Well, after many years of trying, I finally managed to blow up the imp due to too much boost! ;D
The engine has been slightly pressurising the coolant system for a while and I knew that the head gasket was on it way out, so the aim was to up the boost to 10psi (the engine should have a compression ratio of 10.5:1) and see what she would do.
Well I can say that she sure does boogie on 10psi! It was damp here and it was lighting up the tires in second There was a bit of detonation due to the ignition being too advanced for the onslaught on boost at low rpm.
I noticed that the temperature was straying toward 95 degrees, when it usually goes nowhere over 80. Pulled over and sure enough it had lost a lot of water. Fortunately I was only 5 min from home, so I let it cool a bit, topped it up and trundled back, happy in the knowlege that the HG was toast!
This was the result -
Something is not quite right here -
Is this not meant to be round?
The det has pushed the fire ring outwards on No.3 then burned straight past it! It was also on it's way on No.2 aswell
So this gives me the excuse I need to home port the head!
Once the head was pulled I measured the combustion chambers and with a handy calculator provided by Eric (the man with the turbo clan), the compression ratio was pinned down to between 12 - 12.5:1, mental! No wonder the HG didn't last long, the combustion pressures must have been through the roof
A couple of weeks passed due to other fun but non car related commitments, with only the odd hour here and there to dedicate to the imp. Now anyone who has done any porting at home will know how slow the progress can be, very frustrating but in a sadistic way, satisfying too
The only tools available were a clarke rotary tool -
and a single carbide burr, with a flame shape, less than ideal, but the budget does not stretch to a full set of burrs right now, so it will have to do!!
so with vibration white finger, ringing ears, and ingraned dirt the result (95% of the way there) is as follows -
Now I have aimed for a D shaped area around the valve stem bowl and valve seat, and ports are smoothed, a little larger and all reshaped. The combustion chambers are taken out as far as I dare, I have no idea how thick the casting is
Now I know it is not perfect, but it will be a million times better than the stock ports, and the compression ratio should be down significantly.
Left to do -
smoothing all the cutting marks CC'ing the chambers polishing the chambers and exhaust ports reassembly!
I'll keep you updated, and if it works how I think it will, i'll put even more boost into it
i have a l4 engine complete but unknown, so will pull that apart and see what it's like. will be doing pretty much the same mods you've done to your head to lower the compression and improve the breathing and chamber shape. will turbocharge it, may use the lpt saab t25 i have or a smaller one if i can get one cheap ish. blow throu solex 32dis off of a r5gtt. charge cooler, stock dissy with some kind of boost retard and 7-12psi. low budget but should get fairly good gains? 80-90bhp maybe? but lots of grunt as well as revs my first imp build so it may go horridly wrong
was gonna keep rear he rad, maybe add second heater matrix to the front. and deffo big oil cooler will use a charge cooler instead of intercooler because of lack of air flow at the rear. turbo postion is undecieded till i get it in there, will move battery to the front to make some space thou, and turbo will be high enough that i won't need a scavange pump to get rid of the oil. i will try and rig up a retard on the vacum canister, same as i did on my vw. looks like this
just connect up the vac advance pipe as normal, and when it gets positive pressure/boost it pushes the vac back to retard.
There is a big chargecooler core available from XS-Power for not a lot of wedge. I've been using it on my Saab for years. Some of their stuff can be a bit flakey... but the chargecooler can't be faulted really, holds its water and its boost so not really given any trouble.
Looks like exactly what I had in my head! Charge cooler would be spot on, Eric runs one in his clan, I think it was from a conversion kit fitted to calibra turbos?
Where abouts in west sussex are you? My folks are near midhurst, so I visit that way quite often.
yeh my charge cooler was from a calibra too. can't remember the make but was some vauxhall tunning company. i need to get a replacement water pump for it thou, tried using a caravan one but that didn't last very long
i was living in chichester but i'm now in hampshire, hayling island. would like to see your imp, pm me if your out this way