New Much Bigger Cam and Lose 30 RWHP WTF????
08-25-2005, 08:26 AM
#61
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I have the 7.40 push rods in now. I have 1 turn of preload. I checked the top of the valve with a marker. The rocker is close to right in the center of the valve? I am going to try and do a compression and leak down test tomorrow night. Maybe it will show something.
08-25-2005, 08:29 AM
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Originally Posted by as35thss
I have the 7.40 push rods in now. I have 1 turn of preload. I checked the top of the valve with a marker. The rocker is close to right in the center of the valve? I am going to try and do a compression and leak down test tomorrow night. Maybe it will show something.
08-25-2005, 08:33 AM
#63
Oh my gosh, I just figured it out. Thunder Racing had this same problem. When one of their customers tried a T-Rex (virtually the same as the cam you're running) with cats, they made crappy power. But when they ditched the cats and opened up the exhaust, they picked up like 40-50 rwhp. Why? Because the T-Rex has so much overlap, it is incredibly sensitive to back pressure. Basically, it can't have ANY! Just as an experiment, drop the y-pipe, put extensions on the headers and re-dyno. I think you'll find your lost horsepower.
Cats and T-Rex:
Cats and T-Rex:
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2013 Corvette Grand Sport A6 LME forged 416, Greg Good ported TFS 255 LS3 heads, 222/242 .629"/.604" 121LSA Pat G blower cam, ARH 1 7/8" headers, ESC Novi 1500 Supercharger w/8 rib direct drive conversion, 747rwhp/709rwtq on 93 octane, 801rwhp/735rwtq on race fuel, 10.1 @ 147.25mph 1/4 mile, 174.7mph Half Mile.
2016 Corvette Z51 M7 Magnuson Heartbeat 2300 supercharger, TSP LT headers, Pat G tuned, 667rwhp, 662rwtq, 191mph TX Mile.
2009.5 Pontiac G8 GT 6.0L, A6, AFR 230v2 heads. 506rwhp/442rwtq. 11.413 @ 121.29mph 1/4 mile, 168.7mph TX Mile
2000 Pewter Ram Air Trans Am M6 heads/cam 508 rwhp/445 rwtq SAE, 183.092 TX Mile
2022 Cadillac Escalade 6.2L A10 S&B CAI, Corsa catback.
2023 Corvette 3LT Z51 soon to be modified.
Custom LSX tuning in person or via email press here.
08-25-2005, 09:21 AM
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Hey Gomer. Yes I have stock lifters. The 7.350 is a good thought. Loosen them up. But when I checked the rocker on the tip of the valve with the 7.350 it was on the very inside and riding on the inside tip the valve?
08-25-2005, 09:42 AM
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Originally Posted by as35thss
Hey Gomer. Yes I have stock lifters. The 7.350 is a good thought. Loosen them up. But when I checked the rocker on the tip of the valve with the 7.350 it was on the very inside and riding on the inside tip the valve?
08-25-2005, 09:52 AM
#67
Guys, you have to look at the obvious. SLP headers and cats are about the most restrictive long tubes on the market. A cam this big needs 0 back pressure, but the current setup has LOTs of back pressure. Alleviate the obvious bottlenecks and watch your power return.
.
08-25-2005, 11:23 AM
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gomer has a good point. the 7.4's are for unmilled heads. the norm is 7.35's for milled heads. sell your current rockers if they're not stock already and get a set that nasty nate has. Do you still have the ory to replace the cats? i thought slp you could remove the cats and place straight pipe in place. i would try that.
08-25-2005, 12:15 PM
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while I agree that the problem could quite possible be a very restrictive exhaust system, I would assume that the lower rpm power would go up over the old setup then suddenly 'flatten out' if you know what i mean. I don't know just how restrictive it is, but i would think that it wouldnt lower the whole powerband by that much, just the upper RPM's where the exhaust couldnt handle the volume or velocity of the exiting gas.
08-25-2005, 12:46 PM
#73
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Originally Posted by RedHardSupra
ok, our of curiosity, the people who get so much hp out of your stockers, or svo30s, do you happen by any chance to tune your own cars? how is it tuned? do you tune with IFR tables, or is it a calculated table?
i can post screenshots of how i reached 109% duty cycle on stock 26.4s with a z06 cam and stock headers if you'd like.
also, i'd post a link to some very cheap injectors, but since they're from a nonsponsor i'd get my *** booted. pm me if you're interested.
i can post screenshots of how i reached 109% duty cycle on stock 26.4s with a z06 cam and stock headers if you'd like.
also, i'd post a link to some very cheap injectors, but since they're from a nonsponsor i'd get my *** booted. pm me if you're interested.
My stock 24's seen 116% and the WB indicated no lean lean condition was actually rich. Those injector duty cycles need to be taken with a grain of salt and that is how people know the 30's are good to 450 HP. Check around in the pcm and the fueling section and you will see there are big debates on the valididty of duty cycle and why
08-25-2005, 12:48 PM
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Originally Posted by Patrick G
Oh my gosh, I just figured it out. Thunder Racing had this same problem. When one of their customers tried a T-Rex (virtually the same as the cam you're running) with cats, they made crappy power. But when they ditched the cats and opened up the exhaust, they picked up like 40-50 rwhp. Why? Because the T-Rex has so much overlap, it is incredibly sensitive to back pressure. Basically, it can't have ANY! Just as an experiment, drop the y-pipe, put extensions on the headers and re-dyno. I think you'll find your lost horsepower.
Cats and T-Rex:
Cats and T-Rex:
Originally Posted by Mike Norris
We checked the TB and she is at WOT when depressing the accel pedal, TP reading is 98%.
08-25-2005, 01:47 PM
#75
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On the pr length issue. I have a much smaller cam with AFR's milled .030" and an .040" gasket. I'm using Comp 850 lifters and 7.4" pr's and valvetrain is good. With a cam that big the base circle will be much smaller than my baby 'cam' and I'm wondering if he needs longer pr's, however he stated he checked the wipe and with one turn of preload they were close to center.
On the injectors, if the duty cycle is less than 117% they are not maxed out no matter how much power you have going to the wheels with 13:1 afr they are covering it.
I think Patrick is on to something with the restrictive exhaust. A cam like that runs a LOT of overlap so if the cylinders are not getting scavanged efficiently the motor will choke.
If it's not the exhaust or the exhaust is only part of it I'm guessing the cam may be degreed wrong, way too advanced because the peak is pushed way down. Also he says it idles too smoothly, an indication that the dynamic compression is very low. This could be caused by the valves opening and closing with too little dynamic stroke left to make decent compression.
On the injectors, if the duty cycle is less than 117% they are not maxed out no matter how much power you have going to the wheels with 13:1 afr they are covering it.
I think Patrick is on to something with the restrictive exhaust. A cam like that runs a LOT of overlap so if the cylinders are not getting scavanged efficiently the motor will choke.
If it's not the exhaust or the exhaust is only part of it I'm guessing the cam may be degreed wrong, way too advanced because the peak is pushed way down. Also he says it idles too smoothly, an indication that the dynamic compression is very low. This could be caused by the valves opening and closing with too little dynamic stroke left to make decent compression.
08-25-2005, 02:11 PM
#76
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Originally Posted by RedHardSupra
injectors might be not only a huge problem, but also a dangerous one. imagine getting on it, 6000rpm, and suddenly your big cam finally shoves so much air the injectors can't keep up, car leans out, under load, on high rpms. what comes next? the big bang. don't be cheap, get injectors, i just saw some 42s going for 250bux on forums, that ain't much, not comparing to how much money you people can dip into a friggin 12bolt...
and if you don't believe me about injectors, might wanna come over the to pcm forum, i created tools there for sizing of injectors with which i tuned a dozen of cars, and many more have reported great results using them as well.
and if you don't believe me about injectors, might wanna come over the to pcm forum, i created tools there for sizing of injectors with which i tuned a dozen of cars, and many more have reported great results using them as well.
A lean spike doesnt kill a motor the instant it happens
WB, WB, WB if the WB aint seeing a lean condition at 5600 what makes you think you will see one in another 400 rpm. Better yet how much more air can you move at 5600 as opposed to 6000
08-25-2005, 03:59 PM
#77
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I called Paul at Thunder Racing and he agrees with Patrica G. I am still going to do a compression test and leak down. The cam was degreed in and dead nuts dot to dot. I am then going to take it back to Norris Motorsports and have the exhaust dropped and redynoed. Hopefully Patrica G is right. I will recheck the push rods and see what the 7.350 look like on the wipe and how much preload I can get. You guys have been a real help. Thank you all very much. Any outher thoughts please chime in and let me know.