Pushrod pinch discussion...
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From: Spokane, Wa
Pushrod pinch discussion... Maybe Ai or LE could chime in. How much does the pushrod pinch restrict the potential of the lt1 stock casting? Has an offset lifter/rocker been attempted on a stock casting? Does the stock intake affect the way you port in this area, or do the same principles apply when working with different intakes
(single plane)?
(single plane)?
I'm not AI or LE, but I have ported quite a few sets of LT1 heads and have spent significant time on a SF600 flowbench....not that a flowbench is the final dictation of how a head will perform.
For everything that I have done (street cars), the "pinch point" was never really a restriction. At least not to the point where it would have to be welded on the backside to increase the cross sectional area there. I've seen alot of port work in the past where people just lay into that area for absolutely no reason. However, that's not to say that the pinch point is not a restriction at all. If you have the proper bowl shape/volume, throat diameter, and short side shape, the pinch point would start to become a restriction.
I've actually been amazed at how much power you can make with a LT1 head without even touching the port inlets (or intake mainfold runners).
But, like I said, I'm not a pro.
Jason
For everything that I have done (street cars), the "pinch point" was never really a restriction. At least not to the point where it would have to be welded on the backside to increase the cross sectional area there. I've seen alot of port work in the past where people just lay into that area for absolutely no reason. However, that's not to say that the pinch point is not a restriction at all. If you have the proper bowl shape/volume, throat diameter, and short side shape, the pinch point would start to become a restriction.
I've actually been amazed at how much power you can make with a LT1 head without even touching the port inlets (or intake mainfold runners).
But, like I said, I'm not a pro.
Jason
TECH Apprentice
Joined: Dec 2008
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From: Kinston North Carolina
Ive got quite a few hours of testing these heads on the flowbench. I have played with different cross sectional widths at the pushrod pinch. They are rather tight especially towards the top of the port in as cast form. Once i found the combination of bowl shape, size, and valve job that worked the best i started playing with the pinch. I had already opened it up a bit in the beginning but noticed quite a bit of airspeed around the bend, so i opened it up some more to see if it made a difference. I got very little results from the extra area and it did nothing for taming the airspeed. I dont think it would be worth the your money for the gains that you would net from it. The pinch generally isnt a critical area for flow loss if its size is fairly proportional to the rest of the port. A fine example of a massive flow loss in the pushrod pinch would be most of your production smallblock mopar heads. An inch above and below the seat is where your largest percentage of flow is lost.
Thread Starter
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From: Spokane, Wa
its my understanding that the velocity is greatest in at the top corner opposite the pushrod, you're saying its not going to pay dividends to open the port up in this area? Or is it just on a stock cube application there's not much to be gained here? I understand that probably too many head porters focus on the pinch because it looks restrictive in the port, but at what hp, ci, or csa requirement does focus need to be turned to this area?
Thread Starter
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From: Spokane, Wa
I believe most power you're going to find on a sbc casting is "downwind" of the pinch, look at the Stockers running "unported" heads with a killer valvejob making close to 500 hp in an lt1. My thinking is, when you have an obvious csa restriction (pinch) you want to keep velocity as high as possible before this point.
TECH Apprentice
Joined: Dec 2008
Posts: 372
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From: Kinston North Carolina
its my understanding that the velocity is greatest in at the top corner opposite the pushrod, you're saying its not going to pay dividends to open the port up in this area? Or is it just on a stock cube application there's not much to be gained here? I understand that probably too many head porters focus on the pinch because it looks restrictive in the port, but at what hp, ci, or csa requirement does focus need to be turned to this area?
