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    Thread: GX info???

    1. Member skateboards and mk2s's Avatar
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      07-17-2012 03:58 AM #1
      Anyone have specific info on the GX engines? I searched and found some charts and what not but the GX info is always vague at best.

      I beleive it to be a low compression 1.8 making 85 hp.

      Where does the low compression come from? Pistons? Head gasket? Cylinder head?

      I have an ABA bottom about to go in but am wondering about compression values.

      In theory I would like to end up between 10:1 and 11:1

      I will be running a Brazillian hydro 268 cam.

    2. Member ps2375's Avatar
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      07-17-2012 09:44 AM #2
      The compression should be determined by the pistons as I think the heads are all pretty much the same as far as combustion chambers go.
      Tradition is the art of making the same mistake repeatedly, on purpose.

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      07-18-2012 03:19 AM #3
      Quote Originally Posted by skateboards and mk2s View Post
      Anyone have specific info on the GX engines?

      Where does the low compression come from? Pistons? Head gasket? Cylinder head?

      I have an ABA bottom about to go in but am wondering about compression values.

      In theory I would like to end up between 10:1 and 11:1
      Just what "specifics" are you trying to find? As stated, yes the compression is set by using different pistons for the most part. Using the 2.0L ABA bottom end will put you in the 10:1 range, maybe 10.1:1, but why are you so concerned about having the engine produce between 10 and 11 to one compression? I can understand people building engines for boost wanting to limit their compression. You have other things to think about rather then reaching for a compression ratio goal. What about your small valves in the GX head? Why worrie about the squeeze of the engine if it is limited in flow? GX engines didn't have the greatest exhaust systems, working a little there will help. Stay away form the "Bigger is better" trap in automotive circles, like bigger tires are better and bigger camshafts are better and so on. More compression does not directly equal more power.

    4. Member skateboards and mk2s's Avatar
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      07-18-2012 10:07 AM #4
      Quote Originally Posted by WaterWheels View Post
      Just what "specifics" are you trying to find? As stated, yes the compression is set by using different pistons for the most part. Using the 2.0L ABA bottom end will put you in the 10:1 range, maybe 10.1:1, but why are you so concerned about having the engine produce between 10 and 11 to one compression? I can understand people building engines for boost wanting to limit their compression. You have other things to think about rather then reaching for a compression ratio goal. What about your small valves in the GX head? Why worrie about the squeeze of the engine if it is limited in flow? GX engines didn't have the greatest exhaust systems, working a little there will help. Stay away form the "Bigger is better" trap in automotive circles, like bigger tires are better and bigger camshafts are better and so on. More compression does not directly equal more power.
      Here is a better why to ask. Why do you assume I know nothing about vws or engine basics?

      I have simply never seen a GX engine before so was looking for further info.

      I am "so concerend" about compression #s because they are important when building an engine.

      In a round about way you answered some of my questions though. so thank you.

      So in short GX is a small valve hydro head with low compression pistons.

      I wasnt sure If these scored some left over goodies from the 84 gti. VW has been known to use left overs in first production run stuff.

    5. Member skateboards and mk2s's Avatar
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      07-18-2012 10:07 AM #5
      Quote Originally Posted by ps2375 View Post
      The compression should be determined by the pistons as I think the heads are all pretty much the same as far as combustion chambers go.
      Thanks.

    6. 07-18-2012 10:09 AM #6
      The difference is in the pistons. If you look at the GX pistons vs. say a RD motor, they're a bit different. I will also agree with WaterWheels' entire statement

    7. 07-18-2012 10:10 AM #7
      Quote Originally Posted by skateboards and mk2s View Post
      So in short GX is a small valve hydro head with low compression pistons.
      exactly

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      07-18-2012 11:19 AM #8
      You know as they say you should not ask the question if you don't want to here the answer. In this case I have a feeling the answer will either be washed over, dismissed and forgotten or some feable attempt to show just how wrong I am will be made. In either case the answer still stands to the following question.
      Quote Originally Posted by skateboards and mk2s View Post
      Here is a better why to ask. Why do you assume I know nothing about vws or engine basics?
      Because of the questions you ask, how you ask them and because, now, how you respond.

    9. Member skateboards and mk2s's Avatar
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      07-18-2012 11:12 PM #9
      I asked for specifics on a not very common VW engine.

      Not really sure how that makes it sound like I am a silly kid with no clue?

      I apprectiate the help. Not trying to fight or argue with anyone.

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      07-19-2012 06:46 AM #10
      Quote Originally Posted by skateboards and mk2s View Post
      I asked for specifics on a not very common VW engine.
      That I have to say is exactly my point, if you can call it that. The GX engine, going out on a small limb here, is maybe one of the most “common” engines produced during that era. And there you go again with that word/question, “specifics”. Ask what you need information on and not some lame thing like wanting specifics. If I had told you the length, weight, metal composition and bore spacing of the engine you would have responded that that was not what you were looking for, right? People have not yet developed to the point of being able to read minds over the Internet. Provide more detailed questions and ya get better answers.

      Quote Originally Posted by skateboards and mk2s View Post
      Not really sure how that makes it sound like I am a silly kid with no clue?
      Never said you were a kid or silly either. I do have to admit that a log-on name of skateboards . . does bring up visions from time to time but nothing I would lean on in any response. And again “no clue” is rather vague and is not a fair term to use if trying to boost an argument (don’t mean fight but discussion really) as it can later be defined as one wishes when need be.

      Quote Originally Posted by skateboards and mk2s View Post
      Not trying to fight or argue with anyone.
      That’s good because I don’t fight or argue on the Internet, it serves no purpose. I call things as I see them and tell it as it is or I think it to be. If wrong then fine, my mistake (bad I was told is the “in” term) and can accept being wrong. But this is not the place to lay out my philosophy and morals so I won’t. So what other information are you needing?

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      07-19-2012 02:58 PM #11
      I thought i was being specific enough when the thread only really spoke about compression.

      I will admit it was a pretty vague question but don't really feel that it deserved the newbie lecture on engine performance.

      Whatever no harm no foul. I will get tougher skin when I am in the 8V forum.

      I was looking for any specific info related to that specific engine code that would be related to the ABA swap.

      But I have it now. THANKS!

    12. Junior Member BGosnell's Avatar
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      07-30-2012 03:06 AM #12
      I have the GX engine too with the CIS-Lambda and I have the same ?'s about compression. I consumed all the charts that Bentley has to offer and here's what I came up with...(minus Diesel, who cares about those???)
      Engine Code_______GX--------MZ--------HT--------RD--------RV--------PF--------PL--------9A
      Cylnders__________4----------4----------4----------4----------4---------4----------4---------4
      Bore mm__________81--------81---------81--------81--------81---------81-------81--------82.5
      Stroke mm________86.4------86.4-------86.4------86.4------86.4------86.4------86.4------92.8
      Displacement cc____1781------1781------1781-----1781------1781-----1781-----1781-----1984
      Compression Ratio__8.5:1-----8.5:1------10:1------10:1------10:1------10:1-----10:1-----10:1
      HP@RPMx1k +/-.1__85@5.2---90@5.5--100@5.5-102@5.2-100@5.4-105@5.4-123@5.8-134@5.8
      TQ@RPMx1k +/-.1__96@3-----98@3.2---105@3---110@3.2-109@3.8-114@3.8-120@4.2-133@4.4
      FI System________CIS/CIS(E)--CIS-------CIS(E)--CIS(E)---DIGI1/2--DIGI 2 --CIS(E)--CIS(Motr)
      Application Notes___Economy-Canada--GTI/GLI85-GTI/GLI-----------------------16V------16V 2.0L
      IN V Head Dia mm__38---------38---------40--------40--------40--------40---------32--------32
      EX V Head Dia mm__33---------33---------33--------33--------33--------33--------28--------28
      V Stem Dia mm+/-__8----------8-----------8----------8---------8---------8----------7---------7
      IN V Length mm____91---------91----------91--------91--------91-------91--------95.5------95.5
      EX V Length mm____90.8------90.8--------90.8------90.8-----90.8------90.8------98.2------98.2


      ........ WOW I'm bored.... So it makes sense the jumps in HP due to Valve size changes, number of valves and the 9A big block, and other fluctuations due to camshafts and Fuel systems and exhausts etc. but what I don't get is the change from 8.5-1 CR to 10.0 with the same size pistons. Maybe they were just shorter or dished differently...
      I know it's an 87, but it's MY 87.

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      07-30-2012 10:43 AM #13
      Quote Originally Posted by BGosnell View Post
      I have the GX engine too with the CIS-Lambda and I have the same ?'s about compression. I consumed all the charts that Bentley has to offer and here's what I came up with...(minus Diesel, who cares about those???)
      Engine Code_______GX--------MZ--------HT--------RD--------RV--------PF--------PL--------9A
      Cylnders__________4----------4----------4----------4----------4---------4----------4---------4
      Bore mm__________81--------81---------81--------81--------81---------81-------81--------82.5
      Stroke mm________86.4------86.4-------86.4------86.4------86.4------86.4------86.4------92.8
      Displacement cc____1781------1781------1781-----1781------1781-----1781-----1781-----1984
      Compression Ratio__8.5:1-----8.5:1------10:1------10:1------10:1------10:1-----10:1-----10:1
      HP@RPMx1k +/-.1__85@5.2---90@5.5--100@5.5-102@5.2-100@5.4-105@5.4-123@5.8-134@5.8
      TQ@RPMx1k +/-.1__96@3-----98@3.2---105@3---110@3.2-109@3.8-114@3.8-120@4.2-133@4.4
      FI System________CIS/CIS(E)--CIS-------CIS(E)--CIS(E)---DIGI1/2--DIGI 2 --CIS(E)--CIS(Motr)
      Application Notes___Economy-Canada--GTI/GLI85-GTI/GLI-----------------------16V------16V 2.0L
      IN V Head Dia mm__38---------38---------40--------40--------40--------40---------32--------32
      EX V Head Dia mm__33---------33---------33--------33--------33--------33--------28--------28
      V Stem Dia mm+/-__8----------8-----------8----------8---------8---------8----------7---------7
      IN V Length mm____91---------91----------91--------91--------91-------91--------95.5------95.5
      EX V Length mm____90.8------90.8--------90.8------90.8-----90.8------90.8------98.2------98.2


      ........ WOW I'm bored.... So it makes sense the jumps in HP due to Valve size changes, number of valves and the 9A big block, and other fluctuations due to camshafts and Fuel systems and exhausts etc. but what I don't get is the change from 8.5-1 CR to 10.0 with the same size pistons. Maybe they were just shorter or dished differently...
      Thanks I had found most of that info as well. As far as I can tell it is just piston shape and the smaller valve that is responsable for the lowering of the compression. I have found a few threads that spoke of some US production heads being a little taller but not enough to really change to much and nothing that anyone could prove was intentional. All within a rather broad factory spec.

      I was hoping the smaller valves alone were responsable for the lower compression as a head change is way easier than a whole long block swap.

      Thanks for the info!!

    14. Junior Member BGosnell's Avatar
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      07-30-2012 03:00 PM #14
      I'm pretty sure valve size doesn't have anything to do with compression, just flow. You don't cange your compression ratio when you open the TB. I think its all cylinder area (including head) and piston movement. It's gotta be cylinder shape or length or head heighth like you were sayin'. It'd be cool if someone who knew more on this subject chimed in.................
      I know it's an 87, but it's MY 87.

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      08-01-2012 08:15 AM #15
      The only real difference between all those engines to get the diff CR is the piston. The heads (no matter the valve size) have the same size combustion chamber. Except for the 9A and PL, as those are the 16V motors, and shouldn't even be on that chart, for comparing 8V motors.

      I'll say it again, the piston is what VW uses to change the CR on these motors, as the heads are virtually identical, for determining CR.

      And the GX was not a "rare" motor, it was in Golf's and Jetta's from 84-87, and my EKTA has it listed as a 90hp motor. Just not as desirable as an RV, RD or PF coded motor.
      Last edited by ps2375; 08-01-2012 at 08:21 AM.
      Tradition is the art of making the same mistake repeatedly, on purpose.

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      08-01-2012 12:22 PM #16
      My bad on the "rare" comment. I guess what I meant was it is hard to find good detailed info about a US built golf with the GX. As far as I can tell it was the only golf bodied car with an 8v that got CIS E. If you have more info I am still interested for nothing more than learning sake. I have had three different shops tell me three different things about the setup so there is obviously a fair amount of confussion out there.

      My thought on valve size was that a larger area of the combustion chamber is being used up by the larger valve thus creating a "very slightly" higher compression. We are talking about overall combustion chamber volume correct? If removing even 1/1000th of an inch off the bottom of the head can make a change my thought is that the increased material space of the larger valve would equate to a simaller reduction in chamber size. Hence a very slight increase in compression.
      Last edited by skateboards and mk2s; 08-01-2012 at 12:31 PM.

    17. Member ps2375's Avatar
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      08-01-2012 12:25 PM #17
      The CR change would be very small, calculate-able,but probably not notice-able.
      Tradition is the art of making the same mistake repeatedly, on purpose.

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      08-01-2012 12:31 PM #18
      Quote Originally Posted by ps2375 View Post
      The CR change would be very small, calculate-able,but probably not notice-able.
      Thanks!

      Were there any other changes in the GX block? Different crank shape or material used? pick up or pump? baffles?

    19. Member ps2375's Avatar
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      08-01-2012 12:42 PM #19
      Nope, I think that is all stand fare for VW. I've got one in my Rabbit w/ a solid lifter head on top of it, just need a reason to justify rebuilding the RV coded block I have to get the higher CR and added power. Mine has around 70K on it's last rebuild. You could just get some pistons from ne of the other motors w/ the higher CR and drop them in, and wa-la, you have essentially an RV, PF or RD short block.
      Tradition is the art of making the same mistake repeatedly, on purpose.

    20. Member ps2375's Avatar
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      08-01-2012 12:48 PM #20
      And anybody that has worked on VW's for any amount of time, knows that VW mixed and matched fuel/spark systems w/ various block and head combos to meet this and that government's various requirements. A good example is from the same time period, some had carbs, but most had CIS, some had CAT's and some didn't. They did what they needed to do, and some of it made little sense other than financial.
      Tradition is the art of making the same mistake repeatedly, on purpose.

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      08-01-2012 01:25 PM #21
      Quote Originally Posted by skateboards and mk2s View Post
      As far as I can tell it was the only golf bodied car with an 8v that got CIS E.
      Most GX motors are run with CIS Lambda. However, it seemed common to find CIS-E (without knock sensing unit) in use on 85 model year Jetta/Golfs.

      The HT/RD 8v motors also use CIS-E, alongside a separate knock sensing unit.
      I really suck at smog.

    22. Junior Member BGosnell's Avatar
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      08-01-2012 04:52 PM #22
      I heard that they made the GX and MZ Canada motors with such low (8.5:1) CR's to be economy models. I guess less compression equals better gas mileage?
      I know it's an 87, but it's MY 87.

    23. Member ps2375's Avatar
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      08-01-2012 05:06 PM #23
      Quote Originally Posted by BGosnell View Post
      I heard that they made the GX and MZ Canada motors with such low (8.5:1) CR's to be economy models. I guess less compression equals better gas mileage?
      No, lower octane required, thus cheaper fill ups. A higher CR has the potential for better efficiency, thus better economy, but the tradeoff is potentially high fuel costs.
      Tradition is the art of making the same mistake repeatedly, on purpose.

    24. Junior Member BGosnell's Avatar
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      08-01-2012 05:23 PM #24
      Good thing I always fill up my GX with premium.
      I know it's an 87, but it's MY 87.

    25. Member ps2375's Avatar
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      08-01-2012 05:29 PM #25
      Yup, keep those oil company employees off of welfare. I have been trying to use corn-free fuel, as I should expect slightly better mpg's, but there is no reason to pay extra for the higher octane.
      Tradition is the art of making the same mistake repeatedly, on purpose.

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