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Car feels like it is driving itself. Too small converter?

5K views 31 replies 6 participants last post by  BogiesAnnex1 
#1 ·
Hi everyone.

I have a friend with a 1986 Camaro with a L98 350, 700R4 trans and 2400 B&M Converter. Engine was bored .030 over with factory CC spec pistons Has Edelbrock performer heads 350-60859 60cc and a TPIS mini ram intake and Lingenfelter Cam Shaft: part number 74219 (219/219 .525/.525 112deg).

He has had an issue with the car for the last couple years but got fed up with it and has kinda pushed it aside. I went for a ride in it a week ago and idling down the road the car does 25-30 mph. It feels like as soon as you put it in gear it wants to drive. We were able to verify that the lockup converter is locking up while driving down the road and it unlocks if you hit the brakes while crusing. So at this point I feel safe that the converter lockup is not the issue. Could it be that the coverter is too small? Short block was supposed to be built to stock CR but with the 60cc heads I would think he has got to be pushing 9.5-10:1 cr.

I am going to be posting on TGO a datalog from driving around the neighborhood to help figure out an issue with the idle quality. Engine runs very rough but with the stock narrow band it is hard to see where the AF ratio is. I know its richer than stoich but plugs aren't showing anything crazy rich. Maybe the issue with the engine idling/running is also causing the driving issue?

Would you want a larger converter or do you feel there are other issues elsewhere that could be causing the issue?

The vacuum at idle is about 16" which I feel is a little too low but it is steady.

Thanks
Shane
 
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#6 · (Edited)
. I would think with that size cam and EFI and the decent compression ratio, it would idle slightly lopey at about 600 RPMs... although the ECM may not like the vacuum at that low an idle...


. With a 2400 stall converter, should be no problem at all even at 800 RPM idle...


. If the torque converter lockup solenoid is going bad, that can cause problems getting it fully unlocked, such as stalling the engine when braking to a stop... common problem in 200-4R's, not sure about 700-R4's...


. 350's didn't come in '86's except for apparently a special run of 1,000 Camaros where GM might have been using it's customers as guinea pigs to test reliability...


. The TPI 350 is a low RPM torque engine all done building HP by 4500 RPMs, so the stock torque converter stalls way down about 1100 RPMs at which point the rear tires are spinning and rear of car sliding all over when powerbraked... is he sure he has a 2400 stall and not a stock converter... I could see this problem with an 800 RPM idle and stock converter...
 
#12 ·
Sorry for the long time between updates. We followed a couple different procesures and.none seemed to help. The slider was already bottomed out in the adjuster housing. Pulling it out should yield faster softer shifts which it did. Light throttle cruising before any adjustment yielded 1-2 shift around 10mph and 2-3 shift under 20mph. When lengthening the cable the 1-2 shift was under 10 and 2-3 was around 15.

Any ideas?
Thanks
Shane
 
#18 ·
Honestly he got taken for a ride by a local shop. He wanted a reliable car with a little extra grunt over factory and he got a 10:1 cr motor with aluminum heads and forged pistons and a decent cam and now he is having drivability issues with the car and the entire engine shakes. I think the rotating assembly may be out of balance but I want to disconnect the converter to rule that out.

So you think the converter stall is lower than rated? I used to have too small of a converter in my car and it would lurch forward when put into gear so it would make sense
 
#22 ·
Shane;

you really need to get a pressure gauge on that thing before it costs your buddy some more money. Also note; if hes a friend and the trans grenades under your care...people get "weird" fast. Trust me on this one LOL no good deed goes unpunished. Buzz linked you to a Freakshow converter; those aren't 700r4 converters though, that will be a little more money (around $400 I think). However, A phonecall to Michael directly will answer any converter questions you have. He and I aren't friends or anything, but Im a manual trans specialist, and I refer people to him all the time, with zero complaints.
 
#23 ·
I think we are going to unhook the converter fasten it back into the trans and start the engine up and see if it still is shaking. It seems like all of the issues have started ever since the converter was installed.

If it fixes the vibration we will pull the converter and get a different one ordered. Once that is installed we will get it to a shop that has a gauge to set the TV correctly.

Thanks guys!
Shane
 
#24 ·
. That 219/219 cam will lope at idle, but should smooth out as soon as some RPMs up... unless sparkplug wires on the wrong plugs... they have a magical way of getting on the wrong plugs once removed...


. TV cable geometry is critical on 700-R4 and 200-4R trannies... might also have a broken spring in the tranny governor...
 
#25 ·
Plug wires have been checked 2 or 3 times at this point haha. We are going to be installing a wide band in the car soon to hopefully figure out the rough idle. Plugs look perfect but engine shakes at 900rpm idle. With this combo and the stock comverter the engine idled smooth around 800rpm. It has a lingenfelter camshaft in it.
 
#27 · (Edited)
Will definitely do that.

Can you guys recommend some converter brands that he should consider? I have heard good things about hughes and will probably get one for my 200-4r and wanted to recommend one to him.

Also maybe a stall recommendation. I was thinking 2600-2800. I was always told go higher than lower.

Edit:

Forgot about that crazy 1st gear those trans have. Maybe 2200-2400?
http://www.summitracing.com/parts/hup-22-25l
 
#28 ·
I've got two cars with Precision Vigilante converters. I'd have a hard time being convinced there's a better converter for the money. They are expensive (~$800 for a single disc l/u), but the 3400 stall in my turbo truck drives like a dream and it cut over a half second off my 60 ft time and 1.4 secs off my 1/4 mile time. Being a 9.5" unit, they're about half the weight of a restalled stocker and also have anti-balloon plates so you don't wipe the engine's thrust bearing...

Russ
 
#29 ·
Michael @ Freakshow builds custom convertors. These aren't reflashed stockers or rebranded service parts convertors. The prices are usually less than ~$500 and include anti balloon plates along with a fair amount of Q&A to help pick the stall RPM. Service after the sale is excellent, and you're dealing with THE guy. Start with Michael, call the other guys (Coan, Precision, etc)...you'll come back. Also note; he has the "Yellow Bullet" seal of approval, which is pretty damned amazing since those guys hate everyone LOL
 
#31 ·
The LS crowd likes "Yank" converters, I have no experience with them. The "biggies" like B&M, TCI, etc make generic "fits all" converters that may work or may not. A few years back, the turbo Buick guys were all jumping on 9/11 converters, a 9" turbine with an 11" l/u clutch. Things change. Best to get with a custom builder, give them your data, and get a quote.

Russ
 
#32 ·
Just not enough cam to justify that much of a high stall converter. Not going to get into the usual converter arguments but if an advertised 2400 RPM stall converter is tugging the car against a 600-700 RPM idle somethings not right about the converter.

Another thought is if it has a lock up converter it might not release fully which would cause the same problem of tugging.

Bogie
 
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