360 + Trans + Merry Christmas

Bruceynz

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Merry Christmas Everyone! Thanks for all you help and advice over the year!! Have a safe and Happy New Year! Its summer down under and we have Christmas and summer vacation all in one, I finish work on 23rd Dec and not back until 9th Jan.

Ok Guys I go around in circles now and then, this is one of these times. I was trawling through the net and come across a 360 smogger build up. Here is the article here actually Dyno-Test 360 Smog Motor - Mopar Muscle Magazine

So this article got me fizzing at the bung, why does my 360 not perform well? From this article even a smogger can make ok power. Get some comp into it and even better power one would think!

Ok lets start with the trans, my friend from Oz is over on holiday, he has been mopar guy all his life, he has set up the kick down linkages many times before and said they are a right pain in the but, his current 440 uses a lockar cable system. Anyway he checked my set up, we checked the linear travel, I was under the car and he was working the throttle and checking the position of butterfly while I was under there looking at the lever on the trans telling him where it was pointing, his conclusion, "got me beat its set up perfect, couldn't have got it any better myself" so he says the A998 lock up has a problem, I said is it possible its got some sort of economy change points in it, it just wont go over about 3600-3800 1st to 2nd shifts so there is problem 1. I can manually shift it but I did that at 4000rpm the other day and the change was rather drawn out like trans was slipping. It just didn't bag through quick.

I got the vacuum gauge out last night and took some measurements, see attached photos.

IMG-20161222-WA0002.jpeg


IMG-20161222-WA0004.jpeg


So that's 12 inches at idle at 850rpm. give or take the accuracy of the needle thickness, but would be pretty close to 850rpm.

Now what does this suggest, will let the brains see what they think, but to me its got a reasonable cam in it, something like 1800 - 5800 or 2000 - 6000 or their abouts its got quite a rough idle but not what I would call lopey. Gets some revs on and it smooths out nice.

My igniton timing is at 34 degrees, I think I could probably get some more into it, maybe 36?? or 38?????

Now carb size, all the calculators seem to say 600cfm should be fine, but most of the articles I read seem to dump a big carb on a 360, say 800cfm, I have a 770 cfm street avenger would this be worth a try on it? Does a 360 just love a big carb? There are always funny things that can happen in an engine in the runners and how the heads load the fuel in, its to do with piston speed, stroke and how much the engine pulls in.

I am running an edelbrock performer intake and they have the 318 size runners/ports, should I be looking at a performer RPM with the 360 size ports to dump the fuel in?

** So for starters I need to get the trans sorted, with 12 inches or mercury that would suggest a stall converter of 2200- 2300 rpm? TCI offer a rebuilt 904 with a 300- 400 rpm over stock stall with a 350hp rating as a kit for about $1400 I think I saw.

Street Rodder™ Transmission Pkg: '67-Later Torqueflite 904 (318, 340, 360) - TCI® Auto

I think I can dial in some more advance too

I think I may need a bigger carb, got the 770 street avenger there.

Would I be unrealistic to think It would be possible to get 350hp out of a smog 360?

Merry Xmas and Happy F J M bodying!
Bruce
 
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kkritsilas

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Bruceynz:

Your vacuum at idle is low. I am seeing 12" of mercury at idle. This is one clue that your cam is too wild, and that you are losing dynamic compression. Normal factory vacuum is 14-16".

Mopar used Thermoquads (TQs) for most of the 1970s, and really only two basic models with a bunch of small canges to make them work in all sorts of applications. There was an 800 cfm TQ, and am 850 cfm TQ (difference was in the size of the primary venturis/barrels). They put 800 cfm TQs on 318s and 360s, and the 850 TQs on the big blocks, and a few high performance 360s. Truth be known, the carbs are vastly oversized for 318s and 360s. However, unlike most other types of carbs, the TQs operate in a idifferent way than most other carbs. THe primaries are a pretty normal sizem and operate in a pretty standard fashion. THe secondaries however, don't. The TQ has a spring loaded air door. When the engine demands more airflow, the air door spring is overwhelmed by engine vaccum, and starts to open. when it starts to open, more fuel is also sent into the engine. THe massive air flow numbers come from the enormous secondaries, which, as described, only come into play when the engine demands the extra flow. The air door also tends to smooth the amount of increase of air flow, so a properly tuned TQ doesn't bog, as you would expect from a really oversized carb. The air door also tends to act like a venturi somewhat, as the secondary barrels are not venturi shaped in the main body. The 360 is no different than any other engine, it is the TQ that operates differently. Because of the air door flow being based on vacuum, a TQ could have been a 1000 cfm carb, and as long as the primaries were not too large, it would still work fine. The large CFM ratings come from the huge secondaries, but they are a) not in use most of the time, and b) controlled by engine demand, so if the engine doesn't present any demand, they are not in use.

The problem is probably not your carb, unless it has an issue, or there is a gasket leak somewhere.

I have enclosed pictures of a TQ that I have sitting around. The first picture is the bottom of the carb, showing the fairly small primaries, and in comparison, the huge secondaries. The second picture is the top of the carb, showing the secondary air doors, and the "bumps (if you will) that allow them to act as venturis when open.

TQ bottom.jpg


TQ Top.jpg
 
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Bruceynz

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Oh well I remember my friend from Oz also said he thinks my car is leaning out when you hit the gas, carb is a new 600 off ebay. Can you change the ratio on the accelerator pumps to give it a bit more squirt?
 

80mirada

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My 360 hit harder, pulled longer and got better gas mileage on a 750 Edelbrock over a 600 Holley. Carb flow numbers are miss leading, and do not reflect the flow curve in operation
 

Justwondering

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Bruce -- you know I love you dearly -- such a trooper to keep working on that engine ...
BUT
I started chuckling at 'fizzing at the bung', then started a conversation with my husband trying to guess what it really meant til we were both laughing so hard at our made up definitions that we couldn't breathe.

Then I googled it.

Then we laughed even more cause we were so off base. Oh lordy, we are still chuckling about that phrase. I wish you good luck on the engine, but we are too occupied looking up other phrases in the Urban Dictionary...
lol
 

Bruceynz

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Fizzing at the bung, WOW! it must be a down under saying, what about spitting taks or pushing poos up hill with your fingers wide apart?

If you want to start a slang post feel free, I will have you full of giggles! We got some good ones down here!

Oh a good one, Fair Suck of the Sav? try and work it out before you google that beast and you will fall of your chair laughing.
 

jasperjacko

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12" is not bad for a performance cam. I don't think your trans is properly adjusted internally. You need to have the bands checked, line pressure, etc. It should not be slowly sliding into second gear.
 

jasperjacko

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your engine vac. has nothing to do with your stall speed.
 

jasperjacko

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Do you have the right type and amount of fluid in the trans? Seems like a dumb question, but it happens.
 

jasperjacko

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I would check rpms with a digital timing light. Many tachs are not accurate at low rpms. the timing light would be.
 

Bruceynz

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Does anyone know if the 1983 A998 had a economy valve body or something? I can't get mine to change very high in the rev range, come to think of it when it had a 318 in it on the trans it never seemed to rev very high either. This trans is killing my performance I reckon.
 

BudW

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I spy one of the hard to find TQ’s that has a built on choke (doesn’t use the divorced choke that 99.9% of all TQ’s use.

I love TQ’s, and for some reason I have darn near 80 of them in my garage (useable ones). The really odd thing is I currently don’t even have a 4-bbl vehicle at this time (except for my ’70 300/Hurst – but the original AVS is staying on it).


Sure the TQ has problems – but pretty much all carburetors have their own little issues. Once you know what the problems are – the rest is downhill.

Now the interesting thing is once I get my big blocks built (and if I have any money) I have plans on using 4-bbl appearing Fuel Injection setups and make all of those hard starting and cold drivability problems go away.
BudW
 

BudW

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Does anyone know if the 1983 A998 had a economy valve body or something? I can't get mine to change very high in the rev range, come to think of it when it had a 318 in it on the trans it never seemed to rev very high either. This trans is killing my performance I reckon.
Pretty much all Chrysler transmissions have the same governor settings (shift points) except for police and the much older high performance vehicles. So pretty much all Chrysler transmissions will shift at roughly the same times (except vehicles mentioned above) depending on gear ratio/tire sizes/throttle position.

I would agree with others, sounds like worn parts in transmission or another internal transmission problem (sticking valve, loose bolt, broken spring, etc.).
BudW
 

BudW

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Bruce, I don’t see any problem with the package you have selected – except for one “possible” item.

The link provided didn’t indicate that the transmission was indeed for a 904/998/999 anywhere (unless you are seeing something I’m not).
 
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