bgd73 Posted January 25, 2007 Share Posted January 25, 2007 A thought after seeing a video of an oem motorcycle claiming 125mph in an 1/8th mile (is that not like 4 seconds or less?) Are there any tricks to speed that ability to advance like I have seen on motorcycles with a chip mod. I do have an spfi ecu etc, way too proprietary to tinker with. My first carb soob was a lunatic and all I did was clean the distributor to note the various parts inside. it is a basic function, but what stops it from really advancing an engine fast like? power, gears, intake, valves, fuel, exhaust and the advancing mechanisms to make it happen.. Anything to do for a carb distributor to ensure fastest action? Link to comment Share on other sites More sharing options...
[HTi]Savage Posted January 25, 2007 Share Posted January 25, 2007 just clean it like u did with ur other one. I thing thats gonna be a chip mod though. U could advance ur cams a tooth. might bee funny. like varibal valve timing. couldent hurt to try. Link to comment Share on other sites More sharing options...
mikeshoup Posted January 25, 2007 Share Posted January 25, 2007 The carb'd distributors advanced based off of how much vacuum there is right before the throttle plate. At closed throttle, little vacuum at the port, little to no advance. At full throttle, lots of vacuum at the port, and so high advance. If you really want to make sure it advances 'fast', just clean up the vacuum canister and the actuator on it. However, you'll be surprised at how quick the reaction time is on the advance. As for more advance, you can advance the disty by a few degrees and make sure there is no ping. Running premium fuel will allow for more advance. Or you can have your disty recurved. Link to comment Share on other sites More sharing options...
robm Posted January 25, 2007 Share Posted January 25, 2007 Sorry, Mike, it is not as simple as that. Vacuum advance is there to increase timing for part-throttle cruise conditions. This is when engine vacuum is highest, and the throttle plate open so the distributor can see it. At full throttle, there is little vacuum, and therefore not much vacuum advance. Remember, racing distributors didn't have vacuum advance, as they don't spend much time at part throttle (wIth any luck!) and don't care about fuel consumption. The idea of adjusting the cam timing by adjusting it by a tooth is not the best. The cam belt teeth are pretty coarse, one tooth is way too much. Anyone who has slipped a tooth when installing the cam belts can attest to the fact that they don't work too well in this state. I like the SPFI distributor, the best of both worlds, as the basic timing is set by distributor position, so it can be advanced or retarded by several degrees. More modern systems that take the timing off the crank leave the home mechanic no way to fine-tune the timing at all. I find 23 degrees advance improves fuel consumption, with absolutely no noticeable ping. I should try advancing it a bit more, just to see what the limits are Link to comment Share on other sites More sharing options...
mikeshoup Posted January 25, 2007 Share Posted January 25, 2007 Sorry, Mike, it is not as simple as that. Vacuum advance is there to increase timing for part-throttle cruise conditions. This is when engine vacuum is highest, and the throttle plate open so the distributor can see it. At full throttle, there is little vacuum, and therefore not much vacuum advance. Scratch that, I'm gonna correct myself. Vacuum in the distributor is highest at mid throttle. Makes sense to me now why that is. Link to comment Share on other sites More sharing options...
[HTi]Savage Posted January 25, 2007 Share Posted January 25, 2007 M/B I thought u were talking about turbo motor. duh vacume advance on carbs. Link to comment Share on other sites More sharing options...
desertsubaru Posted January 25, 2007 Share Posted January 25, 2007 So what if you have an spfi block with a carb and carbed disty? Where should you set the disty at? Link to comment Share on other sites More sharing options...
robm Posted January 26, 2007 Share Posted January 26, 2007 The SPFI long block has more compression, so the stock advance may be too much. There are other factor involved as well, so... Start with the recommended advance (8 deg. BTDC? Just hearsay, it probably says on a sticker under the hood.) Take it out and drive it. Try sudden full throttle in third or 4th from about 2000 RPM and listen for a rattly sound, like a bunch of dimes in a tin can. That is ping. If it does this, retard the timing a bit, say to 6 deg. BTDC, and try again. A short little rattle is not a big deal, but if it rattles hard and as long as your foot is in it, it is too much! Try it up long hills, too. And keep an ear out for it as the weather changes. Moist air can act as natural water injection, which reduces ping. Link to comment Share on other sites More sharing options...
daeron Posted January 26, 2007 Share Posted January 26, 2007 And keep an ear out for it as the weather changes. Moist air can act as natural water injection, which reduces ping. I have wondered that.. I mean, theoretically its obvious. Practicality is another matter. Anyone else care to chime in and either back him up, or dispute this claim?? No offense intended robm, I simply have always been curious about this, and do NOT want to simply "take someone else's word for it." I just ask for confirmation of information, yanno? false knowledge sucks. These internet automotive forums have helped to disband more false info than they have spawned, I think.. but it goes both ways. Link to comment Share on other sites More sharing options...
robm Posted January 26, 2007 Share Posted January 26, 2007 My experience with "natural" water injection came on a Yamaha SR500 motorbike. 500 cc single, 9.0:1 compression, needed premium to run without serious knock. But I was an engineering student at the time, with a student's typical financial limits, and often tried to get by with the cheap stuff. There was a noticeable difference when it rained. Knock was reduced immensely. It even made a difference when running premium. That engine is so simple, but so sensitive, it is ideal for testing intake, exhaust, carburetion and other engine mods to see how they work. Too bad the ignition was not one of the easy things to play with! My experience with setting distributors came when the engine on that machine met an early demise and it was replaced with a Datsun 510. (No, I didn't squeeze the inline 4 into the motorbike frame, I parked the bike and drove the cage!) I found that 4 deg. more advance improved the fuel economy, but at the expense of knock. I found 2 deg. extra made for better mileage and slightly better power, with minimal knock. I have found the same 2 deg. extra advance to reduce the SPFI's fuel consumption. Link to comment Share on other sites More sharing options...
daeron Posted January 27, 2007 Share Posted January 27, 2007 rob: thanks for the story. As I said, this same idea has been occurring to me lately, as a thought exercise. I was briefly contemplating supercharging my Z, and started doing research.. and found that people often water-inject rather than intercool for practicality issues.. (dont ask me why, I couldn't figure out) Add to that the fact that it has been kinda rainy here in the last week or so, AND the intermittent misfire that my car has developed, and the whole "natural water injection" idea has been on my mind along with a host of other meterological phenomena. I've been wondering how much, and which, atmospheric changes actually made much of an impact on how my car was running at the time. your post was simply fortuitous and timely. Link to comment Share on other sites More sharing options...
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