Paging Simon Atkinson

Wow. A mate of mine is building a 5.2 litre RV8 engine. He's got a pair of
heads from a 1964 buick which have the biggest valves feasible, and forged
pistons etc.

I asked about the turbo because SAAB have found they can get 10% more
horsepower out of their standard turbo engine on LPG than unleaded.

 

That's right - I was agreeing with you.

Bloody hell... You could buy an old Rangie with one fitted for that and
swap over whatever you want.

You'll need to tap a small pipe from the inlet tract upstream of the
mixer (but downstream of the turbo) to the 'atmosphere' side of the
vapouriser so that it understands the pressure it's working at (that
part of the inlet tract would normally be at atmospheric pressure -
unless there was a very restrictive air filter) and then regulates the
lpg based purely on the pressure drop through the venturi in the mixer.
Otherwise it wont release any gas once the turbo starts spinning as it
wont 'see' any suck!

Talk to the chap at RPI (Chris IIRC) he is Mr V8 tuning - it was him
that built the engine in the SD1 for Clarkson.

You will definitely be better off going closed loop - the feedback from
the Lambda sensor will keep the gas mix a lot more accurate - it's only
a stepper motor connected to the regulator and a PIC controller.

Is it a carb'd engine then or injection? If it's injection you'd be
much better off with gas injection - although it's dearer to fit - you
can alter the characteristics via your PC.

 

That's due to the 104 RON. You just need to get enough air and gas
crammed in! And not to worry too much if the exhaust gas doesn't 100%
comply with MOT requirements...

 

I thought that the V12 was a lean burn / high comp engine?

 

It's quite low powered (by most standards) for the size.

 

Is it what I thought it was then?

 

Sure, I was just restating for clarity.

I meant an SGI system

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&category=9895&item=
7940300773&rd=1 'kinell, it went fro 720 quid!

Excellent, thanks for that.

There actually is one in with the kit I got, but the guy threw in a simple
'adjust the screw 'til it works' valve as well. I'll have a go at the
Lambda sensor method if that'll be ok with the turbo.

It's an early injection SD1 from 1983. Injection would be lovely, but see
ebay auction above!

 

Yep. The APC controller in the SAAB allows the boost to increase until
it's about to cause pre-ignition, the higher octane helps prevent pinking
up to higher boost pressures.
I'm wondering if I could fit an APC circuit board from a SAAB to my lash-
up and thereby create a variable boost system.

My TVR exhaaust system is already suitably devoid of nasty resrictive
boxes ;-)

 

Not really. It's a standard comp engine tuned for torque.

 

That's not all that cheap, even for an SGI system. You could buy new
for not too much more (assuming self fitting).

The screw adjustment ones are OK on low reving engines with lots of
torque (rangies - especially if used round town), but as soon as you
floor the throttle the mix tends to go horribly lean (can you say burnt
out valves). Generally with them you rev to 1/2 maximum (about 3000 on
the rangie) and tweak the screw until the engine starts to die, then
back it off half a turn. Not all that scientific, but it works after a
fashion.

Closed loop is the kiddie. Effectively you are monitoring the exhaust
and adjusting the screw with a stepper motor as you drive. Works well.
When I changed my Rangie from the fixed screw to the closed loop I
reckon I got about 2 or 3 mpg more and it felt like double the power
when it kicked down to overtake. If you have the bits already, fit
them and be impressed. You prolly haven't got a lambda sensor fitted,
but it's a doddle, just fit one, at the point (or just after) where the
two exhausts siamese into one (if yours do that). I believe you can
fit two and join their output together, but you'd need an electronics
gizmo to do that properly.

 

It was a new Zavoli kit

Excellent advice, thanks again.

 

tallbloke wrote:

There's also a knock sensor to go with that. It's screwed into the
engine block somewhere and listens for the tell tale changes in sound
that the onset of pre ignition causes. If it's not bolted in the correct
place, or at the wrong torque, it'll give false positives.

 

Simon Atkinson wrote:

Maybe I was hearing about some other lean burn high comp V12.

 

The new Jag Diesel? or is that a six?

 

That's a 6 - and like driving a nicely updated Granada. It's not a Jag
(not a proper Jag).

 

*perk*

 

Naa, nothing new. It was a few years ago, when I was an AXE10 support bod.

 

LPG Saab Turbo company car sir? _Suits_ you sir... ooo...

 

Maybe that was it, for V12 values of clean. ))

 

Not a bad improvement for sure, still better than my 2.25l Land rover
and my old SD1.

Yikes, I thought that replacing the plugs on my SD1 V8 was bad enough...
but 12 of the buggers? No thanks. I don't think I'd want to do
anything else on that motor. Those V12 motors look lovely when painted
up and polished, I saw one in a big bike[1] at a Swedish bike show.

[1]Tractor tires big.