooooth

Edited by jimbob82 on Monday 11th February 16:16

[Evoluzione]

SuperchargedVR6 said:

Why a 2 litre V12 over a V6 or V8, or even a 4 pot?

I'm just thinking that's quite a lot of frictional and pumping losses for such a small capacity?

Just interested really

Presumably 'cos it'll rev to the moon! Read here and check out how long ago it was:

http://www.supercars.net/cars/26.html
I seem to remember even further back than that they had a 1.5 litre 12 cyl pushing out amazing power for its time.

Although it has to be said these days we have much more reliable engineering and lighter materials etc so don't have to go to such a degree of small cc with loads of cylinders, sounds like a fun project though!

[jimbob82]

yeh, low centre of gravity, high revving, silly power and the engine should be VERY light. making it an ideal race engine for the car i'll build around it (sort of Caterham R500 style) but with more aerodynamics.

should make for a pretty nippy little beast

[anonymous-user]

Let me get this clear:

You want to engineer a completely bespoke high performance race engine from scratch, and yet you need to ask how to calculate port flow??

Er, don't take this as negative, but are you sure you have the skills and money to make that work?

[davepoth]

Crankshaft is going to the critical thing IMO - I guess it's the only fully custom part (I assume cylinder heads and crankcases are coming from elsewhere and being welded together?) and it's going to be a pricey job to make it do everything you want since it'll be so long.

Did you consider making an H16 instead? The noise is even more epic than a flat 12...

[jimbob82]

Max_Torque said:

Let me get this clear:

You want to engineer a completely bespoke high performance race engine from scratch, and yet you need to ask how to calculate port flow??

Er, don't take this as negative, but are you sure you have the skills and money to make that work?

Yes I do,

If you don't ask you will never know i've approximated the flow atm (more than likely on the low side of what it would be but I was looking for someone to give some info on how to calculate the theoretical flow through a port. as you probably well know it's all different when you get it on a bench and flowtest it for real but an approximation to see how far off I am would help me judge if the power output is somewhere near or miles off.

I don't often takes things negative unless it's a complete slant. I quite agree with your point and whilst lacking the funds at present I do believe I have the skills.

I can't double quote here for some reason so I'll have to double post - sorry

[jimbob82]

davepoth said:

Crankshaft is going to the critical thing IMO - I guess it's the only fully custom part (I assume cylinder heads and crankcases are coming from elsewhere and being welded together?) and it's going to be a pricey job to make it do everything you want since it'll be so long.

Did you consider making an H16 instead? The noise is even more epic than a flat 12...

crankshaft below (roughly drawn up and needs more work/modifying and the lighting in the pic is awful - i'm still getting to grips with the program). Everything is going to be machined, crankcase, block, heads, cam carriers, sump pan will be made from sheet ally with a kickout and probably gated.

length is approx 590mm so not that long really

I did think about making a H24 like a napier sabre but it would cost 3 times as much and whilst the noise would more than likely justify it the mechanics of it wouldn't, plus it would be heavier and higher which I didn't want.



^^ hopefully I got the code right

[chuntington101]

2ltr v12? That's boring a mad French guy has built a 2.0ltr v16 using destroked Honda 600 cbr engines and top ends! Oh and he uses it in his off road car! Lol you have to love the french sometimes.

[The_Burg]

Didn't Honda build 6 cylinder 125s back in the 60s?

What about a 16 cylinder based on any Jap 400 from the last 20 years? 18k rpm potential in standard form and easily over 200 NA.

[Evoluzione]

You need:

An engine simulation package

An engine (or specifications of) with your 60mm bore and stroke - possibly a motorbike engine? so you can study the head.

A lot of money

[AER]

jimbob82 said:

yeh, low centre of gravity, high revving, silly power and the engine should be VERY light. making it an ideal race engine for the car i'll build around it (sort of Caterham R500 style) but with more aerodynamics.

should make for a pretty nippy little beast

Why do you think it will achieve this?

The ideal engine for a light-weight, high-revving, silly-power engine is probably the four cylinder. Twelve cylinders gets you a load more friction, a heavier crankshaft that's also long and very floppy, eight more inlet and exhaust pipes to plumb as well as the associated valves, injectors, lifters, lobes and sundry bits. Dividing the total combustion chamber volume by 12 also degrades your surface-to-volume ratio, effectively limiting your maximum compression ratio.

A boxer engine doesn't give you the lowest centre of gravity either, by the time you're done with packaging it all. A V is much more likely to end up with a lower Schwerpunkt.

The only reason for a small 12-cylinder engine is the noise* - and an agreeable noise it is too!

BTW, I was told by someone that might know, that of the 12-factorial (or whatever it is) different firing orders available of a 12-cylinder engine, there are only two that will actually work without tearing the engine apart...

• or race formulae

[jimbob82]

Evoluzione said:

You need:

An engine simulation package

An engine (or specifications of) with your 60mm bore and stroke - possibly a motorbike engine? so you can study the head.

A lot of money

performance trends engine analyzer that's how i came up with the approx 640bhp @ 12,000rpm

a lot of money agreed, about 40k covers it, which if you consider all the machining and materials involved isn't THAT expensive for a 1 off.

I suppose a V engine would be simpler but that's the norm IMO, I was looking to do something a bit more...i suppose crazy lol

I appreciate the comments/critics, all taken on board so far.

anyone have any input on the original question re turbos?

[-Bladerider-]

Best suggestions I can give re turbos:

Get on the RX7 rotary forums like mazdarotary.net and have a good read about turbo options people are finding successful in their builds for the 13b engine.

The reason I suggest what seems like the most opposite style lump compared to yours is the rev and flow characteristics. 13b has only 1.3 litres of displacement but obviously rotors have double the firing per revolution of your V12, they therefore rev forever and have very low torque for their displacement. The 13b is rated as standard to about 260bhp in later cars and alot regularly run 350bhp with sensible mods. So I would expect a turbo that runs 300-350bhp on a Rex to be somewhere in the region of what you want.

I dare say it will be something like a gt2871r but with a massive hotside - they do a 0.86 housing, not sure if you can get bigger, maybe have to go for a 3071 with a 1.06 and get a custom trim. Also bear in mind that there are twin scroll billett wheel and variable vane option now available so theres more choice than most people can help with - speak to the guys at Turbo Dynamics who are pretty helpful.

Your cheapest and most readily available source of something to get your hands on and measure/play with would be the stock turbo from a 200sx which is a GT25 style unit. Dont forget that RX7's stock setup is sequentially turbo'd so that would be less helpful as far as looking at size/weight etc is concerned.

J.

[dblack1]

Evoluzione said:

Presumably 'cos it'll rev to the moon!

more cylinders don't have anything to do with how high a motor can rev. a 4 cyl can rev up to 15k rpms, in fact, look at sport bike motors, many of them rev up to 9k+. Most motors have a limiter much lower (and are tuned to operate at lower revs) to make the motor more reliable, cheaper to produce and/or more fuel efficient. 12 cyls do sound wicked tho, but the sound can be emulated by smaller motors (as proved by both nissan and yamaha).

-Bladerider- said:

Get on the RX7 rotary forums

Unless you are trying to increase your cool factor with this motor, you can produce something just as powerful for way cheaper with stuff that is already out there. It would probably be more reliable as well. A rotary motor out of a RX7 (or a cosmos if you want something really wicked) would be a great start if you want to rev to the moon. Many people have built blocks/cranks to double up motorcycle engines as well. There are other more conventional motors you could build up with similar results as well. I don't understand why you would want to go off building a custom flat 12 unless it is just for the coolness factor, but to me, that just means you have money.

[Megaflow]

jimbob82 said:

performance trends engine analyzer that's how i came up with the approx 640bhp @ 12,000rpm

a lot of money agreed, about 40k covers it, which if you consider all the machining and materials involved isn't THAT expensive for a 1 off.

I suppose a V engine would be simpler but that's the norm IMO, I was looking to do something a bit more...i suppose crazy lol

I appreciate the comments/critics, all taken on board so far.

anyone have any input on the original question re turbos?

Assuming you are talking about a fully bespoke engine, with unique heads, block, etc, that won't even scratch the surface.

For example, we buy a *lot* of billet steel cranks from Arrow Precision for prototype engines at work and we pay £3k+ for each one, granted they are bigger than yours, but we have a relationship and they know more will follow.

Edited by Megaflow on Tuesday 12th February 08:14

[Evoluzione]

I think I would worry about building the engine first before getting into speccing turbos....

[anonymous-user]

I think you have a zero missing from your cost estimate!

I think you could just about build the engine you are talking about, from scratch, doing everything yourself (machine everything from billet yourself) for £40K. I suspect the engine would never run, or only for a few seconds before failure however.

To do this with outsourced components that are not std well, i'd suggest £400k. Can i suggest you start a BOM and put in some sensible costs and see where that gets you (btw, as AER suggested above, there are a LOT of parts in a complete V12 engine)

[SuperchargedVR6]

Evoluzione said:

SuperchargedVR6 said:

Why a 2 litre V12 over a V6 or V8, or even a 4 pot?

I'm just thinking that's quite a lot of frictional and pumping losses for such a small capacity?

Just interested really

Presumably 'cos it'll rev to the moon! Read here and check out how long ago it was:

http://www.supercars.net/cars/26.html
I seem to remember even further back than that they had a 1.5 litre 12 cyl pushing out amazing power for its time.

Although it has to be said these days we have much more reliable engineering and lighter materials etc so don't have to go to such a degree of small cc with loads of cylinders, sounds like a fun project though!

Ah gotcha, I get it now

167hp/litre in 1975, blimey!