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Old 05-17-2010, 02:52 PM
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Convertor to Cam Mismatch?

With my recent project I have a new 383 with a lunati street master cam. 221/230 duration @ 0.050 and .454 lift. KB hypers with -18cc dish, 062 vortec heads, edey performer EPS manifold, edey 1405 carb set for slightly rich on the tuning scale (rod and jet combo for #9) 3.73's in the back I am yet to check the plugs to see what they tell me about mixtures. I have set timing for 14 Deg BTDC initial and am running 36 Deg total at 2800 + the HEI vac advance of about another 18. I am pulling about 15 hg vacuum at idle. I installed a 700R4 with a 1800 stall lockup torque convertor. The idle in park needs to be at about 1000 rpm so that when in park I can keep a 650-700 rpm idle. I need to be hard on the brakes to keep it still at a light and the idle quality is kind of erratic. Why is there such a drop in idle from park to drive or 3rd? Could it be the stall is too low? What is this all about? can I help combat this in any other way other than changing the cam or convertor?...or could it be something else. Thanks

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Old 05-17-2010, 05:02 PM
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Quote:
Originally Posted by Custom10
With my recent project I have a new 383 with a lunati street master cam. 221/230 duration @ 0.050 and .454 lift. KB hypers with -18cc dish, 062 vortec heads, edey performer EPS manifold, edey 1405 carb set for slightly rich on the tuning scale (rod and jet combo for #9) 3.73's in the back I am yet to check the plugs to see what they tell me about mixtures. I have set timing for 14 Deg BTDC initial and am running 36 Deg total at 2800 + the HEI vac advance of about another 18. I am pulling about 15 hg vacuum at idle. I installed a 700R4 with a 1800 stall lockup torque convertor. The idle in park needs to be at about 1000 rpm so that when in park I can keep a 650-700 rpm idle. I need to be hard on the brakes to keep it still at a light and the idle quality is kind of erratic. Why is there such a drop in idle from park to drive or 3rd? Could it be the stall is too low? What is this all about? can I help combat this in any other way other than changing the cam or convertor?...or could it be something else. Thanks
Lumpy cams are like that, you're on the upper end of what's comfortable with a stock stall converter. I'm sure it slams real hard when going onto gear and like you said wants to drag you thru stops. You can get a higher stall, locking converter with the 700R4, that will give you the best combination.

Bogie
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Old 05-17-2010, 06:39 PM
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OK thanks bogie but what is actually happen here I mean the convertor is supposed to provide output torque at 1800 why is it pushing so hard at 700rpm? and why does the cam effect this...an rpm is an rpm yes/no?
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Old 05-17-2010, 08:14 PM
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The converter you have is very tight. |Get a high stall. This time don;t be a wimp. Get a 2800-3000 stall lock up converter. 10" diameter or smaller.

When you drop it in gear and its idleing at 700rpm what is the spark timing?
If it drops the distributor advance curve is not right.

If it s factory converter it will have a number/letter code on it as well as maybe a bar code. From the factory code you can establish the "K factor" once you know that you can estimate pretty close the stall you can expect behind a particular CID engine.

The K factor is how GM rates their factory torque converters.

When you go to get a new converter don;t buy a cheap restalled 12" converter. ( all they do is bend the converter fins to tweek the stall. Get a real high stall based on a 10" or 245MM case size.

get the numbers from the converter and google search k factor, stall speed to find how to decifer the numbers.
the highest stall factory th700r4 converter is the 2100 stall used in some |Iroc/corvette L-98 motors and some S-10 with 4.3 V6
Youd'd be much better of wiht a aftermarket 2800 stall lock up conveter.

www.converter.com
www.converter.cc
check the accuracy of the timing tab .. retarded spark will require excessive throttle opening at idle making it crash when you drop it in gear.

Last edited by F-BIRD'88; 05-17-2010 at 08:24 PM.
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Old 05-18-2010, 09:37 AM
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Quote:
Originally Posted by Custom10
OK thanks bogie but what is actually happen here I mean the convertor is supposed to provide output torque at 1800 why is it pushing so hard at 700rpm? and why does the cam effect this...an rpm is an rpm yes/no?
A converter is actually transmitting a lot of torque well below its stall speed. the stall speed in easy terms can be though of that speed where with the brakes locked and the throttle opened to WOT, that the engine RPMs peak and can't climb higher. To use the words of Paul Stookey; "the car is internally hemorrhaging". One of the hallmarks of needing more stall speed is just what you're experiencing of the thing want to move at idle with so much force you have to apply enough brake to where it becomes tiring waiting out a traffic light.

Bogie
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Old 05-18-2010, 10:06 AM
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OK so I can change the convertor much easier than the cam so I will look into a higher stall thanks for the explanation.

As for your responce F-BIRD

"The converter you have is very tight. |Get a high stall. This time don;t be a wimp"

Your experienced input is welcome and appreciated too thanks, but i'll just take the descriptor with a grain of salt as I am sure you meant nothing by it ...wimp? not necessary
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Old 05-18-2010, 11:16 AM
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Quote:
Originally Posted by Custom10
OK so I can change the convertor much easier than the cam so I will look into a higher stall thanks for the explanation.

As for your responce F-BIRD

"The converter you have is very tight. |Get a high stall. This time don;t be a wimp"

Your experienced input is welcome and appreciated too thanks, but i'll just take the descriptor with a grain of salt as I am sure you meant nothing by it ...wimp? not necessary
Discuss the converter with whomever you're buying it from, good sources like Summit or Jegs have technical people who will help you get the right stall for the engine and vehicle combination. Off hand the engine config you
have is a little too aggressive for a stock stall converter, but it isn't so crazy that a super high stall isn't required either. So I recommend you talk with a knowledgeable person from a respected source as you'll find too much stall is as bad if not worse than too little and there is a tendency for people to go a little nuts with this decision. So this needs to be adjusted to a bandwidth kind of solution nothing will be perfect, just better.

Bogie
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Old 05-18-2010, 01:00 PM
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When it comes to selecting a converter for the th700r4 most people either cheap out or wimp out and buy a "2400 stall " " 2600stall" tweeked stock GM 12" converter. These are just stock converters that have had the fins bent over more and or a flat machined on the stator blades to make them slip more. They are not very efficient.
If you want a real high peformance converter for your 383 spend a few bucks and get a real high stall converter based on a smaller case diameter.
These 2800 stalls retain a high perf converter lock up clutch. for cruisability in OD. Many people who are inexperienced with high stalls think that the car/truck will not move unless you rev it up to the stall speed. This is not true. A 2800 stall converter will move from a start as soon ans you add throttle. The rpm will be a bit higher than a stock converter. Thats the whole idea of a high stall converter.
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Old 05-18-2010, 01:05 PM
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Custom 10...I agree with you 100%, I never thought I was a "Wimp" either by the parts I chose depending on the application they were intended for. FB'88 is extremely knowledgeable in all aspects of high perf engine building, especially cam and timing issues and I have learned quite a bit from him.

Sometimes a little off the cuff humor is taken the wrong way and in reality is really not necessary. So back to your problem, as Oldbogie suggests, run your combo by a good trans guy so you don't get too high a stall. A guy I knew thought he had to have a 3800 stall converter behind a "warm" big block. He ended up hating it, trans ran hot and wasted gas, took it out about 3 weeks later and installed a 2800 unit....much better. As FB'88 suggests pay the extra to get a REAL high perf. unit no matter what the stall, you'll be money ahead in the long run..... good luck on your setup.

Last edited by 327NUT; 05-18-2010 at 01:10 PM.
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Old 05-18-2010, 01:20 PM
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I am guessing it is for that heavy truck......make sure you account for that
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Old 05-18-2010, 04:17 PM
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OK well time to do some more homework and get something to improve the setup. It is really not too bad, I am happy with the 383 man what a step up from the 350 I had, also the 350 had a 3 speed manual stick behind it. Night and day for sure. My truck is certainly no heavy weight (for a truck that is) at about 4000lbs or a bit less I am guessing? I see that there are many convertors designed for trucks and/or towing which is something I will do from time to time but not too often. What is the main difference here between these and say a car convertor?
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Old 05-19-2010, 10:39 AM
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I was simply adding that you will need more stall for a 4000# vehicle than a 2800# vehicle. 4000# might not be heavy for a truck but its plenty heavy when the engine is trying to get it moving from a dead stop.
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Old 05-19-2010, 01:53 PM
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You need to truthfully evaluate how you will be actually using this truck and pick a camshaft and torque converter that will perform under those conditions.
The cam is too big for efficient towing. What you have now is a moderate hot rodder cam for a Camaro. A high stall and towing do not go together.

Establish the engine rpm you will be using when this power is required.
the Towing rpm. Then pick a camshaft that works in that rpm range.

Haviing worked with vortec motors and the th700r4 and converters.
I suggest a cam like this

214-224@.050" .442-.465" lift 112LSA
a 1.6 rocker arm on the intake side helps. .471" net intake lift. 1.5's are fine on the ex.
any simular duration cam like this will work very well.
This one is Lunati's "Bare Bones" cam + lifters #10001LK


the 1800 stall you HAVE now will work well. If its actually that converter.
(by your discription what you have there seems very tight)
(GM also has a very low stall factory converter that will definately give you idling issues with the cam you have now.)
I suspect this is the converter you actualy have installed.
A proper stall test will confirm the converter stall speed.
the gm 2100 stall corvette s -10 converter is a good choice too.
it locks up.

Then it will idle correctly and drive and tow with lots of torque and power in the rpm range you will be using. OD will actually be of some benefit.
Do not tow in OD. The trans will break.

watch the amount of vacuum advance. 18deg of vacuum advance is excessive without egr. I would limit it to around 10-12.
Most vortec motors don't need a lot of advance. I would limit the mech advance to around 32-34deg when towing. Excessive advance is not your friend especially when towing under constant engine load.
get a afr gauge/o2 sensor and dial in the carb.
4000#'s is heavy

Last edited by F-BIRD'88; 05-19-2010 at 02:23 PM.
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Old 05-19-2010, 02:42 PM
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Funny you should mention that cam FB, that is the same one that I was looking into originally, blue racer cam that I actually ordered and then changed my mind and went a bit bigger with the lunati..here is the thread
http://www.hotrodders.com/forum/crane-cam-specs-174693.html

Thing is I plan on keeping this motor/tranny combo no matter what happens to the truck. I tow/haul very few times a year but it is nice to have the utility of the truck if I need to. I have always wanted a 67 camero, I kept my old 350 block and 3 speed stick that came out of this C10 and if I find the right project car this 383 and 700 are going into the camero and the spare 350 will be right back to were it started in the C10. You are correct it is really a science to be able to plan and execute an engine build for any custom car/truck, too many of us rush ahead without first thinking about what we are intending to build and for what use, then end up with some type of mismatch of application, mine in this case is a minor one as over all I am very satisfied with the engine/tranny/truck and I learned alot both here and just by doing it mostly on my own with these hands, a couple of friends, a great engine builder (short block) and a few dozen canadian...I am rambling now, this could be in the lounge...thanks to all...peace
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Old 05-19-2010, 03:02 PM
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Try some more initial base idle timing. like up to 24deg at idle.
give it all it wants at idle.
Find out what idle advance the motor needs to idle in gear.
Then recurve the distributor to allow this, without excessive max advance at rpm. (shorten the advance curve stop limit)

if you want to work with the cam you got, get a 2800-3000 stall lock up converter. 245MM. www.converter.com Just right for your future camaro.
A set of 4.30gears would be just right for the 383 lunati cammed truck w OD.
A OD would then be actually usefull. Cammed up motors need rpm, lots of gear and a loose converter.

3.73's is barely getting with the program with this engine combo in a truck with OD. More gear=more fun. remember OD reduces the gear ratio by 30%.
The more gear the more effective the 30% reduction in OD.

4.30 reduces to a 3:1 ratio in OD. The taller the tires, the more you need the gear.

Last edited by F-BIRD'88; 05-19-2010 at 03:16 PM.
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