viven44 Posted June 18 Author Share Posted June 18 The pump shot isn't part of the equation - unless your secondaries open immediately when you floor it and that's a very rare happening. Like you were cruising at 4000 RPM and then nailed it. Usually you nail it and the engine revs up over a few seconds and gets to an RPM where the secondaries finally open. But the pump shot is long gone as it only covers the brief period between when you nail it and the fraction of a second later when the fuel being pulled in via vacuum can respond. (Air is a lot less dense and, therefore, reacts much more quickly than fuel.) I guess I have no earthly idea of how ravenous these engines can be I did recall this video I watched a while back but I didn't think much about it as I had figured these racing engines were a different animal altogether I can totally see that the accelerator pump shot is nothing vs. what is actually flowing Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted June 18 Share Posted June 18 I guess I have no earthly idea of how ravenous these engines can be I did recall this video I watched a while back but I didn't think much about it as I had figured these racing engines were a different animal altogether I can totally see that the accelerator pump shot is nothing vs. what is actually flowing I have what might be considered a mild towing cam. If I really romp on it I'm looking at 7-8 mpg Link to comment Share on other sites More sharing options...
viven44 Posted June 19 Author Share Posted June 19 I have what might be considered a mild towing cam. If I really romp on it I'm looking at 7-8 mpg OK normally I'm a big fan of "if it ain't broke don't fix it" but it has been bugging me why the 78 Bronco doesn't take off from a stop like Big Blue 2WD with its 3.0 gears and 460, despite the fact that the 460 on the Bronco is healthier, has a double roller straight-up timing chain, and has 3.5 gears to boot. Good news is I think I've solved my low-end part-throttle get up and go problem. Now it takes off like a 3.5 rear end should with a 460, I'd even say it takes off better than Big Blue 2WD! The difference is quite remarkable. I had 15 mins this evening to go try 'one more thing'. All I did was move the accelerator pump setting to the leanest position.... if my understanding is correct, by leaning out the pump shot I have less now and since the part-throttle response is better now, it would seem that I was bogging the engine with the bigger shot previously at every get up and go event.... The 'Richest' setting is called the "HotRod" setting in some of the online discussions and videos... I am wondering if that is misleading as correct A/F ratio is the top criteria. In my case the 'Richest' setting gave me the worst result. Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted June 19 Share Posted June 19 OK normally I'm a big fan of "if it ain't broke don't fix it" but it has been bugging me why the 78 Bronco doesn't take off from a stop like Big Blue 2WD with its 3.0 gears and 460, despite the fact that the 460 on the Bronco is healthier, has a double roller straight-up timing chain, and has 3.5 gears to boot. Good news is I think I've solved my low-end part-throttle get up and go problem. Now it takes off like a 3.5 rear end should with a 460, I'd even say it takes off better than Big Blue 2WD! The difference is quite remarkable. I had 15 mins this evening to go try 'one more thing'. All I did was move the accelerator pump setting to the leanest position.... if my understanding is correct, by leaning out the pump shot I have less now and since the part-throttle response is better now, it would seem that I was bogging the engine with the bigger shot previously at every get up and go event.... The 'Richest' setting is called the "HotRod" setting in some of the online discussions and videos... I am wondering if that is misleading as correct A/F ratio is the top criteria. In my case the 'Richest' setting gave me the worst result. I'm kinda surprised that you can't change the cam for a sooner -or later- shot, like a Holley.... Whatever... I'm glad you seem to have it sussed now! Link to comment Share on other sites More sharing options...
viven44 Posted June 19 Author Share Posted June 19 I'm kinda surprised that you can't change the cam for a sooner -or later- shot, like a Holley.... Whatever... I'm glad you seem to have it sussed now! I believe I understand more of it now... I'm starting to think of it as my 460 having excellent vacuum on the stock cam -- the venturi is able to pull all the fuel it needs. Therefore the 'Hotrod' accelerator pump setting was causing a Rich condition. If a lumpy cam was involved, the venturi may not be as strong at idle so the 'HotRod' setting would help bring in more fuel... I probably should try this on Big Blue 2WD as well Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted June 19 Share Posted June 19 I believe I understand more of it now... I'm starting to think of it as my 460 having excellent vacuum on the stock cam -- the venturi is able to pull all the fuel it needs. Therefore the 'Hotrod' accelerator pump setting was causing a Rich condition. If a lumpy cam was involved, the venturi may not be as strong at idle so the 'HotRod' setting would help bring in more fuel... I probably should try this on Big Blue 2WD as well A lumpy "hotrod" cam has lots of overlap. This bleeds compression at low rpm, and allows good filling at higher rpm, when the port velocity is high, and charge inertia is actually carrying unburned fuel into the exhaust headers. This way you can get away with 14:1 static CR (or whatever) and still not see too much at lower rpm. This is the sort of crap you need an MSD for, because nothing wants to light that charge with no dynamic compression So it tries 3 times... below 3k rpm, but then stops giving multiple sparks, because the engine is now turning fast enough to where exhaust tuning and reversion are packing charge into the cylinder from both valves. If you've never tuned an alcohol or nitro car this might seem weird, but that's how it works to make big power. Link to comment Share on other sites More sharing options...
viven44 Posted June 19 Author Share Posted June 19 A lumpy "hotrod" cam has lots of overlap. This bleeds compression at low rpm, and allows good filling at higher rpm, when the port velocity is high, and charge inertia is actually carrying unburned fuel into the exhaust headers. This way you can get away with 14:1 static CR (or whatever) and still not see too much at lower rpm. This is the sort of crap you need an MSD for, because nothing wants to light that charge with no dynamic compression So it tries 3 times... below 3k rpm, but then stops giving multiple sparks, because the engine is now turning fast enough to where exhaust tuning and reversion are packing charge into the cylinder from both valves. If you've never tuned an alcohol or nitro car this might seem weird, but that's how it works to make big power. That’s very interesting!!! I’d watch someone else do that all day!! And no I haven’t any interest in pushing things to their limits for fun on the track. I guess that’s the 3rd world in me Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted June 19 Share Posted June 19 That’s very interesting!!! I’d watch someone else do that all day!! And no I haven’t any interest in pushing things to their limits for fun on the track. I guess that’s the 3rd world in me Plenty of people in the 3rd world seem to like blowing things up. 😉 I sure know I do!!! Link to comment Share on other sites More sharing options...
viven44 Posted June 19 Author Share Posted June 19 Plenty of people in the 3rd world seem to like blowing things up. 😉 I sure know I do!!! :nabble_head-rotfl-57x22_orig: Link to comment Share on other sites More sharing options...
viven44 Posted June 19 Author Share Posted June 19 Plenty of people in the 3rd world seem to like blowing things up. 😉 I sure know I do!!! My parents are here now on vacation and they simply do not understand why I’m working on my cars “like a mechanic”. I asked them if they have never heard of people collecting cars where they live. According to them that is a hobby for the ‘Elite’ only… museum grade typically… so evidently hot rodding is not for the common man, sadly in the third world. You can probably see Where I get it from. Link to comment Share on other sites More sharing options...
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