good compression ratio for supercharged cologne 2.8?

[taz turbo]

My TVR has the turbocharged 2.8V6 from the TVR factory, it ran 6psi boost with the standard 9.2cr standard injection although it also has a 7th injector in the inlet tract prior to the butterfly, also runs the standard ignition again has a second system to retard the ignition while on boost... all worked well. So obviously time to up the boost, I ran it at about 8psi which was about the as far as I could go without detonation.

The clock moved forwards and I was rebuilding the engine, after quite long conversations with a piston company they strongly deterred me away from machining piston crowns, they would of been about 4mm thick, their view was mechanically they would be fine (they use thinner on the F1 engine pistons they manufacturer) but detonation would be more likely due to hot spots, so I went with a custom set of pistons. The biggest single improvement was from replacing the standard ford 2.8i cam with a JW developments cam, a bespoke grind. The car was like chalk and cheese (prior boost was dropping of at higher rpm, now it's on the waste gate all the way) It's now 9.0 cr as the pistons have a small chamber similar to yours. I run too about 10 psi without much issue. Thing to keep in mind (as already said) it's all about spark and fuel control, my car uses a very old school systems from the early 80s, as that was fitted to the car as new and as what the car is and as it's custodian I can't change it. But if it was an xr4i or similar I would fit a modern more manageable system in a heart beat. That said last time it was on the rollers fuelling was very good (more later) and a with timing changes no more power could be achieved. My comment about fuelling, in my early ownership I broke a few pistons, always no 5 and 6, spoke to a very knowledgeable chap at rally equippe who explained about the leaning of ghe fuel mixture on these two cylinders due to (in my instalation) the location of the turbocharger and associated heat issues, his final word was as we look at the average fueling at the exit of the exhaust the fuelling should be set on the rich side to stop detonation on these two cylinders, all I can comment is with the fuelling enriched detonation hasn't been such a problem.

Best thing was last power run it did at a TVR wedge meeting it outperformed all the V8 wedge TVR, which made me smile.

Any questions feel free to PM me.

Chris.

[carbon1993]

I have meassured everything myself.

the head has 43.5CC
the piston dome has 5CC
deckheight is 0.335CC (96mmX0.05mm)
headgasket 9.7CC (95mmx1.37mm)
bore96mm
stroke 71.99
total swept volume 521+58.535(piston dome etc.)
Cr9.9:1


The hot spots on the pistons seem logic and a good reason not to skim them.

But if i am going to get EFI i am probably going to use the old ignition. Due to costs and simplicity. And what are the chances it won't detonate when only controling fuel. I bet pretty low.
What is the best option to lower the CR just 0.4/0.5 orso?

[GreenV8S]

carbon1993 said:

if i am going to get EFI i am probably going to use the old ignition. Due to costs and simplicity.

I don't understand the logic there. By the time you've got an aftermarket fuel system installed you've already done 95% of the work to provide a mapped ignition system. Especially for an forced induction application, compromising the ignition timing seems like a bad idea.

[Boosted LS1]

OP, your pistons are cast items.

[stevieturbo]

You could retain the dizzy/coil if you really had to, but take it under ecu control.

but when say a 6 tower coil would be so cheap and ultimately much much better...it would be silly not to.

As said, look into the Spitronics, when other guys on forums posted costs....it really was incredibly cheap.

[Little Pete]

stevieturbo said:

You could undoubtedly make it safe on the original systems, but there would also be more compromises with performance too and it would also take a lot more testing and tuning.

Modern systems are just very convenient.

I would always say buy a system where you can get good support for...ideally local support. So on that end something from a local supplier might be best

Sorry, the point I was trying to make was that I think the mechanicals will be fine, given what I've seen on an engine using very crude management. I totally agree with Stevie-again!-in that a modern ignition and fuel control system would be all you would need. My point got lost in the anecdote!

[carbon1993]

okay! will look into ecu's then. I heard good stories about ECU masters, a company nearby uses them with great results and good support.

What do i need to get it running with aftermrket ECU?
-map sensor
-coolant temp sensor
-air temp sensor
-throttle position sensor
-hall sensor for TDC
-lambda sensor (already got one in from AEM)

-2.8 EFI inlet
-injectors
-igniton coil(s)


I forgot to say that i did a compression test before i pulled apart the engine to check the CR ratio. And the best cylinder hit 230Psi (16bar). The camshaft wasn't properly on time(too advanced.

A year ago i overhauled the engine because the bearing where almost gone. I also put in some new piston rings. Before this overhaul i meassured 175to190 Psi. but that was with a diffrent compression tester.

though i would like to have a little less CR. Would decompressionplates work? anyone ever used these?

Edited by carbon1993 on Monday 2nd January 23:08

Edited by carbon1993 on Tuesday 3rd January 17:11

Edited by carbon1993 on Tuesday 3rd January 17:13