Facts as they stand: 1970 Datsun 1600, L20B engine, 60 thou oversize, L18 Head. Had a Crow Street/race cam originally, a Series II Bluebird Electronic Dizzy, a T04 Turbo (marked with A/R 65 if I remember correctly) Drawing through a Zenith SU type Carby. Motor's not decompressed, that doesn't seem to be a problem. I run it on Premium and it doesn't ping. Pretty low boost and revs.

I stumbled accross the kit a while ago and it was a rushed fitting just before I moved for work, so I haven't had opportunity to troubleshoot. But now I'm back and not sure how I should proceed.

It worked but initially it was a pig until it 3000rpm, and I mean I was feathering the throttle to keep it going at all. Then it would start pulling at 3500 and hit the 5 psi max just over 4500 and then the revs would slow down. (but that's another story, doesnt matter what I have done to this motor has never reved, cams, carbys, even this turbo) I was thinking it might be the N/A hot cam. So I changed that back to standard. Now it starts behaving at 2500 pulls a bit earlier but doesn't reach max boost. (the other cam obviously allowed the motor to pump more air)

I think it could be just my carby, but this is my first experience with Turbos so I'm not sure where to go next. I'm in two minds as to whether to stay with the Turbo and start troubleshooting or go back to the tried and proven 42mm DCOE's that I have, before I waste more time and money.
But even this experience has given me the taste of the Fun Turbos can give.



I welcome any opinions. I know there have been plenty of Turbo L series threads in this forum. I have browsed to try and find some info. Maybe somone can point me in the right direction

Looking at the carby could be a good place to start. It seems to me that if you had to feather the throttle then it could be running too lean? I wonder if it could be a fuel supply problem as well? Perhaps you could try dropping the seat in the SU by half a turn and seeing how that changes its behaviour. Just throwing arround ideas.

1) if it didn;t rev BEFORE the turbo conversion either - cam timing. you may be out a tooth or two.
2) cam duration. i would say get another cam made up, say a 30/70 absolute MAX. a 25/65 is a fairly decent grind for a turbo too.
3) the SU needle is sticking and making it lean. have that looked at as well.
4) if all this fails, whip off the timing cover and check that the dizzy shaft teeth are where they should be.
5)sounds dumb, but have you checked for vacuum leaks? got a one way valve on your booster line?

_________________
frankenstein projects R us.

The Republic of Western Australia -
Propping up the Nation's Economy since 1901.

have you made sure you got oil in the slide of your SU, will find it wont slide too well without this, tested and proven
is it only me or does a L18 head on L20b seems strange for a turbo setup, isnt the idea to drop the compression??
also have you changed the dizzy from vacuum advance to boost retard, or atleast locked the dizzy?? may find that helps

_________________
SSS610: The Nicer daily
STK610: The Original Daily...Now The Hills Car

S2 TRX: SuckThru Turbo: RETIRED
MR30 Hatch: Daily Driver: SOLD
720 King Cab: Daily Driver V2: SOLD

have you made sure you got oil in the slide of your SU, will find it wont slide too well without this, tested and proven
is it only me or does a L18 head on L20b seems strange for a turbo setup, isnt the idea to drop the compression??
also have you changed the dizzy from vacuum advance to boost retard, or atleast locked the dizzy?? may find that helps

_________________
SSS610: The Nicer daily
STK610: The Original Daily...Now The Hills Car

S2 TRX: SuckThru Turbo: RETIRED
MR30 Hatch: Daily Driver: SOLD
720 King Cab: Daily Driver V2: SOLD

closed chamber head is BETTER for the turbo setup because of the better squish properties it introduces.

better squish = better burn = more power.

the open chamber head also puts uneven force across the top of the piston on ignition - the closed chamber head is reasonably close to equal pressure.

better squish + even flamefront = more torque.

_________________
frankenstein projects R us.

The Republic of Western Australia -
Propping up the Nation's Economy since 1901.

the point is was making was that my L20 head has blowing head gaskets at 15 psi before decompression, i thought an l 18 head would make this worse???

_________________
SSS610: The Nicer daily
STK610: The Original Daily...Now The Hills Car

S2 TRX: SuckThru Turbo: RETIRED
MR30 Hatch: Daily Driver: SOLD
720 King Cab: Daily Driver V2: SOLD

headgaskets blow due to detonation.

you could run 12.0:1 CR and 20psi of boost (if your engine could handle it) and if it didn't detonate you wouldn't ever have a problem.

poor tuning blows head gaskets, not closed chamber heads + turbos.

_________________
frankenstein projects R us.

The Republic of Western Australia -
Propping up the Nation's Economy since 1901.

I beg to differ on this one......
The std nissan head gasket (on a L block) is known to handle only around 17psi (give or take a couple of PSI) if you want any more boost you will need orings fitted to the block.... (Or some sort of special head gasket)

Detonation does play a part - but in this case, boost it the main limiting factor... even with no detonation most people seem to find 15-17psi to be the limit (with std gasket and no o-rings on an L block)

LOL james...if i WERE running an L with those specs i don't think i'd be using a stock nissan gasket...! more like a think copper shim

_________________
frankenstein projects R us.

The Republic of Western Australia -
Propping up the Nation's Economy since 1901.