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Thread: 18rg tuning, LONG!

  1. #1
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    Default 18rg tuning, LONG!

    Hello mates!

    Please forgive the long post, i just want to give you all as much infomation as possible.

    I am hoping to get some help from you guys with the experience on tuning and maximizing the parts I have on it now. I am a 21 year old kid that is learning engine and carb tuning with this motor.

    First, here is my current setup:

    18RGEU block
    10.5:1 pistons
    18RGEU stock head
    304 intake cam (TRD) timed as straight us as i can get it
    288 exhaust cam (TRD) timed slightly advanced if anything
    single bolt adjustable cam gears (the one with the removable pin)
    "short" intake
    Mikuni 44mm carbs
    200 air jet
    135 main fuel jet
    60 idle jet
    40 accelerator pump jet
    OA jet holder in the carbs (holds the main and the air jets)
    stock “points” distributor and matching coil (running 18degrees base timing, no vacuum advance connected)
    TRD high-rise header
    2 ¼ inch exhaust all the way back (no muffler, straight pipe out the back)

    I am at about 6500 ft elevation, so the air is rather thin up here (about 21% thinner/less oxygen)

    Since added the 304/288 cams, the car is much more lively, but does not really pull all the way through 7000 rpm. There also seems to be a “hole” in the power-band from about 2000-3200 rpm. It gets better using a little more timing, but then I get detonation around 5000rpm.

    Here is the thing, I am looking for any advice about how to tune this thing better. Here is what I have been told to try doing.

    Try running the intake cam at 100 degrees, and the exhaust at 98 degrees. That should allow for best mid to high rpm power. Problem is that I have no means of degreeing the cams that exactly. Does anyone know the cam center lines for these cams? Or have any suggestions as to where the cams should be put? My butt-dyno says intake straight up, exhaust slightly retarded. But that’s just what my butt says.

    I have been told that the venturies need to be changed out for something like 38mm ones. I am in the process of getting those. If I understand my readings correctly, using the 38mm in please of the 34mm will allow for more flow at high rpm, but will also decrease the efficincy(worse atomization with th 38’s than the 34’s). is that correct? Anyone have any thoughts on which venturies to use?

    I have also been told that my carb jets sound a little weird. I have been suggested to try a 200 air, 165 main, 60 air, and a 45 or 50 pump jet. That sounds like a lot of fuel on what I already think is a rich setup. Any thoughts there? Suggestions either?

    I am running no vacuum advance on my distributor at the moment. That is how the previous owner was running it as well. I do not know exactly why yet, but I am in the process of finding out. It is set at 18degrees at idle, and I assume there is a mechanical advance in there somewhere. Don’t know what that amount might be though. any ideas?

    My experience is that the motor when cruising has an audible lurching issue. By that I mean that the car is holding throttle and rpm, but the car ever so slightly tries to accelerate. It almost sounds like a very slight misfire and then a pinch of power mixed in there.

    Idle is a bit ruff as well. I expect that to a degree, but this is a bit more than I would expect.

    When I floor the accelerator peddle, there is a bit of hesitation. Actually, it is almost a loss of power, then comes back and continues on. It pulls just off idle rather well, gets to about 2200 and there is a defeat loss in power. Once it hits about 3200, there is a huge serge of power, which seems to fall off as I approach and pass 5500 on my way to 7000rpm.

    I know that was REALLY REALLY LONG! But like I said, I am trying to learn as much about the theory and possible and apply it to the car. What I have learned on my own is what has gotten me to this point. Now I am looking for people that have actual experience and true knowledge about these things.

    Any help would be greatly appreciated mates!

    Cheers, and thank you for reading!
    Ryan

  2. #2
    Junior Member Grease Monkey
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    Default Re: 18rg tuning, LONG!

    the surging at cruising speed can be fixed by changing the jets, I've done it to an old fiat with del-orto carbs once before. We just got a whole heap of different jet sizes and changed them until the problem went away. Or you can, get on a dyno with a AF meter and you will be able to get the jetting perfect.

    The problem when you floor it and the motor dies sounds like the accelerator pump is either not working at all, or is working too well and flooding the motor when you push the throttle quickely.

    I would be getting the vacuum advance setup first, it may fix some of the 2000-3000 flatspot. The carbie itself may be in need of reconditioning

    By far the best way to solve these problems is on a dyno with some who really knows there stuff about carbies. But when they are setup properly it will give the engine more response than an efi engine (in my opinion)

  3. #3
    Forum Member 1st year Apprentice
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    Default Re: 18rg tuning, LONG!

    Thank you for reminding me. As far as i know, there is noone in my local area that has extensive experience with the mikuni carbs, nor do they have the jets that are used in them.I will be continuing to search around, but it is not looking too hopeful as of right now.

    thanks!
    Ryan

  4. #4
    Junior Member Domestic Engineer tricky's Avatar
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    Default Re: 18rg tuning, LONG!

    Hi Ryan!

    First up, the issue with the car bogging down when you floor it at low RPM's... Well you can't get around that with big throttles and long cams. You just have to drive at low revs by easing the throttles open, 'cos the gas velocity just isn't high enough at WOT. This would only get worse switching to bigger venturis.

    It sounds like you might want to get your dizzy regraphed also. The dizzy is meant to run with vacuum advance, but obviously the amount of advance you require varies according to the engine setup, and with yours, it won't be pulling much vacuum anyway. This isn't a do at home job, and if your doing it, you might as well get a mallory dizzy anyway. They are a bit more stable and they don't suffer from points bounce. Your low redline could be due to points bounce (does the power suddenly fall of, or does it slowly reduce up to redline?) or it could be a balance issue. Was the rotating assembly balanced when the motor was built? There should be a fair bit of power lurking in the cam timing too. To do it precisely, get yourself a 360* protractor, put it on the crank pulley, confirm TDC and use a dial gauge to check the timing at 0.040". You should be able to track down some recommended specs for the cams. Time them accordingly and use that as a base setting.

    As far as the lurching at low RPM is concerned, my RG does that to. Again you can't get around it. It's because of the lumpy idle, and the surging 'lurch' is due to efficient combustion events in a sea of less efficient events.

    As for the jets, you'll find out by experimentation, but be careful! What to the plugs look like after a run? If they are black, it's rich. You won't ever be able to lean it out enough at low revs if you are running at stoich up high (or if you do, it won't idle!), it's just what you have to deal with using big carbs and long cams. For best results, get a dyno tune, or an on road tune from a carb guru. It might cost a bit more, but at least you know you won't fill your engine with carbon.

    BTW, are TRD grind cams easy to come by over there? I'm looking for 304/304 and a spare 288 exh cam for my RG beast in planning. And are the TRD headers 4-1?

    Hope that helps!
    Nikita the RA23 is almost finished .

  5. #5
    potato Automotive Encyclopaedia joecoolmk2's Avatar
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    Default Re: 18rg tuning, LONG!

    i'd say your exhaust is a bit too unrestrictive for a start. i'd use two inch if you're not gonna run any mufflers, this should give you a bit better response in the lower rpm.

    well, of course you're gonna have SFA down low with huge cams, big carbs and SFA air at 6500 ft! no offense by that by the way.

    on the jets, i'm no specialist on carbs but i think that's pretty much what i'm running in the way of jets, i've only got 40mm solexes though.

    so basically, why did you go a 2 1/4" exhaust straight through?
    beer me!

  6. #6
    Hopefully soon a 5S-GTE Chief Engine Builder MWP's Avatar
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    Default Re: 18rg tuning, LONG!

    Quote Originally Posted by rcodea
    I am running no vacuum advance on my distributor at the moment. That is how the previous owner was running it as well. I do not know exactly why yet, but I am in the process of finding out. It is set at 18degrees at idle, and I assume there is a mechanical advance in there somewhere. Don’t know what that amount might be though. any ideas?

    My experience is that the motor when cruising has an audible lurching issue. By that I mean that the car is holding throttle and rpm, but the car ever so slightly tries to accelerate. It almost sounds like a very slight misfire and then a pinch of power mixed in there.
    No vac advance will kill your effiency at cruise conditions.
    I wouldnt be supprised if its causing your "lurching".
    Re attach it, and if you then have pinging problem, retard the ignition until it stops.

    When I floor the accelerator peddle, there is a bit of hesitation. Actually, it is almost a loss of power, then comes back and continues on.
    Well you do need a bigger accel pump jet then.

    OT... I just spent 2 weeks in Cripple Creek Colorado after driving south through the hills from Estes Park.
    Quite a spectacular place.
    Pitty my van broke down, it would have been nice to continue my trip south west into Utah
    Last edited by MWP; 17-08-2006 at 03:51 PM.

  7. #7
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    Default Re: 18rg tuning, LONG!

    Quote Originally Posted by tricky

    Your low redline could be due to points bounce (does the power suddenly fall of, or does it slowly reduce up to redline?)
    The power seems to slowely fall off.

    I am working on getting on the dyno we have at school for a baseline graph to show around and get some speculation.

    Quote Originally Posted by tricky
    Was the rotating assembly balanced when the motor was built?
    To the best of my knowledge it was. The short block was used previously as a racing block, so I would assume that he had it balanced.

    [QUOTE=tricky]
    ...and the surging 'lurch' is due to efficient combustion events in a sea of less efficient events...QUOTE]
    So then how do I get rid of the less efficient ones! haha

    Quote Originally Posted by tricky

    What to the plugs look like after a run?
    They are a clean combustion, thought it would side more on the rich end than the lean end.

    Quote Originally Posted by tricky

    BTW, are TRD grind cams easy to come by over there? I'm looking for 304/304 and a spare 288 exh cam for my RG beast in planning. And are the TRD headers 4-1?
    Nope, they are extremely hard to find! I had to get mine from a guy in Japan. I have been lucky enough to find a guy that seems to really know his stuff out there with these RGs. It is his input that has me asking all these questions in the first place(and my desire to get the most out of my motor, but that is a given). Good luck finding those cams. Its going to take you a long while to get them from here, unless you want to pay a full $600 USD for them.

    The header I have is the 4-2-1 TRD one. It uses the same lower 2-1 section that the stock cast manifold used, but the 4-2 section is a mandrel bent tubing.

    thanks!
    Ryan

  8. #8
    Forum Member 1st year Apprentice
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    Default Re: 18rg tuning, LONG!

    Quote Originally Posted by joecoolmk2
    so basically, why did you go a 2 1/4" exhaust straight through?
    came on the car like that sounds AMAZING THOUGHT!
    Ryan

  9. #9
    Toymods Net Nazi Too Much Toyota river's Avatar
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    Default Re: 18rg tuning, LONG!

    Hi,

    Get the dizzy vacuum advance working first, then let's see how she's going and work on the next thing.

    seeyuzz
    river
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  10. #10
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    Default Re: 18rg tuning, LONG!

    Quote Originally Posted by MWP
    OT... I just spent 2 weeks in Cripple Creek Colorado after driving south through the hills from Estes Park.
    Quite a spectacular place.
    Pitty my van broke down, it would have been nice to continue my trip south west into Utah
    You should have told the guys on classic-celica.com that you were comming through here. there are at least 4 of us that would have loved to talk and show off our cars!
    Ryan

  11. #11
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    Default Re: 18rg tuning, LONG!

    Quote Originally Posted by river
    Hi,

    Get the dizzy vacuum advance working first, then let's see how she's going and work on the next thing.

    seeyuzz
    river
    OK, sounds like a reasonable enough idea. I'll do that first and see what happens from there. Hopefully I'll have that done by this time tomorrow.

    I'm trying to find out why the previous owner removed it in the first place. It might be that the vacuum advance is busted on that distributor...I dont know.

    Ryan
    Ryan

  12. #12
    Backyard Engineer Domestic Engineer airfireman1's Avatar
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    Default Re: 18rg tuning, LONG!

    If you are after mikuni solex carby parts there is a company that sells on ebay called Wolfcreekracing .They do kits and parts, also have tuning manuals.maybe they can help if you think you have any carby issues.
    cheers

  13. #13
    I even do the dishes as Domestic Engineer Rodger's Avatar
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    Default Re: 18rg tuning, LONG!

    Ryan,

    A long response to your long starter query.

    For a competion spec engine you either get all the power up high and little or no low down driveability.

    Or you have the drivability and loose out up high.

    Basically you are running out of air and fuel above 7000rpm. You are correct the #34 outer venturi is limiting the amount of total air. Your thoughts about the #38 is correct and it is due to the lack of air speed past the inner venturi, which the #34 is good for.

    When I ran my TRD speced 2T with 44 Mikunis in sprints I ran; #220 Main air, #170 Main, #65 pilot and 38mm outer venturies. It gave me heaps of top end power over 5000 rpm and pulled sweatly to 9000rpm.

    I tried to run this at a couple of grass motorkhana events and it would not pull the "skin off a custard" and had no throttle response at all. Not good for this event.

    So I had two set ups. The motorkhana set up used the same #38 outer venturies (did not want to pull the carbies apart), #170 main air, #140 main, and #57.5 pilot. It then had lovely throttle response and pulled well in mid range, just ideal for the event.

    Of course back at the sprints it did not pull above 6000rpm and started pinging at those revs.

    Anyway My advice.

    First up choose what you want to do with the motor.

    The set up as it stands is definately a mismatch of ideas.

    The #200 air jet and the #135 main jet is making the whole main system too lean. Hence the pinging and some of the lack of power.

    The small sized outer venturi as said before reduces the top end power

    The cruising and off idle response is caused both by the lean main system and possibly worsened by the #60 pilot jet.

    To get a nice drivable car is a compromise.

    Off the top of my head static timing for an 18R-G is 12-15 degrees BTDC which should be good also for your spec motor. Also the max timing is around 36 degrees.

    Someone correct me if I am out. Suffice to say how this is acheived is up to you. Vacuum advance or not.

    Try:
    #170 Main air
    #140 main
    #60 pilot
    and keep the #34 outer venturi

    If the off idle and cruising is still a problem the try a #65 pilot. The idle mixture can then be leaned down to get a good idle back.

    The pilot system is the primary means for fuel/air supply for the first 20% throttle opening and is used during cruising. When it is correct you wont have the slight hesitation or miss whilst cruising. If it is a bit lean you have a miss every now and then or as you said a slight surge.

    The #34 outer venturi and the #170 main air will now restrict the top end and it may well run out of air at the 6000 rpm mark.

    So to loose some of the drivabilty and gain a few more revs try the following:

    #200 main air
    #160 main
    #65 pilot

    Go to a #36 outer venturi as it will be a better compromise.

    It should still cruise and it will pull perhaps to 7500rpm without power loss or pinging.

    Now the next thing to check is the pump jet action. The size of #40 is ok. Some of the throttle hesitation could be from either (as said before) blocked pump jets, but also if one carby is pumping a different amount or time.

    Make sure both pump levers are moving the same distance. If not adjust so they are. Standard is around 6mm at the tip with the split pins in the middle hole. Then you can try the higher (longer stroke) and the lower (shorter stroke) positions.
    The length and amount of fuel delivered is changed by stroke lenght and jet size.

    I could go on but enough for now.

    Try these things and see what you get.

    Regards

    Rodger

  14. #14
    Junior Member Automotive Encyclopaedia
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    Default Re: 18rg tuning, LONG!

    The LAST thing you need is a vacuum advance!!!
    I'll assume the mechanical advance is working OK since it pings when advanced too far, and is probably about 15 to 20 plus your 18 degree base.
    See if the mechanical advance is working OK with a timing light. It is
    the only really good use for them.

    The vacuum advance won't work too well with the low vacuum those cams will have. It will have zero advance when accelerating and nearly zero at 3/4 to WOT. It will give lots of advance when there is lots of vacuum - and that will only happen when engine braking/down shifting, so it is basically usless, except that the movable plate holding the points is probably worn out and the point gap/dwell will be changing all over the place.

  15. #15
    Junior Member Backyard Mechanic
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    Default Re: 18rg tuning, LONG!

    i've heard my friend saying that TRD N1 AE86 is running on a locked ignition.. how true it is to run a locked out timing on a race engine? i heard some turbo-ed 3TC run locked out timing too...

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