Tuning a TBucket Dart 400 cuin Engine
- Thread starter Indycars
- Start date
bytor
Well-Known Member
I can't agree more. I love the Quadrajet. A well tuned Quadrajet is about as close as you can get to EFI while still running a carb. Those small primaries make for great street manners and a very flat fuel curve. Then the secondaries open. Lookout! Love that sound.
8
87vette81big
Guest
Yes Bytor.
The 1973 -1974 Pontiac SD-455 800 CFM Q- Jet is king of the Hill of all Rochestor Q-Jets.
I have plug gauged all the tiny Emulsion Tube orfices in the past.
It is truly unique.
#2 Pick is the 1970 Pontiac Ram Air IV - 4 750 cfm Q- jet.
I own them both still after all these years, keeping them too.
Rick is over 60 now, he don't have the time & patience to dial in the emulsion circuits right in the Demon carb.
He might be there still in 2016 working on it.
If mine it would be set aside. Stick it on ebay for $200 bucks.
Post my Holley Picks later today.
I checked timing and it still on 35° total advance with 12° advance initial timing.
- Warmed the engine to 197° and no air cleaner.
- Checked the AFR after setting the RPM to 850 and it was 12.5-12.8, maybe its different when in gear and idling at ~825 RPM.
- Turned all 4 mixture screws in 1/4 turn, adjusted the idle down to 850 RPM and the AFR was now 14.2-14.6
- Turned all 4 mixture screws in 1/8 turn and the AFR was now 15-16 and idling lower and rougher.
- Returned all mixture screws to previous setting of 3/4 turns out.
- Warmed the engine to 197° and no air cleaner.
- Checked the AFR after setting the RPM to 850 and it was 12.5-12.8, maybe its different when in gear and idling at ~825 RPM.
- Turned all 4 mixture screws in 1/4 turn, adjusted the idle down to 850 RPM and the AFR was now 14.2-14.6
- Turned all 4 mixture screws in 1/8 turn and the AFR was now 15-16 and idling lower and rougher.
- Returned all mixture screws to previous setting of 3/4 turns out.
Bytor,
For this test I put the trans in 3rd gear and accelerated enough get thru 1st and 2nd. When
it shifted to 3rd gear I started to accelerate(Start of Test) slowly and consistently until I
reached WOT (End of Test).
What do you suggest now?
BTW, when I started the car and it was cooler (150°F) it was running very lean, like AFR of 17.
It was having trouble to keep running. But once it warmed up it was back to about AFR of 14.5 .
The choke has been removed.
For this test I put the trans in 3rd gear and accelerated enough get thru 1st and 2nd. When
it shifted to 3rd gear I started to accelerate(Start of Test) slowly and consistently until I
reached WOT (End of Test).
What do you suggest now?
BTW, when I started the car and it was cooler (150°F) it was running very lean, like AFR of 17.
It was having trouble to keep running. But once it warmed up it was back to about AFR of 14.5 .
The choke has been removed.
8
87vette81big
Guest
Pull all the spark plugs and read them .
What I would do Rick.
What I would do Rick.
bytor
Well-Known Member
You curve look similar to what I had out of the box with my 650 Speed demon.
Take a look at http://garage.grumpysperformance.co...-1st-street-383-build.6962/page-10#post-30290 post #190
In your curve you can see 12-12.2 rich idle/cruse then you can see the transition slot curve going lean towards 13 AFR just after your start of test line. Thats normal. If you lean out your idle/cruse, this will flatten out. Next after the transition slot runs out of steam at 13 just after your start of test, the mains are coming on line strong 11-11.5AFR. This is the strange AFR curve I was referring to that seems to be related to too many emulsion holes. Mains start very rich and progressively lean out towards the power valve opening. At 0:09 looks like your secondaries starting to opening. The rich, then lean , then rich startup curve "could be" caused by you secondary squirter being too large. Drop if down a few sizes and see if the secondary startup flattens out.
Make a few more runs and recordings before you touch anything.
My Speed demon curve out of the box.....
Take a look at http://garage.grumpysperformance.co...-1st-street-383-build.6962/page-10#post-30290 post #190
In your curve you can see 12-12.2 rich idle/cruse then you can see the transition slot curve going lean towards 13 AFR just after your start of test line. Thats normal. If you lean out your idle/cruse, this will flatten out. Next after the transition slot runs out of steam at 13 just after your start of test, the mains are coming on line strong 11-11.5AFR. This is the strange AFR curve I was referring to that seems to be related to too many emulsion holes. Mains start very rich and progressively lean out towards the power valve opening. At 0:09 looks like your secondaries starting to opening. The rich, then lean , then rich startup curve "could be" caused by you secondary squirter being too large. Drop if down a few sizes and see if the secondary startup flattens out.
Make a few more runs and recordings before you touch anything.
My Speed demon curve out of the box.....
8
87vette81big
Guest
If the Spark Plugs are Fouled out it will not be possible to Tune correct.
Why I keep saying pull all 8 spark plugs and look at them.
So You don't waste anymore Time.
Only a Vertex Magneto will fire Fouled out spark plugs. High Amperage AC Current At spark plug gaps creates a Super Hot Flame Kernel that No MSD Cd Box can't duplicate.
I know this from Racing with both in.my own.
Why I keep saying pull all 8 spark plugs and look at them.
So You don't waste anymore Time.
Only a Vertex Magneto will fire Fouled out spark plugs. High Amperage AC Current At spark plug gaps creates a Super Hot Flame Kernel that No MSD Cd Box can't duplicate.
I know this from Racing with both in.my own.
This carb uses vacuum secondaries, therefore there is no secondary squirters.
I made three more runs today, somewhat in the rain, it was misting on and off. I was much
better on the switch to start/stop the logging, so I did not need to insert start and stop lines.
Wish I could get a better RPM trace, but it's still obvious what it should be. I can use a math
channel and smooth out these traces if you think it would help.
8
87vette81big
Guest
Better than Demon Rick.
Sorry.
But True.
Sorry.
But True.
I found this procedure for determining your WOT timing using an AFR meter, has
anyone ever tried something like it ???
http://www.britishv8.org/Articles/Ignition-Tuning-201.htm
The following tuning procedure is for wide open throttle (WOT) operation ONLY, so please find a safe place
to drive where you can keep an eye on the gauge or find a driver to help you out while you watch the meter
and take notes. You are looking for an air/fuel ratio of 12.5-13:1 at WOT. You can replace carburetor jets and
needles until you are somewhere in that general ballpark. You may see your fuel mixture go slightly leaner as
RPM rises - that's excellent!
Make a few runs from 1500-2000 RPM in second or third gear up to 4000 RPM or so. Take close notes
regarding your air/fuel ratio (AFR).
2000 RPM --- _______ : 1,
2500 RPM --- _______ : 1,
3000 RPM --- _______ : 1,
3500 RPM --- _______ : 1
4000 RPM --- _______ : 1
You should have very consistent AFR readings from run to run unless the driving conditions have changed
markedly. (Make a note if there are any unexplained inconsistencies between runs.) Repeat each run on the
same stretch of road if you can. Once you've established this baseline, you can start making changes to your
ignition timing.
The next step is to begin "mapping" the optimum timing curve for your engine. But how? The idea is to
determine the amount of advance your engine likes at each RPM range (i.e. 500 RPM increment). The trick
is to do this by methodically taking AFR readings at incrementally adjusted initial timing settings. In principal,
you might like to test from about 2 degrees BTDC to about 20 BTDC, in 2 degree increments. In practice, you
won't have to take that many test runs to get what you're looking for!
Initial timing? Yes, initial timing. You're not looking for the initial timing setting that gives you the best
performance across the RPM range, and you don't really have to be concerned at this point with the existing
mechanical or vacuum advance mechanisms (so long as they're behaving consistently). Instead, you're looking
for data points or "spots of perfection" that taken together can be used to create a "perfect distributor".
Changes will be made to your distributor's curve to match the total amount of timing needed at each rpm.
So, as you're making test runs and writing down notes, how will you know when you've found the best timing
settings? You're looking for the timing adjustment that will provide the leanest observed AFR (at WOT) for
each engine RPM range! The best amount of ignition advance will show on the gauge as a leaner mixture,
with no engine pinging. (Pinging? See below.)
If your AFR gauge readings get richer after making a timing adjustment, you've either gone in the wrong
direction or you've gone too far - and your engine isn't burning fuel efficiently.
Just keep repeating the testing process until you find the best timing settings at 2000, 2500, 3000, 3500, &
4000 RPM. Don't worry if any given initial timing adjustment causes a flat spot or hesitation somewhere, as
long as it improves performance in one given spot. Disregard any off-throttle or part-throttle information for
now. If you change your timing enough to go leaner than 13:1 at WOT, make a fuel mixture change between runs.
Don't worry about drawing an actual map. You don't need to plot out an elaborate "curve". Typically you will
see results that entail setting the base timing higher and gradually removing advance from the distributor up
to the point where the cam falls off. Your notes at the end of the session might be as simple as this: "16 degrees
BTDC at 2000 RPM, 14 degrees BTDC at 2500 and 3000 RPM, and 10 degrees BTDC at 3500 and 4000 RPM."
It's fairly typical to gain 10 percent power (or considerably more in some cases) by going through this process
and making subsequent adjustments. While a stoichiometric rate of 14.7:1 is great for fuel mileage, it is too lean
for high load conditions such as wide-open throttle. Once you get the basics down, we can move on to tuning for
fuel mileage or cruise-tuning later. After all, it's all about WOT anyway, right? But those are more advanced
topics for a follow-up article.
Keep in mind that all this tuning must be done on an otherwise properly running engine. It is assumed that a
basic tune-up has already been performed and all the ignition components are in good working order. This
process is to enhance a good running engine, not troubleshoot a drivability issue, although the A/F meter can
potentially be used for that too.
Having an air/fuel meter allows you to check critical data from your engine that you previously took for granted!
That's why computer controlled cars usually run so well - they're constantly going through this same process
and automatically making programmed corrections. We need to make our corrections the painstakingly difficult
way - and live with the results. So take your time, set your car up right and reap the benefits!
anyone ever tried something like it ???
http://www.britishv8.org/Articles/Ignition-Tuning-201.htm
The following tuning procedure is for wide open throttle (WOT) operation ONLY, so please find a safe place
to drive where you can keep an eye on the gauge or find a driver to help you out while you watch the meter
and take notes. You are looking for an air/fuel ratio of 12.5-13:1 at WOT. You can replace carburetor jets and
needles until you are somewhere in that general ballpark. You may see your fuel mixture go slightly leaner as
RPM rises - that's excellent!
Make a few runs from 1500-2000 RPM in second or third gear up to 4000 RPM or so. Take close notes
regarding your air/fuel ratio (AFR).
2000 RPM --- _______ : 1,
2500 RPM --- _______ : 1,
3000 RPM --- _______ : 1,
3500 RPM --- _______ : 1
4000 RPM --- _______ : 1
You should have very consistent AFR readings from run to run unless the driving conditions have changed
markedly. (Make a note if there are any unexplained inconsistencies between runs.) Repeat each run on the
same stretch of road if you can. Once you've established this baseline, you can start making changes to your
ignition timing.
The next step is to begin "mapping" the optimum timing curve for your engine. But how? The idea is to
determine the amount of advance your engine likes at each RPM range (i.e. 500 RPM increment). The trick
is to do this by methodically taking AFR readings at incrementally adjusted initial timing settings. In principal,
you might like to test from about 2 degrees BTDC to about 20 BTDC, in 2 degree increments. In practice, you
won't have to take that many test runs to get what you're looking for!
Initial timing? Yes, initial timing. You're not looking for the initial timing setting that gives you the best
performance across the RPM range, and you don't really have to be concerned at this point with the existing
mechanical or vacuum advance mechanisms (so long as they're behaving consistently). Instead, you're looking
for data points or "spots of perfection" that taken together can be used to create a "perfect distributor".
Changes will be made to your distributor's curve to match the total amount of timing needed at each rpm.
So, as you're making test runs and writing down notes, how will you know when you've found the best timing
settings? You're looking for the timing adjustment that will provide the leanest observed AFR (at WOT) for
each engine RPM range! The best amount of ignition advance will show on the gauge as a leaner mixture,
with no engine pinging. (Pinging? See below.)
If your AFR gauge readings get richer after making a timing adjustment, you've either gone in the wrong
direction or you've gone too far - and your engine isn't burning fuel efficiently.
Just keep repeating the testing process until you find the best timing settings at 2000, 2500, 3000, 3500, &
4000 RPM. Don't worry if any given initial timing adjustment causes a flat spot or hesitation somewhere, as
long as it improves performance in one given spot. Disregard any off-throttle or part-throttle information for
now. If you change your timing enough to go leaner than 13:1 at WOT, make a fuel mixture change between runs.
Don't worry about drawing an actual map. You don't need to plot out an elaborate "curve". Typically you will
see results that entail setting the base timing higher and gradually removing advance from the distributor up
to the point where the cam falls off. Your notes at the end of the session might be as simple as this: "16 degrees
BTDC at 2000 RPM, 14 degrees BTDC at 2500 and 3000 RPM, and 10 degrees BTDC at 3500 and 4000 RPM."
It's fairly typical to gain 10 percent power (or considerably more in some cases) by going through this process
and making subsequent adjustments. While a stoichiometric rate of 14.7:1 is great for fuel mileage, it is too lean
for high load conditions such as wide-open throttle. Once you get the basics down, we can move on to tuning for
fuel mileage or cruise-tuning later. After all, it's all about WOT anyway, right? But those are more advanced
topics for a follow-up article.
Keep in mind that all this tuning must be done on an otherwise properly running engine. It is assumed that a
basic tune-up has already been performed and all the ignition components are in good working order. This
process is to enhance a good running engine, not troubleshoot a drivability issue, although the A/F meter can
potentially be used for that too.
Having an air/fuel meter allows you to check critical data from your engine that you previously took for granted!
That's why computer controlled cars usually run so well - they're constantly going through this same process
and automatically making programmed corrections. We need to make our corrections the painstakingly difficult
way - and live with the results. So take your time, set your car up right and reap the benefits!
It's going to be a fair amount of work to get there. Wonder how far from the tried and true
of initial = 12, total =36 and all in by 2500-3000 rpm. Theoretically the line is straight and
a set slope. What if your test determine determine a different slope from one RPM to the next,
not going to do that with springs. Guess that leaves me out with my lowly distributor.
mathd
solid fixture here in the forum
Well for supercharged application i can see that article very attractive. can't just bump the timing until it ping and different forced induction/engine need different timing(like turbo vs "small/big"supercharger vs procharger). knock sensor are cool but :/.
I think, despite that we use analog ignition box(non computer controlled/programmed box) it can be very helpfull to guesstimate the best base and total advance and all in @ wich RPM is cool.
I don't trust EGT ignition tuning, seat-of the pant not bad. datalogger can estime HP and torque that is helpfull too(like a portable in-car dyno).
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busterrm
solid fixture here in the forum
Hey guys, I rode my bike up to Ricks place Saturday morning. We have been doing some tuning on his T bucket. I am sure Rick will make a report soon. I wish you were here Grumpy and Bytor, this has been pretty cool, make a adjustment and go test it, record data on the AQ - 1 come back download the data and look and make another adjustment. We are narrowing in on the primary made a final adjustment and Rick will test it later.
For better or for worse, this is what I have done so far. I decided to make two test
per carburetor change, acceleration test in 3rd gear and cruise test at 65 mph.
Went from ported vacuum to manifold vacuum to the distributor. This helped
bring the idle up without moving the butterflies and maintain the T-slot adjustment
of .020 inches.
It was great help to have Bob hear to bounce ideas off of..... thanks Bob !!!
Below is my base run, there was no cruise test done. This was before I decided to do
both test for each carburetor change.
Changes are noted on each curve plot.
IFR = Idle Feed Restrictor in the metering block.
AFR = Air Fuel Ratio
I do NOT have an acceleration test to go with this cruise test.
The Idle Air Bleeds (IAB) really have a big effect on the carburetor's performance for the size of change made.
per carburetor change, acceleration test in 3rd gear and cruise test at 65 mph.
Went from ported vacuum to manifold vacuum to the distributor. This helped
bring the idle up without moving the butterflies and maintain the T-slot adjustment
of .020 inches.
It was great help to have Bob hear to bounce ideas off of..... thanks Bob !!!
Below is my base run, there was no cruise test done. This was before I decided to do
both test for each carburetor change.
Changes are noted on each curve plot.
IFR = Idle Feed Restrictor in the metering block.
AFR = Air Fuel Ratio
I do NOT have an acceleration test to go with this cruise test.
The Idle Air Bleeds (IAB) really have a big effect on the carburetor's performance for the size of change made.
darn impresive , being able to data log whats going on as you adjust and change things, heres
bits of reference material.
Id try to get as close to the basic listed parameters below as a start point as you can, and the slight hesitation on acceleration might require a larger accelerator pump cam curve , or a power valve that kicks in at a bit higher vacuum level, example swapping from a 7.5 to and 8.5, make only a single change at a time and keep good detailed notes on results, and don,t discard parts, label them, keep in zip lock bags with labels
yeah I might not be up on the latest electronic data loggers but I have a good idea what an engine wants as far as a fuel/air ratio and combustion conditions and ignition advance curves and can read spark plugs, and while each engines a bit different you may be amazed at what consistent condition to start from does to help isolate any tuning problems
http://garage.grumpysperformance.com/index.php?threads/holley-accelerator-pumps-cams.1790/#post-4544
http://garage.grumpysperformance.com/index.php?threads/holley-carb-power-valves.1639/#post-4545
http://garage.grumpysperformance.co...annular-vs-down-leg-boosters.5229/#post-15353
set the float levels and verify the fuel pressure consistent at about 5 psi entering the carb inlet port.
your fuel/air ratio should be in these ranges
Idle- up too about 2500 rpm try for 14.7:1-15:1 f/a ratio
from about 2500 rpm- too about 4500 rpm try to smoothly and predictably transition the fuel/air ratio mix richer to about 13.5:1
from about 4500 rpm- too about 6500 rpm and higher ,try to smoothly and predictably transition the fuel/air ratio mix richer to about 12.5:1
this is only a starting point on the tune but it generally gets you in the ball park and tends to reduce the chances of the engine reaching detonation conditions.
the ignition advance curve needs to be checked, the chart below is a very good starting point to work from
set the plug gaps at about .045, make sure the valves are adjusted correctly
http://garage.grumpysperformance.co...ng-piston-pin-height-compression-height.5064/
Specs
- Comp Height 5.565" Rod - 1.561
- Comp Height 5.7" Rod - 1.433
- Comp Height 6.0" Rod - 1.13
- Pin Diameter - 0.9272
if you change to much cheaper and much stronger 5.7" connecting rods the less common compression height pistons are not an issue
youll have dozens of choices in a 4.125-4.165 bore diam. with a 5.7" rod
keep in mind the old O.E.M. rods have already been through millions of stress cycles and they are a weak design
resizing, , refurbishing the original 400 connecting rods, and replacing
just the connecting rod bolts will cost far more than the SCAT 5.7" aftermarket rods that are at least TWICE as strong
.
http://www.scatcrankshafts.com/rods/
https://www.speedwaymotors.com/KB-Claimer-Chevy-400-Hypereutectic-Pistons-Flat-Top-57-Rod,33222.html
5.565 rods
http://www.herbertcams.com/espcrs5565b-3d-sb-chevy-5-565-4340-forged-h-beam-rods/
https://www.stevemorrisengines.com/...cks/sbc/sbc-4340-forged-h-beam-rods-5565.html
5.7" rods
https://www.speedwaymotors.com/Smal...el-I-Beam-Rods-5-7-Inch-Bushed-Pin,29376.html
https://www.speedwaymotors.com/Scat...340-I-Beam-Rods-5-7-Inch-Bushed-Pin,6608.html
piston for 5.7 rod
https://www.summitracing.com/parts/slp-h615cp
piston for 5.565 rods
https://www.summitracing.com/parts/slp-h400cp
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