TH400 Vacuum Requirement

[Supercharged111]

My trans worked fine at 7”.

There's a joke in there, but being the gentleman that I am I'll let it slip by.

 

[69hurstolds]

My trans worked fine at 7”.

 

[pagrunt]

 

[mikester]

You sure it's completely broken in? I made 20-30 Dyno pulls and my motor wouldn't break in. Took about 10 minutes on the race track to get those rings to set. Then they continued to set in over the season. Granted that was a Dustin garage hone and nothing professional, but that was 2015 and it's no worse for the wear now. What's your duration, LSA/ICL?

LSA is 110 but heres the rest of the specs from comp cams.

Specifications:​

Engine Make/Size
Chevy Small Block (262-400)
RPM Range
2300-6500
Lifter Type
Hydraulic Flat Tappet
Int. Duration Advertised (Deg)
284
Exh. Duration @ .050 in. (Deg)
246
Exh. Duration Advertised (Deg)
296
Int. Duration @ .050 in. (Deg)
240
Usage
Street/Performance
Quantity
Sold individually
Lobe Separation (Deg)
110
Exhaust Valve Lift with Factory Rocker Arm Ratio (
0.51
Intake Valve Lift with Factory Rocker Arm Ratio (i
0.507
Valve Lift with Factory Rocker Arm Ratio
0.507 int./0.510 exh.
Advertised Duration
284 int./296 exh.
Computer-Controlled Compatible
No
Valve Springs Required
Yes
Cam Style
Hydraulic flat tappet
Exhaust Duration at 050 inch Lift
246
Intake Duration at 050 inch Lift
240
Duration at 050 inch Lift
240 int./246 exh.
Advertised Intake Duration
284
Advertised Exhaust Duration
296
Basic Operating RPM Range
2,300-6,500
Grind Number
CS XE284H-10
Exhaust Valve Lift
0.51 in (12.954 mm)
Intake Valve Lift
0.507 in (12.878 mm)
Manufacturer's Part Number:
12-250-3

 

[Supercharged111]

240/246 on a 110 on a small block? Yeah I can see that coming up a bit light on vacuum.

 

[mikester]

240/246 on a 110 on a small block? Yeah I can see that coming up a bit light on vacuum.

Yeah, it sounds pretty nasty. Still need a solution though. LOL

 

[83StreetMachine]

Does that vacuum guage read zero when not in use? Cuz if it doesn't, it's junk.

 

[mikester]

Does that vacuum guage read zero when not in use? Cuz if it doesn't, it's junk.

Yes, it does.

 

[CopperNick]

From where are you getting your reading? Vacuum at a carb port is going to vary from that right off the manifold. If you haven't, try getting a second reading off the same vacuum port that drives your power brake booster, if you run one. Otherwise there ought to be a pipe plug or some kind screwed into the manifold behind the carb and between it and the timer. Unscrew that and replace it with a vacuum fitting and/or reducer to screw it into place and try for a vacuum reading again.

Also, when you go for that reading, if the engine is at idle, give the throttle lever a fast whack and see if the vacuum numbers pop up.



Nick

 

[mikester]

From where are you getting your reading? Vacuum at a carb port is going to vary from that right off the manifold. If you haven't, try getting a second reading off the same vacuum port that drives your power brake booster, if you run one. Otherwise there ought to be a pipe plug or some kind screwed into the manifold behind the carb and between it and the timer. Unscrew that and replace it with a vacuum fitting and/or reducer to screw it into place and try for a vacuum reading again.

Also, when you go for that reading, if the engine is at idle, give the throttle lever a fast whack and see if the vacuum numbers pop up.



Nick

I got the reading from the fitting on the manifold behind the carb. Everything else was plugged. I kinda knew there was an issue the first time I drove the car. Brakes felt hard. I already planned on getting an electric pump for the booster but I hadnt checked the vacuum with a guage at the manifold. I thought I'd find a higher number. Especially after talking to the guy at Comp Cams. Told him it was a street car with power brakes and an automatic. The guy that built the motor said to take it down the road after I square the brakes away and see how it shifts. He said I might be able to adjust the modulator.