good compression ratio for supercharged cologne 2.8?

[carbon1993]

Hello,

I have an 1984 XR4i with a 3.1 cologne v6. I want to fit a sprintex/power engineering. This supercharger normally will fit on a stock 2.8 cologne.
The stock 2.8 has a CR of 9.2:1 and my engine has a CR of 9.9:1 which is pretty high for an old N/A engine.
I know that some turbo technics cars have a CR of 9.2:1 or 8.9:1 and i believe the tickford capri also 9.2:1

How much will this 0.7CR extra have an effect on the engine. Has anyone ever tried a high CR on a boosted car.
the car will run about 8psi max. and it will run a intercooler.

[carbon1993]

I still don't know how i want tun run the fueling. The original kjet or EFi with an aftermarket ECU.
And also it has Volvo b23 or b230 pistons. So 9.9 won't be a problem for 8psi boost as long the spark timing and fueling is right.

[carbon1993]

It has diffrent pistons from a volvo b230 or b23 engine. They are reinforced but it still looks like cast pistons. If your capri 2.8 ran on 9.2:1CR on 9psi boost and was almost detonating i guess the 8psi i want to run won't work with 9.9:1CR.

But then what is safe number to run on standard ignition?

[carbon1993]

I don't know which fuel system i want to use. I might keep the K-jet or get an programable ECU which will only control the fueling probably semi sequintial. The fueling i use is something the firezone sells here in holland called 102 competition. Which has a higher octane rating than super 98.

what is smart and safe to do just skim a bit off the pistons to be safe?

[carbon1993]

these are the pistons,i had the whole engine balanced with the clutchcover and flywheel. The deckheight is 0.05mm(0.002inch)
If i skim the pistons till its flat that wouldn't hurt the pistons too much right? I am just affraid of detonating. And i don't won't spend too much money and time in getting the highest horsepower out of the engine. Just wan't to get it runnig reliably at the cheapest possible method without engine faillure. As a student i don't have 3K to spend on the engine.

Oh and i have zero experience building boosted engines.

i think the pistons are casted but they don't have very rough casting lines in the pistons.

Edited by carbon1993 on Sunday 1st January 23:23

[carbon1993]

Do i really need that squish effect? Normally that's used on flat cylinderheads.It only needs 1.4mm to get the dish out. If its machined 0.7mmm of it is already on 9.45:1CR. Normally the pistons are flat in this engine.
I bought the car for a daily driver but taxes changed i only driven 3000kilometers in 4 years now (because things broke all the time). I wan't to use the car a little more like 3000Km a year.

Can i calulate how much pressure it is going to deliver when i know the size of the pulley's?

The blower is a sprintex s102 sold by power engineering. It was a straight bolt on kit for the 2.8 back in the days (9.2:1CR). Here's some info: http://www.vondrachek.org/automotive/tech/screwed/...
http://www.xrstyle.co.uk/forums/showthread.php?412...
http://www.pistonheads.com/gassing/topic.asp?t=367...

this is the shapeof the cylinderhead.

[carbon1993]

already did some modifications on the kjet my self with a lot of help, it's alot of testing to get it right. If i am informed right a supercharger at the same PSI would be less likely to detonate as the temps are lower. So that's a advantage!

The dish is now 66.1mm*1.4mm. If i machine it to 80mm it would give a CR of 9.6 if i would flatten it completly it would give me a CR of 9.18:1
Maybe i should start looking into a aftermarket ECU.
.

[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?

[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