Engine Teardown of Razzyh 2056 Type 4 engine

Discussion in 'Mech Tech' started by Patrick Nguyen, Mar 13, 2018.

  1. 5cc if stock ...

    Sent from my SM-G930F using Tapatalk
     
  2. 77 Westy

    77 Westy Supporter

    Yes, but we don’t know if they’re stock.
     
  3. Yes

    Or post 39 onwards to give it context
     
  4. 77 Westy

    77 Westy Supporter

    All good stuff there about CR but as soon as the engine spec deviates from standard you can’t say 7.5:1, 8:1 or 9:1 or any other CR is correct.

    The fuel we use we’re more or less stuck with but head design (ports, valves and combustion chamber) and in particular the cam determines which CR is best. Each cam has a fairly small range of CR which will allow it to give good performance, a low CR will lose power but using a higher CR than the cam needs will simply result in extra heat.

    The hydraulic cam in this engine is mild but still has more duration than standard and will need more static CR to work well, however, if the CR is 10.3:1 it’s too high.

    John Maher (JMR) wrote an article that is well worth reading and I hope he doesn’t mind me copying it here; it’s freely available on his website.

    For maximum power output and engine efficiency, you should use the maximum CR your engine can safely handle. Major determining factor is the fuel you intend to use. Higher octane fuel is more resistant to detonation.

    I think in terms of an engine as having three compression ratios…. Static, Dynamic and Effective.

    1. Static CR is the mathematical ratio as measured on the assembly bench. Determined by deck, chamber volume, piston notches/dishes (if applicable) and engine capacity.

    2. Dynamic CR…. you arrive at this by calculating piston position at the point the intake valve closes following the completion of the intake stroke. In theory, this is the point at which cylinder pressure changes from negative (intake) to positive (compression). The intake valve usually closes between 50° to 70° after BDC. If you measure how much stroke is left before the piston reaches TDC, input this stroke figure into your normal CR formula. Due to effective decrease in stroke (the piston is already on its way up the bore when the intake valve shuts), Dynamic CR is always lower than Static CR. The longer your cam’s duration the later the valve closes), the bigger the difference between Dynamic and Static CR. Rod length also plays a small part in the equation because different length rods will alter the piston’s position at a given valve closing.

    Take a street engine as an example… for best efficiency and good power output on regular fuel, you probably want to run Dynamic CR somewhere in the region of 8:1. A stock (short duration) cam has a dynamic CR fairly close to its Static CR, because it closes the intake valve sooner than a long duration cam (i.e. closer to BDC), therefore Static CR won’t be a million miles away from your static figure of to 8:1. Fit a longer duration cam e.g. FK10 and you now find Static CR needs to be up around 9.5 to 10:1 to achieve a dynamic CR close to 8:1.

    There are various DCR calculators on the web but there’s another factor at play which is much more difficult to pin down….

    3. Effective CR is the term I use, others may call it something different. It’s a way of better estimating the actual CR the engine actually ‘sees’ at any given point in the rpm range (talking about wide open throttle testing here). Yes, Effective CR changes throughout the rpm range, generally maxing out at peak torque.
    Static and Dynamic CR don’t take into account what happens under running conditions. Both formulae assume the intake charge stops entering the cylinder when the piston hits BDC on the intake stroke. They also assume the cylinder gets a 100% fill i.e. 100% volumetric efficiency (VE). Few engines (n/a) achieve 100% VE.
    E.g. on the dyno, say an engine achieves 90% VE @ 6000rpm and Dynamic CR was mathematically calculated as being 8.0:1.
    What the engine actually ‘sees’ is… Effective CR = Dynamic CR x 90%.
    i.e. 8.0 now becomes 7.2:1
    In other words if my plan was to hit an Effective CR of 8.0:1, I have to raise Static CR, which in turn raises Dynamic CR.
    E.g. a low CR engine fitted with an FK89 under performs – dynamic CR is way too low for the system to function efficiently.
    A race engine with a well-developed tuned length induction and exhaust system can easily exceed 100% VE by optimising manifold lengths and exhaust primary pipes. Engines of this type manage to ‘ram’ high pressure intake charge into the cylinder such that it continues to pile in after the piston has hit BDC and starts it path upward on the compression stroke. Ideally the intake charge will keep coming in up to the point the inlet valve closes. An optimised engine can be tuned to push VE above 120%. Using the same example engine as above, Effective CR now becomes…
    8.0 x 120% = 9.6

    That’s all a long winded way of coming back to what I said at the start…. there’s no simple answer.

    To summarise…. the milder the cam, the lower the CR (Static CR). The wilder the cam, you need more CR.

    Higher octane fuel can tolerate more CR.

    Intake and exhaust systems should also be taken into account because they have a major influence on VE, which in turn affects Dynamic CR etc. etc.
    In the real world you either stick with a tried and tested combination, relying on the experience of others, or you experiment on the dyno if it’s a unique combination and you’re looking to exploit the engine’s fullest potential.

    Having said all that, minor increases in CR make very little difference to power output. It’s very much the law of diminishing returns.
    If for whatever reason you’d built a 2276cc engine with FK89 and set CR (static) at 8.0, you’ll see a healthy increase in power by stepping up to 10.0
    However, the difference between 10.0 and 10.5 will be very small. The exact number to aim for will be a judgement call based on all that stuff I discussed above.
     
    Chrisd, V.R.M., DubCat and 4 others like this.
  5. 77 Westy

    77 Westy Supporter

    Was the oil pressure low right from the initial start-up?
    With a 30mm pump the problem should be too high pressure and a risk of bursting the oil filter, especially with 20w/50 oil, and normally with a large oil pump 5w/30 is used to try to prevent too much pressure.
    It would be really nice to know if the oil pump drive shaft is slipping but if the bearing failure occurred at or soon after start-up no matter how big the pump is the pressure would be low.
     
  6. 77 Westy

    77 Westy Supporter

    I’ve asked a couple of times what the deck height is but still don’t know, so…
    Assuming the deck is zero and the piston dish is 5cc and the AMC Head combustion chamber is 58cc, the compression ratio would be 9.2:1
    Still with no deck but with flat top pistons, CR 9.9:1
    That engine with that cam would work with either of those compression ratios although 9.9 is too high – it wouldn’t work with zero deck but it wouldn’t fail because of the CR and obviously the CR would decrease if we add deck height.
    I know what assuming does but I’m interested and want to keep the thread at the top of the page.;)
     
    Razzyh likes this.
  7. Razzyh

    Razzyh Supporter

    No initially it would be fairly high I’ll check where but once warmed up it would barely move.
     
    77 Westy likes this.
  8. The pistons were pretty much flat dished, had a tiny V in them. I only managed to get 1.5ml in them from memory. The pistons had zero deck height to measure as with the cylinders bolted up and with the standard thin case gasket, the piston was flush with the lip. I thought that the piston would have hit the cylinders at full whack with no clearance. The carbon lip was thinner than what I usually see. Interestingly the carbon lip in the barrels was not even in height.

    The inbuilt lip in the head I measured as 6 thousandths. I am measuring with feeler gauges as it is all I had and feeling for when it felt flush. So my not be 100% accurate
    The heads had 53ml volume.

    I only did one barrel and thought that was bad enough, but can check the others if I am bored this weekend.
     
    77 Westy, Razzyh and snotty like this.
  9. 77 Westy

    77 Westy Supporter

    Interesting; the step in the head should be about 0.030” (the thickness of the gasket). With zero deck there should have been 0.030” piston to head clearance but with 0.006” step and zero deck the pistons would have hit the head. The step sure looks more than 0.006” in the pic. and there is no indication that the piston has kissed the head but it is what it is. @nobody wins.:thumbsup:
     
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  10. Razzyh

    Razzyh Supporter

    [​IMG]

    If I remember correctly on standard 10/40 oil it was at 50 psi and then when I went over to valvealine it went to around 60psi, once oil warmed up/hot it would barely move the needle at tickover.
     
  11. Those don’t sound right at all.
     
  12. Razzyh

    Razzyh Supporter

    As in it should be something different?
     
  13. I'd assume type 4 pressures are much the same as type 1s, so 50/60psi is a bit barmy. On a type 1, the pressure will top out at about 3bar/42psi. Gauge and sender mismatched?

    100psi gauge doesn't help when reading them ;)
     
  14. Razzyh

    Razzyh Supporter

    It’s all what the builder fitted. None of my work. I can only say what the gauge showed.
     
  15. Maybe he wasn't any good at fitting those either :oops:
     
    Razzyh and art b like this.
  16. davidoft

    davidoft Sponsor

    Meeeeoooowwww!!
     
    art b, womball, Razzyh and 4 others like this.
  17. Audi quattro vdo guages and senders oil just warming up ticking over on drive ... 2ltr type 4 probably still on choke [​IMG]
     
    DubCat likes this.
  18. 77 Westy

    77 Westy Supporter

    That’s ^ with a standard oil pump. This engine has gone from a 24mm to a 30mm pump and with cold 20w/50 oil the pressure relief valve would have been saturated and unable to dump oil back to the sumps quickly enough to avoid very high pressure - IF the bearing clearance is correct. The valve would also be bypassing the oil cooler in an attempt to increase the temperature, thin the oil and reduce the pressure.

    In my opinion a new engine with a big oil pump and 20w/50 oil is a bad combination and a more or less standard engine like this only requires the standard 24mm oil pump, or maybe a 26mm if an external cooler has been fitted and the con rods have been modified for piston oil spray cooling. A 30mm pump will easily exceed 60psi/4bar and can burst the oil filter.
     
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  19. 77 Westy

    77 Westy Supporter

    I still don’t think the cause of the failure has been discovered and it would be nice to know if the oil pump drive shaft is slipping in the gear or the tang isn’t properly engaged in the cam but I guess Patrick is a bit busy putting out fires and changing tyres.
     
  20. And getting the van ready for a proper MOT. The previous owner used "a mate of his"

    After Razzy confessed to getting 93mph out of his auto box bay window. I am guessing the engine must have been screaming at 6K rpm. Is that a factor as well to the investigation?
     
    art b, pkrboo and mcswiggs like this.

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