I have a GS 400... The 400 is bored to a 435 with 400 hp... decent cam, stage 1 heads, and 750 QJ. I am using a 200 R4 with a 2400 stall. Whenever I shift into gear, I lose a ton of vacuum and the engine wants to stall... especially when it is colder. I have a couple other friends that have the same problem with their 200 R4. Is this typical? Anyone have any ideas? Thanks!
First thing to do is plug all vacuum lines and see if the problem goes away....if so, you have a vacuum leak. If not, possible the converter goes into lock-up mode immediately???
Cason... engine is perfect.... George... all new front to back... already checked, no leaks... Also, like I stated, I have a couple friends with Olds and Chev with the same issue. We are all looking at the tranny... The Olds did not have an issue until he had his tranny built for the hp. o No:
I have a 200R4 in my car and do not have a problem like that. Sounds like your losing spark timing advance. How is your distributor set up? Put a timing light on it and see if you are losing advance when put into gear. With longer duration cams you will need to run more initial timing to help out the idle qualitiy.Weak springs on the advance weights may be allowing the mechanical advance to be in at say 900rpm when you set timing and drop out put into gear at say 650rpm causing low vacuum and wanting to stall. What are your cam specs and idle speeds? Are your friends running bigger cams in their cars? Carb setup will may have to be tuned on also to help out the idle quality.
What is the vacuum with the engine running, in Park, fully warm? What is your initial timing, and do you have lighter springs in the distributor? What are the specs on the camshaft? It could be a lot of things. The converter may be too tight for the cam you are running. You say it is a 2400 stall, but it may not stall to that behind your engine. Manufacturers typically specify a stall speed, but it doesn't really mean much. Unless you have a converter built for your combination, it may stall quite a bit lower.
Trans: I think torque converter as well. Sounds like its bogging the engine down at a stop. The vacuum loss could be a result of the motors impeded rotation. another thought: Distributor: are you in the mechanical advance curve enough in P or N such that when you select a Drive gear you lose not only the normal amount of RPM but also a bunch of timing as the weights come back in, causing loss of more RPM etc...and bogging the motor? (EDIT: LoL three timing posts in like 4 minutes. maybe something to it)
I don't see how it could have anything to do with the transmission. The 200-4R doesn't have any vacuum to it. Sounds more like a carburetor adjustment. What is your idle speed in neutral? What is your stall speed? All this comes into play when you engage the transmission. I would think if were the lock up it would kill the engine instantly. The lock up doesn't work in 1st gear which is what you would be in at a standstill. Maybe you could try a different carb. Bob H.
This is actually a very common problem, and it has nothing to do with the transmission. It's usually a combination of timing and carburetor. The converter may be too tight, but if he is in the mechanical advance curve at idle speeds, it will cause a rapid loss of RPM when put in gear. Running a small block carburetor on a big block can also contribute to this.
Thanks to everyone who responded. I will need to get the car out and start checking vacuum, rpm, etc. I do not remember the specs on the cam. I was looking for some additional thoughts before pulling things apart and/or replacing things. It is always better to get a few opinions to find out how common an issue is and what others have done to correct it. Thanks!
I agree with Larry. Combination of timing and too small a carb. That 750 might be enough for a 350 or a mild 400, but is too small to feed 435 C.I. Carb is secondary to the timing issue though. Simple test would be to put in some strong springs on the mechanical advance weights, reset the initial timing, and fire it up again to see if that helps it.
Just to let you know. On my 200 r4 I drop from 900rpm to 750 when I put it in gear. Mild mods on the trans, 2800 stall D5 converter. Will idle just great in gear. I have a 413 cam and run 22 degrees of initial advance. I do know that a "big " cam on a Buick likes all the initial you can start the motor with. Just for a trial start the motor, kick the timing up, adjust the idle and then put it in gear.` Too small a carb will not cause this type of problem. I just switched from a ported Holley 950 HP to a QuickFuel 650 BAN and had no issues with idle and general drivability.
