Xu10j4rs tuning, maximum compression for pump fuel
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Thread: Xu10j4rs tuning, maximum compression for pump fuel

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    Default Xu10j4rs tuning, maximum compression for pump fuel

    Hi all,

    I have an Xu10j4rs in my 205 with forged pistons about to go in for 11.5:1 compression. As far as I know the head hasn't been skimmed. The engine builder is worried that the quality of 98 octane in Tasmania is so poor that 11.5 could cause issues with pre-ignition. I have read that dynamic compression is more important than static compression but these things are a bit beyond me. The inlet cam being used is a Cat Cams 4903109, duration at .1mm = 274 and a max lift at TDC = 2.0 mm.The ignition is mapped via a Haltech E8 running direct fire if that makes any difference.

    Have people had any trouble running this kind of compression on pump fuel? Would it be sensible to run a slightly thicker gasket to reduce compression (say a 1.4mm xu10j4 rather than the 1.2mm xu10j4rs)? I have noticed that Cometic gaskets are available to order.

    As a side note, I ordered the pistons (86.5mm) and rods from Pure Performance Motorsport in Melbourne and they delivered them within two weeks of the order going through. The valve pockets seem suitably large ...

    Regards,

    Michael

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    1000+ Posts PeterT's Avatar
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    If your engine builder doesn't know the answer to this question you should be finding another engine builder!

    To answer your question in part however, it depends on the dynamic CR, not the static CR. For example, it's quite possible to run 12+:1 with 320 deg. cams and 98 RON fuel. The dynamic CR is determined by static CR, inlet closing time and rod length.

    '92 205 Mi16
    '90 Mi16x4

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    Fellow Frogger! Karoshi's Avatar
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    Gone done some reading...

    http://www.popularhotrodding.com/eng...o/viewall.html

    Peter, would an engine builder start with the dynamic compression ratio they were after and work backwards from there?
    If so, what dcr is street/pump gas suitable?

    If I get more time I'll do more reading.

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    Fellow Frogger! Karoshi's Avatar
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    http://cochise.uia.net/pkelley2/DynamicCR.html

    This one explains it at the end. It says basically aim for 8.2 dcr and mix and match all to get that. It's talking about v8's.....

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    Thank you for pointing me in the right direction. I did some reading and found this calculator for dynamic compression ratio: http://www.rbracing-rsr.com/comprAdvHD.htm. It took me a while to get my head around the concepts and the TLAs (three letter acronyms).

    From what I could gather the standard XU10j4rs runs a dynamic compression ratio of about 9.1. That assumes an Intake Close Angle (ICA) of 56 after BDC on the standard cam and a static compression ratio of 10.8.

    The Catcam 430109 with 274 duration should close the inlet valve about 10 degrees later or so (ICA = 67 ABDC assuming the intake centre line = 110 ). With a static compression of 11.5 the calculator returns a dynamic compression ratio of 8.9.

    So now I am a little reassured although I am sure to have made some incorrect assumptions. From looking at other cam profiles the power band should be from 3000 - 7500pm. I suppose 7500 rpm would be a good spot for the rev limit to prevent hydraulic float. In hindsight, I would have been better off getting Peter T to regrind my cam. It had some minor damage from a flat lifter (beware the ticking).

    The whole exercise has been fascinating but expensive and a little frustrating.

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    1000+ Posts PeterT's Avatar
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    Your calcs are correct and inlet camshaft choice will be fine. You'll also notice if you retard the inlet cam 4 crank, it will lower the DCR to 8.6:1 if desired. That is the advantage of twin cam. You didn't say what exhaust cam you are using however. The standard exhaust cam is too small to use with that inlet.

    11.5:1 would certainly be the maximum. If still concerned, I wouldn't use a thicker gasket, as that will increase the squish distance. It's more preferable to take some metal off the piston dome.

    '92 205 Mi16
    '90 Mi16x4

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    Fellow Frogger! Karoshi's Avatar
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    Well done getting the calcs out!
    And backed up by Mr T!

    I had wondered about the theory of advance and retard of intake cam to adjust dynamic compression....some loss of possible torque down low advanced/ loss of top end power retarded?

    I hope its all coming together well for you,
    Cheers,
    Bill

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    Attachment 35675Attachment 35676

    After various delays and minor issues my car is finally ready for tuning. For various reasons it has been in the shop for 6 months and I am hoping that the roughness on startup might be related to old fuel. We were waiting 8 weeks for the correct ram tubes and air cleaner to arrive before opting to cut our losses and go through a different supplier. Unsurprisingly 90mm ram tubes didn't leave much clearance but 40mm tubes have left enough room for socks (forgot to take picture). Notice that the wiring has been cleaned up a little ...


    Xu10j4rs tuning, maximum compression for pump fuel-tight-fit.jpgXu10j4rs tuning, maximum compression for pump fuel-cleaned-up.jpg

    I am getting very excited. Down the track I might look at getting an airbox rather than socks.
    Last edited by Mangy; 24th October 2012 at 05:49 AM. Reason: Fixing images

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    It looks like the links to your attachments don't work.

    i don't know what else you've done to your engine, but I learned something really interseting last time I had my xU9J4 on the dyno. I run 11.4:1 CR and have never calculated the dynamic compression ratio on this engine - although I use the next cams up on the Cat Cam catalogue with solid lifters and standard valves.

    I have a Jenvey quad throttle kit on my engine. I have 90mm trumpets. I had the air cleaner sitting directly on the end of the air box for initial timing work.

    To prove the air cleaner was producing no restriction, we removed the air box lid completely. There was absolutely no difference - so having the air cleaner at the end of the air box was just the same as having bare trumpets.

    then we stuck about 400mm 3" tube on the end of the air box and put the air cleaner on the end of that. The engine torque response improved and peak power went up around 4kW.

    i can only figure out that it is all about the physics of the pulse length and the longer total inlet tract makes the manifold pressure more stable under load.

    Watch out for that when you get the car on the dyno. Next time mine gets tuned (t-15 days) I'm hoping for 140kW at 8400rpm.

    Good luck and keep us posted.
    racing 405
    1:59:09 last time at Phillip Island - less than standard Mi16.

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    Thanks for the information.The power you are getting is really impressive.

    I reckon my inlet length is going to be far too short to be optimal. The guy building my engined was perplexed as to how increasing the inlet at the intake end (rather than the manifold end) would improve power and it's all far too hard for me.

    My engine has 11.5 CR pistons from Pure Peformance Motorsport, a standard XU10j4rs head and 45mm Jenveys along with the 109 cat cams and a set of Magic's extractors. It's been bored to 86.5mm but I stuck with the standard crank (in hindsight I could have gone to 88mm since I replaced the rods anyway). I would be delighted to get anywhere near 140kw atw but that sort of power in a 205 would surpass my driving skills and it wont get close with a safe 7500 rev limit for the hydraulic lifters.

    I would be interested to see how you have set up the air-box. Is their much more room in a 405?

    I get the car back today after to run in before dyno tuning. It may be a challenge to resist the urge to drive it hard after six months of driving my wife's very civilized e30 325i automatic.

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    i've never worked on a 205, but I am pretty sure there would be a bit more room in the front of the 405. For what it is worth, I didn't go the 45s, my TBs are only 40 (or are they 38s) - not sure, but did some math at the outset and decided with the standard valves, the size I picked would provide more than enough flow and keep the air velocity where I wanted it at full noise.

    Post your dyno chart when you can.



    two pics attached, one shows the air box and blue silicon line that extends to the back of the passenger side head light - that was removed and the air filter placed right on the end of the air box. The air box is a standard Jenvey unit and I have 90mm trumpets in there. The second pic shows the extractors I have used - from Holland. They fit straight into a 205 but are a bit of a clash on the power steering on the 405 - so i have thrown the hydrauilcs away and use an electronic power steering box inserted in the steering column (actually a backward step, but too late now).Xu10j4rs tuning, maximum compression for pump fuel-eps_mi16header.jpgXu10j4rs tuning, maximum compression for pump fuel-pa090124.jpg
    racing 405
    1:59:09 last time at Phillip Island - less than standard Mi16.

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    1000+ Posts PeterT's Avatar
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    Mine is restricted more from height than length. Without rotating the engine, or having curved inlets, the natural line is for the the trumpet to poke out through the bonnet.
    Attached Thumbnails Attached Thumbnails Xu10j4rs tuning, maximum compression for pump fuel-205_enginebay3.jpg  

    '92 205 Mi16
    '90 Mi16x4

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    I got my car back briefly to run in the new pistons/ rings. There was no pinging or anything else untoward but I am told that the ignition timing has been retarded a lot for safety because the map was very rough. Some of the 98 octane sitting in the tank had been there since March and it seemed that the engine was happier after running through two tanks of fresh petrol (could have been my imagination). The fuel economy was around 11L/100km which isn't bad considering I did a lot of mountain driving.

    The dyno is booked for Monday. Regardless of the power, the throttle bodies sound great and even with a rough tune the car is quite drivable with decent low range torque. With a 274/236 (advertised/duration at 1mm lift) duration inlet and a 267/228 duration exhaust cam I am hoping the power band isn't going to extend too far beyond the safe rev limit for hydraulic lifters. Down the track I may want a better solution than socks.



    Has anyone set a rev limit over 7500 with standard lifters on a xu10?
    Attached Thumbnails Attached Thumbnails Xu10j4rs tuning, maximum compression for pump fuel-socks-1.jpg   Xu10j4rs tuning, maximum compression for pump fuel-socks-2.jpg  
    Last edited by Mangy; 10th November 2012 at 01:56 PM.

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    1000+ Posts PeterT's Avatar
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    The 7500 limit is for Mi16/S16. The RS valve train is a little lighter, so you can "possibly" extend a few hundred more. However, I doubt with those cams you'll need to. The socks will definitely suck hp. I'm selling a cold air intake, but it may not match your throttle bodies. You're welcome to try before you buy however.

    '92 205 Mi16
    '90 Mi16x4

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    The final tuning was a little disappointing. 101.3kw atw on a dynologic dyno is supposed to correspond to roughly 185hp at the flywheel. Apparently they were unable to run much ignition advance (only ?10 degrees at high revs) due to pre-ignition. I was warned that Tasmanian 98 octane tends to be poorer quality but I suspect there are other issues. Regardless of what the number says, the car drives nicely. Any ideas why torque drops off quickly at 6000 RPM? Intake temperatures didn't get past 35 C.

    Sorting out an airbox may help a bit. I wondered whether retarding the cam timing might allow more ignition advance but I was told that you rarely get net gains the shift in the power band would be unhelpful. I am not keen to keen to get the pistons machined at this stage after having the car off the road for six months. There is an outlet with e85 around the corner but that would mean new fuel lines, probably bigger injectors and possibly a new fuel pump.

    Xu10j4rs tuning, maximum compression for pump fuel-dyno-1-cropped.jpg
    Last edited by Mangy; 16th November 2012 at 04:04 PM. Reason: Correction

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    1000+ Posts alan moore's Avatar
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    As Peter said the socks will cost you Hp. Did a test years ago on an L20 engine in a Datto 1600 rally car. It made 8 hp more at the wheels with the same ram tubes inside an airbox over socks.

    Lately I have seen the results with a couple of engines using longer ram tubes, one an M10 single cam 4 cyl BMW, the other a twin cam KA 24 nissan. It seems that the longer you can make the ram tubes the more power you make everywhere, in these cases anyway. The BMW went up 10Hp at the wheels going from 100 to 200 mm ram tubes and made it at 5600 instead of 7400rpm. I retarded the cam 4 crank degrees and picked up another 10hp now at 6700 which saves me flogging as hard as before. So now making 150Hp at the wheels on a conservative dyno.

    The KA 24 (2.4L 4 cyl Late Bluebird motor) ran 250hp at wheels directly after on the same dyno with 300mm ram tubes and large airbox. The owner saying it just gets better and better the longer the tubes. He can't make them any longer to fit in the engine bay.

    Made my BM look a bit weak at 150. 35 years newer technology, 8 more valves and an 300 more ccs helps, and still has plenty of torque for motorkhanas. He fortunately won C class in this Datto 1600 at the recent Australian Champs having only done two motorkhanas in two years.
    Last edited by alan moore; 16th November 2012 at 02:16 PM.
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    Quote Originally Posted by Mangy View Post
    Apparently they were unable to add much ignition advance (only 10 degrees at high revs) due to pre-ignition.
    Don't understand this comment. Ten degrees more than what? Sounds like it has too much CR, inlet cam not big enough, thus cranking pressures too high. For what it's worth, mine is 11.8:1, slightly bigger cams and 22 deg at 7000. Post your ignition table. Did your verify software timing equals actual timing with a timing light? What cranking pressures do you currently have? One solution may be to buy a bigger inlet cam and fit the inlet to the exhaust side.

    '92 205 Mi16
    '90 Mi16x4

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    Thanks for the suggestions. I will post the ignition map when I get my cable back ... Lacking skills and knowledge myself means that I rely on the professionals and I don't always ask the right questions.

    It seems that it will be difficult to fit an airbox or longer ram tubes without relocating the power steering pump and I am told this would not be straightforward.
    Last edited by Mangy; 16th November 2012 at 05:08 PM.

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    1000+ Posts jo proffi's Avatar
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    Quote Originally Posted by alan moore View Post
    The owner saying it just gets better and better the longer the tubes. He can't make them any longer to fit in the engine bay.
    Vauge memory recalls reading about a jaguar engine that achieved 110% volumetric efficiency from just well tuned and long inlet tubes.

    Jo

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    1000+ Posts BIGRR's Avatar
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    Icon8 That Datto!

    Quote Originally Posted by alan moore View Post

    The KA 24 (2.4L 4 cyl Late Bluebird motor) ran 250hp at wheels directly after on the same dyno with 300mm ram tubes and large airbox. The owner saying it just gets better and better the longer the tubes. He can't make them any longer to fit in the engine bay.

    Made my BM look a bit weak at 150. 35 years newer technology, 8 more valves and an 300 more ccs helps, and still has plenty of torque for motorkhanas. He fortunately won C class in this Datto 1600 at the recent Australian Champs having only done two motorkhanas in two years.
    Alan,

    you told me that the Datto 1600 was standard!
    My 2.0L 205 has 100i'sh less hp at the wheels, with a standard Pug inlet manifold.

    Wish my 205 had had a clutch when the Datto 1600 won the C class at the recent Australian M
    otorkhana Champs! (Though that Datto 1600 was the car to beat in C class.)

    Robert
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    I talked to the tuner and he said that he was unable to get more than 6 degrees ignition advance down low and no more than 16 at high revs. The previous ignition map had a lot more advance. We tried a compression test and the pressure got to 230 after a few cranks and was rising which seems high for 11.5: 1. The piston manafacturers couldn't tell me much about the pistons they sent other than that they always sent the right ones and the individual who assembled the engine had bothered to do measurements. I thought about getting the pistons re-machined but figured that having high compression (probably a bit over 12) would be useful if I ever wanted bigger cams. So I decided to convert to e85.

    Unfortunately there is only one station in Tasmania for e85 and hence I decided to fit a flex fuel sensor. This meant upgrading the Haltech e8 to a Platinum Sport 1000 which is going in tommorow. The rest of the conversion was fairly straight forward except for the fact that the fuel tank had to be replaced because it had been monstered during some previous work. The fuel lines and fuel pressure regular have been replaced with E85 compatabile items and the fuel pump has been replaced with a Walbro unit and the fuel injectors with Bosch 440cc injectors (green tops). Without the need for a new computer, switching to e85 isn't that expensive ...

    It will be interesting to see what happens ... I am hoping that with some ignition advance the engine may work to its potential. Fingers crossed that there are no further complications.

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    1000+ Posts PeterT's Avatar
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    If you're upgrading to a Sport 1000 I can send you the variable trigger angles. Much better than a fixed angle which doesn't take into account variations with RPM.

    '92 205 Mi16
    '90 Mi16x4

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    My car has been retuned for petrol with the new computer and bigger injectors. I got a pleasant surprise - the tuner had a much better time with the newer software and maximum power is up 6kw to 107kw atw (on the same dyno). It could be a statistical blip but the car feels much torquier at lower rpm. The idle and cold start is also improved.

    The e85 tune will hopefully happen before Easter - and the only station with e85 in the state will hopefully get another shipment as supplies are low. Buying it by the drum is not cheap ...

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    1000+ Posts PeterT's Avatar
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    Nice work. Did you add the variable trigger map? A service station nearby now has E85, so I'm going to do the same.

    '92 205 Mi16
    '90 Mi16x4

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    I provided the map but I am not sure whether they used the variable trigger angles - I will check out the map tonight. I may be able to figure out how the add the trigger angles myself.

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