423 SBC combo help

[prairiehotrodder]

to answer a few questions :

the timing is at 38

a few of the pushrods do rub on the heads

the springs are the ones that came with the heads. Its not floating the valves or anything.

I would like my friend to get rid of the plastic intake, it always leaks oil. He has re-sealed it many times but it still leaks. I know a tunnel ram would be nice but he just purchased this big QFT 1050 so i think he will stay with a single carb for awhile. It would be nice to get this combo working right before moving on to other upgrades such as the t-ram.

The previous cam was way down on power as well, thats why we changed cams. Its running 10.50's after we leaned up the carb 2 jet sizes. checking for reversion sounds like an easy and worthwhile idea. I'm not going to post timeslips because i don't have them and it would be a bunch of guessing.

Also porting the heads might be a good idea. I wouldn't be the guy to do it, there is just to much money in them for me to want to touch them. We paid extra to get the fully CNC race version of these heads, shame that they would require porting at this level.

[PRH]

Reading through the other previous thread relating to this build, it seems like the new cam is noticeably slower.

So, you have to find a couple tenths just to get back to where you were.

I’d be inclined to put the old cam back in.

[Monza355]

At what rpm is the shift point and how much rpm drop after the shift ? What brand, type & size converter ?

[allens]

Attached are the latest times from last weekend, and the first run on the 16th data showing RPM, AFR and manifold vacuum, that's all the data I have to work with right now.

2020-08-16.png

2020-08-15-16-times.png

[maxracesoftware]

Attached are the latest times from last weekend, and the first run on the 16th data showing RPM, AFR and manifold vacuum, that's all the data I have to work with right now.
2020-08-16.png
2020-08-15-16-times.png

here's simulation of these 2 Runs :
10.500 ET @ 126.09 = 497.8 Peak HP @ 680.0 Feet
and
10.552 ET @ 125.88 = 491.3 Peak HP @ 682.0 Feet

[prairiehotrodder]

wow, can't have any better data than that ! Now we just need an interpreter.

From the graph :

2 step at 3500 RPM
flashes to about 5500 rpm
1 st shift at 7000 falls back to 5900
2nd shift at 7200 falls back to 6000
goes out the top at about 7200 probably holding it a bit beyond the finish line.

AFR about 11.0 most of the way

Seems the first 1/8 is better than the last half. Nothing is obvious to me other than its pretty rich. What do the pro's say ?
Thanks for becoming a member and posting Allen.
Brian

[Monza355]

Converter might be 3-400 rpm to tight based on the 7200 rpm shift. But however it seems to me it does recover nicely after the shift. Have you verified that the tdc is correct ? And have you varied the ignition timing at the track ?

[prairiehotrodder]

with a 29.5 tire and 4.56 gear and no slip at 7000 rpm its should be going 134.7 MPH. So i guess the actual number of 126 represents the amount of slippage in the convertor ? 126 is 94 % of 135 according to my math. Is that about normal ?

We did verify TDC last time the motor was apart. i think 38 was what it seemed to like. We definitely could use more testing. Is that about normal for a small block ? I'm used to my 555 BBC and thats it wants.
brian

[6.50camaro]

Wallace racing calculators say at 126mph the motor should be 6544 with 0 slippage . Going thru the traps at 7200 rpms shows 9.1% slippage . Thats how I would figure it. Dan

[maxracesoftware]

So i guess the actual number of 126 represents the amount of slippage in the convertor ? 126 is 94 % of 135 according to my math.
Is that about normal ?

i use 94.0% Lockup percent as a Program baseline for Converters , that's what i used in the simulations above ,
and it also calculates very close to 94.0 % from your Data .

[PRH]

5500 doesn’t seem like quite enough flash stall for that combo with a 274@.050 cam.

11:1 AFR....... seems like the carb could use some tuning....... no??

Did the old cam/converter combo 60’ any better?
Any data log info from the old combo?

My experience has been that those 1.590” venturi 4150 carbs can be a challenge to get to leave hard.

I’d have gone for the 950(1.450” venturi).

[Old School]

Is it possible to put up a chart/graph with the best run from the old combination?

[PRH]

Here’s a question for Larry.......

If you put that motor as it sits on your dyno........ do you think it would only make around 500hp?
Or do you think there are issues with the car/combo that are contributing to the power numbers looking way lower than what you’d see on the dyno?

To me it seems unimaginable that motor would only make the kind of power that the ET/Speed calculators/programs are coming up with.

In other words, if you didn’t know what the car ran, and was just looking at the engine build itself, like if it were someone bringing in the untested engine for you to dyno test....... what kinds of numbers would you be expecting to see?

[6.50camaro]

You went down two jet sizes and its still 10.8 to 1 AFR ? Nobody noticed this before .

[prairiehotrodder]

yes, it needs to be leaned out more. The track is 1500 feet elevation. Are other factors making it appear rich ? Such as reversion that was allready mentioned ? I've always thought that a carb shouldn't have to be changed more than 4 or 5 jet sizes from the box calibration or there is a problem.
Maybe the carb does have alot to do with the poor performace ?

Allen - you got any data logs from your 10.39 last year with the old cam and no exhaust ?