Car slower with CNC ported heads?

MEV

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Sent my heads in to have them CNC'd. They look beautiful. Flow numbers were a big improvement over unported.

While the motor was out, I installed new bearings, Installed a windage tray, and had the motor line honed.

Other than that, I made no changes. Yesterday I went to the track and went slower than my times with the stock stealths.

Last year I ran (stock stealths)

1st run 12.84@ 104.43, 60' 1.782
2dr run 12.90@ 103.16, 60' 1.754
3rd run 12.80@ 103.95, 60' 1.761


Yesterday I ran (CNC ported stealths)

1st run [email protected], 60’ 1.847
2nd run [email protected], 60’ 1.846


505 stroker, stealths, full TTI exhaust, 830 quick fuel, perfromer RPM
Comp hydraulic roller XR280HR-10
2800 Stall
4767lbs race weight
3:23 gear with detroit locker
275/60/15 M&H racemaster drag radials


This is frustrating, anyone have any ideas?

UPDATE: Played around tonight, the trans is shifting weird. Its taking about 2-3 seconds between the 2-3 shift. I will mess with it to see if it was part or all of the problem.
 
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1st run 12.84@ 104.43, 60' 1.782
2dr run 12.90@ 103.16, 60' 1.754
3rd run 12.80@ 103.95, 60' 1.761


Yesterday I ran (CNC ported stealths)

1st run [email protected], 60’ 1.847
2nd run [email protected], 60’ 1.846

Reaction time, temp, humidity, track stickiness, tires, have you gained a lot of weight? was it the same track?

plus what stan said probably
 
That's too bad that you have these results but if is not surprising.
I'm not intending to be critical but I've seen this happen all too often.
I Agree with Stan's comments 100%

I rarely comment on threads like this but if you will indulge my comments here.
I offer this text all due respect to the car owner that is trying to improve the performance of their baby. :)

I used to work for a performance parts supplier and I can't tell you how much stuff we sold to guys that had no solid information on what would work other than seeing their buddies with a set of Hooker headers or a big 4BBL CFM carb.
Every weekend we would see them back in buying more stuff maxing out their CC's or fists of cash trying to fix the problems they had created for themselves. the owners loved it and would warn us against advising the customer on how to correctly buy the right parts..

Most bolt on upgrades have to work in conjunction with other off the shelf items in order to gain good results over the OEM design, and it will never be perfect.

If you are doing the upgrades based on a friend or parts jockey telling you that it will increase performance is a sure ticket to spending money hand over fist and never finding the true reason or never getting the results that you want to see.

There's no mention of blower or S/C to scram the air/fuel mixture down the throat of this beast.
If it naturally aspirated then it may be starving for fuel...
What about the exhaust? is it tuned for the extra easier flow? too long or too short will either cause a bottle neck or evacuate the heads faster than they should be and a huge loss in HP

The volumetric efficiency may have gone down but there are other things to consider as well

Even the timing being off a bit can have a negative affect...
What about weather conditions? hot or cool day? damp or dry and sunny?
It needs a good computer to diagnose this at the track.
The #1 tool in the box these days is the on board computer & laptop.

No race technicians can go by their gut feeling anymore these days and it's not trial and error like back in the 60's of drag racing..

100% positive results will never be achieved without computerizing this setup or bench testing on the dyno
It's all trial and error and depends how deep your pockets are.:(
You are probably back to square one...

And I haven't even touched on the trans & gear ratio's :rolleyes:
 
Torque and horsepower most likely moved up the RPM range with better flowing heads. The tenth you lost in the 60' is showing directly in the total time. You need more converter and gear to get the engine to the higher torque level higher in the RPM range to gain your 60' back. You also need to make timing and fuel laps. Write down your timing specs make a pass bump it up 2° make another bump it up 2° until it goes slower, then the same with fuel, but with your carb and a air/fuel meter and a deserted road you can get close.
I am having these same issues with my Challenger with a 400 no bottom end once it hits 3000 it becomes a different animal. Good luck.
Went back and read OP, did not realize you had same steaths. Timing will most likely not change, I would focus on fuel and converter.
 
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Who CNC'd them?

Who flowed them? Just because the sheet says they flowed X before and Y after might not be so.

How do the mid lift numbers compare? Giving up mid lift flow to max out peak numbers can change your cam requirements.

Modern is who does them for 440Source and they have an excellent reputation.



I'd check all the obvious stuff first. Too much preload on the lifters comes to mind as that would have been disturbed changing the heads.

Carb jetting and air bleeds could be out of wack now because of increased flow.

Kevin
 
Forgot to say this is a street car, I drive it year round.

I drive it to the track 70 miles and bolt on the drag radials and make a few passes, then change tires and drive 70 miles back home.

There is no room under the hood the performer RPM has the air cleaner about 1/4" from the hood with the drop-base air cleaner baseplate.

The flow was better at all lifts form .100 to .750

I will add some timing.
 
Your 60 foots are off a ton. If the track & track conditions are same or very close then there's your problem. Your lower end grunt moved up the RPM band. Also your ET's are very inconsistent. That's a lot of weight your are carrying down track.
 
I will add some timing
Although easy to do, I would look at fuel, that carb is as good as it gets for adjustability so your power is in there just go find it. A air fuel ratio meter and someone to write stuff down as the car pulls through the rev range would be invaluable at that point. Most of the readings you are after will be from 0-60 mph so you don't even really need to go to the track, some deserted roads or even freeway on ramps can work.
 
Assuming the flow sheet isn't BS, I'd add some jet and see if it slows down. If it goes faster, keep adding fuel until it slows down.

Timing should be good at 36 total. You can try a couple degrees +/- .

Kevin
 
I had my 520" stroker professionally built for street and strip duty by a place that builds a lot of drag racing engines and wild street engines. One of the things that gave this engine builder a lot of success and respect is that he custom ordered the cam based on what the heads flowed, the cars weight and rear gear. My engine was built with an emphasis on torque, not horsepower since it would be pushing 4500 lbs of '68 Sport Fury down the track with me in it. I agree with the others that say that you have moved the power band up the rpm range. Strongly recommend someone putting a bung in the exhaust for exhaust gas readings and tuning the car accordingly.
 
Moving more air, jetting needs to be richened up?
I thought I could read plugs and tune a carb until I got an AFR gauge. Money well spent.
Torque curve definitely moved up. Might be time for a converter swap.

PS did the intake get matched to the heads ?
 
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Who CNC'd them?

Who flowed them? Just because the sheet says they flowed X before and Y after might not be so.

How do the mid lift numbers compare? Giving up mid lift flow to max out peak numbers can change your cam requirements.

Modern is who does them for 440Source and they have an excellent reputation.



I'd check all the obvious stuff first. Too much preload on the lifters comes to mind as that would have been disturbed changing the heads.

Carb jetting and air bleeds could be out of wack now because of increased flow.

Kevin


Modern Cylinder head ported them. They outflowed the stock head at all lifts from .100 up to .750.
 
Moving more air, jetting needs to be richened up?
I thought I could read plugs and tune a carb until I got an AFR gauge. Money well spent.
Torque curve definitely moved up. Might be time for a converter swap.

PS did the intake get matched to the heads ?


The intake was matched to the heads as well as the gaskets.
 
While I am no expert on V8's I do know that on my Turbo BOOMNI I use a wide band O2 sensor so I know if I am within the air fuel range that I won't go BOOM! I do wish I had a dual wide band O2 on my Fury but since I don't push her I just read the plugs. But in your situation I would want more data.
 
Played around tonight, the trans is shifting weird. Its taking about 2-3 seconds between the 2-3 shift. I will mess with it to see if it was part or all of the problem.
 
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