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  1. #1
    Senior Member ProVK's Avatar
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    Default Turbo Holden 355ci Roller Cam Choice

    After forgetting to have on hand a roller cam bronze oil pump drive gear when i was throwing the 383 together for my VS Ute Engine i whipped the timing cover of my VK (Sitting on stands getting a cage built atm) and borrowed the one from my good engine.

    Now the 355ci Engine in my VK has 9:1 Compression, -9 Yella Terra Heads with 2.08 and 1.625 Valves, Flow Figures as listed below. I run std VN V8 Cast iron (match Ported) Exhuast manifolds feeding a Garrett T51R Ball Bearing Turbo with a 1.22a/r rear exhuast housing. It also runs a walkinshaw intake manifold.

    With 11psi of boost the car made 500rwhp with the injectors maxed out well before 5500rpm, very little timing (more timing leaned it out too much) and a 5200rpm converter when it comes on boost.

    This combo ran a 10.6 @135mph in a 1450kg VK plus driver.

    The head flow figures are (28" Bench)
    Inlet
    0.100" - 82cfm
    0.200" - 137
    0.300" - 199
    0.400" - 241
    0.500" - 276
    0.550" - 284
    0.600" - 292
    0.700" - 302

    Exhaust
    0.100" - 44cfm
    0.200" - 97
    0.300" - 148
    0.400" - 196
    0.500" - 214
    0.550" - 222
    0.600" - 230
    0.700" - 237

    I havent got any info on cross sectional dimensions or port volume handy.

    I run a crane solid roller cam that was previously on a blown HP heros car (many years ago when 500rwhp was huge) It 236@50in and 244@50ex, its ground on 114 lobe centres and has just under 600thou lift at the valve. I went this way with the cam as the engine was originally going to see a Vortech Blower.

    Now im thinking of changing cams whilst the timing cover if off to get something a little more turbo suited.

    I have had some cam specs sent to me from a reputable aussie cam grinder, specs as follows.

    254@50in and 245@50ex 606in Lift, 590ex Lift, 114 Lobe Centres with the cam installed with a ICL of 107deg.

    Would i see a worthwhile improvment in power in the midrange and or top end with this type of grind or should i be looking at a different grind syle or stick with what i have.
    Last edited by ProVK; 07-10-2008 at 10:41 PM. Reason: Bench Rating

  2. #2
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    Never use backsplit cams with turbos (waits for the hate to rain down upon thy head) - simple reason, you are shoving more air in, but restricting its way out - bit odd eh?

    I build heaps (& I mean heaps) of turbo donks, currently that is the area of my biggest workload, with well designed header manifolds a forward split cam ALWAYS results in qicker spool - but with stock or log type manifolds reversion can be an issue with a big forward split, particularly with smallish turbos - restrictive ex housing make, but you don't have that problem.
    I still lean towards a slight forward split tho.
    The other thing to consider is that boost extends the usable rpm range of the cam - so a smaller cam is often more effective as it gets the thing on boost quicker but won't run out of puff as early as you would think.

    I'd stick to mid 240's duration, something like 244/246-8 on 114 centres will work nice, despite the longer duration than your old cam you may well find it comes on boost sooner - it just depends on how much reversion was going on with the big forward split you were using.

    The other thing to note is that bigger cubes can tolerate biger forward splits even with crap manifolds - my old 383 was a prime case, cam was 231/240 on 114 centres - but the sheer volume of ex gas from the big(ish) cubes was enough to overcome reversion as soon as you cracked the throttle.
    Last edited by TK383; 07-10-2008 at 11:10 PM.

  3. #3
    Senior Member ProVK's Avatar
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    It seeme to nose over on the curve from 6000rpm, but not sure if a better tune could have helped it or if the reversion was killing it.

    I thought the back split with smaller ex duration would have helped stop the reversion ?

  4. #4
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    Reversion happens at lower rpm - before the ex gas speed gets high enough to stop it going backwards.
    A back split cam will help with reversion issues - but will cost power & spool time. You won't be having reversion issues with the turbs you've got & your manifolds are not that bad.
    If it was nosing over at 6000 the extra 10 deg of intake duration will fix that, should peak closer to 6500 - but with turbo engines it's a bit of a guestimate, too many variables to be sure.
    You were simply running out of cam.

  5. #5
    Senior Member ProVK's Avatar
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    The other little issue i have is im limited to 600 thou lift as the oil band of the lifter will pop out the tops of the lifter bores if i go any more.

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    Someone shouldn't have been a cheapskate & shoulda forked to sleeve the lifter bores eh?

    Easy tho - just get a 'cheater' grind - lifts to a max, holds there for a bit, then closes, plenty of cam companies do them, often for classes with a lift limit but no duration limit.

    I also heard that there is a new lifter on the market to work around this prob - it has a more shrouded roller to avoid exposing the gallery untill higher lift - cant' f'ing remeber where I heard it or who makes it tho, sorry.
    Last edited by TK383; 07-10-2008 at 11:27 PM.

  7. #7
    Senior Member ProVK's Avatar
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    I wasn't a cheapskate, the lifter bores have been sleeved, but that was back win the engine was a naturally aspirated combo with a flat tappet cam still.

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    lol, bugger.

    Don't matter, just jam in an extra psi or 2 to make up for the lower lift - ain't turbos great?

    Damn, I gotta screw my sh|theap back together, I'm getting itchy thinking about cubes + boost again, nothing quite like a boosted V8.

  9. #9
    Senior Member ProVK's Avatar
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    I'm even thinking of just jaming on the timing cover and leaving the cam till i have real reason to pull the engine.

    Its got a M800 Motec and some 96lb Injectors on the way in the next week or so, should fix the fuel issues and let me put 15psi plus in it.

  10. #10
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    Just re-read your first post - converter is flaring pretty bad, yeah? - that may well be a contributor to the power nosing over, if the motor is running over the converter it'll do all sorts of bad things to the amount of torque (power) getting to the wheels.

    For a turbo V8 - tight converter FTW.

    My ol 383 was blowing through the converter real bad - converter flashed to 3200 behind the aspirated 388, but with boost it was flaring past 5000 - & the sod was heaps slower than it shoulda been considering the torque required to blow through the converter like that. I switched to a real tight converter & viola, she's stretching arms & breaking loose at 120km/h (which, BTW, is mucho fun).
    You want the converter -just- loose enough to get the donk on boost on the converter, any looser & it'll flare, any tighter & it'll bog, for racing a tighter converter with a small shot of gas to get it up on boost is the gun setup - maximises the torque without blowing through the converter.

  11. #11
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    Its got a M800 Motec and some 96lb Injectors on the way in the next week or so, should fix the fuel issues and let me put 15psi plus in it.
    Dude, feed it some real boost!!!
    I had 14psi in the 383 when I smashed the ring lands - the rest held up just fine, hell, I pumped 10 psi on $30 durapro head gaskets, they only let go at 12psi.

    It's all in the tune - don't crank timing in to a holden, 28 deg total, all in before 3000rpm, then 1 deg of retard for every psi boost. ie. for 15psi you'd have 13 deg total in it.
    AFR's down around 11.5-12:1, keep it fairly fat, detonation is the enemy.

    anyways, I gotta hit the sack, baby is likely to be up in a coupla hours so I've already squandered precious sleep time.

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    Senior Member ProVK's Avatar
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    I agree with the converter, it smashes the tyres at any speed in first or top as soon as it comes on boost, but it does feel like it is wasting some rpm when it flares to 5200rpm on the slicks, i was worse but we had it tightened up some, on the street it blows the tyres off around 4500rpm.
    Im confident with more boost and a more aggresive tune i will have the box out and converter getting tightened propbaly b4 it sees the strip again.

    I want to try the transbrake...

  13. #13
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    Go easy on the tune man - that's where holdens come unstuck, they burn fast compared to a chev, so they build cylinder pressure pretty quick, add boost to that & cylinder pressure can get very high, very early in the stroke - that's when you push out head gaskets, bend rods, smash ring lands etc - it doesn't have to ping to break sh|t, it just has to rise to quickly on the cyl pressure & bust stuff with that pressure alone.

    I have promised myself I will not use the trans brake untill I have some better axles & a new tailshaft at a minimum - preferably not untill I get the 4-link in either.
    Using it straight away when I get the motor back in would just destroy everything from the front yoke back, could get messy.

    My converter is now too tight for the stock stroke grenade, but rather than fork out for another converter I'm just gonna hook up a 2 stage nitrous setup - 50hp to get it up on the converter & 100hp once it's moving to test the compressive strength of A9L rods...

  14. #14
    casual poster VKCalaisV8's Avatar
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    Made any dicission on the Cam choice Matt? or are going to stick with the Blower cam from RGV for the time being just to get the Beast back on the road again?

  15. #15
    Senior Member ProVK's Avatar
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    Sticking with the blower cam as i wanna see what it can do with a decent tune in it, that way if i do change cam at a later date i have some real figures to compare with.

    Should be a good thing with some more boost and E85.

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