Ignitech ignition question - non Laverda (Honda CBX turbo)

20 pounds boost? Fucking hell Paul I have to admire your bravery.

When I was messing around with my Saab 900 Turbo, the mechanic at the local garage thought I was pushing it at 14 psi - he suggested I go for water injection if I went any higher to calm things down inside.

I am not up to speed with calculations but 20 psi sounds like effectively doubling the capacity of the engine and then some more.

If it all holds togther at 20 psi then that must be some rocket?
 
Spoke to a local lad that does some hillclimbing in his Subaru turbo.
They use about 21psi with a massive intercooler.
He sent me a link to stop me asking what I thought were simple questions.
http://legacygt.com/forums/showthread.php/technical-question-much-boost-can-stock-engine-turbo-handlei-28845.html?s=fe46f51850d249fbde84edc0584650f3&
Now my head hurts. ???
 
SimonR501 said:
20 pounds boost? Fucking hell Paul I have to admire your bravery.

When I was messing around with my Saab 900 Turbo, the mechanic at the local garage thought I was pushing it at 14 psi - he suggested I go for water injection if I went any higher to calm things down inside.

I am not up to speed with calculations but 20 psi sounds like effectively doubling the capacity of the engine and then some more.

If it all holds togther at 20 psi then that must be some rocket?
Click to expand...

Hi Simon

I had an older Saab 900 Turbo for many years. Had a mechanical waste gate, easy to adjust boost pressure allowed. Blew the head of the Saab not once, but twice, before I settled on what the real mechanical limits were.

On the CBX Turbo the internals are heavy duty and built for purpose. Falicon Crank, Carillo rods, custom cylinder liner and custom pistons, etc., etc. The sad reality is that at 20 pounds boost the engine cases and head/barrel connections don't seem up to the task, with head bolts snapping bolt heads off and the engine cases walking around and flexing. The turbo also bit the bullet at 20 pounds boost, the compression ring on the turbine shaft (like a tiny piston ring) actually snapped from the blow back from the engine cases through the oil drain line as it appears the crankcase ventilation was not sufficient.

The head is now back on, the two broken bolts that were threaded into the head are now drilled for through bolts, but I am still waiting on the turbo rebuild parts. This time around I think I am going to stick to less than 10 pounds boost, that really wakes up the motor, and my ZX 14 is still faster than a an old CBX running 20 pounds boost anyway.......

I have had my fun with the CBX turbo build, learned a lot, improved the handling as well as the engine, now I need to settle down a bit and get it running reliably and oil tight..... ;) That is what I eventually did with my own Saab 900 turbo, eventually got tired of changing head gaskets and other parts.

Paul LeClair
 
sonicboom500 said:
Spoke to a local lad that does some hillclimbing in his Subaru turbo.
They use about 21psi with a massive intercooler.
He sent me a link to stop me asking what I thought were simple questions.
http://legacygt.com/forums/showthread.php/technical-question-much-boost-can-stock-engine-turbo-handlei-28845.html?s=fe46f51850d249fbde84edc0584650f3&
Now my head hurts. ???
Click to expand...

appreciated the link. Nothing particularly earth shattering there. The more boost the more cylinder pressure and heat, need to deal with both ignition retard (which started this thread here) to limit/prevent detonation, and with air/fuel ratios, and use the best most detonation resistant fuel possible. Adding water injection can take away some heat and reduce risk of detonation.

having now had the head off and back on this particular CBX engine three times now, the most practical solution is to limit boost, it is a huge task and time commitment to remove and replace a CBX 6 cylinder head, not too interested in having to do it  fourth time if avoidable by keeping boost maybe 10 pounds or slightly lower.....

Paul LeClair
 
I loved that Saab, it was a rocket ship in plain clothes.

Many times did I surprise folks that thought they were quick.
Not an Audi Quattro though, he was definitely faster than me and so it should be with 2.1 litres, turbo and five bloody cylinders.

I got tired of taking my cheque book to buy parts in the end :D
 
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