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Gains with lift beyond the point of max airflow?

General engine tech -- Drag Racing to Circle Track

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GARY C
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Re: Gains with lift beyond the point of max airflow?

Post by GARY C » Thu Jan 09, 2020 5:41 pm

CGT wrote:
Thu Jan 09, 2020 4:41 pm
steve cowan wrote:
Thu Jan 09, 2020 4:01 pm
interesting information from camking but my question is it possible to have reversion issues at IVC??
Absolutely..the piston is going the wrong direction. Increased rpm, displacement, or anti-reversion methods can allow a later one(ivc) before that point occurs...valve size, dc, seat angle etc are also factors.
Wouldn't this be due to duration and not peak lift?
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Re: Gains with lift beyond the point of max airflow?

Post by CamKing » Thu Jan 09, 2020 5:42 pm

steve cowan wrote:
Thu Jan 09, 2020 4:01 pm
interesting information from camking but my question is it possible to have reversion issues at IVC??
Reversion is a factor of having more pressure below the intake valve, then the pressure above it, when the valve is open.
You wouldn't have reversion issues at IVC. Having reversion issues between BDC and IVC is possible, but that's mainly controlled by duration not lift, and it would have to be way too much duration. The most common reversion issue happens right after IVO, because the exhaust duration and lift wasn't enough to drop the pressure in the cylinder below the pressure above the intake valve, when the intake valve starts to open.
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Re: Gains with lift beyond the point of max airflow?

Post by dannobee » Thu Jan 09, 2020 7:19 pm

Back when Super Stock had to run "stock" heads, they had huge cams and the throttle response wasn't bad at all.

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Re: Gains with lift beyond the point of max airflow?

Post by steve cowan » Thu Jan 09, 2020 9:04 pm

Camking,
Appreciate the response, going back to Travis original question, I still stand by my comment of increasing the ratio in his application with those heads won't net anything obvious in my opinion.
The valve, intake port is to small to feed a cylinder 351ci. Yes of course it will run but no matter what you throw at it as in cam and rockers it will be done before 5000rpm
I don't know those heads but I assume 1.75" Intake with a 160cc runner??
Hopefully Travis will clarify.
I ran my 10.5:1 comp 383 sbc last year with 165 cc cast iron darts 1.94"-1.5"
Runner 178cc 261 cfm at 0.600"
I kept the PRP small on purpose it was fast at 380 ft /sec
Over 12 months and 50 plus passes
2 x cams SFT
1.5,"1.6" rockers all different combinations
Cam timing sweeps 6 degs each way (belt drive) lash loops, different lengths of pushrods for different geometry including increased lift.
2 x converters, rpm shift sweeps from 5800 rpm-7200rpm
Timing and sparkplug heat ranges, timing retard but all this netted next to zero.
The only obvious gain was from rpm airgap to single plane victor junior, 2 tenths and 2 mph over the quarter.
I would bet money if I sized the pushrod pinch area better it would of picked up straight away before anything else, the single plane intake made more air available to the engine and might not go sonic choke at 6000rpm, would be more air available at all rpm.
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Re: Gains with lift beyond the point of max airflow?

Post by n2omike » Thu Jan 09, 2020 9:53 pm

steve cowan wrote:
Thu Jan 09, 2020 9:04 pm
Camking,
Appreciate the response, going back to Travis original question, I still stand by my comment of increasing the ratio in his application with those heads won't net anything obvious in my opinion.
The people actually doing it have proven otherwise.

If an engine is cylinder head limited, you want the valve to be open as high as possible, for as long as possible (within the duration requirements) in order to attempt to flow enough air to feed the engine. The higher ratio rockers get the valve open to the higher flow numbers faster... and provide more lift area under the curve withing a given duration.

More lift within a given duration is always a good thing... as long as the valvetrain can control it and there is no parts breakage.

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Re: Gains with lift beyond the point of max airflow?

Post by steve cowan » Thu Jan 09, 2020 10:37 pm

n2omike wrote:
Thu Jan 09, 2020 9:53 pm
steve cowan wrote:
Thu Jan 09, 2020 9:04 pm
Camking,
Appreciate the response, going back to Travis original question, I still stand by my comment of increasing the ratio in his application with those heads won't net anything obvious in my opinion.
The people actually doing it have proven otherwise.

If an engine is cylinder head limited, you want the valve to be open as high as possible, for as long as possible (within the duration requirements) in order to attempt to flow enough air to feed the engine. The higher ratio rockers get the valve open to the higher flow numbers faster... and provide more lift area under the curve withing a given duration.

More lift within a given duration is always a good thing... as long as the valvetrain can control it and there is no parts breakage.
respectfully,
i am not saying it wont help,i understand more area under the curve,i am saying in a near stock streetcar situation i doubt anything obvious by the seat of the pants type deal.
steve c

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Re: Gains with lift beyond the point of max airflow?

Post by travis » Fri Jan 10, 2020 3:55 am

These heads are closer to 130cc’s intake port, 1.78/1.45” valves :lol: The bowls are tiny, but they are thin where I really need to open them up, so I am am extremely hesitant to open them up any further. I need them to last longer than a few heat cycles!

1 of my big character flaws...I will second (and third) guess everything until everything is bolted together and running. I drive myself nuts with this stuff sometimes.

What was/is throwing me off is that running this thing through EA, it predicts a pretty sizable power increase when adding a bunch of lift to it, with similar durations and LSA’s...like going from .480-ish lift to .544”. Big enough gains that it is making me reconsider using these small heads and saving my aftermarket heads for a more worthy project (for a number of reasons).

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Re: Gains with lift beyond the point of max airflow?

Post by steve cowan » Fri Jan 10, 2020 4:11 am

travis wrote:
Fri Jan 10, 2020 3:55 am
These heads are closer to 130cc’s intake port, 1.78/1.45” valves :lol: The bowls are tiny, but they are thin where I really need to open them up, so I am am extremely hesitant to open them up any further. I need them to last longer than a few heat cycles!

1 of my big character flaws...I will second (and third) guess everything until everything is bolted together and running. I drive myself nuts with this stuff sometimes.

What was/is throwing me off is that running this thing through EA, it predicts a pretty sizable power increase when adding a bunch of lift to it, with similar durations and LSA’s...like going from .480-ish lift to .544”. Big enough gains that it is making me reconsider using these small heads and saving my aftermarket heads for a more worthy project (for a number of reasons).
Travis,
Thanks for clarifying sizes, intake port way smaller than I could of imagined,
All I will say is you have to try things for yourself and collect your own data, you have proven that you want to learn and we have discussed before about the cost of the so called hobby we have.
Try 1.6,1.7,1.8 rockers if you have them throw the kitchen sink if you have to , I really like it when people report back with dyno or time slips etc, means that they done the best they can I guess. :D
steve c

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Re: Gains with lift beyond the point of max airflow?

Post by travis » Fri Jan 10, 2020 4:23 am

Best I will be able to offer is a “SOTP report”, but I have some 20 years or so experience with these trucks with many mild variations of 351w’s so my SOTP meter is fairly well calibrated :lol:

If I ever get these other projects finished and sold I want to build something much nastier, but if I don’t get rid of some stuff first I may not live long enough :lol:

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Re: Gains with lift beyond the point of max airflow?

Post by PRH » Fri Jan 10, 2020 11:53 am

For these mild street apps....... I don’t overthink the cam.
For this application the heads are going be a big restriction....... and the motor likely won’t even make 1hp/ci.

I’d find an appropriate cam for the application out of your favorite cam suppliers catalog...... and then iiwii.

When I was involved with trying to sort out some oval track combos based on rules with limitations(heads, valve sizes, intakes, carbs, compression).
My experience with those was that you can make some pretty noticeable changes in the cam dept........ and have not make much difference at all on the dyno sheet.
You had to be totally out to lunch to lose 15hp.

We would use 1.2 rockers for cam break in.
Even swapping those out for 1.5’s or 1.6’s didn’t make as much difference as I’d have expected.

We tested an awful lot of cams that were within a few tq/hp of each other.

However...... on one of the lower class motors that used hyd cams, less cr, and no headers....... there could easily be a 15hp spread between the “preferred” head casting vs the less desireable ones........ with the rest of the build being equal.
And.......the preferred heads actually flowed less than several of the others.
Somewhat handy with a die grinder.

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Re: Gains with lift beyond the point of max airflow?

Post by n2omike » Fri Jan 10, 2020 1:15 pm

travis wrote:
Fri Jan 10, 2020 3:55 am
These heads are closer to 130cc’s intake port, 1.78/1.45” valves :lol: The bowls are tiny, but they are thin where I really need to open them up, so I am am extremely hesitant to open them up any further. I need them to last longer than a few heat cycles!

1 of my big character flaws...I will second (and third) guess everything until everything is bolted together and running. I drive myself nuts with this stuff sometimes.

What was/is throwing me off is that running this thing through EA, it predicts a pretty sizable power increase when adding a bunch of lift to it, with similar durations and LSA’s...like going from .480-ish lift to .544”. Big enough gains that it is making me reconsider using these small heads and saving my aftermarket heads for a more worthy project (for a number of reasons).
Sounds like 289 Ford heads, which come in at 126cc. I ported a set for a 306 that use to power the mustang. Got them HUGE at 155cc. Bowls were super thin (one cracked, but was fixed with JB Weld from the water jacket side) 1.94"/1.60" valves. Flowed 217 intake/176 exhaust. Ran 7.48 @ 92 in the 1/8 in a 3300 lb w/driver 1966 mustang with a toploader. Pump gas, 236/248 110 LSA solid flat tappet. Car was set up for nitrous. Ran 6.73 @ 103 and 10.63 @ 129 with a 200 hp plate.

The heads are terrible, but can work with smaller cubes IF ported to the max. I did these heads right before all the aftermarket stuff came out. I had more money in them (even with me doing all the port work) than a set of decent aftermarket heads can be bought for today. However, I did a LOT of street racing back then... and on paper, should have gotten beaten almost every race. Car did VERY well for itself back then. Back before aftermarket heads, stroker kits etc came out, 95% of the Fords out there didn't run for sh*t... and it was EASY to get races.

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