Vacuum for this 228/236 duration cam? 455

So heres the latest:

I had the engine up and running, tuned the carb around town and ran into a problem where the engine would lose power, break up and backfire out the exhaust anywhere over 4250 rpm. any gear.

Long story short, I chased fuel and ignition til I was ready to lose my mind....assuming the engine builder knew what he was doing. Then with the help of Jim Weise, Larry the Wiz and Chris S (thanks you guys are the best), I took a good look at the valvetrain.

The installed pushrods were horribly long. Thanks to Rhett (Bigpig455) for the adjustable set!

And as Chris mentioned above, I had the (clearly new) dual valvesprings checked, and they had been installed at the wrong height, or were just super weak. the valves were floating.

The adjustable pushrods and a new set of Manley valvesprings later, the breakup / backfire is gone.

So Friday night, Rhett and I took our cars to the Dragstrip to tune a bit.
my best was a 13.3 at 101.2 with a 1.94 60 ft.

this was prior to my best tuning on the carb, which caused traction problems.

I started having real traction problems with the old 255/60-15s and my 60fts suffered, but by the end of the night I got the mph up to 102.04

I think if I can get the traction under control I could hit a 13.1 without changing much else.

(locked timing at 35, 2800ish stall converter th350, 3.23 posi rear)

I just went out and checked the vacuum readings and they are consistent with what Ive posted previously. I guess its just where its going to be. runs fine. Lots of power. though it smokes a little out the exhaust. not sure if its blowby or valveseals.

 

Gonna get you a set of 90/10's for your birthday although if you can get that car to hook, I'm im trouble!

Seriously, that was a lot of fun. Best racing I've done for a while.... I'll try to post pics when I get home. See if you can load that video to you tube!

 

Yep I had a blast. I just This morning told the wife *you know I'm going to have to get it in the 12s now right?*

I'll try to get the video up.

 

Time for some Drag Radials if those are regular street tires. Trying to tune a car for low ET's with regular tires takes half the fun out of it when you are trying different stuff to go faster. The inconsistent tire spin just adds another question mark. They make 255 60 15 M/T DR's If you are trying to go fast for a FAST or Stock Appearing class that is another story. If they are Drag Radials already how old are they or maybe time for some suspension work. Try removing the front swaybar to get the front end to come up faster. That is quick and easy and can easily be reversed.

Old news but that 187 cranking compression seems awful high with only 9.5:1. Where those valve springs dual or just a single with a damper? I can't believe duals would be that low seat pressure if they were actually made for a Buick head.

 

The old springs were duals. The machine shop locally that checked them suggested that they were probably for a pontiac application.

The tires are street tires.

Again, the 9.5 to 1 May be wrong. I've measured the compression myself, and have receipts for the pistons etc so that's what I would trust over the last owners word on the CR

I'm happy with how it runs now. I can blow the tires off on a low speed 2- 1 downshift.

 

update

added MT drag radials 255-60/15
added lots of fuel in carb
34deg total timing
holding shifts to 5500rpm

ran 13.1 at 102.17 w 1.94 60ft
air wasn't too great

Rhett and I were about dead even every time. wins by .017, .004 close!

looking for ways to trim more time!

 

I have a similar combo--TA 290-94, 9.3 with Sealed Power forgings, iron intake and exhaust. (and a carb from Ken )
I also have most of the same findings--likes lots of idle timing, etc. vacuum is around 12". My question is, how stable should that be? Mine is "around 12," but moves a lot between 11 and 13 or so. Not a steady pattern like a valve, just kinda constant, random fluctuation. I would post a video, but the car is in the paint shop. Will do that when I get the car back, but in the mean time looking for feedback. I always see numbers, but wonder how "steady" that should be.

 

Mixture and tuning issues may contribute to drifting needle.
Throttle blade position and relationship to transfer slots as well as power valve cut-in might be considerations.
RPM slightly creeping around...inconsistent valves sealing and/or valve job will definitely affect this, the list goes on....

Absolutely perfectly machined engines with tighter tolerances held behave very differently than ones with similar but inconsistent machining specs.

Timing moving around, obviously

 

I like this post.

Timing is the first thing to come to my mind when we see vac fluctuation at idle. be sure your mechanical isn't cutting in at idle rpm.

Next I think of throttle position and nozzle drip. if its dripping primary or secondary, it will wave the idle.

too rich of an idle mix will make for a wavy idle.

low vacuum can spawn power piston issues too.

after that, it gets a bit deeper.

 

Edited...it supports the direction of your last post.

(Thanks!)

 

I am going to add some more fuel to the secondaries and pull another degree of timing. I get some pinging at WOT in the pre winter cold air.

 

On the Dyno I always end up @ 34-35* on pump gas street engines.

 

When I first put the motor together I had a "bad valve" tick on the vacuum gauge, confirmed by a leakdown. Had the heads rebuilt again, and another leakdown test confirmed I have a good seal.
First head rebuild included "new valve springs." Granted an unknown quantity. Im assuming the rebuild of the heads by the more competent shop included checking them, but maybe not? Could weak valve springs be "in play" at idle?
After the head rebuild compression was still all over the place still, and I blamed lifters. Changed cam and lifters (from the previous TA 212 to the current 290-94H.) Have not done compression test sinceneed to.
Carb was built by Ken to my TA 212 specs. I have since opened idle air bleeds and mixture discharge holes.
Motor responds to mixture screws. Throttle plate/transition slot relationship was fine when I installed the carb, but have not evaluated since tuning.
I adjusted idle and mixture to get to the best possible rpm on the dwell tach, and vacuum. When I pulled off the vacuum gauge the motor speeded up, so I tuned the mixture more, to where an added vacuum leak slightly hurt.
I have not checked for nozzle drip. Ive seen John Osborne put two fingers down my carb. I know, academically, what Im checking for, but not sure whether I trust myself (No experience here)
Initial timing is 18. Im going to buy a MSD 6AL, and hope that helps, at least some.
Need to do a compression test again, obviously
Have not played with power piston, which I should Didnt think of that
I feel pretty confident that mixture and ignition are right
Finally, just trying to read between the lines I gather I should at least see a very STEADY 12?

 

Thought I would update this since I finally got back to the track.

My qjet was close to what it needed to be and is now running on the rich end of lean if that makes sense.

Track rental day with beautiful weather. First three passes 12.9@103 12.9@104 12.9@104

small changes to secondary rods, pulloff release, and timing really made a difference.

by the end of the day, about a dozen runs later, I ran a best of 12.68@105.78

The big change I had made was going with a set of 3.73 rear gears. The engine really responded well shifting at 5500.

Running without vacuum advance the car likes 34-35 degrees timing. Anything past that will ping on 93Octane pump gas.

I had another run where I went 12.877@106.08

my best light was an .002
and my 60 fts were about 1.83

 

That was a great day of racing...and of course the most important part: everything got driven home. I'd love to know true compression of that car and spec a cam to work with it. I think that car has low 12's in it easily. Meanwhile my combo is probably maxed out... gonna try headwork and back to cast iron up and down this winter..

 

Now that its hustling I've been working on the distributor for driveability etc

It really likes 20 deg initial. It starts immediately and gets great vacuum and idles smooth. BUT it's a bit much I think. It starts smoking out the tailpipe a bit.

So I've backed initial down to 16deg. The smoking stops at about 18 initial. Idle rpm 800 in N, about 650 or700 in D. It doesn't start as immediately.

10 degrees vacuum advance has had a HUGE effect on part throttle responsiveness .

I think there might be a little more in this setup, and I am thinking it's in higher shift points, more rpm, and most importantly a high quality converter.

When shift points got over 5500 5600 the power eased off. And I thought I heard it break up a little once. I am thinking a little more valvespring pressure cures that.

Great day of racing!

 

Very well could be. I know I have at least one seal coming apart. Although they were new a year ago.