Koda

I am slowly putting this H/O right. It was restored by one previous owner, and a later owner did a chassis restoration and hotrodding. Many things deemed unnecessary were gone. I put some of them back, like a backdrive linkage, but have left the TPS tree gone. The distributor is on manifold vacuum. I tuned the carb to highest vacuum and idle 650 in gear, AC off. AC drops idle to 600 or so. It idles about 1100 out of gear at those idle settings. This is similar to another quadrajetted GM car I have that idles at 1000 out of gear, 650 in gear, and 600 with AC on.

There is a somewhat rowdy cam in it. I have not taken the engine apart to read the numbers, nor degreed it. There is lope to the idle, it is fun to drive, and it has no vacuum to speak of unless it has warmed up a little. There is a cleverly hidden coffee can sized vacuum reservoir in series with the brake booster for more vacuum reserve. It has no vacuum related drivability issues once it has warmed up off the first fast idle stop.

From a stop, letting off the brake in gear with no gas presents a decent rolling start. It is not bad, but I think it could be less. When putting it into gear, it jerks a little going into drive, and a lot going into reverse. I would like to correct this behavior. Car drives and shifts well, with only issue being the kickdown does not work (separate issue).

The root cause of this behavior is that the idle out of gear is too high. I can't lower the idle because the car will not run at idle in gear. Either I need to make the engine idle "stronger" so that it drops less idle while going into gear, or I need to find out what converter is in the car and get a new one that has a slightly higher stall so that the converter does not pull the idle in gear down as much. Either way, there needs to be less difference between in gear idle, and out of gear so it lurches less going into gear. While it is possible there is a broken mount somewhere, I think that the idle drop from out of gear to in gear is too much, regardless. If I've still got a stock converter, I would think it would stall at 1800-2000. Stepping up mildly to a 2400 stall or so might improve the issue, but still keep it at the same manners on the street.

Other than the cam, I believe it to be stock 72 455, th400, 3.23. Tires are 225/70/r14 Cooper Cobras. It has a slightly rougher than stock idle when warm (really rough when cold) and will boil the tires on command.



I enjoy the car having extra power over stock, but do not drag race it and I drive normally most of the time.

matt69olds

Can you bump up the initial timing a bit? That would raise the idle speed, and allow you to back off the curb idle screw. Does the vacuum advance add a bunch of timing at idle?

A good quality converter won’t feel mushy at part throttle. You could easily go 2500-2800 and it will drive like a stock converter, until you stand on the loud pedal.

Fun71

I agree. My engine responded favorably to increasing the idle timing to 18* and connecting the vacuum advance to manifold source. Prior to that the idle vacuum was a bouncy 14-15 which caused issues with the power brakes, but afterwards it was a solid 16 and the brakes worked like factory.

My car has a Hughes Performance 2500 converter, and during normal driving it feels just like the factory converter - normal shift points, no noticeable slip and typical RPM during low throttle operation and highway speeds, but 2500 RPM at WOT.

fleming442

If you're not taking it to the track, you don't need it. I have a friend that put a high stall converter in his IROC, and he hates driving the car anymore because it's always in stall at cruise speed. You only need to flash the converter higher to hit the tire harder on sticky tires. You'll never need it on the street.

matt69olds

Sounds like a cheap converter.

To a certain extent, stall speed os related to input torque. Let’s assume a converter has a stall speed of 2500 in a lightweight underpowered car. Take that same converter and put it in a big heavy car with a stout big block, that same converter now has a 3000 stall speed. Nothing changed but the load.

One of the things cheap converter builders use to do is bend and weld closed the “windows” in the pumps and turbines. While that does increase stall speed, it makes for a very sloppy, unresponsive car. The converter makes a ton of heat, lots of stall speed, but the car doesn’t go anywhere. Remember the GER converters and transmissions that were advertised in car craft/hot Rod magazine 30 years ago, they were well know for that nonsense.


Cheap builder would bend and pean the vanes on the pumps/turbines to close them off, basically making them useless. Very inefficient.

Fun71

Matt, it seems you are saying efficiency and stall speed can be independent of each other. It’s good to hear the real information from someone who knows this stuff. Keep it coming, we all benefit from your knowledge!

Koda

I could add. One issue is that I think my distributor curve is also not good because I have too much on the top end. I will confirm the vac advance at idle.

Noted. I will report back with timing and vacuum settings. It may be next month.

I don't want a high stall converter, I may want one a little higher than stock. With a 3.23 rear end, 2400 stall on 225/70/r14s puts you that rpm at 58 mph.

I'll get more info once I have time to work on the car late this spring.

Fun71

FYI, my car had a 2.56 rear for a while during the 3.23 rebuild and the Hughes 2500 converter worked very well. No excessive slippage when cruising below 1800 RPM, performed just like the factory converter. I would say any of the quality converter will have low slippage at nominal RPM, then flash to the rated stall at WOT.

fleming442

My point was more of: why do you even need a higher stall if it's just going to knock the tires off?
Automatic transmissions are voodoo.
Yes, the guy with the IROC probably cheaped out. The funniest part is that his buddy is spoda be a trans guy. 🤣

OLDSter Ralph

John, think about what Matt69olds is telling you. I think you are trying to overcome a carburetion/ignition timing issue with a higher stall torque convertor. My W-30 cams (308/308 and 328/328) idled at 900-950 RPM's. The higher your curb idle is in neutral/park, the harder it will slam into gear (forward or reverse).

Koda

Ralph, I appreciate it. This is just getting knowledge now. I really think my distributor does not have enough initial timing because it has too much centrifugal, which blows my WOT way out of whack. My issue is the idle change between the park and gear is too big. This can happen due to many things, of which I need to narrow down. I want my in gear idle min of 650.

I am going to see if the vacuum can is in play at out of gear idle. Simple fix for that is putting it on ported (it's on manifold now). Then I'm getting more timing data.

Were either w-30s automatic?

OLDSter Ralph

John, you may want to think about what effect the TPS tree had on things.
Start by setting total timing at 34-35 degrees with all centrifugal advance in (vacuum advance disconnected and vacuum line plugged). From there you can start working backwards to find your initial timing. You'll also need to figure out what adjustments have been made to the carburetor, that are messed up.
I have used the 308/308 in two cars. My '65 442 (with '66 E block) was a Muncie M21 with 4.33 gears. The 2nd car was a 1968 H/O (w/o A/C, W-45). It was a TH400 because manual transmissions were not available.
328/328 was in the 1970 W-30 with a TH400. .

matt69olds

The late 80s Grand National, Olds 442 and more than likely the Monte Carlo SS used the D5 coded converter. The turbo GN could push that converter to 2800, the lesser V8 engines would go to about 2500. GM would have never signed off on a converter design that would result in customer complaints or warranty work.

Im sure Joe probably has a parts book with the specifications, but the automatic W-31 and other rowdy engines all used special higher stall converters.

Flemming, you say automatics are voodoo, I feel the same with manuals. People say manuals are more fun, to me, whatever makes the car faster is more fun.

People also swear manuals are lower maintenance. For daily drivers, I’ll agree they have a slight edge, but in a race car forget it!! I know this is a bad example, but look at the Hot Rod garage or Roadkill shows, they are always tearing up clutches, driveshafts, no thanks!!

A friend use to own a stout (for the time) 4th gen Camaro with a 6 speed. The car ran mid to low 11s, but he was always tearing up ring and pinions and clutches. Granted, the rearends in those cars were made of glass. It was a trade off, the car ran quicker dumping the clutch, but at the risk of tearing up the rearend. Be easy on the launch, the car was a little slower, and harder on the clutch. He finally went to a 400 trans, the car ran just as good, and he rarely had to work on it. Once again, in my opinion, same performance, less maintenance, equals more fun! Win win!!


My first new vehicle was a 93 GMC step side short bed truck with a 5 speed 305 engine. It was a gorgeous truck, but underpowered. I wanted the 5 speed because it was cheaper. For the most part it was ok, until I got caught in a 3 hour bumper to bumper traffic jam around Chicago, I decided then manuals suck as daily drivers!!!

Koda

Ralph, the reason I asked about the w-30 cars is I was wondering what idle drop, if you recall, you experienced going from neutral to drive.

I will confirm timing and report back.

I do not have a TPS tree, removed by previous owner.

My understanding:
First function: If engine is "hot" as defined by sending unit in base of tree, put tree into mode to give manifold vacuum to distributor vacuum can at all conditions until cooled off from "hot."
Second function: Deny vacuum to distributor vacuum can until car is in top gear, then allow ported vacuum.

One would think this switch should be just manifold, since the transmission keeps it locked out at idle, so the ported part seems unnecessary.

Putting all this together for my issue, I need to see if park idle is high enough to be pulling vac advance on manifold. Also need to make sure I am not pulling ported vacuum at idle by having too much throttle. I will check with vacuum can disconnected for change.

OLDSter Ralph

I don't recall what the "idle drop" was. I can tell you that I didn't drive it with one foot on the gas and one foot on the brake pedal with the 308/308. I should also mention the factory '68 H/O used the same torque convertor as a Pontiac OHC 6. How do I know that ? Because I was headed to the 1969 NHRA Spring Nationals in Dallas, Texas in a couple days and the torque convertor needed replacement. They literally went down and pulled one off the assembly line and sent it "Next day Air" to my dealer. This was done under "warranty".

Matt69olds has good ideas and Joe P could provide some wisdom.

GEARMAN69

Any 12" slightly looser converter rated 2000-2200 or prefer 2300-2600 rated 12 inch would reduce the drag at idle and dropping in gear softening that load and have much less rpm drop so you can then finer tune your idle to what's best.. A 455 that has enough cam to lope should have something looser than a super tight stock 13" th400 converter or its a mismatched poor combo .. Had a Hughes HD BOP GM25 converter was pretty good lasted a long time while be driven and drag raced on 455/454 12 and 13 sec combos in heavy vehicle with 3.08's but for just cruising and such plenty of options but the C10 eventually shredded it (the Hughes)

69HO43

True. D5 converters were used on the "performance oriented" 200-4Rs. Obviously they were slight stall converters. GM did sign off on the 83-85 OZ shift calibrations which by 1986 they finally did something about the complaints they received up til then from the unknowing public about the hammer-shifting 200-4Rs in the 83/84 H/O and 85 442. While still "firmer" than the average slushbox transmission, the 1986/87 KZF shift quickness was dialed back so the 1-2 shift especially wasn't as harsh.

I can personally attest the OZ transmissions shift new off the dealer lot would break both tires loose on a spirited throttle auto shift from 1st to 2nd. As the clutch plates wore in, the hammer shifting did smooth out a bit, but on a wet road that could be a bit troublesome to adjust to.