grtskydog
04-04-2009, 02:47 PM
Summit Carb Part 3: Driving Test
First off, my apologies for how long it’s taken to finish this review. A little back story: The original Summit carburetor (from the first 2 Parts of the review) had to be sent back. The rear bowl was flooding and could not be adjusted down. I cleaned the float valves, and even replaced them with some known good ones from my personal bin. No luck. I tried clearing the passages again, and still no luck. After a discussion with a Tech at Summit, we concluded it would be best to just send it back and get a replacement. I’m not sure, but I suspect a culprit was clogging something, or allowing fuel to seep past the float valve.
The new carburetor arrived March 20th, and I gave it the same inspection I did the last one. This time, I noticed the machining/casting seemed to be much better. There was no trash in the bowls, and the baseline mixture/idle settings were more realistic…1 ¼ turns out per side, with a “square” transfer slot showing under the throttles.
I mounted the carb as shown, routing the fuel line behind the carb and around to the pump. On initial startup, fuel was spewing from the primary flared fitting, and from the flare-to-3/8 nipple at the back (arrows).
http://i249.photobucket.com/albums/gg218/grtskydog/Summit%20carb%203/initialmount.jpg
Post-mortem on the Summit fuel line showed no obvious defects where the flare sealed, but who knows. I may have gotten the 1 in 100, or 1 in 1,000 bad ones that didn’t get flared properly.
Seen below is my solution. Note the rubber line going around the carb. This is only temporary, as I plan to run AN fittings and braided line in its place, should all go well.
http://i249.photobucket.com/albums/gg218/grtskydog/Summit%20carb%203/russelline.jpg
I used an Innovate LM-1 wideband A/F reader to record idle, cruise, and wide-open throttle conditions. I also have their RPM converter, but unfortunately I had trouble getting it to work. I tried several solutions using their forums to troubleshoot, but no luck. When you’re talking about potentiometers and calibration with computer audio output (and it still doesn’t work), then you need to take a step back and re-examine your product…rant over.
http://i249.photobucket.com/albums/gg218/grtskydog/Summit%20carb%203/innovate.jpg
Startup and idle--
Notwithstanding the first attempt, the Russell line performed flawlessly upon the next startup. Fast idle went to 2,000 RPM, and with a tap of the throttle immediately went to 1,500 RPM…perfect. The float levels (easy to see in the big sight glasses) were a tad high and only required about a half-turn to correct. The idle mixtures were a little on the lean side and required about 1/8 turn each to get better manners. All told, the wideband was showing 13.5-14:1 and the engine idled with 17” vacuum.
http://i249.photobucket.com/albums/gg218/grtskydog/Summit%20carb%203/idlefloats.jpg
Road test #1: Box stock settings—
With the idle squared away, it was time to hit the road. It was a sunny 59º day and Coastal North Carolina is pretty much sea level. Throttle response was very crisp…no doubt thanks to the annular boosters. It really reminded me of the way a well-tuned 4180 can run. On light throttle shifts, there was a very slight rich bog. I could see the wideband dip down into rich territory when I shifted, but under slightly more aggressive throttle, the bog was non-existent. The stock accelerator pump nozzles were #35 on mine. I could try a smaller shot. Otherwise, little if any tuning will be required here.
Low-speed cruise was done at 40 MPH and 2,000 RPM. A/F ratio was just under 13:1 at this speed in 4th gear. Next I tested highway cruise, running at 65 MPH and just over 2,000 rpm in overdrive. On a level stretch of road, the wideband was showing between 13.5 and 14:1. Good…maybe a tad rich. Some may say spot on for a carb. Vacuum showed an average 15” in highway cruise.
Here’s a pic of the Innovate data logged on the first WOT run. I let off at 5k as I didn’t want to hit any kind of real speed in 3rd gear. The red graphics are added by me as notes. You can see for yourself where the secondaries come on as it gets rich again, then starts to lean out at the top. I’ve seen better and worse curves, but all-in-all not too bad out of the box. The stock jetting is 67 in front, 73 in back.
http://i249.photobucket.com/albums/gg218/grtskydog/Summit%20carb%203/WOT10.jpg
Road Test #2: Slight tuning
Based on the earlier test run, I decided to go leaner in primary mains and delay the secondary opening a little more. I went with 65 jets and a brown spring from my tuning kit. The jet change/spring swap happens simultaneously, since with the air horn off, all 4 screws on the secondary spring housing are accessible. Loosening the choke to get the rod free is a pain, but after a few times, you submit and get used to it. At the top of the pic you can see where the air horn just flops out of the way (with flexible fuel line). The red arrow shows the only fuel I spilled changing the jets and spring.
http://i249.photobucket.com/albums/gg218/grtskydog/Summit%20carb%203/jetswap.jpg
The road driving showed a leaner mixture this time as expected. Conditions were 72º and sunny. 4th gear cruise (2,000 rpm) went between 13.2 and 13.5. Highway cruise in overdrive bounced between 14.2 and 15.1, with uphill climbs creeping up to 16:1. If the car was to be kept with this jetting, a 9.5 (stock is 6.5) power valve would definitely be in order to keep away from that lean condition.
Here is the second WOT run, again up to 5,000 RPM for safety’s sake. Notice the black line. On this run I had the RPM converter connected, and even though it read double my actual RPM, I was able to use the data (notice my “corrections”). I was using the record feature and had no idea the RPM data was logging. You can see this is a leaner run. The a/f ratio went from 12.7 to 13.2 at the top with just 2 jet sizes on the primary alone. This is a bit lean if you try to imagine this curve going to 6,000 RPM. The stock jetting might not be that far off after all. With the wideband data logging capability, and the fickle yet usable RPM data, I’m going to have a lot of fun playing with this carb.
http://i249.photobucket.com/albums/gg218/grtskydog/Summit%20carb%203/WOT22.jpg
Daily Driver notes—
After the initial driving and tuning, the car sat for a week and a half. I went out one evening to fool with the RPM converter some more. Conditions were 61F with high moisture from on-and-off rain. I pressed the gas once to close the choke and turned the key. The engine fired up instantly, right to 2K, and with another tap down to 1500 RPM...just beautiful. I let the engine get up to operating temp (185º) while I was attempting to tune the RPM channel. The idle A/F showed 12.5:1, even when warmed up. I shut it off and let it sit for about 10 minutes to let it heat soak. With a turn of the key (didn’t touch the gas) it fired right back up. This time A/F was closer to the 14:1 I set, with no adverse idle issues from the heat-soak. All I used was the provided insulator gasket…no heat shield. It displayed very nice manners. I also drove the car on my 10 mile commute to the airport. This is mostly highway speeds, using the jetting from run #2, and with no ill effects.
The Good, the Bad, the Ugly: A Summary
The Good: First and foremost, this is a very nice driving carburetor. I have a well-tuned, fairly mild (280-300 fwhp) 5-liter, and this carburetor does it justice. I never sensed that the carb was holding back the engine…it just kept pulling. Plus I think that the jetting is pretty appropriate right out of the box, at least for my combo. For me, Summit has always had a nice no-hassle customer support system. Returning the first carb was a no-questions-asked deal. I even got an email from their tech support checking to see if the replacement they sent was cutting it. Another obvious advantage is the carb’s simple design. With the exception of swapping power valves, tuning is a spill-free affair. As already mentioned most parts are Holley interchange, with the model-specific parts like gaskets, air bleeds, and fuel lines sold by Summit.
The Bad: None of these are really “bad” as it were, but they are things I would like to have seen. First, it would be nice to have screw-in bleeds in the power valve channel to allow this circuit to be tunable. Maybe there will be a version 2.0. In addition, I would like to see them take a page from the Edelbrock manual and make it a little easier to pull the air horn off. With the Holley design, however, I’m not sure how it could be done without redesigning the choke rod linkage altogether. Also, the included fuel feed line seems to be a hit-n-miss affair. The first one I had didn’t leak, the second one did.
The Ugly: As indicated in earlier parts, some casting imperfections can be found. I find, especially with aluminum parts, that this stuff can be “buffed out” so to speak. I had to remind myself that it’s not a $400 carb, so don’t expect a $400 finish. In the spirit of my venerable 5.0 GT, it is a “bang for the buck” product in which I found a nice amount of bang.
That’s it folks. I hope that this little review helped you if you’re trying to decide on a carburetor. Maybe you were just curious, and you learned a thing or two about the inner workings of this product. Please keep in mind that I had a hit-n-miss experience that required an exchange. You might also, but you might not. I can only hope mine was more of an exception than the rule, and that the majority of them are like the one I have now. In case you are wondering, I have decided to leave this carb on my car. No good review is complete without a more long-term test…right? Besides, I love the way it drives. I personally hope this line of carburetors enjoys much success, and that future parts and improvements come down the road someday. I have a few ideas myself.
First off, my apologies for how long it’s taken to finish this review. A little back story: The original Summit carburetor (from the first 2 Parts of the review) had to be sent back. The rear bowl was flooding and could not be adjusted down. I cleaned the float valves, and even replaced them with some known good ones from my personal bin. No luck. I tried clearing the passages again, and still no luck. After a discussion with a Tech at Summit, we concluded it would be best to just send it back and get a replacement. I’m not sure, but I suspect a culprit was clogging something, or allowing fuel to seep past the float valve.
The new carburetor arrived March 20th, and I gave it the same inspection I did the last one. This time, I noticed the machining/casting seemed to be much better. There was no trash in the bowls, and the baseline mixture/idle settings were more realistic…1 ¼ turns out per side, with a “square” transfer slot showing under the throttles.
I mounted the carb as shown, routing the fuel line behind the carb and around to the pump. On initial startup, fuel was spewing from the primary flared fitting, and from the flare-to-3/8 nipple at the back (arrows).
http://i249.photobucket.com/albums/gg218/grtskydog/Summit%20carb%203/initialmount.jpg
Post-mortem on the Summit fuel line showed no obvious defects where the flare sealed, but who knows. I may have gotten the 1 in 100, or 1 in 1,000 bad ones that didn’t get flared properly.
Seen below is my solution. Note the rubber line going around the carb. This is only temporary, as I plan to run AN fittings and braided line in its place, should all go well.
http://i249.photobucket.com/albums/gg218/grtskydog/Summit%20carb%203/russelline.jpg
I used an Innovate LM-1 wideband A/F reader to record idle, cruise, and wide-open throttle conditions. I also have their RPM converter, but unfortunately I had trouble getting it to work. I tried several solutions using their forums to troubleshoot, but no luck. When you’re talking about potentiometers and calibration with computer audio output (and it still doesn’t work), then you need to take a step back and re-examine your product…rant over.
http://i249.photobucket.com/albums/gg218/grtskydog/Summit%20carb%203/innovate.jpg
Startup and idle--
Notwithstanding the first attempt, the Russell line performed flawlessly upon the next startup. Fast idle went to 2,000 RPM, and with a tap of the throttle immediately went to 1,500 RPM…perfect. The float levels (easy to see in the big sight glasses) were a tad high and only required about a half-turn to correct. The idle mixtures were a little on the lean side and required about 1/8 turn each to get better manners. All told, the wideband was showing 13.5-14:1 and the engine idled with 17” vacuum.
http://i249.photobucket.com/albums/gg218/grtskydog/Summit%20carb%203/idlefloats.jpg
Road test #1: Box stock settings—
With the idle squared away, it was time to hit the road. It was a sunny 59º day and Coastal North Carolina is pretty much sea level. Throttle response was very crisp…no doubt thanks to the annular boosters. It really reminded me of the way a well-tuned 4180 can run. On light throttle shifts, there was a very slight rich bog. I could see the wideband dip down into rich territory when I shifted, but under slightly more aggressive throttle, the bog was non-existent. The stock accelerator pump nozzles were #35 on mine. I could try a smaller shot. Otherwise, little if any tuning will be required here.
Low-speed cruise was done at 40 MPH and 2,000 RPM. A/F ratio was just under 13:1 at this speed in 4th gear. Next I tested highway cruise, running at 65 MPH and just over 2,000 rpm in overdrive. On a level stretch of road, the wideband was showing between 13.5 and 14:1. Good…maybe a tad rich. Some may say spot on for a carb. Vacuum showed an average 15” in highway cruise.
Here’s a pic of the Innovate data logged on the first WOT run. I let off at 5k as I didn’t want to hit any kind of real speed in 3rd gear. The red graphics are added by me as notes. You can see for yourself where the secondaries come on as it gets rich again, then starts to lean out at the top. I’ve seen better and worse curves, but all-in-all not too bad out of the box. The stock jetting is 67 in front, 73 in back.
http://i249.photobucket.com/albums/gg218/grtskydog/Summit%20carb%203/WOT10.jpg
Road Test #2: Slight tuning
Based on the earlier test run, I decided to go leaner in primary mains and delay the secondary opening a little more. I went with 65 jets and a brown spring from my tuning kit. The jet change/spring swap happens simultaneously, since with the air horn off, all 4 screws on the secondary spring housing are accessible. Loosening the choke to get the rod free is a pain, but after a few times, you submit and get used to it. At the top of the pic you can see where the air horn just flops out of the way (with flexible fuel line). The red arrow shows the only fuel I spilled changing the jets and spring.
http://i249.photobucket.com/albums/gg218/grtskydog/Summit%20carb%203/jetswap.jpg
The road driving showed a leaner mixture this time as expected. Conditions were 72º and sunny. 4th gear cruise (2,000 rpm) went between 13.2 and 13.5. Highway cruise in overdrive bounced between 14.2 and 15.1, with uphill climbs creeping up to 16:1. If the car was to be kept with this jetting, a 9.5 (stock is 6.5) power valve would definitely be in order to keep away from that lean condition.
Here is the second WOT run, again up to 5,000 RPM for safety’s sake. Notice the black line. On this run I had the RPM converter connected, and even though it read double my actual RPM, I was able to use the data (notice my “corrections”). I was using the record feature and had no idea the RPM data was logging. You can see this is a leaner run. The a/f ratio went from 12.7 to 13.2 at the top with just 2 jet sizes on the primary alone. This is a bit lean if you try to imagine this curve going to 6,000 RPM. The stock jetting might not be that far off after all. With the wideband data logging capability, and the fickle yet usable RPM data, I’m going to have a lot of fun playing with this carb.
http://i249.photobucket.com/albums/gg218/grtskydog/Summit%20carb%203/WOT22.jpg
Daily Driver notes—
After the initial driving and tuning, the car sat for a week and a half. I went out one evening to fool with the RPM converter some more. Conditions were 61F with high moisture from on-and-off rain. I pressed the gas once to close the choke and turned the key. The engine fired up instantly, right to 2K, and with another tap down to 1500 RPM...just beautiful. I let the engine get up to operating temp (185º) while I was attempting to tune the RPM channel. The idle A/F showed 12.5:1, even when warmed up. I shut it off and let it sit for about 10 minutes to let it heat soak. With a turn of the key (didn’t touch the gas) it fired right back up. This time A/F was closer to the 14:1 I set, with no adverse idle issues from the heat-soak. All I used was the provided insulator gasket…no heat shield. It displayed very nice manners. I also drove the car on my 10 mile commute to the airport. This is mostly highway speeds, using the jetting from run #2, and with no ill effects.
The Good, the Bad, the Ugly: A Summary
The Good: First and foremost, this is a very nice driving carburetor. I have a well-tuned, fairly mild (280-300 fwhp) 5-liter, and this carburetor does it justice. I never sensed that the carb was holding back the engine…it just kept pulling. Plus I think that the jetting is pretty appropriate right out of the box, at least for my combo. For me, Summit has always had a nice no-hassle customer support system. Returning the first carb was a no-questions-asked deal. I even got an email from their tech support checking to see if the replacement they sent was cutting it. Another obvious advantage is the carb’s simple design. With the exception of swapping power valves, tuning is a spill-free affair. As already mentioned most parts are Holley interchange, with the model-specific parts like gaskets, air bleeds, and fuel lines sold by Summit.
The Bad: None of these are really “bad” as it were, but they are things I would like to have seen. First, it would be nice to have screw-in bleeds in the power valve channel to allow this circuit to be tunable. Maybe there will be a version 2.0. In addition, I would like to see them take a page from the Edelbrock manual and make it a little easier to pull the air horn off. With the Holley design, however, I’m not sure how it could be done without redesigning the choke rod linkage altogether. Also, the included fuel feed line seems to be a hit-n-miss affair. The first one I had didn’t leak, the second one did.
The Ugly: As indicated in earlier parts, some casting imperfections can be found. I find, especially with aluminum parts, that this stuff can be “buffed out” so to speak. I had to remind myself that it’s not a $400 carb, so don’t expect a $400 finish. In the spirit of my venerable 5.0 GT, it is a “bang for the buck” product in which I found a nice amount of bang.
That’s it folks. I hope that this little review helped you if you’re trying to decide on a carburetor. Maybe you were just curious, and you learned a thing or two about the inner workings of this product. Please keep in mind that I had a hit-n-miss experience that required an exchange. You might also, but you might not. I can only hope mine was more of an exception than the rule, and that the majority of them are like the one I have now. In case you are wondering, I have decided to leave this carb on my car. No good review is complete without a more long-term test…right? Besides, I love the way it drives. I personally hope this line of carburetors enjoys much success, and that future parts and improvements come down the road someday. I have a few ideas myself.