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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.

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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.

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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.

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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.

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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!

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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.

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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?

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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.

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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.

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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.

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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.

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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.

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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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      08-03-2012 01:51 PM #26
      Thanks guys. All awesome info. Now the dilemma I am having is.

      I have the GX in the car running fine and a complete 96 2.0 gti in the garage that needs a head gasket.

      If anyone feels like throwing in their preference and experiences it would be great.

      A. Change pistons and get larger valve head?
      B. ABA bottom with larger valve head and stay CIS?
      C. Swap the whole ABA over?

      Its a daily that goes to the track once a month or so.

      I have been into VWs and racing for years but always on the suspension end of things.
      This is my first "built" I use the term loosly engine. So my apologies if I am asking a bunch of dumb questions.

      It seems that all I hear around the vortex is ABA stuff but over at clubgti.com many of the purpose built cars are still building 1.8s

      My last autocrosser was an 87 golf gt. with TT header, TT cat back, 268 cam, Eurospec cam gear. Cam timing was retarded 3 degrees if I remember right. The car was a blast and won two seasons in a row until they put the Suzuki swifts and Datson 510s in the class.

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      08-04-2012 02:59 PM #27
      Quote Originally Posted by skateboards and mk2s View Post
      Thanks guys. All awesome info. Now the dilemma I am having is.

      I have the GX in the car running fine and a complete 96 2.0 gti in the garage that needs a head gasket.

      If anyone feels like throwing in their preference and experiences it would be great.

      A. Change pistons and get larger valve head?
      B. ABA bottom with larger valve head and stay CIS?
      C. Swap the whole ABA over?

      Its a daily that goes to the track once a month or so.

      I have been into VWs and racing for years but always on the suspension end of things.
      This is my first "built" I use the term loosly engine. So my apologies if I am asking a bunch of dumb questions.

      It seems that all I hear around the vortex is ABA stuff but over at clubgti.com many of the purpose built cars are still building 1.8s

      My last autocrosser was an 87 golf gt. with TT header, TT cat back, 268 cam, Eurospec cam gear. Cam timing was retarded 3 degrees if I remember right. The car was a blast and won two seasons in a row until they put the Suzuki swifts and Datson 510s in the class.
      aba bottom end, gti head, drop it in the car..

      you have alot of good parts to bolt on it.

      GTIs and GLIs had heads with bigger valves.. i, personally, have not noticed a big difference between a small valve, and large valve head.

      my 85 GTI had a HT engine in it (10:1, big valve head, CIS-e) and my 86 Golf is FASTER than it was.. yes.. an engine with smaller valves, and less compression..

      the 85 had HT w/ a neuspeed 268*, a twin tube downpipe and mani, a modified intake system, and K&N pannel filter as well as a free flowing exhaust..

      my 86 has a GX with the same neuspeed 268*, a real header, the same intake system, and a catless exhaust with a flowmaster 40 series at the end..

      the 86 gets better economy, and has better power as well..

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      08-04-2012 03:19 PM #28
      I too dream of doing a 2.0 16v swap for my GX, I'm glad to hear you actually plan on making it happen.

      My plan was to take the 9a engine(keepin' it mk2) and throw in as big a pistons as practical and run it at around 10.5 or 11cr , port and polish and regrind the valve seats for mid to fully oversized TT valves, 276 cams with advanced cam timing for street use, TT race header with cat back Borla, HD engine mounts, upgraded intake mani and throttle body and a bunch of odds and ends to fine tune the oil pressure and operating temp. I plan on running mine on the CIS Lambda that my GX came with and possibly upgrading to a beefier fuel distributor/air flow meter setup.

      My main concerns would be keepin it knock free on premium keepin' a smooth idle. I assume advancing the cam timing would help with that but now I'm wondering if that's more of a spark timing fix?

      I'm not too sure about the ABA's, weren't those the 2.0 16v's out of the mk3's? I know there's tons of write-ups on the how, what, why and when's of the ABA swap though.

      You gonna turn this into a build thread? I'd love to follow your progress.
      I know it's an 87, but it's MY 87.

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      08-04-2012 03:31 PM #29
      Hmmmmm I'm not too sure it sounds like you had much less exhaust restriction on the 86, you don't honestly believe that 8.5:1 GX with small valves actually has more potential than the 10:1 HT with bigger valves.... do you???

      I have a question though what did you do to your intake? I've heard a lot of ideas about opening up the airflow on CIS mk2 intakes, mostly bad though.
      I know it's an 87, but it's MY 87.

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      92 Jetta GLI 1.6TD Ripper (VNT20 Turbo), 86 GTI (Wolfsburg Golf), 86 Audi Coupe GT
      08-04-2012 04:25 PM #30
      Quote Originally Posted by BGosnell View Post
      Hmmmmm I'm not too sure it sounds like you had much less exhaust restriction on the 86, you don't honestly believe that 8.5:1 GX with small valves actually has more potential than the 10:1 HT with bigger valves.... do you???

      I have a question though what did you do to your intake? I've heard a lot of ideas about opening up the airflow on CIS mk2 intakes, mostly bad though.
      i cut a hole in the front of the air box, and installed a duct to pull air from under the passenger side headlight.. it is not swiss cheesed. i left the original intake duct there as well. removed the warm air bypass, and installed a K&N panel filter..

      and no, im not saying the GX has MORE POTENTIAL than the HT.. i NEVER said that.. im just saying that in stock, to slightly modified form, i cant tell the difference between engines.. ive dealt with alot of RDs, HTs, GXs, and a few other CIS/CIS-e engines, and all my experiences have been the same..

      when the cars were stock, my GTI would smoke my Golf, but once they had mods, it was the low compression engine that did better. but only by a TINY bit. im saying that unless you are gonna build the holy hell out of your engine, that i dont think it really matters what head you use. i never noticed any BIG GAINS to be had from the head with bigger valves.. honestly, i think my golf has more TORQUE than the GTI did tho..

      i figured that 10:1 compression, CIS-e, and knock sensing ignition would make more power hands down.. but it was ALOT closer than i thought it would be..

    31. Member
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      90 fox, 85 gli
      08-04-2012 05:28 PM #31
      the close ratio paired with the HT sure is fun though. I miss that the most about my old 85 gli
      I really suck at smog.

    32. Member
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      92 Jetta GLI 1.6TD Ripper (VNT20 Turbo), 86 GTI (Wolfsburg Golf), 86 Audi Coupe GT
      08-04-2012 09:46 PM #32
      Quote Originally Posted by ziddey View Post
      the close ratio paired with the HT sure is fun though. I miss that the most about my old 85 gli
      i like the wider spread of gearing with the ACN tho..

      my GTI had a 9A in it original, but i bought it with no reverse..

      i swapped in an ACN trans, and i LOVED it..

      my 86 Golf came with an ACN original..

      my GTI never ran as good as my Golf tho.. it would lose prime if you parked on a hill.

      was also very picky about fuel. it DID NOT like regular unleaded..

      ive got my Golf timed @ about 20*, and it still runs great on regular.. my GTI required premium with the timing set at 15*

    33. Junior Member BGosnell's Avatar
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      87 Jetta GL with GX CIS-Lambda
      08-04-2012 11:27 PM #33
      That's interesting. So many variables it's hard to say. I like your air box idea. Did you notice any big differences? Also isn't there an issue with operating temp? That's what I've heard about blocking off the warm air. Do you have any pics?
      I know it's an 87, but it's MY 87.

    34. Member skateboards and mk2s's Avatar
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      85 audi coupe, 85 audi 4000, 85 GTi, 87 scirroco, 87 golf GT, 96 GTi, now 85 Golf.
      08-05-2012 04:17 PM #34
      Wow great stuff guys thanks.
      Air intake right now is stock with the front fender side cut out and a K&N I also took the tube from the exhaust and ran it down the fender where the factory tube was.

      I am having the priming issue on hills as well as some bogging on hot startups. Once it clears out it feels ok.

      It also feels like it pulls the hardest at 3/4 throttle. The cable is set right.

      On your GX are you still running all the stock CIS E stuff? Vacuum advance?

      Right now it feels great until 4200 rpm and then it is just done.

      The exhaust helped and I know that the stock manifold and downpipe are the worst
      so maybe I will try the header before I do which ever swap I decide on.

    35. Member
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      90 fox, 85 gli
      08-05-2012 04:20 PM #35
      Go to the cis section and check the stickies. Longitudinal wrote a great write up on tuning / power tuning cis-e.

      Cut the Bosch o2 sensor harness for euro cars if this era. Perfect for building a dpr test harness.

      You could also upgrade to the later cis-e ecu and add a wot switch and wires. I don't know if it's the same ecu or not. Cis-e with knock sensing had a wot switch for full throttle enrichment in open loop.
      I really suck at smog.

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