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Old 06-18-2019, 09:39 PM   #1
roflcopter
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Default Weber DCOE Tuning Questions

I have done a decent bit of poking around and it's hard to come across a 'similar setup' to base any of this off of, so I'm going to appeal to the masses and see if anyone with broad experience has any input.

As was stated in the other thread, the motor in question is a B20 that has the Isky vv101 cam, 11:1 compression, and ported head, and two DCOE40s. The current setup provides 13.5 afr at 3500 RPM, leans to 16.1 afr at 5000 RPM and then slides back down to 13.0 at 6800 RPM. After digging into the carbs today I found that the main circuit is set up as follows:

choke : 30mm
main: 115
emulsion tube: f11
air corrector: 200

From my few days of reading on these carbs this deviates a LOT from what any of the rules of thumb seem to state. For a 2000cc motor (making 120-130hp) it seems something in the neighborhood of a 145 main, f16 or f2 emulsion tube, and air corrector in the 180-190 range, along with probably a 36mm choke(which would probably be even better in the DCOE45).

My question to you is this, does what is in it seem reasonable, or should I be closer to the 'guidelines' found in a lot of the weber tuning documentation?

I am not past believing that whoever set these carbs up did by purely by the seat of their pants and happened to stumble across what's in there now as a 'working' but incorrect solution.
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Old 06-19-2019, 01:47 AM   #2
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30 chokes are too small for a 2.0l engine that needs to rev over 6000 rpm. This chart (on the right) from the Weber tuning manual shows that a 36mm choke is the minimum size you'd want to use on an engine with a displacement of 500cc/cyl.



Make sure the float valves are the largest ones made. I once fought a lean issue at the top end and it turned out the float valves weren't flowing enough fuel to keep up.

Try using the setup for 45's with an F cam in the jet chart I posted in the other thread as a starting point but I think you need larger carbs (and chokes) if you want to rev the engine a lot higher than 6000 rpm.
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Old 06-19-2019, 01:54 AM   #3
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I would suggest that you go with something more like the guidelines.For 500cc per cylinder 40s are a bit small but if its what you have then go with it. A 34mm venturi with 140 mains and 180 air correctors would be a good start. Maybe JohnV can help out with a good choice for eemulsion tubes,but I would go with an f7 or f9 to start. What kind of wideband are you running? Can you get on a chassis dyno?
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Old 06-19-2019, 07:59 AM   #4
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Thanks for linking that PDF, I will get to reading! And thanks for the reassurance. I am a bit leery to to do a wholesale change up of the carb setup since the car does run currently, but knowing that other people think it's way off too makes me feel better.

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Originally Posted by bongo View Post
I would suggest that you go with something more like the guidelines.For 500cc per cylinder 40s are a bit small but if its what you have then go with it. A 34mm venturi with 140 mains and 180 air correctors would be a good start. Maybe JohnV can help out with a good choice for eemulsion tubes,but I would go with an f7 or f9 to start. What kind of wideband are you running? Can you get on a chassis dyno?
I would definitely rather run 45s but I'm not going to spend the money soon to switch over. Thanks for backing up what I *think* the car should have before I spend the money to switch everything out. All the numbers I have currently were from a chassis dyno, including the wideband readouts. I have easy access to one and the car is not street legal at all so all the tuning will happen there.

EDIT: I will also add that this is 100% a racecar, I'm not worried about street mannerisms, or even being able to have an idle under 1k. It will see nothing but road course and the occasional autocross.
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Old 06-19-2019, 08:36 AM   #5
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It's easy to get a car to run on random jets. And it's fairly easy to get it to run 'pretty good'. But to get it to run 'right' is probably an art that takes a long time to cultivate. I've been repeatedly told that the 40's on my PV 's motor are too small, but it pulls nice and hard up to about 7500 rpm, and doesn't even really drop off there, I just figure flinging cast B21 pistons around any faster probably isn't a good idea*.

I never really experimented much with the jetting on mine. I got them set up for a 'B18' (?) on eBay. A matched pair of carbs, and a manifold, and linkage. One of the carbs was missing all the jettings, so I just got matching for that and gave it a go. I had a wideband on it for a while. And it was 'pretty good', certainly some variation in mixture as you went up through the rpm range and throttle openings, but not much in the way of noticeable running issues. Although it is amusing to see it go lean in a hard left turn, rich in a hard right turn. Lol, sloshing fuel in a bowl.

That was with a more stock engine - B21 pistons, but a stock F head and a D cam, with 32mm chokes. Out of curiosity, I bought some 36mm chokes and tried them, and it didn't work well. Mostly it wuold bog badly as the throttle opened, you had to open it *slowly*. I'm assuming the engine just didn't pull enough air to make vacuum when the throttle was opened to wide at lower RPM's, and it would just do a lean bog. The 32's went back in.

Later on with the R-Sport head, 1.7:1 roller rockers and an Isky VV81 cam, I tried the 36's again, all without touching the jetting (bad practice??) and they worked very well with the increase in air flow. I'm sure there is plenty of rom for improvement - it's sneezy and snorty when the engine is cold, and the weather is cool (like, below 50?). It makes fuel smells of various intensities (I think some of it is fuel sloshing out of the vent holes? Some of it is reversion spitting fuel out the inlets, some of it is rich mixture going out the exhaust?)


* - The PV is currently sitting, waiting for a tear-down and inspection. There's low compression in #3. The same thing happened a few years ago when a chunk flaked off one of the pistons in a fairly non-destructive manner. Perhaps this time around (assuming it's another busted piston - leakdown shows it leaking into the block) maybe I should get something lighter and forged instead of stock and cast.
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Old 06-20-2019, 01:14 AM   #6
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well then by all means go bigger on the venturis! just remember that wen you go with a bigger venturi like a 36 in your 40s you will have a much weaker vacuum signal over the jets,this is often why it is hard to make them drive well in the lower rpms. road course? no problem,but you might want to keep some low end for autocross. if you are a cheap bastard like me then just chuck up the venturis in the lathe and make them whatever size you want. same with the jets,drill baby drill! solder them closed if you go to big....
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Old 06-20-2019, 04:58 PM   #7
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The plan is to just regasket them and hope that fixes all the weeping, swap to 36mm chokes, start with a 145 main with probably a 190 air corrector. I haven't decided whether the F2 or F16 e-tubes will get purchased yet, may leave the F11 in there and see how it does before spending the money. All of this will have to wait a little while as the motor is coming out this weekend so I can do some chassis work easier and get the drivetrain all cleaned up.

Another question... one of the rebuild kits that came with the car is a 175 needle valve, I'm assuming they bought what was already in the car so I should be good, but does that sound right? I've had trouble finding much info on sizing needle valves other than "if you drain the bowl, get bigger ones."

And bongo, I don't think 'cheap bastard' and vintage racecars get along too well.
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Old 06-24-2019, 01:48 PM   #8
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Motor is out and it shouldn't be too much of a pain from what I've seen so far. Once it's all put back together I'll be making a trip back to the dyno to do some real tuning...

On that note, does anyone have a 'kit' of jets/airs that they would loan out? I'm more than willing to pay a fee and replace whatever I end up using with new stock, I'm just trying to avoid sinking $$$ into parts that will sit in the drawer forever when they turn out to be wrong.
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Old 08-09-2019, 02:46 PM   #9
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Bumping this back up to the top due to issues...

I got everything rebuilt and back together. Went with 145 mains, 180 air correctors, 36mm chokes. Took it back to the dyno and the AFR sniffer was saying 14.1:1 AFR at WOT but still making right at 120whp, so we drilled them up to about a 155 and that brought it into the low 13s which I was happier with, but we leaned it back out a tad by putting the 200 air correctors back in. Fuel was good per the gauge and the 36mm chokes should have been flowing more, but we were still making 120whp (at 5200RPM mind you). After lots of head scratching and thinking I decided to play with timing more, we swept base timing all the way from 5 degrees to 22 degrees and the car made within 3hp at all points. This makes no sense to me. I called it a night and went home.

After going through everything in the car yesterday I was going to head back to the dyno and see if we could find anything else at all, on the way I had the idea that maybe the P.O. had the cam a tooth off to try and gain low end torque for autocross. Pulled the cover and it is set straight up. I may pull it all apart again and make sure there isn't an offset key in there or something. But basically this is where I am currently:

-Fueling looks correct, plugs seem to agree
-Timing set to what it should be, plugs seem to agree
-Centrifugal advance is working properly
-Cam seems to be timed correctly
-Peak torque is at 4300rpm, peak power is at 5200rpm

Is this all I can reasonably expect? I would that thought this cam (vv101) would have pushed things up higher in the rev band. Any clues as to why changing timing doesn't seem to affect power much?
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Old 08-10-2019, 01:37 AM   #10
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Restrictive exhaust? What are you running? Are you using an airbox? Velocity stacks? Did you check the cam to make sure that it has the advertised lift etc? Three year old fuel? An extra 4 quarts of oil in it? 700# triple valve springs? Unfortunately you may be about out of carb I think.
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Old 08-10-2019, 10:26 AM   #11
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Tri-Y header, 2.5" exhaust with a high flow muffler, no filters with just the velocity stacks, measured lift to be as advertised (need to actually degree it and make sure it's timed right and is as advertised), fuel is brand new VP110, oil is good, it does have double valve springs and all the chromoly stuff (basically the chevy kit).

I didn't think it would be possible to run out on the DCOE40s at 120whp... aren't there people making more?
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Old 08-10-2019, 02:42 PM   #12
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I think a drag speed calculator indicated mine had about 160 - 165 hp at the rear wheels. Figuring 2350 lbs with me in it. I've never put it on a dyno, though.
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Old 08-10-2019, 09:11 PM   #13
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I think the problem is that, according to this calculator your dynamic compression ratio is ~7:1 with that cam. Either get a cam with less overlap or mill the head to 14:1 or more. That will get the dynamic compression up to 9:1.
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Old 08-12-2019, 09:44 PM   #14
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I am also leaning towards the cam being the problem... the power band does not make sense for what it should be doing.

Today I did what I could with the motor in the engine bay, first to see if maybe an offset key was being used, then to verify what I thought was in the car. I'm not 100% sure this is a vv101 anymore, and if it is, it is dead.

Measured lobe centers at 111 (111-113 depending on where you call it, tough in the car) which matches what the vv101 should be, but the lift is wayyy less than advertised at 0.435", measured duration at 0.050" was 308, which is larger than the real world numbers I have seen for this cam. Do you think it has been swapped or just a very tired example?

I went through the spare parts that came with the car and dug out the other came that came with it. I do not have any angle measurements but the events appear far apart to the eye (lots of LSA) and the measured lobe height is 0.0395", which should add up to roughly 0.566" lift with the 1.5 rockers and lash taken into account. I will get my v-blocks back from my friend and see what the angles look like on it soon hopefully. Any thoughts on this cam? I'm assuming it's a regrind of some sort, but that lift is HUGE from what I've seen for these engines.
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Old 08-19-2019, 02:39 PM   #15
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I'm going to piggy back on this thread as long as it's relevant, otherwise I'll start my own thread. I've cross posted this on various Facebook group pages as well to get some input from the Swedish tuners as well.

I'm preparing to break in my metric 8 bolt B20 big bore 2130cc engine with stage two cylinder head (injected head with bigger intake valves, worked over combustion chamber and revised exhaust ports, and single high rev springs), 9.5 compression, KG Trimming KG10 camshaft, 123 programmable distributor and Weber 45 DCOE's on long runner intake manifolds. This is mated to an M41, stock ratio rear end, with 205/60 tires. Using standard NGK BP6HS plugs with factory gaps and Bosch blue coil, I may use my my Bosch distributor for break in until I completely understand how to use the 123 distributor. I also set initial lash on both intake and exhaust side to .018 since I really don't know what this engine should be set to and the head will be getting torqued again after break in.

The idea for this engine and car is reasonable daily driver characteristics on crappy California 91 pump gas. The car will be used for a moderate 40 minute round trip commute a couple days a week and eventually longer weekend tours to southern and northern California, perhaps even a tour up 395 when I feel comfortable enough with the car.

As far as the DCOE's are concerned these came from the off the shelf conversion kit but being as I'm a Redline Weber dealer I have an infinite amount of parts at my disposal. The standard conversion specifications are based on a compromise of installing this kit on either a standard B18 or B20 which obviously this is slightly more in every respect. Standard specs are as follows: Main Venturi 36mm, Secondary Venturi 4.5mm, Emulsion Tube F16, Main Jet 145, Air Correction 155, Idle F60/8. It's also recommend to set floats to 14mm drop with 2mm needle set. Standard air horns are 2.5 inches but I'll be installing 1.5 inch horns for daily use with an ITG filter ( I also have a set of 5 inch horns with screens but I would imagine using these even for fun would require a rejet).

Right off the bat I can see some issues with the base setup but inputs would be greatly appreciated.

Ian and Eric, what could I bribe you with to come up to San Luis Obispo and spend a day tuning my car? I have a 4 gas analyzer at my shop ;o)
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Old 08-20-2019, 12:08 PM   #16
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Quote:
Originally Posted by R32RennSport View Post
Ian and Eric, what could I bribe you with to come up to San Luis Obispo and spend a day tuning my car? I have a 4 gas analyzer at my shop ;o)
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Old 08-20-2019, 12:18 PM   #17
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Quote:
Originally Posted by hiperfauto View Post
I think the problem is that, according to this calculator your dynamic compression ratio is ~7:1 with that cam. Either get a cam with less overlap or mill the head to 14:1 or more. That will get the dynamic compression up to 9:1.

This x 1000
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Old 08-20-2019, 03:53 PM   #18
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Quote:
Originally Posted by John V, outside agitator View Post
This x 1000
Question...

When I run the numbers for that calculator I get 8.97:1... would you guys be willing to post what numbers you used?
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Old 08-20-2019, 04:14 PM   #19
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What does a compression gauge say? Although I guess most of those are probably inaccurate to some degree.
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Old 08-20-2019, 04:49 PM   #20
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The numbers I used assumed you had the VV101 cam. The calculator says to use seat to seat valve timing numbers for best results but the closest I could find were valve events @ .020" lift using this site for reference. That means that dynamic compression is actually a bit lower.



Using the numbers for a VV71 it works out to 8.90:1.
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Old 08-20-2019, 05:03 PM   #21
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Quote:
Originally Posted by hiperfauto View Post
The numbers I used assumed you had the VV101 cam. The calculator says to use seat to seat valve timing numbers for best results but the closest I could find were valve events @ .020" lift using this site for reference. That means that dynamic compression is actually a bit lower.



Using the numbers for a VV71 it works out to 8.90:1.

Yep that's my favorite calculator except that everything is in some units made up based on a mythological kings thumb ferfawkssake.....

What's nice with that is you can keep banging in numbers till you get dynamic up to high 9s maybe 10:1---then see whatchoo need for "static" to get that number.
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Old 08-20-2019, 05:22 PM   #22
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Well now that's quite handy, thanks!
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Old 08-20-2019, 06:53 PM   #23
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I got the rod length wrong. It's 5.7" not 5.71" but it made no difference in the calculation.

Edit:

Then again maybe not. 6 bolt crank rods are 5.7", 8 bolt crank rods are 5.713".



Looking at the specification books again it's just a conversion error. They're both supposed to be 145mm.

Last edited by hiperfauto; 08-20-2019 at 07:03 PM..
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Old 08-26-2019, 01:06 PM   #24
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Ah okay, I was missing the seat-to-seat part of that.

I'm going to do a little more research and come up with a plan. The owner from the PNW says the car definitely had the vv101 in it when he sold it (he pulled a vv71 out to put the vv101 in) and he also said the guides have been cut down, but not the spring seats, for clearance. I wonder if that extra little lift on the U cam would cause issues there... If I can get away without pulling the head and machine work for the time being that would be ideal, I'm sure the motor will need a refresh in a couple of seasons anyways.
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Old 08-26-2019, 01:12 PM   #25
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I setup my 45 DCOEs last night for what I think will be ball park settings based on multiple other setups that are near my engine. I'll report back with numbers as soon as I have them. Specs as follows:

37mm chokes
150 main
200 air
60 idle
200 needle/seat
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