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#21
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Nice write-up and pictures, John. I appreciate the way you were able to get in print some of the difficulties in going fast. Many who haven't done it think it's simply plug and play. (plug in more money and play faster).
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#22
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I'm hoping Langer will share more details on his belt incident- as you said, we need to know how this happens. If you look at Gates info of the last couple of years, you'll see that GT-3 is now recommended for severe applications. It's a very small change to tooth profile compared with GT-2, but improves belt/tooth contact under high load. Bottom line for me- I'll be nervous as hell when my engine goes on the dyno Wednesday......
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Anybody else on this planet campaign a M/T hemi Pontiac for eleven seasons? ... or has built a record breaking DOHC hemi four cylinder Pontiac? ... or has driven a couple laps of Nuerburgring with Tri-Power Pontiac power?(back in 1967) |
#23
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It said it right in the article, the valves hit the pistons which made the belt jump.
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First Pontiac powered street car in the 7's 7.940@170.84. 3460#s |
#24
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@Jack, thanks. I'm flat-footed on the GT3, but the tooth design difference for more severe duty is a tell-tale of a potentially better balt.
@ LiL Jack, Left a chicken-egg choice on this reader. Favoring a belt-jump. You have a point to pursue; does a hung-stuck exhaust valve load the cam train;no. but a closed-stuck exhaust valve does. The rocker popping off is a big clue. |
#25
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"The exhaust valve was touching the piston because the camshaft belt drive had slipped"
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#26
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I heard the heads were milled too much
Which caused the destruction
__________________
First Pontiac powered street car in the 7's 7.940@170.84. 3460#s |
#27
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Let's get the facts from Langer.
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2023 Best ET Slip 60’ 1.224 330 3.186 1/8 4.784 MPH 152.07 1000 6.175 ET 7.347 MPH 189.92 Weight 3650 YouTube Channel --> https://www.youtube.com/channel/UC21...rWwgFdfTRqShGQ FaceBook Group --> https://www.facebook.com/groups/220092308823847/ |
#28
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Incorrect.
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#29
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When you kick off an exhaust pushrod it puts incredible stress on the intake valve since you have all of that pressure inside of the cylinder and it can't be released. This pressure can cause stress on the intake pushrod which causes stress on the lifter and subsequently the cam shaft. This "can" cause the belt to "jump" a few teeth. Now the million dollar question is why it kicked the exhaust pushrod initially.
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#30
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That scenario makes sense, John. Thanks for posting. I'm confident you'll find the answers to the jumped pushrod.
I know about the extreme load on an intake when exhaust valve doesn't open. When I was fighting breakage of exhaust rockers in my hemi V8, a broken exhaust would almost always result in that intake rocker also breaking. [rockers were all fragile 392 Chrysler cast steel pieces back then]
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Anybody else on this planet campaign a M/T hemi Pontiac for eleven seasons? ... or has built a record breaking DOHC hemi four cylinder Pontiac? ... or has driven a couple laps of Nuerburgring with Tri-Power Pontiac power?(back in 1967) Last edited by Jack Gifford; 03-26-2018 at 01:36 AM. |
#31
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Are you sure that's right? Better look at in cylinder pressure when the valves are opening and against what pressure.
Congrats on the coverage for sure! PPTTFMF! Langer;5862676]When you kick off an exhaust pushrod it puts incredible stress on the intake valve since you have all of that pressure inside of the cylinder and it can't be released. This pressure can cause stress on the intake pushrod which causes stress on the lifter and subsequently the cam shaft. This "can" cause the belt to "jump" a few teeth. Now the million dollar question is why it kicked the exhaust pushrod initially.[/QUOTE] Last edited by Aaron Quinton; 03-26-2018 at 02:02 AM. |
#32
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If the exhaust valve never opened after the power cycle wouldn't the intake valve see must higher than normal cylinder pressure than during a normal cycle? Not knowing when John's intake valve is set to open I would not be surprised to see anywhere between 250 and 325 psi at that point. Stan
__________________
Stan Weiss/World Wide Enterprises Offering Performance Software Since 1987 http://www.magneticlynx.com/carfor/carfor.htm David Vizard & Stan Weiss' IOP / Flow / Induction Optimization - Cam Selection Software http://www.magneticlynx.com/DV Download FREE 14 Trial IOP / Flow Software http://www.magneticlynx.com/DV/Flow_..._Day_Trial.php Pontiac Pump Gas List http://www.magneticlynx.com/carfor/pont_gas.htm Using PMD Block and Heads List http://www.magneticlynx.com/carfor/pont_pmd.htm |
#33
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With aluminum rockers you will most likely break the intake if you kick the exhaust. With steel jesels your not going to break the rocker. If the cylinder fires and the exhaust doesn't open, it puts incredible strain on the intake. Even at 1500rpm imagine how many times the valve opens and closes every second.
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#34
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#35
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#36
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John, Sorry for your troubles but many thanks for sharing the story and the diagnosis.
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Jim www.raceV8s.com 1972 Trans Am drag car, 3300lbs, 468 ci, Iron D ports, 428 block, 9799103 crank, 9.48 @ 143mph, 6.0 @ 114mph in the 1/8th. |
#37
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Hi Stan,
I don't disagree on the pressure estimate. I would think (haven't looked at the data) that given the constraints on Pontiac head and a max effort NA engine, the intake valve size would take priority (2.35+). Driving the exh valve smaller (1.70ish or less) even with a 300 + cfm exhaust port, driving a 320+ seat to seat exhaust event. I would think the cyl pressure would be high (600 psi plus) at exh opening normally but need to look at it. If so, the load on the exh at opening is likely similar or higher than an intake load with extra cylinder pressure and larger valve area. If we assume 100% mass is trapped due to exh push rod kicking and an estimate on heat rejection would get close on a PV calculation. Brother you are WAY better at this than me so if you rough calc I'm in! I have no idea what margin is in the belt drive but I'm wondering if it's worth the effort. I'm beginning to think chain drive, LS coils, cam trigger and a crank tone wheel with the Holley Dominator system is the answer? Do you do that or run the belt drive, belt driven distributor, etc? I'm thinking coil on plug. Thanks for the value added post sir. Aaron Quote:
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#38
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I appreciate the feedback and the engine gets the final vote for sure. Good info on the rockers for sure. If you ran it long enough with no exhaust and continually building cylinder pressure cycle after cycle with no exhaust, I could see how it could happen.
Man if it was me I'd look at why the exhaust kicked a 1/2" push rod. I wonder if that isn't the root cause of the problem, mechanical lock up as it kicked the push rod out drove the load to jump timing? That's where my heads is without looking at the parts. But I'm only looking at part of the story. Would a grossly loose lash jump out of the cup causing the valve to hit the piston? I would think the pistons would help tell the story. Quote:
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#39
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Using a 572 ci engine, Bore = 4.375" Stroke = 4.75" Rod = 6.75 and CR = 15:1. If we say that peak cylinder press is @ 12.5 ATDC and is 1650 psi. This decay graph is based solely on PV changes no heat added or removed. The green line is done using a K- Exponent of 1. Most of the Paper I have seen say it is around 1.38 so the red line is done using K-Exponent of 1.4. I do not know where John's exhaust valve is set open, but a 320 degree exhaust in @ 110 ecl evo 90 ATDC, @ 118 ecl evo 98 ATDC. The Rod and Crank are 90 Degrees to each other @ 70.62 ATDC. Stan
__________________
Stan Weiss/World Wide Enterprises Offering Performance Software Since 1987 http://www.magneticlynx.com/carfor/carfor.htm David Vizard & Stan Weiss' IOP / Flow / Induction Optimization - Cam Selection Software http://www.magneticlynx.com/DV Download FREE 14 Trial IOP / Flow Software http://www.magneticlynx.com/DV/Flow_..._Day_Trial.php Pontiac Pump Gas List http://www.magneticlynx.com/carfor/pont_gas.htm Using PMD Block and Heads List http://www.magneticlynx.com/carfor/pont_pmd.htm |
#40
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Dang brother, I need some time to have a look!
Unless that engine is a tall deck I'm not sure how he's keeping piston skirts on the pistons. I would think it would be closer to 4.40" bore but skirts look to be a problem? If pistons every 40 runs is no object then rock on? Quote:
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