ryant67 Posted September 12, 2016 Share Posted September 12, 2016 It will be really interesting to see what sort of numbers you achieve with the 45's, since theoretically the 40's have been holding your engine back a little. Here's hoping you get some good luck going this time and everything works out! Quote Link to comment Share on other sites More sharing options...
Leon Posted September 13, 2016 Share Posted September 13, 2016 Thanks for the cam gear tip, Mark! I'd guess there won't be much power difference between 40mm and 41mm venturis as I believe the restriction at the butterfly is effectively a 40mm venturi. Would definitely be interesting to see the results! Quote Link to comment Share on other sites More sharing options...
zredbaron Posted September 13, 2016 Author Share Posted September 13, 2016 (edited) Anytime! Regarding the 40-41mm venturi, I don't expect much difference either. I still reference this Weber chart, particularly the note about aux. venturi performance. (EDIT -- comment about carb body's exit removed, as I was mixing up the numbers with the 40mm carb body.) I have no idea how accurate my "209 cfm per cylinder" flowbench measurement from yesteryear is. A 5-10% variance between that and the chart would translate to a + 2mm venturi size accuracy. That's a blind guess, so it renders this chart conceptual. It's still nice to know that, in theory, around 39mm you're starting to get all that you can out of the 45mm carb body. Road testing will quickly determine which > 39mm venturi offers the most mid-range drivability, no doubt. Edited September 13, 2016 by zredbaron Quote Link to comment Share on other sites More sharing options...
steve260z Posted September 13, 2016 Share Posted September 13, 2016 Regarding the PDF above, is there another graph showing the "signal"? It references a 50% signal drop going from 36s to 34s. Quote Link to comment Share on other sites More sharing options...
zredbaron Posted September 13, 2016 Author Share Posted September 13, 2016 (edited) Nope. The image came from the internet, but I own the book as well and can confirm that's all we get. There's one other potentially useful graph, which bases venturi selection on cylinder displacement and peak horsepower RPM. The numbers on the chart are lower than what road race engines use, so it too is more interesting than useful for our purposes. I feel the book(s) could provide a LOT more charts, to include distinction between "street" charts and "maximum performance" charts. In my experience those that tinker on carbs do not value books very much past initial familiarization, because, well, that's all they're useful for. (EDIT: In practice, what matters is what works, not why. "Why" fosters improvement; knowing what works fosters repetition.) Perhaps this is part of why the carburetor books "lack" tangible, scientific data relative to other industries in the information age? (EDIT: Yes, fuel injection, I know. Carbs are still purchased new!) Carburetor "theory" without solid carburetor "data" decades after the theory was written? Hard to improve if we never circle back with upgraded, modern perspectives. Doesn't seem like the industry is interested in such a thing, either. Sounds like our government! I digress... Edited September 14, 2016 by zredbaron Quote Link to comment Share on other sites More sharing options...
T-Bone028 Posted September 14, 2016 Share Posted September 14, 2016 (edited) Glad to see this build still going. Really looking forward to seeing dyno results between the 40 and 45's, along with the change in venturis. Maybe this is already widely known...but one thing I found was that there is an ebay seller that doesnt say it's Pierce Manifolds out of California, but I'm pretty sure they are based on the shipping label. The price difference between the pierce manifolds website and the ebay store were close to 30-40% less. Havent checked ebay lately, but might be worth poking around if you want to buy a couple of different main venturi sizes. At ~$25/per, it gets expensive! Edited September 14, 2016 by T-Bone028 Quote Link to comment Share on other sites More sharing options...
steve260z Posted September 14, 2016 Share Posted September 14, 2016 Yea, that sounds familiar to me as well. Regarding the graph, I'm running 36s in my DCOE 40s and think I have some 34s round here. I'll have to put those in and see the difference ...see if power remains the same but response quickens up. Quote Link to comment Share on other sites More sharing options...
bajcsi Posted September 15, 2016 Share Posted September 15, 2016 (edited) In my build, I started with 36mm with the 40DCOE and settled on 32 after working my way down. High compression stroker build (12:1 with e31, electromotive hpx ignition, etc.) - I didn't go with nearly as much cam as OP. I'm also running fairly retarded with 26 degrees all in so I can run on pump gas most of the time and adjust for 104. I found the 32's far more drivable for around town and plenty fun with auto-x. On pump gas I still got decent dyno results as well, 222/220 rwhp/rwtq. If I were down at VIR with it, sure, I'd go bigger. But honestly for around town and entrainment on country roads the 40/32 combo has been pretty satisfying compared to the 34s or 36s. Yea, that sounds familiar to me as well. Regarding the graph, I'm running 36s in my DCOE 40s and think I have some 34s round here. I'll have to put those in and see the difference ...see if power remains the same but response quickens up. Edited September 15, 2016 by bajcsi Quote Link to comment Share on other sites More sharing options...
steve260z Posted September 15, 2016 Share Posted September 15, 2016 In my build, I started with 36mm with the 40DCOE and settled on 32 after working my way down. High compression stroker build (12:1 with e31, electromotive hpx ignition, etc.) - I didn't go with nearly as much cam as OP. I'm also running fairly retarded with 26 degrees all in so I can run on pump gas most of the time and adjust for 104. I found the 32's far more drivable for around town and plenty fun with auto-x. On pump gas I still got decent dyno results as well, 222/220 rwhp/rwtq. If I were down at VIR with it, sure, I'd go bigger. But honestly for around town and entrainment on country roads the 40/32 combo has been pretty satisfying compared to the 34s or 36s. Good numbers on 26 degrees, I'll try my 34s or 32s. Its one of the two I have on hand. Quote Link to comment Share on other sites More sharing options...
zredbaron Posted September 15, 2016 Author Share Posted September 15, 2016 (edited) Thanks for sharing your experiences! I also experimented with 34s and 36s with my 40 DCOEs. I thoroughly expected to find the 34mm to be the overall winner. For my engine, though the 34mm did offer some bonus drivability, the 36mm wasn't different enough down low. Both performed and sounded gargly down low. Top end was more impactful, so I went with 36mm. Volumetric Efficiency... Header selection, port work and cam selection probably accounts for the bulk of the difference between our experiences. I also run race gas, not pump gas. Possibly a factor? Not a chemist. In theory, early next week Joe will be ready for me to schedule our time on the dyno. Just sent him the motor mounts. Edited September 15, 2016 by zredbaron Quote Link to comment Share on other sites More sharing options...
zredbaron Posted September 19, 2016 Author Share Posted September 19, 2016 (edited) Final assembly pics before engine dyno. Getting close! The second pic shows that Joe "pinned" the intake manifold to the head to ensure the ports are aligned. (The purple marking.) Pretty slick. Perhaps that's a technique commonly found in comparable engines... but it's the first I've seen it? Edited September 19, 2016 by zredbaron Quote Link to comment Share on other sites More sharing options...
Leon Posted September 19, 2016 Share Posted September 19, 2016 Final assembly pics before engine dyno. Getting close! The second pic shows that Joe "pinned" the intake manifold to the head to ensure the ports are aligned. (The purple marking.) Pretty slick. Perhaps that's a technique commonly found in comparable engines... but it's the first I've seen it? Looking good, is that a Mikuni manifold? Rebello pinned my intake as well, it's pretty common in the race engine world. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted September 19, 2016 Share Posted September 19, 2016 Seem to recall it's a Cannon manifold, has the cast balance tube integrated. Quote Link to comment Share on other sites More sharing options...
zredbaron Posted September 19, 2016 Author Share Posted September 19, 2016 Yes, both are identical Cannon manifolds (except for 40/45mm respective port matching). Quote Link to comment Share on other sites More sharing options...
Leon Posted September 19, 2016 Share Posted September 19, 2016 Yes, both are identical Cannon manifolds (except for 40/45mm respective port matching). Interesting, it looks much shorter in the photo, must be the perspective. Quote Link to comment Share on other sites More sharing options...
zredbaron Posted September 26, 2016 Author Share Posted September 26, 2016 Dyno day is set for next Thursday, October 6th.... Quote Link to comment Share on other sites More sharing options...
zredbaron Posted September 26, 2016 Author Share Posted September 26, 2016 P.S. Very excited to have friend, competitor and comrade Jon Mortensen in attendance! Quote Link to comment Share on other sites More sharing options...
JMortensen Posted September 26, 2016 Share Posted September 26, 2016 I can't wait to see what it does. Quote Link to comment Share on other sites More sharing options...
Rob L Posted September 26, 2016 Share Posted September 26, 2016 I'm rooting for you ...hopefully you will have a video for us to watch Quote Link to comment Share on other sites More sharing options...
TimO Posted September 27, 2016 Share Posted September 27, 2016 Good luck on the dyno. You should have some really good numbers!!! Can't wait to see your results. Quote Link to comment Share on other sites More sharing options...
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