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I checked the timing, and perhaps some good news -- it was beyond 20 degrees BTDC at idle without vacuum advance. This based

on setting the best idle RPM by 'ear' instead of on the light. Shooting the timing from the side through the wheel well appeared to

work fine tonight -- there was some previous discussion that it 'needs' to be from the top, but I suspect the difference in angle makes

little matter in this case, as the marks are at the 10-o'clock position or so anyway.

Spec is 7 BTDC US, 10 BTDC Canada. The Weber 32/36 likes a little more timing, so I put it at 10 BTDC or as near as I could

gauge.

The distributor centrifugal timing per the book adds 24 degrees as I recall, for a total of 34 degrees.

If the previous was at 20+ BTDC, the engine was getting a total of 44+ degrees of timing beyond 4000 RPM, which could arguably

be too much, and pulling initial timing back to spec might keep it from lying down past 4000 rpm.

The 3TC either is very knock-resistant, or has low enough compression that you just can't advance it enough to knock?

I did a round the block test drive and it sounded good and drives well, but we'll see how it does on the timer tomorrow weather permitting.

I am predicting we'll see a reduction in that initial torque and an increase in power past 4000 RPM

Bruce

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Timing way too advanced??? I suspect that with a regular-gas engine of 1977-1985 vintage with an aluminum head and a hemi combustion chamber might well run without detonation if you use mid-range or premium gas in it. Another layer peeled off the onion.

Now, about the air corrector jet and tuning at mid *and* high RPM ranges...

A fundamental principle of fixed-Venturi carburetor design is that the Ventri effect produces a vacuum that is proportional to the square of the air velocity. This means that if you have a simple fuel flow from a float bowl, through a jet and into the fuel nozzles in the small booster Venturi in the center of the throat, a jet big enough for a rich mixture at full-throttle at high RPM will be too lean at mid-range. So, carburetors use two jets and a power valve to adjust the mixture at full throttle through the RPM range.

The power valve is vacuum operated and, for four-stroke engines, is held closed by engine vacuum, opening at low vacuum to enrich the mixture. When the power valve is open, it adds fuel flow from its jet to that from the main jet.

The fuel circuit from the float bowl at full throttle is through the main jet and the power valve jet, up through the emulsifier tube, then out to the fuel nozzles in the booster Ventri. Air enters the top of the emulsifier tube through the air corrector jet and partially relieves the vacuum produced by the booster Venturi. This air also mixes in the emulsifier tube to produce a fuel/air mixture in the fuel nozzles in the booster Venturi.

Which brings us to how the three jets tune the mixture at mid and high RPM at mid and high throttle.

  • At the full throttle and high RPM, booster Venturi vacuum is highest and the power valve is open, producing the maximum flow of fuel from the main jet, the power valve jet, and the air correction jet.
  • At lower RPM but full throttle, the power valve is open but there is less vacuum produced by the booster Venturi and the booster Venturi, placed at a level near the float level to provide fuel at low vacuum, so that the main jet and the power valve jet determine the mixture.
  • At partial throttle and mid to high RPM, the power valve closes and the main jet and, if the air flow is high enough, the air correction jet, determine the mixture.

The air corrector jet leans the mixture at high RPM and full throttle, and its leaning effect decreases as intake air velocity decreases, allowing larger main and power valve jets to give a sufficiently rich mid-range mixture. Using this as a guide with data from the A/F gauge should help provide a more direct path toward evaluating combinations of main jet, air corrector jet, and power valve jet.

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Initial test run this morning sadly didn't have the memory card in the Performancebox, so no data was captured.

Good news is the 0-60 run took 13.5 sec, which suggests we are on the right track and back from topsy-turvey results.

Filled up with gas and grabbed the memory card and hopefully have time for a repeat test before church.

Bruce

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Today's runs 2 and 3 with base Timing at 10 BTDC, full tank of fuel:

Run num Speed(mph) Time(s) Dist(f) Graph run Description

2 0.00 0 0.00 Speed Start
2 10.00 1.07 8.33 Speed Line
2 20.00 2.60 42.69 Speed Line
2 30.00 4.52 113.34 Speed Line
2 40.00 6.60 220.28 Speed Line
2 50.00 9.39 405.06 Speed Line
2 60.00 13.55 741.29 Speed End

3 0.00 0 0.00 Speed Start
3 10.00 1.14 8.54 Speed Line
3 20.00 2.68 43.32 Speed Line
3 30.00 4.60 113.57 Speed Line
3 40.00 6.68 220.92 Speed Line
3 50.00 9.52 409.85 Speed Line
3 60.00 13.68 746.16 Speed End

Good news is these are new lows. Head-scratching news is the shape of the curve is roughly the same.

Comparison+of+2+runs+today.jpg

Hmmm. Ran some tests this morning with the 130/125 main/aux jets, and not the hoped for results.

New test results:

Run num Speed(mph) Time(s) Dist(f) Graph run Description

1 0.00 0 0.00 Speed Start
1 10.00 1.09 8.46 Speed Line
1 20.00 2.63 42.99 Speed Line
1 30.00 4.55 113.70 Speed Line
1 40.00 6.68 223.35 Speed Line
1 50.00 9.50 410.64 Speed Line
1 60.00 13.69 748.99 Speed End

Comparison+of+3+runs+Virt+Dyno.jpg

Good news is more power. Still not getting the smooth ramp to 5000 RPM I would expect from this engine.

Graph shows 8/24 with 20+ BTDC timing and 130/125 jets, 9/14 current jets but 20+ BTDC timing and 9/15 (today) 10 BTDC timing

WOT ~12.2:1 on this run.

Bruce

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What does the A/F gauge say during the run? You can have someone hold a phone taking a video of it and a watch with a sweep hand strapped to it and get data to plot along with your other data.

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-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
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-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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Almost constant ~12.2:1 at WOT. So that could stand to be a bit leaner. Thinking of going from 160 aux jet to 140 aux jet

Bruce

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Back to thinking about the final drive ratio again. What I see: 3rd gear, 2500<->~50 mph, 2600<->~55 mph.

This equates to ~3.8:1 final drive (3.9 for 50/2500, 3.7 for 55/2500). (argh)

Toyota overstock shows a corolla with 3-speed floor shift got 3.72:1

41201 singlePixel.gif FINAL GEAR KIT, DIFFERENTIAL, REAR. N=41:11
COROLLA (AE71); ATM,3-SPEED FLOOR SHIFT

I also was surprised to find that 6000 rpm in 1st did not get over 60 mph, as it should with 2.929 rear end.

I still see that in 1st gear the tach and speedo match up well, which suggests the lower drive.

When I put together a virtual dyno based on a 3.72 final drive ratio, the curve changes to expected:

Final+drive+3pt72+comparison.jpg

added a K&N filter to the Weber 32/36 on the 3TC:

IMG_1310.JPG

Here is the old and new filter side by side on the trunk before installation. The K&N is custom made for the 32/36, and is 3.5" tall instead of 2.5" for the old one, and

is longer & wider, so more filter media, and drove the AFR's all leaner.

The car feels good but when I ran up in the middle of the afternoon to test didn't show any additional power (lost 1 hp). It was warmer than this morning's test, but there you are.

Run num Speed(mph) Time(s) Dist(f) Graph run Description
2 0.00 0 0.00 Speed Start
2 10.00 1.11 8.57 Speed Line
2 20.00 2.66 43.23 Speed Line
2 30.00 4.62 115.56 Speed Line
2 40.00 6.75 225.20 Speed Line
2 50.00 9.62 416.34 Speed Line
2 60.00 13.91 763.41 Speed End

So as confusing as this has been with not being able to correctly determine the final drive ratio, if the 3.72 is correct then the engine is a stock 3TC putting out around 75 hp

at the crank perhaps as expected. I was hoping it would be making a bit more, but the important thing is establishing a baseline for mods from here.

Bruce

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If you use the rule-of-thumb of 80% of crankshaft power at the drive wheels, the motor is making 94 hp. That may be what it is supposed to do.

But I don't truly understand the torque curve. I have a problem with a stump-puller torque curve on an under-two-liter engine. But if Toyota didn't have my American attitude and designed it that way for driveability and beyond-its-displacement everyday performance, then this could be right. The exact shape of the torque curve, with its main peaks and such, is determined by resonances in the intake and exhaust as well as the cam and heads. Both the intake and the exhaust are totally different from any Toyota 3T-C application. So, the big low-end torque peak may be in part due to a volume resonance in your free-flowing exhaust.

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-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
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Yes, I was Jims_97_ETC before I changed cars.

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First of all, thanks for commenting. I know I post as if I know what I am talking about, but please consider this WHOLE thread thinking out loud if that was not clear. I

am playing it by ear trying to figure out a consistent test method, good tune, etc.

20% loss from auto would be 61 whp / (1-0.2) = 76.25 hp at the crank. problem with that is a 75 hp, 98 lb ft of torque Roadster when I plug it into cartest can't go 0-60 in under 17 sec.

The stock 80-81 3T-C has 75hp @ 5000rpm and 95 ft lb of torque @ 2600rpm with a C/R of 9.0:1.

In cartest a 2325 lb Roadster that can do 0-60 in 13.9 sec needs to make 103 hp at 5000 rpm and 112 lb-ft of torque at 2600.

So, a couple of issues with my test method to keep in mind:

  • This is a gear 1 pull and not a gear 3 (1:1) pull. Higher gearing (2.452:1 vs 1:1) means more loss (unknown amount)
  • The auto torque converter has a visible effect from launch -- read the torque peak as if it happens ~2600 rpm ~79 lb-ft / .8 = 100 lb-ft of torque at 2600
  • Relative back to back readings show improvement (or loss) as long as method is consistent

So, I am kind of keeping 2 sets of books -- one in the simulation to see if this car at this weight with that gearing can do 0-60 in x,

how much hp / torque is needed? And the other the virtual dyno result, which hopefully show the shape of the dyno curve.

History+with+current+thinking.jpg

The latter is of interest especially when we see a dip (as with too much timing and rich) or improvement.

The car loved way too much timing as long as too lean a fuel mix -- but luckily makes same power if correct timing and fuel mix.

And of course we may figure out something tomorrow that invalidates everything we think so far...

Bruce

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When final drive is unknown and /or is hard to determine... use the old fashioned shade tree method of jacking up one rear wheel and turn it EXACTLY one revolution, while counting the times the driveshaft turns...

If the drive shaft turns 3 3/4 turns... you have the 3.72.

If the drive shaft turns a hair less then 3 turns... you have the 2.92

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Thanks; that will narrow it down nicely. It seems one needs to turn one tire twice and count the revolutions of the driveshaft once, or turn the tire once and double the revolutions of the driveshaft.

In my case, I raised one rear wheel, put the car in neutral, and marked the wheel with tape, and the driveshaft with tape.

Then I carefully rotated the wheel, counting rotations of the driveshaft.

In 2 turns of the wheel, the driveshaft turned 3 times with about 15 degrees of wheel turn left to go remaining, so I am guessing the final drive is ~3.08:1 -- no, that would be ~3.3:1.

There was a Toyota ratio at 3.31 (S414).

So to validate I would need to turn the wheel 6 times and see if the drive shaft is just short of 10 turns.

This leads me to more questions.

Bruce

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Well, I'm posting from inference, deduction, and research, having absolutely no experience with small family sedans in the 1980 time period. At that time I was driving a 1977 Malibu wagon with the 350 four-barrel, a competent daily driver, commuter, and road car. Other than maintenance and tune-up, I never touched the drive train, which was solid as a brick. In keeping with the economy, Government regulation, and emissions mania of the 1970's, Toyota and others kept the good stuff overseas in those years, although the potential was in the hardware they sold here. Those years, and the 1977 Malibu, was a low point in my automotive interest and involvement.

Changing the final drive ratio in a performance model should scale the torque up and down and the RPM inversely with the torque magnitude, and the horsepower (computed from speed, weight, and acceleration) should be unchanged except for the RPM scale. So, what you have should be OK for horsepower and modeling. An exact final drive ratio will nail the RPM scale and the torque. So your last curve is as good as any we see published in the car magazines.

Published specs for the 3T-EU (EFI Japanese, TTC-C) are about 103.5 hp @ 5400 RPM and 162 lb-ft @ 3600 RPM. The peak torque of about 121 lb-ft is approximately right for magnitude, allowing for 80% efficiency of the drivetrain (less in low gear, as you point out) but happens at under 1000 RPM, waaaay below 3600 RPM. The horsepower of about 62 compares to an expected 83 hp and is seen at about 4200 RPM, way below the 5400 RPM in the published spec.

So, yes, the horsepower is down, some resonance that isn't seen in Toyotas brings us a not-unwelcome torque peak off-idle but we don't see the "real" torque peak, and the problem is in the mid and high RPM range. NOW I'm caught up. To yesterday.

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-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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Certainly interesting that the 3T-EU had another 25+ hp just from EFI; perhaps emissions differed in Japan domestic market as well.

They found a ton more torque, which suggests it had a different cam as well -- or perhaps those long curved intake runners

were dynamite.

8337083599_179bfbf98f_h.jpg

Specs for our carb version:

The 80-81 3T-C has 75hp @ 5000rpm and 95 ft lb of torque @ 2600rpm with a C/R of 9.0:1.
The 82 3T-C has 70hp @ 4600rpm and 93 ft lb of torque @ 2400rpm with a C/R of 9.0:1.

Small changes: I checked the sparkplugs, and all looked good. I opened the gap per the MSD ignition suggestion by .05 to .5".

I rechecked the timing with the light and made sure it was on the 10 degree BTDC mark. Tried it at 12.5 degrees but the car

got a slight shake so I put it back at 10 BTDC.

Bruce

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Yeah, my 1941 Chevrolet shook when I put high octane gas in it and timed it at 26 BTDC, too. I didn't care; I was 15. I don't recommend that kind of wildcat tuning for an engine with aluminum pistons, which the Chevrolet inline six didn't get until 1954.

The intake manifold is a conversion unit, unless you have an adapter for the Weber on a Toyota intake manifold. If it is a true high performance intake manifold, it will have constant-length tuned intake runners. If the carburetor flow is clean at high RPM and full throttle, and the air cleaner doesn't break up the flow, there should be a resonance peak at high RPM. That doesn't mean that the engine reaches that RPM range, though. Those runners on the DFI engine look pretty long, and they are apparently tuned to provide charge enhancement around 5500 RPM. If your runners are shorter, the intake manifold isn't providing a helpful intake resonance.

That overall torque curve, declining from about 1000 RPM onward, is something you see with exhaust restriction, intake restriction, retarded cam timing, spark problems, and such, all of which we have eliminated, except cam timing which is not very likely. If the A/F is steady at a little over 12:1 through the RPM range at full throttle, you have the carburetor under control except for possibly trying it a tad leaner or some such, so that isn't the problem. Unless the centrifugal spark advance isn't working, the spark is OK.

Is there a drag in the wheels, brakes, or even tires???

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-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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I am not sure on the intake. I had assumed it was a mod but it could in fact be stock toyota intake.

I did recheck tire pressures. We do know the suspension needs alignment although no shake, vibration or pulling. Trip back to spring shop pending for rear suspension and then alignment. No big changes til the suspension is done.

Next I will try the headers for fit. Need to make the call betw sidedrafts or EFI. Not certain sidedrafts will fit due to limited space.

Going efi would make adding turbo later easier. Need to decide if over the winter I will want to pull engine for new cam, heads. Alternate is get built 2nd 3tc engine and swap it in - BRD Racing offers built examples to spec.

Bruce

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I would offer up the idea that 3T engines are inexpensive. Compare the cost of pulling down your motor an making the mods versus buying a rebuild that has been run on a dyno and comes with the dyno sheet.

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-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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BRD Racing suggests $5,500 for a normally aspirated 150+ hp rebuilt 3TC with sidedraft carbs included, plus shipping.

Bruce

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Today I have one step more understanding of how the choke works (wasn't working) on my Weber 32/36 carb. Mine as you perhaps recall

is the DGEV electric choke. So I have had the choke plugged in (one wire, not tricky). The way that the choke works is that there is

a 'butterfly' valve at the top of the carb actuated by the choke. Inside the choke is a coil that is heated by the electric current. When it is

hot, it actuates the butterfly valve so that it opens. When it is cold, it keeps the butterfly closed so less oxygen-rich air floods into the engine

until it has a chance to heat up.

IMG_0969.JPG

Now, the butterfly valves ride on a shaft that connects to a actuating lever, which is held onto the butterfly shaft with a tiny c-clip.

That was lost in the taking the carb hat on and off and jet adjustments, but if one bends the actuating lever slightly it often stays

on the shaft and the butterfly valve opens properly.

Under WOT, the linkage also forces the butterfly valve open 75% or so regardless of choke.

Today I got a new clip to replace the c-clip and study the choke in more detail. I discovered the power source for the electric

choke was not a power source (plugged into the wrong slot). So the choke was never opening the butterfly even with the engine

hot (it was always 'on choke'). If the butterfly came off the actuator, as it sometimes would, it would be flipped open against its

spring by the engine intake rush of air, but it was not properly just sitting open. If the butterfly were on the actuator, as could

(properly) happen, the engine would open the butterfly to 3/4 as mentioned.

Now the electric choke is actually powered, heating, and when I pulled in from a drive the butterfly was open 100% at

no throttle.

I am hopeful that this also had a muting effect on acceleration at WOT, and will test when the weather improves.

Oppenhauser says their replacement intake manifold for the 32/36 on the 3TC gives 'up to' a 22% HP improvement.

So finding one of those in good condition would be a good swap in the current configuration.

Bruce

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Choke Fix runs: Today I restested after fixing the carb choke so that it is working properly. Cold air day (~61F) , early Sat morning.

The car did a new best, but not quite the improvement hoped for:

Run num Speed(mph) Time(s) Dist(f) Graph run Description
2 0.00 0 0.00 Speed Start
2 10.00 1.25 9.12 Speed Line
2 20.00 2.63 40.09 Speed Line
2 30.00 4.41 105.62 Speed Line
2 40.00 6.42 209.57 Speed Line
2 50.00 9.18 392.57 Speed Line
2 60.00 13.14 712.51 Speed End

3 0.00 0 0.00 Speed Start
3 10.00 1.12 8.64 Speed Line
3 20.00 2.50 39.54 Speed Line
3 30.00 4.29 105.40 Speed Line
3 40.00 6.32 210.53 Speed Line
3 50.00 9.08 394.27 Speed Line
3 60.00 13.02 712.19 Speed End

Previous best:

Run num Speed(mph) Time(s) Dist(f) Graph run Description

2 0.00 0 0.00 Speed Start
2 10.00 1.07 8.33 Speed Line
2 20.00 2.60 42.69 Speed Line
2 30.00 4.52 113.34 Speed Line
2 40.00 6.60 220.28 Speed Line
2 50.00 9.39 405.06 Speed Line
2 60.00 13.55 741.29 Speed End

Today's Virtual Dyno file (3.31:1 final drive assumed)

2013-09-21+Choke+Fix+Runs.jpg

So the good news is in cool air this run moved from 62-63 whp (78-79 hp) to 68 whp (85 hp).

Still a flat HP plateau from 4000-5400 rpm, which suggest the engine could pull more power -- perhaps as much as 75 whp?

Approx 12.4:1 AFR during the WOT run. Nice consistent results; the idle was a bit low and the car didn't

launch smoothly off idle or it might have done a bit better.

Comparison+of+Choke+Fix+to+Previous+Runs

Torque peak moved to the right significantly from previous run. 14 lb-ft better at 1878-1890 rpm range.

Bruce

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I went out this morning to check the centrifugal advance. I can reach the throttle and shine the light at the crank but

can't examine the crank timing marks closely while also being able to reach the throttle.

With the vacuum advance disconnected and capped, the centrifugal advance does add additional timing up to

4000 rpm. No more timing comes in after 4000 rpm.

The choke and new clip checked good on examination.

Bruce

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I went out this morning to check the centrifugal advance. I can reach the throttle and shine the light at the crank but

can't examine the crank timing marks closely while also being able to reach the throttle.

With the vacuum advance disconnected and capped, the centrifugal advance does add additional timing up to

4000 rpm. No more timing comes in after 4000 rpm.

The choke and new clip checked good on examination.

And the curves flatten after 4000...

It may be possible that the initial timing needs to be advanced just a little...

It is puzzling to me why it flattens so quick at 4000 and then starts dropping off.

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I guess next I need to log the AFR and make sure where we are staying at 4000-6000 RPM.

I also recall a discussion of 'flat spots' and air correction jet carb tuning:

Also, you should keep in mind that the air corrector is a finer adjustment that the main jet. Example: One step upward in the main jet (richer) equals about the same as three steps down on the air (less air: richer). A change of air corrector would be appropriate; for instance, if the engine pulls strong to 5,000 rpm and then goes flat. This would mean she's going lean on you up top; drop the air corrector three sizes or so, and you'll probably be able to buzz that engine right up to 7,000 rpm. If the motor feels sour all the way up, go one or two sizes heavier on the mains only. No magic! So, tell me, what's so hard about jetting these Webers?

I have not observed a difference in AFR 4000+ RPM but it does get busy at that point. I believe it is staying at 12.4:1 though.

I have some larger air correction jets; the current jetting is 150ac160/160ac185. Default carb jetting was 140ac170/140ac160.

Bruce

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Very interesting telecon with Randy Davis at BRD Racing today. They did a lot of 3TCs for kit cars

back in the day because it was light, and wakes up well.

Stock cam, valve springs, distributor all need updates to start waking engine up -- even to rev past

4k well. Little point in pushing engine until cam, vlv springs, distributor tuned. Frequently

distributor as much as 6 degrees off stock.

They offer two packages plus myriad options. New rebuilt exchange engine making 120 hp for

$3500 re-using my intake and 32/36 carb, or 228 hp max NA effort for $5500 w sidedrafts.

Plus either will need several $hundred miscellaneous. Options in engine color, powder coating, etc.

Sidedrafts perhaps add 20 hp over 32/36 for $1300 but require more frequent tuning.

$2000 deposit, 4-6 wk build time, arrives w dyno sheet in a crate.

To do right now:

Update to blaster coil

Measure intake manifold to see if 4.5" bolt to bolt 'good' stock one or other

Get custom header done

Figure out engine choices

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