Sanity Check My Tuning
Printed From: TheAMCForum.com
Category: The Garage
Forum Name: AMC V8 Engine Repair and Modifications
Forum Description: AMC-made V8 engine mechanical, ignition and fuel from basic repair to high-perf modifications
URL: https://theamcforum.com/forum/forum_posts.asp?TID=88558
Printed Date: Apr/19/2024 at 5:48pm
Software Version: Web Wiz Forums 12.03 - http://www.webwizforums.com
Topic: Sanity Check My Tuning
Posted By: Red20
Subject: Sanity Check My Tuning
Date Posted: Jul/15/2017 at 8:55pm
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Anyone using the vacuum advance canister that came with their MSD billet distributor? I've been running without one, and though it runs great, gas mileage isn't exactly good. This is my daily driver and I'm getting a painful 8 mpg. I do drive it like I stole it and cruise down the I-5 at 3000 rpm. I put the canister back on today. According to my cheap dial back timing light, this thing is adding 18* at idle! Off of the car with a vacuum pump, it started moving at 5 in.Hg and was at full travel at 15 in.Hg. I haven't actually checked it installed and in the car. I pulled the Quick Fuel SS 680 vacuum secondary carb (basically a Holley with billet metering blocks and base and secondary spring rate adjustable externally via a screw) also and checked the idle transfer slot exposure which was way too much. I cranked it back down to about .040 or a "square" portion of the slot showing. Then I adjusted the secondary throttle stop to slightly expose the secondary transfer slot. I also backed off the fast idle screw to ensure it wasn't holding the throttle open any. Once back on the car, with vacuum advance disconnected and at 14* initial, I adjusted idle to 800 RPM and since I dont have a large overlap cam, adjusted all 4 idle mixture screws to best vacuum which was a pretty steady 17 in.Hg. After, hooking up the vacuum advance, I lowered the idle with the secondary throttle blade stop screw. From there, I rechecked the idle mixture screws and made a very minor final idle adjustment with the idle speed screw to about 750-800 RPM. Finally, I kicked in the fast idle cam and adjusted the fast idle (which is always a few hundred higher with a fully warmed engine) to 1500 RPM. So with the aggressive MSD vac advance can, I'm idling at 32* BTC. Now all of that is according to my cheap timing light and old balancer. I haven't used or made a TDC checker on this engine. I also didn't hook up my multimeter on the Tachometer setting (which is cool) to see what total I was getting and what RPM. I just revved it up and turned the dial on the light to keep up until the mark stopped advancing which is hard to do all at once and saw it go a little past 50*. Vacuum at idle with vac advance hooked up is an extra inch or two. Distributor setup is as follows: MSD billet dizzy with 21* bushing and one heavy silver and one blue spring. Even without vacuum advance, I was getting too much advance too soon and pinging at part throttle up hills, so I slowed the curve. Mechanical only, I'm at 14* initial 35* total, all in around 2800, if I remember correctly. After getting it all dialed back in, I took a drive through town through 25 to 45 mph zones and on the interstate from 65 to 115 mph. I purposely slowed down to lug a little up a hill in 3rd gear and didn't hear any detonation (TH350 w/2500 stall converter). The exhaust note is slightly different at some lower RPMs, I notice. It pulls at lower RPMs with noticeably less throttle angle required. I've read varying numbers for fuel efficiency gains when installing a vacuum advance canister with most guy's reporting 20% increases. I hope to see something similar. SO...anyone see anything concerning or something I could do better? ------------- 1969 Javelin SST "Screamin' Banana" - Totaled Feb 2018 1973 Hornet Sportabout X "yellajack" - 360/727/TracLoc DAILY DRIVER |
Replies:
Posted By: Red20
Date Posted: Jul/15/2017 at 8:58pm
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Well crap that was long. If you read the entire thing, I probably owe you a beer. ------------- 1969 Javelin SST "Screamin' Banana" - Totaled Feb 2018 1973 Hornet Sportabout X "yellajack" - 360/727/TracLoc DAILY DRIVER |
Posted By: ccowx
Date Posted: Jul/15/2017 at 9:19pm
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So, where do I collect my beer? It all looks pretty darn good, the basic advance numbers are all reasonable, the idle being set with the secondaries is nice to see and overall looks pretty good to my eye. The butt dyno rules and if it feels good and is not pinging, then mission accomplished. I don't know about 20% more mileage, but maybe since it was so poor before you will get there. 20% of 6 mpg is only about .8 of a mile, so perhaps more reasonable than I think! Seriously, your post reads like a tutorial of how to set up the timing. Please keep us single digit mileage guys posted on what final results you get! Thanks! Chris PS: Only thing that springs to mind is to do a plug read as a final check. If it is running a bit advanced you could consider restricting the vac advance a few degrees. If the engine likes what you have, great, but perhaps a few degrees less might be ok too. |
Posted By: Red20
Date Posted: Jul/15/2017 at 9:31pm
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Thanks Chris! I've gotten pretty confident in basic tuning over the years thanks in a large part to guys like you and many others here and at the IFSJA forum on top of what I learned from my Dad and Grandps as a teenager. It helps to have a few people sanity check you though. I'd really like to see vacuum, advance, and o2 readings while driving. Better would be logging load, tps value, rpm, afr, egt, etc. I haven't even touched the base jetting of this carb yet. This is a 9.3:1 CR .030 over 360 with forged pistons, stock heads with just a touch of exhaust port smoothing and stud mounted roller rockers. Patriot shorty headers and 2" straight pipes (serious restriction) through Thrush welded mufflers. Performer grind cam and Air Gap manifold. 2.87 gears on 235/60R15 Cooper Cobras. It's a fun daily driver. ------------- 1969 Javelin SST "Screamin' Banana" - Totaled Feb 2018 1973 Hornet Sportabout X "yellajack" - 360/727/TracLoc DAILY DRIVER |
Posted By: Red20
Date Posted: Jul/15/2017 at 9:41pm
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Oh, and the beer is in Oceanside. SoCal. I'll do a WOT shutdown and read a plug when I get a chance. And I'll pull them all after a couple hundred miles. I looked at a few today before doing anything. Looked good. And here's a tip for anyone looking for TDC on the compression stroke of #1: Get a brass fitting that fits a spark plug hole with a hose barb on the other side. Thread it in and run a hose down next to your face under the car while you turn it over by the crank nut. When it starts coming around on the compression stroke it'll blow right on your face and you'll feel and hear it very clearly. Then you can set your balancer at about 15* BTDC to be safe and drop in your distributor and point the rotor tip at the #1 terminal. You should be able to eyeball it +/- 5* of the 15* you were shooting for and get it to fire and idle. http://s1082.photobucket.com/user/frazierjoshua/media/Mobile%20Uploads/7FFBA8BE-FB12-4FCC-9168-D215D44A884F.jpg.html" rel="nofollow">  ------------- 1969 Javelin SST "Screamin' Banana" - Totaled Feb 2018 1973 Hornet Sportabout X "yellajack" - 360/727/TracLoc DAILY DRIVER |
Posted By: ccowx
Date Posted: Jul/15/2017 at 10:29pm
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WOT shut down is a great idea, but that will give you a plug read for WOT. I would suggest that in addition to WOT, you also do a shut down after a few minutes of steady highway cruising. With you having over 50 degrees of timing at cruise it would also be worth a check. Probably fine with your lower compression, but still worth a look see. I also get single digit mileage and am cruising at around 3000 rpms on the highway, so I am curious to see what you get. Thanks! Chris |
Posted By: Red20
Date Posted: Jul/17/2017 at 10:56am
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I'll let you know what mileage looks like when I get through a full tank. I need to make a stop plate to limit the vacuum advance total. I'm not getting any discernible detonation, but I can feel when it's going too advanced and lugging a little. There's definitely a point of diminishing returns with ignition advance. I think I'm going to shoot for 10* total vacuum advance and see how that feels. Without a dyno, it's all by feel, but I'm pretty in tune with AMC 360s these days. ------------- 1969 Javelin SST "Screamin' Banana" - Totaled Feb 2018 1973 Hornet Sportabout X "yellajack" - 360/727/TracLoc DAILY DRIVER |
Posted By: ccowx
Date Posted: Jul/17/2017 at 1:32pm
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You might want to just take a chunk of rubber, say a kid's eraser, that fits over the pin on the vac advance can. You can make something fancier if you like later, but that is a cheap way to try it out. Make a couple with different levels of restriction and see what it likes. Thanks! Chris |
Posted By: needafasterAMX
Date Posted: Jul/18/2017 at 8:47pm
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It all looks fairly good, the only thing I did not see is the quick un-scientific exhaust test. Does your eyes and noise burn when you stick your face in the exhaust when it is running. Or the scientific way with a O2 sensor. the only way to go to get the best fuel mileage. The two quick fuel carbs that I had /have on my car where way Fat. ------------- 74 AMX, 401 Viper spec T56 6 speed trans Hydroboost brakes with rear disks from a Avenger 3:73 TG rear,now Trutrac with 3:15 A Turbo is in my future. |
Posted By: Red20
Date Posted: Jul/18/2017 at 9:05pm
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Well, since the exhaust just dumps after the mufflers, I'm gonna have to shimmy under the back end to be unscientific. And to be scientific, I haven't dropped the money on an o2 sensor, sender, and gauge, but I sure wish I had. I have a bung in the exhaust still from when I was running EFI. ------------- 1969 Javelin SST "Screamin' Banana" - Totaled Feb 2018 1973 Hornet Sportabout X "yellajack" - 360/727/TracLoc DAILY DRIVER |
Posted By: Red20
Date Posted: Jul/21/2017 at 9:35am
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I made a vacuum advance stop plate for my MSD billet distributor. It was advancing 18* (advertised 16*) and I'd really prefer about 10*. http://s1082.photobucket.com/user/frazierjoshua/media/Mobile%20Uploads/96C24515-FBA6-49F3-B83B-CB8F43A796C7.jpg.html" rel="nofollow">  BUT...I mismeasured when I trimmed the stop tab (see yellow arrow) and it now advances 17*. I just shook my head and went inside. I'll make another one later today. I'm pleased with the design though. ------------- 1969 Javelin SST "Screamin' Banana" - Totaled Feb 2018 1973 Hornet Sportabout X "yellajack" - 360/727/TracLoc DAILY DRIVER |
Posted By: Bandana
Date Posted: Jul/21/2017 at 10:13am
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Interesting modification. Never really looked how the vacuum advance works on these. I also seem to be getting too much advance from my billet and have disconnected it for now to keep from pinging. When you get yours set to limit the advance to 10 degrees can you post more detail on it? I assume you need a longer tab on the stop? |
Posted By: ccowx
Date Posted: Jul/21/2017 at 10:28am
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You could try a set up like this. Easier to adjust but the same effect. My edit is that there is no way to upload an image!!!!!!!!!!! If you want a picture of something similar to what you have that is adjustable and basically free, please PM me. Thanks! Chris PS: Yes, I have done the image upload and post many times, it is not working now. |
Posted By: Red20
Date Posted: Jul/21/2017 at 11:36am
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I emailed you, Chris. ------------- 1969 Javelin SST "Screamin' Banana" - Totaled Feb 2018 1973 Hornet Sportabout X "yellajack" - 360/727/TracLoc DAILY DRIVER |
Posted By: Red20
Date Posted: Jul/21/2017 at 11:42am
I'll take a few more pictures when I pull it off in a bit. I'm anxious to see what ccowx's solution entails. Adjustability is certainly good. As for the piece I made, it's just a piece of aluminum I cut on a scroll saw with a fine tooth wood blade. I mocked it up first in cardboard from the end flap of a 12 pack box. Probably took me 15 minutes. The rear screw for the canister is pretty short, so I counter sunk it a hair with a forstner bit. I like aluminum because if you're not going for fine finish work, a lot of wood tools will cut it just fine. ------------- 1969 Javelin SST "Screamin' Banana" - Totaled Feb 2018 1973 Hornet Sportabout X "yellajack" - 360/727/TracLoc DAILY DRIVER |
Bandana wrote:Posted By: Red20
Date Posted: Jul/22/2017 at 12:17am
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I've got it about as close as I can get to my 10* vacuum advance goal now. I made another plate and ended up 6* advance. Just the slightest touch up on the grinder and I was at 9.5*. I used my vacuum pump to ensure it travelled smoothly through the range and after a slight tweak had it good. The vacuum advance starts at about 6 in.hg and is all in by 11 in.hg. Initial is 14* mechanical plus 9.5* vacuum for 23.5* at 750 RPM idle. I'm pleased with that for now, but I haven't taken a test drive just yet. I'll probably run over to a cars and coffee cruise in tomorrow morning and see how she does. Here's the first attempt and the second side by side. http://s1082.photobucket.com/user/frazierjoshua/media/Mobile%20Uploads/8C50DFAD-9449-43D7-80DF-0F1C9D8F7CD2.jpg.html" rel="nofollow">  Here it is in the distributor. The stop arm was bowed up here from the way I wedged it into place causing the breaker plate to bind up slightly. I straightened it all out on final fitment. http://s1082.photobucket.com/user/frazierjoshua/media/Mobile%20Uploads/25D2EEEE-3039-47D6-B92F-50385F00FD64.jpg.html" rel="nofollow">  Here's the scroll saw I cut the aluminum with. My bandsaw cuts a lot more smoothly, but I didn't have a blade on it and this was quick and ready to go. http://s1082.photobucket.com/user/frazierjoshua/media/Mobile%20Uploads/8FCCA07F-AF5B-4DBF-808F-7AA7C26D96A8.jpg.html" rel="nofollow">  ------------- 1969 Javelin SST "Screamin' Banana" - Totaled Feb 2018 1973 Hornet Sportabout X "yellajack" - 360/727/TracLoc DAILY DRIVER |