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Thread: safe compression ratio for supercharged 2.8 cologne

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    safe compression ratio for supercharged 2.8 cologne

    Hello,

    I have an 1984 xr4i with an 3.1cologne. It is bored(96mm) and stroked (71.99mm). I want to fit a sprintex/power engineering supercharger kit which will blow about 8psi and 1.1L air per revolution.
    The problem is that my engine has a CR ratio of 9.9:1 right now.

    The supercharger normally works with a compression ratio of 9.2 on the stock engine.
    I've never build an engine an i really don't know if the CR is too high for the old lump. I don't wan't any holes in my pistons.

    The pistons are reinforced and probably N/A volvo b23 or b230 pistons.

    Superchargers normally run higher compression than turbo's but is this 9.9 too much?

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    Re: safe compression ratio for supercharged 2.8 cologne

    With e85 would be just fine.

    Did run mine with 10:1, 1bar of boost and e85.

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    Re: safe compression ratio for supercharged 2.8 cologne

    Sounds like a nice project, please post some pictures on the project section

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    Re: safe compression ratio for supercharged 2.8 cologne

    I run my car on 102 octane fuel. But it still has the old mechanic fuel injection and stock ignition.

    I guess your car run on a aftermarket ecu?

    After some insecureties i'm going to order custom headgaskets that lower the compression to 9.4

    Will look into making a project page.

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    Re: safe compression ratio for supercharged 2.8 cologne

    I would tend to disagree with your comment about superchargers running higher CR with a caveat. Subject to the SC type, you'll make boost from idle up to max revs, so when the engine is mid revs, when its most efficient re airflow / max torque, you'll be adding boost so may force the CR over the top. A turbo in comparison is/can be boost poor at these rpm's so CR is less critical IMO. I'd be inclined to run less CR, or underdrive the SC to lower the boost a bit or use a centrifugal type Procharger which has output more akin to a turbo.

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    Re: safe compression ratio for supercharged 2.8 cologne

    Never thought about that! but comparing some cars with superchargers and turbo's most supercharged cars have a higher CR. Good example is the chevrolet cobalt SS. don't know why this is. maybe heat production?
    The kits were made for 9.2CR on a 2.8. I am going to lower the CR to 9.4 as my car is an 3.1 i hope that's enough to run it even with the K-jet. Ihope this CR is good enough for my usage

    btw made a project page
    http://www.turbosport.co.uk/showthread.php?t=1187057
    Last edited by carbon1993; 30-01-2017 at 00:34.

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    Re: safe compression ratio for supercharged 2.8 cologne

    Katana got it right, at low RPM, round max torque or where it begin you may expect pinking. I had it on the historic (Eaton) supercharged Volvo 1800 cc round 1500 RPM.

    Those supercharger kit made for standard (high) compression engine are using centrifugal (turbo housing like) superchargers. The pump zero to nothing at low RPM, more the extra help where the original engine start to fall. Higher RPM's and that's where they hurt less because engine efficiency drops.

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    Re: safe compression ratio for supercharged 2.8 cologne

    BTW, hope you are using a standard camshaft or one special designed for K-jetronic with almost zero lift at TDC

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    Re: safe compression ratio for supercharged 2.8 cologne

    It has an origanal 2.8 EFi camshaft in it. has about 6 or 8milimeters lift.
    Why is the lift so important?

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    Re: safe compression ratio for supercharged 2.8 cologne

    its lift at tdc which is important, any more than a very small amount of lift at tdc will mean you need a lot of revs to make the turbo work properly

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    Re: safe compression ratio for supercharged 2.8 cologne

    Standard K-jetronic cam is perfect for turbo Cologne. Got the profile on my computer, lobes at 114°. I'm currently building a 2600 RS engine with turbo for Capri 1 for a friend of mine. Turbo but carburetor to stay in the right century. I do have a "special" turbo profile for this engine if you would ever feel the standard one is at the end of his job. It has slightly more lift with almost the same duration.

    Lift at TDC is important but has a relation with the rest of the profile.

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    Re: safe compression ratio for supercharged 2.8 cologne

    I am going to meassure the lift at tdc.

    Is the S/C pressure going to kill horsepower when the inlet opens before TDC. How does that work the piston tries to compress going upward and the S/C is also bulding pressure on that piston that is going upward? So there are 2 forces acting against each other?

    How does a turbo affect back pressure and spooling of fuel through the cylinders. A supercharger probably won't have back pressure what are the effects?
    Last edited by carbon1993; 07-02-2017 at 22:13.

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    Re: safe compression ratio for supercharged 2.8 cologne

    If cam is original I can tell you the lift at TDC but is on my other pc . Is very low.

    The higher the CR the higher the final end compression. Because the turbo at extra air in the cylinders, more are has to be compressed and if to much temperature in cylinder will be to high so high it will pre-ignite and you got detonation killing your engine in a short time. There is a max and I would lower the CR to start with. 9,9/1 is not going t work.

    BTW, all that 102 octane as sold at the gas station as not going to make a big difference. It will heat up , no matter what you do.

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    Re: safe compression ratio for supercharged 2.8 cologne

    is 9.4 compression ratio better start with then? I can get some bigger headgaskets that will lower it to9.4. Its about the thickest gasket i can run without getting trouble to fit the manifold.

    i can also mill doen pistons. But i think they might get to thin...

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    Re: safe compression ratio for supercharged 2.8 cologne

    As far as I remember my CR calculation I went for 8,5/1 to be on the save site. I'm using forged DP pistons from Greece.
    Last edited by Dyno; 08-02-2017 at 22:11.

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    Re: safe compression ratio for supercharged 2.8 cologne

    the cam duration is about 263 degrees, the valve opens 28 before tdc with the proper valve clearance. it has about 1.85mm lift at TDC.

    The cam needs to be 2 degrees retarded to meet stock timing specs.

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    Re: safe compression ratio for supercharged 2.8 cologne

    Not sure you are measuring at inlet only and maybe wrong times but original cam has far from 1,85 mm. Numbers are a lot lower. If you measure an average for in and exhaust of 1,85 mm it's not a standard cam in your engine.

    Please note, the 263° is of no use. I mean, say nothing about the camshaft. It's like advertising degrees.

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    Re: safe compression ratio for supercharged 2.8 cologne

    this was meassured at the inlet valve springcap. Not quite sure what you you ment wuth that last sentence..

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    Re: safe compression ratio for supercharged 2.8 cologne

    Just what I have written. With this numbers only, you can't judge what the cam will do for you. But never mind, more important for you, where did you get the 1,85 mm at TDC? What was exact lift number for in- and exhaust? If correct timed, this is more like a fast road cam. Can't work well with K-jetronic, let alone turbo's.

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    Re: safe compression ratio for supercharged 2.8 cologne

    it has EFI stamped in the back and low lift don't really think its a fast road cam.

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    Re: safe compression ratio for supercharged 2.8 cologne

    Than you got it wrong time but is easy to find out, please measure the lift at TDC for inlet AND exhaust and let me know. It should be zero or almost zero and than you know you got a standard cam wrong timed.

    No idea the standard cam has EFI stamped in it. I've probably missed all the time. Please note, they can have it regrind as well and many older cam profiles have very low lift, compared to the duration. Pinto FR31 from KENT is or BP270 Piper are good examples. Duration is much to long for such a low lift profile

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    Re: safe compression ratio for supercharged 2.8 cologne

    Quote Originally Posted by carbon1993 View Post
    the cam duration is about 263 degrees, the valve opens 28 before tdc with the proper valve clearance. it has about 1.85mm lift at TDC.

    The cam needs to be 2 degrees retarded to meet stock timing specs.
    Just checked my PC. If you got an original V6 cam you should measure approx 0,6 - 0,7 mm at TDC. If you measure 0,8 mm there is still nothing wrong.

    This is average. if you measure 0,4 for exhaust it will be approx 0,8 mm for intake. But never ever 1,85 mm. That's wrong timed (measure exhaust as well and you know it) or fast road cam and not one that will not work with K-jetronic, for sure not with the turbo.

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    Re: safe compression ratio for supercharged 2.8 cologne

    was busy with it today eassured 1.8 for inlet 0.4 for exhaust but i will get a more decent timing disc and meassure again.

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    Re: safe compression ratio for supercharged 2.8 cologne

    You don't need a timing disc to measure these numbers. You are making it a lot more complex as it is. No reason for any degree disc if you got both inlet and exhaust lobe at one camshaft.

    First you need the average number. Use original mark at crank as a reference and measure what you got for both inlet and exhaust. If it is indeed 1,8 and 0,4 mm it is an average of approx 1,1 mm and not a standard camshaft. The reason it is 1,8 and 0,4 is probably because the mark is not correct TDC or the cam is wrong timed. But for sure, not a standard cam.

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    Re: safe compression ratio for supercharged 2.8 cologne

    The tdc mark is correct. So i need a good degree disc to be sure the cam is timed correctly. All the inlet opening and closing variates every time i meassure

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    Re: safe compression ratio for supercharged 2.8 cologne

    Quote Originally Posted by carbon1993 View Post
    The tdc mark is correct. So i need a good degree disc to be sure the cam is timed correctly. All the inlet opening and closing variates every time i meassure
    then there is something moving or in accurate about your measuring gear driven cam really should come up exactly the same every time

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    Re: safe compression ratio for supercharged 2.8 cologne

    Quote Originally Posted by carbon1993 View Post
    The tdc mark is correct. So i need a good degree disc to be sure the cam is timed correctly. All the inlet opening and closing variates every time i meassure
    then there is something moving or in accurate about your measuring, gear driven cam really should come up exactly the same every time
    Last edited by Graham; 13-02-2017 at 21:38.

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    Re: safe compression ratio for supercharged 2.8 cologne

    I think the problem is in the timing disc... meassured a cam duration of 305 degrees today when it was 260 friday..

    Something diffrent should i check my valve spring. before putting my engine back together? and wil the springs have an effect on performance? the car most likely wil not run over 6000 RPM.

    This is how it's set up. Meassured BDP first with the other gauge. then set it up like this:


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    Re: safe compression ratio for supercharged 2.8 cologne

    Waw, what a complex setup, I can hardly follow up what you are trying to do. For sure, you re making it to complicated. Let's keep it simple and accurate. Put the degree disc back in your tool box because it will only confuse you. Plus, don't try to measure camshaft duration this way, it will not work and we don't need it anyway.

    TDC mark is correct you say. Perfect. Turn the engine approx 90° or more before TDC. Inlet valve should still be closed and will go open soon. Set dial on inlet valve and set dial to zero. Turn the engine to exact TDC. Measure, the result. Keep the engine in this position and set dial on exhaust valve. Set dial to zero and turn engine until exhaust valve is fully closed. These 2 numbers are all what is needed to know camshaft is OK for turbo, OK for K-jetronic and correct timed. DO NOT TURN BACKWARDS

    If you can't follow up this simple exercise, put the engine in the back of your car and come over to my place.
    Last edited by Dyno; 13-02-2017 at 23:29.

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    Re: safe compression ratio for supercharged 2.8 cologne

    And yes, the problem is the timing disc because you don't need it.

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    Re: safe compression ratio for supercharged 2.8 cologne

    Why is CR still so high if you use disced pistons?

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    Re: safe compression ratio for supercharged 2.8 cologne

    engine is bored and stroked to 3123cc thats why the CR is still high. Will try to use your method. But i still need a timing disc to set my camshaft on the correct timing.

    thanks for the help so far!

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    Re: safe compression ratio for supercharged 2.8 cologne

    longer stroke is not a problem but boring out and than turbo, hope you did not bored to much.

    No, you don't need the disc for timing. We time just the same way as I explained. Can not be a special designed profile, it's standard or classic grind. You readjust the camshaft until you find little bit more lift for inlet as for exhaust. Let say, 0,7 mm inlet and 0,6 mm exhaust for a standard cam.

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    Re: safe compression ratio for supercharged 2.8 cologne

    1.8 inlet and 0.8 exhaust. how it is now...

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    Re: safe compression ratio for supercharged 2.8 cologne

    OK, average 1,3 mm. And cam to far advanced. Is not a correct cam for K-jetronic, nor turbo. You may check for a grind number. For sure it is not standard so a grind number will be at the front or rear. If you want to go turbo, skip the cam. Go for standard.

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    Re: safe compression ratio for supercharged 2.8 cologne

    will look if i am able to find and get a standard efi or kjet.

    by the way there is a chance i will get an aftermarket ECU later on.

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    Re: safe compression ratio for supercharged 2.8 cologne

    For an NA engine, to a degree it will work (special with ECU). But as long as you use one throttle plate I would be able to build up a much better camshaft. If you change to ITB this may be the right cam for you in a road engine.

    Because of your high CR, , big bore (small liners), fast cam already in the route to use ITB's and programmable ECU is much closer to you as turbo conversion. ITB does bring a nice and strong torque curve in the lower revs and make the engine feel a lot stronger as it is now (power will not go up to much but it's not what you feel in 90% of your driving).

    For a turbo it is a nono

    I assume you have measured the lift at TDC correct.

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    Re: safe compression ratio for supercharged 2.8 cologne

    Meassured your way. and has the same results as my way. Now i need to find a good camshaft....

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    Re: safe compression ratio for supercharged 2.8 cologne

    managed to get a camshaft out of a 2.8
    don't know if the number matches for a 2.8 ? it says 7P83 and H2 on a diffrent spot

    Meassured again today and it is 0.9inlet(valve starts to open) and 0.1 exhaust(valve almost closed) at TDC. inlet starts to open at around 23 degrees before tdc.

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    Re: safe compression ratio for supercharged 2.8 cologne

    Sounds like a standard camshaft to me but your need to tune it to let say, 0,5 - 0,6 inlet and 0,3 - 0,4 mm exhaust. 0,1 - 0,2 mm difference between in and exhaust and inlet should win.

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