Hi or low comp???

Question again for DG. Sorry to be a pain!!!

I have just been reading through some of the old threads and came across one which caught my attention.
In it you said :

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

DG,you have recently advised me against going this route and have also said the Z7W intake manifold is better than the A610/GTA.
Which is right?
Did you ever build up a high comp low pressure engine and get crap results???

I missed this post, sorry.

When I talked about a low boost setup, that was on a standard high compression engine, 9.5:1, with say only 5psi of boost. That was just for someone trying to retain the feel of the normal atmo engine, but wanted a bit of oomph on top. You could buy a cheap £200 Laguna engine, stick the GTA turbo setup on (hence why you'd need the 610 manifold (central inlet) and have a bit of fun..

You could go 'highish' comp and more boost, but only if you invest in decent forged pistons, sodium valves etc, so its not a cheap project, and I still wouldnt go any higher than 8.5:1

With the standard Z7X engine you would expect to see say 230-250bhp, (if it can cope) and no more, but you can acheive this easily with the standard 2.5 as we know..depends what you want...

Things have moved along since that post. I didnt have the chargecooler systems and standalone ecu available back then, and this was a conversion for somebody that wanted more ooph in an atmo GTA, that pull a Z7U turbo out and replace it with a Z7X low pressure setup (hence why i mentioned don't bother with the carbs)

Inlet manifold wise, yes the Z7X/25 atmo manifold is better than the 610. When I said crap I was thinking of the restrictive intake system that leads to the inlet manifold on the R25 V6. It is properly ported to each cylinder, has a large plenum, provision to mount a larger body, but you can't use it if you have the turbo at the back of the engine.

I was looking to fit forged pistons anyway. As for valves,sodium to cope with the extra heat of the high comp?

Is anyone else using this valves on their uprated engines?

Do you know if the Z7W uses the same forged rods as the Z7U?

Would you mind telling me a little more of your concerns about the high comp.You say no more than 8.5:1,but i was looking more at 9.5:1.
Is it the fact you don't think the bottom end will handle it,cos looking at the other threads the engine does seem to be bulletproof!?

I would like an engine that will give almost instant power for it will only be used as a street car and am not worried about top end.
I don't want to go low geared incase i have to make any long trips - would cost a fortune in fuel!!!

Rods are the same .The block has cross bolted middle journals so is stronger than the U ..........

I was looking to fit forged pistons anyway. As for valves,sodium to cope with the extra heat of the high comp?

Is anyone else using this valves on their uprated engines?

Do you know if the Z7W uses the same forged rods as the Z7U?

Would you mind telling me a little more of your concerns about the high comp.You say no more than 8.5:1,but i was looking more at 9.5:1.
Is it the fact you don't think the bottom end will handle it,cos looking at the other threads the engine does seem to be bulletproof!?

I would like an engine that will give almost instant power for it will only be used as a street car and am not worried about top end.
I don't want to go low geared incase i have to make any long trips - would cost a fortune in fuel!!!

All the turbo engines come with sodium cooled valves as standard.

There's no real concerns about 'high comp. You just run less boost, and less ignition advance, but ultimately you are limiting your power potential. And seeing as the GTA engine bay is an extremely hot environment higher compression is not as desirable.

If you imagine, an A610 is more or less a standard Laguna engine with the compression dropped and runs 11psi. So with a high comp variant you could get the same with say 7psi. Doesnt mean you can increase the boost further, it may well be the limit..

So the question is.. why change the engine, fit forged pistons and have to fit standalone management to acheive 250bhp?

The bottom end is fine, the heads are fine etc (within limits) Does'nt matter how 'bulletproof' an engine it, any sniff of det (which is increased by running high comp) can kill any piston, forged or not.

If you want instant power you could supercharge your existing Z7U, fit some nat asp manifolds and silencer, run say 12psi and make more power than we do with 12 psi on a turbo currently. That will make a perfect street car. Ive considered every option in the past, and this would suit alot of people, make less underbonnet heat, no lag etc, .. If somebody wants it done I can do it...

I am still waying up all the options and i must say that the supercharger does sound good.
Has anyone gone this route up til now?
Can you supply the charger?

Thinking more into the possible setup,surely you would have to go onto the crank pulley due to the timing chain setup!!??

For me this route sounds more appealing the more i think about it!No need to get new manifolds fabricated,no need to buy another uprated turbocharger and no need to uprate the engine,(Although i still like the idea of 3 litres)!!!

Obviously your ecu/injectors will be ok for this route??

If you imagine, an A610 is more or less a standard Laguna engine with the compression dropped and runs 11psi. So with a high comp variant you could get the same with say 7psi.

Can I quote you on that?

If you imagine, an A610 is more or less a standard Laguna engine with the compression dropped and runs 11psi. So with a high comp variant you could get the same with say 7psi.

Can I quote you on that?

You just did.

I have friends with R5 GT's getting 200bhp at 10psi on 9.5:1 on the 1.4 litre C1J (not a dini though.. ) as a comparison of what increase can be make raising the compression..cracked ring lands though if played with too much...

If your worried about pistons Martin, if you read the whole thread properly he did mention he wanted to go the forged route...(still no guarantee)

Even though there are supercharged A310 conversions running standard 10.5:1 compression and 8 psi of boost...

I hope this isn't going to turn into another thread hijack/war of words....

No no no, I think it's fair to say that Dave and I keep things polite and even relish the discussions.

You might be able to tune a specific engine to make better use of higher comp and lower boost, than lower comp and higher boost. However at a physics level, the potential for greater power at higher boost is obvious - you're getting more air into the engine and more air = more fuel = more potential power.

One very basic example is the Skyline RB25 engine - can run a max boost of 1.2 bar on a standard engine. Put a thicker head gasket in, you can run more boost and get more power from the engine.

But that's a NIssan engine. Dave's cited a different example that has shown the reverse, but I'd suggest that that is unusual.

But that's a NIssan engine. Dave's cited a different example that has shown the reverse, but I'd suggest that that is unusual.

Politely.. Which example do you mean?

[quote="spryboy1974"]I am still waying up all the options and i must say that the supercharger does sound good.
Has anyone gone this route up til now?



quote]

One is in the pipeline I believe ...................................

I am still waying up all the options and i must say that the supercharger does sound good.
Has anyone gone this route up til now?



quote]

One is in the pipeline I believe ...................................

And the Ozzie guy...

I am still waying up all the options and i must say that the supercharger does sound good.
Has anyone gone this route up til now?



quote]

One is in the pipeline I believe ...................................

And the Ozzie guy...

I think it was a NZ car ,I've got the article somewhere ,I've deleted it from my webpage ,I'll dig it out Spry ,not much detail though http://www.renaultalpineownersclub.com/ ... percharger

Don't ever call a Kiwi an Ozzie David ............

It will be interesting to see any info if you can find it Lee!!

Any thoughts on my other questions DG?