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I would use the 195's because of the rising AFR at high rpm with the 210's in 4th gear. My tests have always been up to about 7000 rpm and I have always seen a falling AFR above peak HP with Webers with reasonably correct jetting.

It is interesting that you are much leaner in 4th gear than in 3rd. I have seen that but not as pronounced and it is the reason that I after doing a lot of tuning runs in 3rd gear I do one in 4th to make sure that I do not have a high rpm lean situation. Are you using a high capacity fuel pump and regulator?
 

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Following with interest. Just to clarify, one needs a laptop in the car to log. Correct?
 

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The shape of the curve with the 210s mimics the shape of the curve with the 195s. The second (210) graph above is misleading for the fourth gear run as I had to let off at about 5600. If the run had continued, the slope would have become negative above 5700 or so.

My tests have always been up to about 7000 rpm and I have always seen a falling AFR above peak HP with Webers with reasonably correct jetting.
Good to know that the behavior of the Dellortos is similar to Webers. Maybe this engine with 32mm venturis and small exhaust makes peak HP around 5600? Lower than I expected, if that is the case.

It is interesting that you are much leaner in 4th gear than in 3rd. I have seen that but not as pronounced and it is the reason that I after doing a lot of tuning runs in 3rd gear I do one in 4th to make sure that I do not have a high rpm lean situation. Are you using a high capacity fuel pump and regulator?
The curves in fourth gear are certainly flatter than third. A possible, partial explanation is that I have not be able to run the engine to 6500+ in fourth. I expect the AFR would continue to decrease at engine speeds above 6200.

The pump is rated for 30 gph. I confirmed fuel volume output when it was installed two years ago. Last week, the rear fuel filter and the front filter-regulator were replaced to address an intermittent fuel starvation issue. The new filter-regulator is a Filter King with the 67mm bowl and is set for 3psi. There have been no starvation symptoms since those changes however it has not been 95 degrees over the past several days so vapor lock is still a possibility. I don't think fuel delivery issues are currently impacting AFRs.
 

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Hope it's ok if I join in....
I can't log data but I can get it. I recorded my screen of the 123 during my runs and recorded the afr's with a tach. Pretty southern but cheaper than a laptop.
At 6500 in 3rd I have 13.7 which is lean obviously and the advance is 37 degrees. If I backed it off to 35 which I think I should do anyway will that change the afr numbers? !'m running 135 mains, 50f8 idle, and 210 AC.
200s are going in next and back off the timing to 35. Thoughts? Thanks
 

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200s are going in next and back off the timing to 35. Thoughts? Thanks
That is what I would do. Ignition timing should have little if any impact on AFR.
 

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Thanks Ed, always nice to have confirmation. I did back off to 35 max and brought it in with [email protected], [email protected], and [email protected] The 200's done good.
4th gear cruise [email protected] cruise
3rd gear [email protected]
2nd gear [email protected]
3rd gear progression
[email protected]
[email protected]
[email protected]
[email protected]
Not as good as logging but stepping frame by frame in my editing program got me there. Now only if the guys at 123 or the afr folks would BlueTooth all this data and bring it into one unit we'd be sitting pretty. btw I got 10 Fine-Thread 18-8 Stainless Steel Thin Hex Nut, M10 x 1 mm Thread from McMaster for the windage tray and they worked great in lieu of the pal nuts on the main caps. Also got longer 7mm bolts for the oilpan to make up for the thickness of the tray and extra gasket. You saved me on that.
 

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That looks pretty good no 10's or 13's anywhere and 12.8 at the top.
Did you measure the CR?
 

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I did not measure the CR and have not done a compression check. I did take a sample of my first oil at 1000 miles and send it to Blackstone Labs for analysis. Mainly to check for the absence of any bronze from the oil pump drive gear. I'll post the results when I get them.
 

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This is interesting stuff. Mike, what size venturis are you using? What is the ambient temperature when you do your runs? Good numbers and impressive sound and acceleration.
 

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Thanks, I appreciate.
When I did those last runs yesterday afternoon it was 95 degrees. We had a mini front move through last night which brought lower temps. Normally the lows are 78 with high humidity. This morning it's 75 and low humidity. Really nice actually! I just got back from a couple of runs and got some 13s up top. I don't know if the temp had anything to do with it but I wanted to double check my numbers from yesterday. I'm glad I did.
As it stands now I'm at:
DCOE 32s
34 venturis
50f8 idle
f11 tubes
135 mains
200 ac
I'm not sure if I have any 195 ACs. If I do I'll try them first then go with a 140 main jet. 140 seems awful big though.
 

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Richard Jemison
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AFRs

At 6500 in 3rd I have 13.7 which is lean obviously and the advance is 37 degrees.
Actually 13.7 isn`t a "lean" mixture as such. 13- 13.8 is my target in the race cars for power.

I would attempt to lean the 11s a bit to get over the rich range for better power.

Typically your cruise AFRs should be in the mid 13s to 14. And idle (no load) is rich. Have you tried closing the idle mixture screws a quarter or half turn.

145 F8 idle jets?? Never had such small idle jets work in any Alfa.
 

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Thanks Richard. I'm since gone to 50f8 idle jets and adjusted for high 12s to 13 at idle. With the temp being 75 this morning as opposed to 95 yesterday in third gear @ 6300 the afr is 13.2
From reading the Weber book it appears to me the F11 tube is richer than a F9. fewer holes and smaller diameter, less air more fuel=richer. IF I'm reading correctly. So I'll stay with the F11.
 

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Thanks for the specs. Your ambient temperatures are very similar to mine. I am going to hold the current setup static for now but may try 34mm venturis in a few months.

At 3000 rpm in fifth gear, part throttle, AFRs are in the high 14s to mid 15s. At 4000 rpm in fifth, part throttle, the AFRs are in the mid 14s. Suspect there will be some jetting changes required after the temperatures cool down.
 

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Stable RPM plot from ZT2

Hopefully it is appropriate to post some Dellorto tuning results here. If not, I trust the moderators will advise.

I have been setting up a pair of DHLA 40Ls (emissions carbs) in the '78 Spider with a modified 2L. The engine came from Ed Prytherch and is essentially the same as the first engine Ed describes in his "79 Spider on the Dyno" thread. That is, it has Venolia pistons, 10.6:1 compression, a Richard Jemison head, and Richard's 575 intake cam and 785 exhaust cam. I thought it might be useful to post the jetting specs and results and solicit comments.

The original jetting was, as far as I can determine, stock for a 2L Alfa.

148 Main Jets
57 Idle Jets
210 Air Correctors
32mm Vents
7848.3 Aux Vents
41 Pump Jets
7772.1 Emulsion Tubes
8.5g Float

After a fair amount of experimentation, the current jetting is:

140 Mains
60 Idles
195 Air Correctors.

The following graphic shows AFR by RPM in 2nd through 4th gear. These Dellortos seem to go a little rich after about 5700 rpm. Larger air correctors can keep the AFR in an acceptable range but if too large, the AFRs are too lean around 5400. Of course a larger main jet can be used along with larger air correctors but the same "rich" trend occurs at slightly different engine speeds. The current setup seems to be a reasonable compromise. Comments?
Hi. Nice stable logging output you have there! I also have a ZT2 and am really struggling to get *any* rpm signal, notwithstanding the issues discussed previously with respect to taking a noisy analogue signal from the -ve terminal of the coil....

Can I ask how you connected your ZT2 and what source you are using for the RPM input?

I contacted Zeitronix about the 99999 rpm I am currently seeing and they suggested I have a "ground loop" issue and that I should "connect the brown wire to the coil". The brown wire in their documentation is shown as the sensor ground - the RPM signal is not coming from a sensor though? Where on the coil would folks suggest I connect the brown ground wire to? Is it preferable to just connect this straight to the battery negative terminal?

At the weekend I observed 10 and 11s as the AFR when accelerating WOT in 3rd, which gradually leaned out as the rpm rose. For reference I'm using a ported 2 litre nord with stock valves, Richards cams (RJ 785 intake) and 40 DCOE 28s where the venturis have been profiled correctly and are now 33m diameter.

MJ 130
AC 180
IJ 55F8

I was running 55F9 and a 135 MJ, so switching to the combo above has given me a bit more urgency in the mid range, as I'm not running as rich. Without being able to log RPM, I'm having to glance over at the laptop every few seconds, which is sub optimal from a safety perspective, even on rural UK roads!

Thanks in advance.
 

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Hi. Nice stable logging output you have there! I also have a ZT2 and am really struggling to get *any* rpm signal, notwithstanding the issues discussed previously with respect to taking a noisy analogue signal from the -ve terminal of the coil....

Can I ask how you connected your ZT2 and what source you are using for the RPM input?

I contacted Zeitronix about the 99999 rpm I am currently seeing and they suggested I have a "ground loop" issue and that I should "connect the brown wire to the coil". The brown wire in their documentation is shown as the sensor ground - the RPM signal is not coming from a sensor though? Where on the coil would folks suggest I connect the brown ground wire to? Is it preferable to just connect this straight to the battery negative terminal?
I am using a Marelli-Plex ignition on the '78 Spider and use -ve on the coil for the tach input. Ed Prytherch (alfaparticle) built an interface to protect the ZT-2 from voltage spikes so the wiring for tach input is -ve on the coil to the interface, output from the interface to the green input wire for the ZT-2, and ground wire on the interface to chassis ground. All other connections are per the ZT-2 instructions with a common ground to the chassis. I don't understand the advice to connect the brown wire to the coil to solve a ground loop. Ed may be able to shine some light on this issue.
 

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I spoke with Mark Robinson yesterday and he is also using the same interface circuit with a Pertronix distributor and a ZT2 and he has good rpm plots. I think that I posted the circuit on the ABB.
Make sure that the ground wire to the ZT2 is a very good one. "ground loops" are often associated with high resistance in that circuit.
 

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Thank you Mr. Hunt. I guess that keeping out of the 13s AFR @wot with an F11, 135 mains, and 34 venturis means my headwork must be doing something right. btw I ran a compression check yesterday and got 195 psi +- 5 psi on all four. I don't recall exactly without looking it up but my LCs are 104 on each cam. 472 intake and 785 exhaust.
I don't know if anyone has used the Track Addict app but it is pretty slick. It gives you 0-60 times, 1/8th, 1/4 mile times in the drag mode and in the track mode it records times, accel, braking, etc. I'd been using the free version and just plunked down my $8.99 for the pro version so I can record more than three sessions. I got a 5.3 second 0-60 time in my Giulia and I'll give the GTV a try next. finger's crossed :)
 
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