Engine Mods (again)

Just wanted more of DG's theories on the low pressure turbo idea.
Take a late V6 engine (perhaps from a Laguna!) change the bottom casing and sump, machine the top of the pistons... are turbo heads necessary?... add turbo manifolds and a turbo with suitable blow through carbs... ignition remap, bonkers exhaust.
Seems a reasonably cheap way to get a pretty powerful sprinting engine?
What else is needed then?

You think doing all that sounds cheap??? Once David has his paws on the programmable ECU hes due to get, all you'll need for 300bhp from the standard engine is a hybrid turbo, exhaust, bigger injectors and a rolling road session. You wont need to take the standard engine out or fiddle with the internals.....of course if you fancy fiddling he has some tempting cams that will add a whole dollop of torque and extra stallions

You should also check the regs for any speed class that you may wish to enter. Certainly the national road car and modified production classes specify that all cars must have an engine that was originally fitted to the vehicle. I have fallen foul of this previously and ended up running in sports libre class.....in a Metro 1.8.....against several Mallocks and Radicals.....I didnt go to win but it would have been nice to have finished in the same minute as the opposition!!!!!!

For sure it would be cheaper to start with a 2.5 turbo engine and play with that, but I have this laguna engine lying around....I understood that this late engine can be remapped, and DG had suggested fitting blow through solexs from a R5 GTt with a low press turbo. Wanted to clear my head about what can be done with it....

Rupert, the point of the low pressure conversion, is not to have to modify the insides of the engine, and still retain the injection system (not bother with the carbs and not machine the pistons). The Laguna Z7X heads are identical to A610 heads in every way (cams, valve sizes etc) except for the valves not being sodium cooled. If the standard Laguna management worked ( which you know why it doesnt) , or you used late 25 management, you could increase the basic fuel pressure to cope with the small increase in boost pressure. Obviously with aftermarket management, its even easier.

The main reason for the low pressure conversion is a standard GTA turbo has 200lbft @ 2500 rpm with 10psi of boost...the standard 25 2.8V6 has 170lb ft @ 2500rpm with no boost, (bearing in mind thats in a 25 with a long restrictive exhaust, crap inlet manifold design) and is way torquier than the GTA below these revs because it simply cannot make boost that lowdown, therefore lag. The increase in CC's and the higher compression will make the turbo spin up from idle, so youll have a car with zero lag, and because of the low boost level, not need for larger turbos/more efficient intercoolers etc. On 'standard' management peak power still wouldnt be much more that 250bhp, but would be so much faster to drive than the original turbo engine, even at the same power.

My car should be ready by around Christmas, going to be stripping and rebuilding the chassis next week.

Anybody need 6 x 802 injectors - have set unused since being refurbed these flow enough to make a safe 300bhp at standard fuel pressure. Make me an offer! And I love the way everybody knows how much all these engine conversions make when no one has done it yet. Its all guessing - I don't reckon a hybrid, exhaust and a remap will make 300 bhp without running lots of boost so better add a bigger intercooler to your equation.

The mist is beginning to clear....
Thanks to all.... Oh, and don't paint the car David!
Maybe I'll hang on to the laguna lump after all....
Tho' the current project is definately having the Citroen beast engine!
Now is this pic gonna work??

Tony.....David has clocked 297 with the mods Ive listed and a little ignition advance and fuelling (and a good chunk of boost).......with the precision of a fully mappable ECU 300 seems easily acheivable! May be interested in your injectors.....I was intending to get a 2nd hand set from an R21 turbo.

On the subject of ignition advance, I was working out if this was feasible, instead of trying to get at the difficult TDC sensor to alter the timing.





By enlarging the holes on the standard distributor cap, an advance or retard of around 3 degrees should be possible. The large insert on the inside of the cap keeps the cap rotation dead centre with the end of the cam so there shouldnt be any problems. Ill be testing this later on my own car.

When you consider, on a normally aspirated GTA, my RR tuner acheived 10bhp extra on the standard engine, with more midrange torque, through ignition advance.

BTW, this was the power plot of the said vehicle, 170bhp @ flywheel, quite alot of transmission loss due worn driveshafts, but such a smooth,flat power curve, this is why the Atmos are so driveable. Red trace was first run, blue is final run. The first peaks are going through 1st, 2nd and third gear, and then the final power fun in 4th from 1200rpm to 6000rpm.

Tried the above today, and the metal inserts in the cap are set it when its moulded. Drilling them out shatters the cap!

Im now having new metal distributor backplates made up which will now allow you to advance or retard the ignition but upto 10 degrees, by rotating the whole distributor assembly, and doesnt require any modifications. Should be around £50.00
I would only recommend setting this up on a rolling road, but it will sort out the low end lag, and more midrange pull.

By moving the distibutor on a GTA turbo, no change will occur in the advance as it is controlled by the ECU and the flywheel pickup. The distributor in this case only distributes the sparks. I believe that is why the rotor button has such a long conductor, to accomodate the ECU derived advance.
If you did move it far enough you would get just end up with it making a longer arc inside the cap, or firing the cylinder before. Certainly that is a lot of advance!!

How much additional advance do standard turbos seam to like? Although I admit I am limited to 98 RON fuel over here, I don't know how much better your fuel is.

[Alpineandy]

Although I admit I am limited to 98 RON fuel over here, I don't know how much better your fuel is.

98 RON,.... Luxury.
Actually I think (rarely, but sometimes) Optimax is the only 98 and BP & Esso do 97. Normal is .... 94 (at a guess).

[simontaylor]

Andy, 98 RON with our climate is good enough, all that "cool" air is just what my Turbo likes.

Your right, Ive been thinking about the Atmo setup too much lately. Moving the dizzy cap just makes a larger gap for the spark to jump and burn out the edges of the contacts. Back to moving the TDC and burning your arms on the back of the turbo!

Gosh... DG has been caught napping!