Light Weight Normally Aspirated Or Heavy Weight Force Fed???

[Duk]

I know I do this from time to time and it probably won't make much difference, but it's cold out there and I'm bored..............

Anyways.

Question, and maybe this is the wrong crowd, but for a road going 75 V6 (Potenziata), what do you people think would achieve the best over all driver enjoyment?
A warmed up normally aspirated 12 valve engine.
A centrifugally supercharged engine.
A twin turbocharged engine.

Every method brings to the party its own pro's and con's:

The wamed NA engine brings music, more consistant throttle behavior, the least amount of weight (something I'm leaning towards. Overall weight and where the weight is located) and would be the nicest to the transaxle (a significant concern).
But overal power and torque numbers will never match a forced fed engine.
Technically the simplest and because of the lowerer power/torque numbers, there is temptation to create a lightened gear set for the gearbox, to make the overal combination even more enthusistic and precise.

The centrifugal supercharger would allow the engine to achieve some very decent outright power numbers, but because of the progressive boost pressure nature of centrifugal superchargers, the average torque number won't be as high as a good turbo or positive displacement supercharger set up. The more progressive torque nature of the engine should be nicer to the transaxle and having a conventional exhaust system would allow a more Alfa Romeo V6 exhaust note, but stepped up a notch or 4.
Fine tuning boost pressure is more expensive than doing the same for a turbo setup, as different pulleys would have to be bought or machined to achieve a desired boost pressure. And there is no real practical/efficient way to lower boost pressure if it's needed.
Straight cut internal gears and centrifugal compressor whistle would add some music that is all its own to the Italian V6.

Done well, a pair of small turbos would give the best, highest average torque numbers. Peak power numbers may go slightly in favour of the centrifugal supercharger set up (internal back pressure of the turbos causing additional heat retention in the combustion chambers, meaning the ignition maps would probably be more conservative to keep knock at bay), but the higher average torque should have the car being effortlessly fast for basically any gear. If you haven't driven a car that has masses of torque pretty much everywhere, then I'd say you're missing out. But when you do drive such a car, going back can be a hard thing to do...............
But the high torque numbers will give the transaxle a very hard time.
Turbo's cause massive heat retention in the exhaust manifolds and turbine housings. And that heat will cause huge problems if not dealt with correctly.
Weight and where that weight is located again shows up.
The turbine housings and and turbine wheels also take lots of energy from the exhaust gasses and that changes the note of the exhaust. Much easier to keep the overal high flowing exhaust quiet, but the music tends to be lost.
Fine tuning boost pressure is easy and being able to impliment a lower boost pressure for safety is easy too. With the right programmable computer (which mine is capable of), boost pressure by gear ratio is even do-able.
Throttle behavior also tends to be rather non-linear. Not a huge problem and the elastic throttle (where the car can continue to accelerate after a decent throttle push and march onto boost, even tho you are easing off of the throttle) can be a bit of fun once you're use to it. Incidentally, the elastic throttle behavior is very mush gone in cars like the BA/BF/FG Falcon turbos, where they have an electronic throttle body. I'm sure the manufacurers 'cured' the cars of such behavior.
Cruise fuel economy should be slighly better than the centrifugal supercharger.
And strangely, creating a more simetrical engine bay look would be a bit easier.......... 

Like I said, I'm bored. 

[carlo rossi]

well for me the sound of naturally aspirated webers being sucked
through with great voluminous gulps of air does send the hairs on my neck off
and the reliability is another feature that I enjoy
not having to rebuild an engine every 150K
the wine of a charger is great but boring after a while
and attracts police like sharks to a carcass
I suppose  it comes down to application
race or road .

[Duk]

well for me the sound of naturally aspirated webers being sucked
through with great voluminous gulps of air does send the hairs on my neck off
and the reliability is another feature that I enjoy
not having to rebuild an engine every 150K
the wine of a charger is great but boring after a while
and attracts police like sharks to a carcass
I suppose  it comes down to application
race or road .

Yeah, I won't be putting any carbies on a computer controlled engine. An ITB setup could be an option, but an unlikely 1.
I'm not sure how or why you believe that carbs are more reliable.
And as for rebuilding a force fed engine after 150,000km, um again I'm not sure how you've come to that conclusion.

[carlo rossi]

I know its hard to fathom my like for carbs but they are reasonably simple to tune and repair
and the sound ahhhh if i want whining I can go upstairs for that.
I dont have an electrical engineering background so for me the idea of restoring a computer controlled car
with mapping and programs that have been superseded is a nightmare
imagine attempting to redo the electrics in 20years imagine a tesla with touch screens and such ( great car but sell it after 5 years)
we have come to nexus point I believe that any vehicle built after 2000 thereabouts
will be virtually impossible to drive in 40 years time.So the idea of Classics is dead in modern cars
we as a society in our attempts and ambitions to be Greener have never been so brown

The rebuild well this is from experience turbos only live for 150k +- 20k
the unit that is,and is also a recommendation in most manuals (european)
the engines themselve s having all that extra stress do indeed wear faster, fact of life
rings,seals ,valves, bearings the lot .
you asked for preference not logic
So thats mine! but thats not to say a twin turbo is off the cards !
in fact it is is my ambition to buy the new 500hp alfa (twin turbo)
but i wont keep it more than 5 years or over 80k

[Dna Dave]

I would go, and property will, a 3.2 24v gta motor, good ecu, good headers and standard engine will achieve just under 270hp atw's, and i do know a guy in vic that is making conversion kits and this is all tested and proven.

Cheers

David

[Duk]

I know its hard to fathom my like for carbs but they are reasonably simple to tune and repair
and the sound ahhhh if i want whining I can go upstairs for that.
I dont have an electrical engineering background so for me the idea of restoring a computer controlled car
with mapping and programs that have been superseded is a nightmare
imagine attempting to redo the electrics in 20years imagine a tesla with touch screens and such ( great car but sell it after 5 years)

Again, ummmmmmmmmmm, your comparisons are strange.
Carbies easy to tune??? I'll take a programmable computer over carbies any day. You haven't even mentioned ignition timing. And there's no way I'd ever consider combining forced induction, archaic ignition timing control and carbies on the 1 engine.
By the way, I'm no elctrical/electronics engineer either. Just a Fitter and Turner car enthusiast.
And going from a electrically simple car like the 75 and comparing it to a Tesla is, ummm, again, strange.

The rebuild well this is from experience turbos only live for 150k +- 20k
the unit that is,and is also a recommendation in most manuals (european)
the engines themselve s having all that extra stress do indeed wear faster, fact of life
rings,seals ,valves, bearings the lot .
you asked for preference not logic
So thats mine! but thats not to say a twin turbo is off the cards !
in fact it is is my ambition to buy the new 500hp alfa (twin turbo)
but i wont keep it more than 5 years or over 80k

My Falcon turbo would spend a very small amount of it's driving life on boost and I would expect similar boost/dring behavior from most turbo cars. The Falcon is also my 4th force fed car and I haven't seen anything like the bad engine/turbo life you've mentioned from any of them and 1 of them in particular enjoyed many miles of enjoyment and various stages of modifications. It went off the road when its supercharger died (the coating on the rotor edges came off and I think that coating may have munched an internal shaft seal), but at a guess that happened after it had been swallowing 7psi of non-intercooled (IE: quite hot) turbo air for quite a long time.

When the Busso engine was designed very few production cars had turbos the cam belt de tensioner the head gaskets the synchros the differential none of these components will cope very well. The slow 1st to 2nd gear change will take a second out of 0-60 leave it N/A and less stressed and buy yourself Nissamazota 13btwinblower they are so much better suited to force feeding

I think you're missing the point and at the same time spreading false tales about Alfa's.
First of all, the car is intended to be a Driver's Car and not a traffic light warrior. The addition of forced induction, if it happens, would also reduce the pure number of gear changes required. Bigger, fatter torque curve and all.
The diff is a concern, tho. 1 idea is to implement a small pump that circulates the transmission oil thru a cooler and then pumps oil directly onto the ring gear and pinion.
I doubt that head gaskets would be an issue. It's the exact same thing for any engine. Don't let it knock, don't over rev it and don't run it lean and you won't brake things. You must have control of the engine to stay on top of all of those things and I'm confident that I have those boxes ticked.
And what does the hydraulic detensioner have to do with forced induction?
If I wanted another Japanese turbo toy I'd buy 1. I still have my supercharged MR2 and an F6 Typhoon.

This thread is intended to get some input from people about what they thought would provide the best driver enjoyment from a 75 Potenziata.

[Duk]

My list of available options are in the first post. Normally aspirated, CENTRIFUGALLY supercharged or twin turbo.

What suites you top end turbo or lower down torque of a supercharger

This sort of stuff annoys the absolute cr@p out of me! Perpetuating the rubbish that a positive displacement supercharged engine has more low down torque than a well executed (not that the old dinosaur Calloway cars were well executed, but their exhaust manifolds were nice) turbo car.
My supercharged MR2's torque peaked at 4400rpm.
The supercharged VY V6 made it's peak torque (375Nm) at 3000rpm.
My F6 Typhoon's torque (550Nm) peaks at 2000rpm......................... It's held (electronically) to 4250rpm.
Audi, Volvo, Saab and others have also achieved impressive torque numbers at similar low engine speeds.

[carlo rossi]

I realize its hard to fathom (sorry metre)but some of us out there
énjoy light weight natural carby induction
you wont be able to plug in your computer
into these cars in 15 years time
I recently saw a Montreal that had the injection ripped off
and webers put on
and guess which goes better and sounds brilliant?
i would put the carbs on from the euro v6
they are out there and cheap and keep working for 100 years

[julianB]

Mechanical injection from a monty deserves to be ripped off, thrown in the bin and replaced with carbs.
But aftermarket EFI? No way i would ever prefer carbs over a proper EFI setup.
As for the turbo torque Vs blower torque argument, I hear you loud and clear Duk.

The only reason I'd pick the centrifugal over the other three in your conundrum is thus:
When you're pottering around town, changing gears at light load and low rpm, who cares how much grunt it makes? When you want the grunt, it's in the midrange-top end where you expect it.
Off boost fuel economy and drive ability is factory.
As for turbos- why you would go to the effort of building a TT V6 and not running at least 1 bar of boost into it, I have no idea- it's so much effort that your reward should be a whistling, singing engine that boosts hard...nothing comes close, but kiss the transaxle good Bye!

As for the engines not dealing with it- that's absolute rubbish. My old mechanic built a 3.0 12v to take boost AND rev to 8000 and it absolutely loves it.
400rwhp, boost limited to 15psi and rev limited to 4000, heaps and heaps of part throttle grunt... Easy to drive. Gorgeous

So I'm with Dave on this.
Forget the 12v and build a 24v... Modern engine, more top end for less work, and they are more musical than the 3.0 12v.
If you want music and lightweight... 2.5 FTW!

[Duk]

Cheers for your input JulianB.

The reason that I didn't put a 24 valve engine on the list is largly because I want to work with what I've got (engine and parts) and also because, from what I've seen on forums, getting a 24v in a TA car is a lot of work.
Especially if you're working with post 164LS engines, which is what most people would be working with in Aus. And while I could do most or even all of it, I'm not that convinced that it would be worth the effort and expense.

Getting a genuine 300+hp from an internally standard 12v with forced induction is very real. Getting 300hp with a NA 24 valve would take considerable changes to compression ratio, 4 rather expensive camshafts, 4 adjustable cam gears and probably a custom made inlet manifold. (I've left out programmable computer and extractors because they're already part of my plan). And most, if not all gains will be made further up the rev range and probably at the expense of low rpm torque/drivability.

[gtv6sv]

12v engines are A LOT cheaper to work with than 24v engines. However if you have the funds, a warmed up/ boosted 24v would be a lot of fun. Although a lot of funds would be needed to find and fit a stronger transaxle...
Duk I currently have my 12v supercharged Potenziata engine sitting on the stand waiting to be dropped into my GTV6. I'll soon be able to tell you how fun it will be to drive😁 currently has 5pds boost, produces 220rhwp. So should be interesting in the GTV6!

[Sheldon McIntosh]

If it were me, in a road car I'd go for a warmed-up NA, and concentrate on weight loss, or at the very least not putting weight on with a force-fed set-up.  One of the main issues affecting the handling of a transaxle car is the high weight of the engine (high both in kgs and height). 

A race car could probably be made to handle the power from a turbo or supercharger, but you can't do quite as much to a road car if you want it to be driveable, (and I know you've got the handling mods under control).  I'm just not sure a 300bhp Transaxle would be that much fun, other than in a straight line, I'm not sure the handling and road holding would cope.  And as you say, the transaxle is a little temperamental with big power running through it.

Lower gearing would be nice too (I don't know, does the Potenziata have the same gearing as the 3.0?).   I've driven a 3.0 75 and I found the gearing incredibly frustrating, and that it really blunted the driving sensation. 

All just my opinions.

And yes, turbos can create great torque figures.  Only took me one drive of a rotary turbo to work that out.  And my turbo vehicle for work creates 843Nm at 1500rpm......

[Duk]

Hey Sheldon.

Something, which for some reason slipped my mind, after I started the 75 Parts Weight List thread, was that after looking at it, giving it some decent thought and chunching some numbers, I reckoned I could get a genuine 50+Kgs off of the front wheels of my car. Now the car wouldn't necessarily be 50+Kgs lighter as some of the weight was relocated to the rear wheels, but............ 
And while that would involve making carbon fiber guards, bonnet and bumper bar, it still retained air conditioning (I mean, it's Australia................ ) and a boot mounted electric power steering pump.
So the thought of adding weight back to the car, especially mounted up high and far forward, does put me off a fair bit.
But then there is the pure grunt factor. And unless you have plenty of engine capacity, getting propper, big fat spread of torque and decent outright power type of grunt requires forced induction.
I'd love a 4 litre interpretation of the Alfa 24 valve engine (would need a 100mm bore and a custom 82mm stroker crank), but unless lots of money lands in my lap, I can't see that happening soon.
Having a slightly mad grunt machine is so very tempting. Probably becuase I'm use to having a reasonable amount of umph under the right foot.

The battle continues.

[Sheldon McIntosh]

Come on, you don't need air-con or power-steering, is this car for driving in the hills or for commuting?  That's what the F6 is for right?  I took the PS off my 90 track car, and it had a 320mm steering wheel, on wide slicks; definitely a pain in the arse to park, but how often do you do that?  Made no difference to driving over 10km/h.  Okay, maybe 30...

Don't forget, if you were to force-feed her, you'd probably need a bigger radiator as well, adding weight to the worst possible place.

I know what you mean, grunt can certainly be addictive, but I'd go for handling with just enough horsepower, over an overpowered car every time.  Grunt is good in short bursts, but handling is forever.

Yeah, I've often thought myself about how a 4 litre would have been, with a TA that could cope with it.  The 3.0, and even the 2.5, was considered a 'big' engine in the 90 and 75 in period, but times have certainly changed.  I look with envy at every Mercedes C63 I see.

The TA cars are really well balanced, and reasonably light, so I always figured I'd enhance those characteristics, rather than trying to make them into something they're never going to be.

Something that I've occasionally thought about to help the handling, but wouldn't have the skills to do myself, is to lower the engine in the frame.  Don't even know if it would be possible, but you clearly have some skills and knowledge.  Trouble with that is that it would have to be dry-sumped in all likelihood.  That, and get the biggest tyre footprint you can.

Again, just my opinions, I know FA.

[Darryl]

So given all that, you should "just" put together a twinspark with say 20lb boost, plenty of space for aircon and PS and a big snail doesn't weigh much