What is the actual ideal compression of a VG30DETT

The thing to remember is that boost and compression are not the same thing.'

A turbo engine allows more air to be forced into the cylinder (and therefore more fuel) before compression, thereby making more power.

A higher compression engine with lower boost generally will not have the same power capability as a lower compression engine with higher boost.

Can you run higher boost on a high compression engine? Yes but now you're getting into detonation territory. E85 fuel, a very well built engine and a very good tune help.

 

well, what would be better?

a TT with 170psi compression running 8psi boost

or an na moded to have 200psi compression?


compression is needed for low end acceleration, obviously if there is no compression, you have no power until you start to boost (issue I have at the moment) but then the potential to boost higher can increase the amount of power you can get out of the engine while boosting with less risk of damaging the engine which is more likely to occur with a higher compression boosted engine.

the NA had great take off, but it only took it so far, then it was underwhelming and didnt have what it takes to keep that momentum going.

the TT has terrible takeoff, but once you are going, you can feel more acceleration building as you go and boost higher (of course)



I've never taken that the psi of boost was directly related to the psi of the cylinder. just that a lower compression cylinder can accept a higher psi of boost with less risk of destruction. exactly the reason why TT's are lower in compression. and also why simply throwing turbo kits onto any naturally aspirated engine which was not built for a turbo tends to end in head gaskit failure if you boost too high.

obvoiusly 171psi must be the happy medium that Nissan came up with to compromise between having the compression needed to get the Z moving under its own power, but not having too high compression, or as high compression as the NA which would open it to risk of damaging other engine components which wouldnt deal with the added pressure during boost.



here is my new plan, and I already have half the parts needed as of today.

TT block honed and bored 20 thou
.5 oversized pistons
stock heads with new valves and valve springs
high flowed turbos (rebuilt)

I'm not sure what compression that would be getting, But that should be a reasonable street build short of also adding racing cams or pro street cams.

 

Wayne the reason your TT has terrible takeoff is because your engine is rooted lol.

For a street zed this is all you'll need to restore factory performance.
Add an EBC and Nistune and you're done.

Don't need fancy cams.
Don't need stroker kits.
Don't need whatever other fancy term you come up with in subsequent posts

 

Oversize pistons?

When an engine block is bored oversize it has to be honed, which provides the finished bore size & cross hatching.
The block is normally bored before purchasing the replacement pistons & rings.
No point having .020" oversize pistons if the bore has to be taken out to .030" or more.

 

And the Accelerator pedal flat to the floor. Closed butterflies means you will have to crank longer to get a stablised figure.

 

Screwdriver through the throttle linkage is easier

 

Here we go....

The reason the butterflies need to be open is:
The engine is an air pump.
When the piston moves down the cylinder it doesn't "suck" any air into the cylinder.
Atmospheric pressure "forces" air into the cylinder.
If the butterflies are closed, they will restrict the air entering the cylinder, just as they do at idle speed compared to full throttle.

 

Our 'big yella' had only 115 psi per pot ran 15psi boost and still did a 1.24 at Grand prix circuit Oran Park which is right up there with only about 2 better on this forum, so the motor did blow smoke at low idle revs so was worn but still goes like stink at 15 psi boost

 

It would be difficult to quantify as there are so many variables, but it would be nice to have some sort of gauge as too what sort of KW 's are lost with lower compression.

 

There is one.......

.......it's called a dyno.

 

at 15psi boost you say.

but how was the engine typically from take off?

I can get mine going if stay in gear long enough to get the revs and the boost up. I even get the tail end moving around in 2nd if I want it too. but that is what I meant in another thread by 'needing to be brutal to get anything out of it'

in my mind, I should be able to get wheel spin from the moment I take off, not have to wait to build up boost to get acceleration.




I'm interested to see what the compression would be like if I did it again. I never had the butterflies open the last time. I could be lucky. I might even have 130 in each cylinder

 

Just wondering, what diff setup are you running? NA or TT?

 

NA

 

you really need to look into something like a BBC but be prepared to pay when you are dealing with 8 litres. personally I would save for a house first if I was you.

fingers crossed my next car will be EFI BBC powered. then you can plant your foot and do a wheel stand.

 

Make sure all the numbers are fairly close, within 14PSI difference. The number doesn't really count for squat, all compression testers are different and will read differently. Emile's (MoulaZX) old zed ran low 13.2's and 105MPH pretty much with an exhaust, side mounts and 15PSI....his engine had around 130-ish on all 6.

 

well it had a print out on the dyno of 236 rwkw which is relatively mild but very tractable
and was running dunlop R's semi slicks, top package coil overs about 75mm clearance to the road FMIC gutted cats etc

 

LS1 conversion territory.


I've been suggested that by a few people now.

honestly I just want an engine that runs like a performance engine.
I had a bit of a think last night to reassess the situation.

On both the NA and the TT i've spent 10k on the motors alone and I still have a shit Z

half of me is saying sell it off, but who would by it.
if I do anything else, It's getting built by a pro.

I'd also like to keep it rather stock, considering its such a collectors type car and is only getting older, If I have it completed nicely in future and do take it to some shows, it would look better to still have the VG30DETT in it rather than having it too heavily moded.

also why I basically have no aftermarket body mods on it, just rims.

 

What you want is a NA power plant. You never get instant response from a turbo engine. My shit won't get interesting to 4500 rpm WITH nitrous. Once it's there it stays in the 4.8-7 range.

If you want that na power you need a cubic inches and nos. think a vt ls1 commodore with a t400 and a 200 shot.

Bottom line sell the zed and go for the vt setup. The zed ain't gonna make you money been a collectors car.