383 Intake & Header swap power ?
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383 Intake & Header swap power ? I bought a '98 w/ a 383 that has Patriot Stg 2 heads and a 236/239 596/598 112lsa cam. Right now the car has an LS6 intake and Mac Midlength headers with Offroad Y. Car made 420rwhp and 430rwtq.
Aren't the intake and exhaust really choking this motor? I feel like I would get significant gains swapping to a 90/90 and LT's considering the 383 cubic inch motor. What do yall think?
Also, I have been reading about cams for larger ci motors. Doesn't the cam in this motor sound a little small? My last 383 made 503rwhp with an G5X4 cam (and the better bolt ons).
Any help would be appreciated. Dyno sheet posted. Anything you think mentioning worth about my power curve, etc. would be great.
Don't know a whole lot about the tune so there could be a little missing there as well.
Not sure why the power just fell off at around 6k either. Valve springs maybe? I beleive the car has Patriot Golds with around 6k miles but I have a new set of Comp 921s I could put on if yall believed it would help.
Aren't the intake and exhaust really choking this motor? I feel like I would get significant gains swapping to a 90/90 and LT's considering the 383 cubic inch motor. What do yall think?
Also, I have been reading about cams for larger ci motors. Doesn't the cam in this motor sound a little small? My last 383 made 503rwhp with an G5X4 cam (and the better bolt ons).
Any help would be appreciated. Dyno sheet posted. Anything you think mentioning worth about my power curve, etc. would be great.
Don't know a whole lot about the tune so there could be a little missing there as well.
Not sure why the power just fell off at around 6k either. Valve springs maybe? I beleive the car has Patriot Golds with around 6k miles but I have a new set of Comp 921s I could put on if yall believed it would help.
Last edited by dlc1609; Aug 13, 2009 at 10:56 AM.
A ported fast 92/92 combo and a set of 1 7/8 headers will go a long ways. To me that looks like valve float. I'd change the springs. Those mac headers if they havnt been modified have a 2 1/2 inch collector which is really chocking down that 383. U could have the collector cut and weld up a 3" pipe instead but you'd be better off with a different disign like the set from TSP. The cam could be a little better but I bet it's an excellent driver with a bunch of midrange torque. I have a 396 with a 242/250 .595/.602 on a 112+2. it's a bit rowdy and I bet I could get close to the same top end with more under the curve with a smaller cam.
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Haven't seen any results on TSP's 1 7/8 header... Do they make good power? Would i be better off with them instead of a set of Pacesetter 1 3/4s?
I'm trying to come out somewhere around 460-475rwhp. Doubt I'll hit the 500rwhp mark like my other setup, but shouldn't be far off.
Thanks for the help. Anyone else have experience with a change like this?
I'm trying to come out somewhere around 460-475rwhp. Doubt I'll hit the 500rwhp mark like my other setup, but shouldn't be far off.
Thanks for the help. Anyone else have experience with a change like this?
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My 383 that made 503rwhp had:
hand ported 243s, milled .010, comp 921 springs, stock rockers
g5x4 cam
fast 90/90
pacesetter 1 3/4" headers into tsp y-pipe w/ cutout
all other bolt ons (bigger maf, pulley, lid, truck coils, injectors)
tuned by me (probably could have used work)
stock 10bolt w/ 3.42s
heavy 17x11 zr1 wheels
6spd car
#s were almost identical corrected and uncorrected. Right at 500rwhp.
Cars power was a little sluggish below 3k but at that pount would come on like a rocket and pull extremely strong well past 7k rpm.
Im just trying to get back to anywhere near this power w/ the new car. Not having built this new setup, its harder to tell exactly where im at. Thats why i posted up about the bolt on items.
(posted from iphone, im outa town)
hand ported 243s, milled .010, comp 921 springs, stock rockers
g5x4 cam
fast 90/90
pacesetter 1 3/4" headers into tsp y-pipe w/ cutout
all other bolt ons (bigger maf, pulley, lid, truck coils, injectors)
tuned by me (probably could have used work)
stock 10bolt w/ 3.42s
heavy 17x11 zr1 wheels
6spd car
#s were almost identical corrected and uncorrected. Right at 500rwhp.
Cars power was a little sluggish below 3k but at that pount would come on like a rocket and pull extremely strong well past 7k rpm.
Im just trying to get back to anywhere near this power w/ the new car. Not having built this new setup, its harder to tell exactly where im at. Thats why i posted up about the bolt on items.
(posted from iphone, im outa town)
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Looks like you have realistic goals for it. I think it's doable with a couple better parts. I think to get anything close to 500 you'd probably need a different heads/cam setup. First off I'd take care of the valve float issue or whatever it is. Good luck with it!
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From: Princeton, Texas
I didnt build the motor so i dont know what pushrod length, but i do know its got harland sharp rockers (not sure if adjusted right or if they can even be adjusted). When i get back into town ill swap the valve springs pretty quick. I plan on getting the headers swapped out almost immediately as well. Then on to the fast intake etc. I must make 500rwhp!!! =)
You car sounds similar to mine. 2000 Z that I bought had 383 with mac mids, ls6 intake, PRC LS6 2.5 heads and a 238/240 comp cam. Thru the A4 (3600 stall) and stock rear (373) it made 440/430. I have the 92 fast and TB to go on it, but still need the headers and the rest of the exhaust. Hope to get the headers and electric water pump in by winter and retuned. Looking to get 480ish out of it, but we will see.
Can you keep me posted on what headers you buy and how you like them? Especially if you pick the TSP 1-7/8's because that is the ones I have been eyeing.
Oh yeah, looks like valve float too.
Can you keep me posted on what headers you buy and how you like them? Especially if you pick the TSP 1-7/8's because that is the ones I have been eyeing.
Oh yeah, looks like valve float too.
Yes, they are heavy. And with heavier rockers, you need stronger springs, which in turn, are heavier as well, and result in valve float because the valve spring can't control all that extra weight. Chances are good that he's got a bigger intake valve as well, which adds more weight too.
Get a set of PAC 1518 nitrided valve springs which are the beehive style, and good to .650 lift, go back to a factory rocker arm, and you'll see that valve float go away and it'll pull to 6800 without issue. Weight over the valve stem is killer for high rpms, look at what GM did with the Z06 (c5 and c6). They put in light weight valves to be able to raise the limiter and still warranty the motor.
Get a set of PAC 1518 nitrided valve springs which are the beehive style, and good to .650 lift, go back to a factory rocker arm, and you'll see that valve float go away and it'll pull to 6800 without issue. Weight over the valve stem is killer for high rpms, look at what GM did with the Z06 (c5 and c6). They put in light weight valves to be able to raise the limiter and still warranty the motor.
You'd be suprised how much power is left on the table. Just because the valve float doesn't become truly apparent until 6K, I can assure you the valvetrain is unstable before that. I have seen power and torque increases accross the board by switching from heavy stud mount rockers back to plain old stock GM ones. I've even picked up power going down from 1.8 ratios to the stock 1.7's. I know many of you won't believe me, but if you look at my website there is an absence of aftermarket stud mount rockers for LSx applications. Sorry guys, GM really did their homework on the valvetrain in these engines. You won't normally make the aftermarket stuff work without exotic parts...
I have only used aftermarket rockers in ultra high end all out race situations where the customer was willing to pay for shaft mount rockers, lightweight valves, special lifters, and the associated (read VERY expensive) springs to make it all work together.
In 99% of cases you will be better served by the factory rocker. If it makes you feel better, just upgrade the trunions and have billet stands made. It makes for a killer setup.
These are facts. I am obviously not selling anything here as I had nothing to do with this build. Just trying to spread truth from experience.
Shane
I have only used aftermarket rockers in ultra high end all out race situations where the customer was willing to pay for shaft mount rockers, lightweight valves, special lifters, and the associated (read VERY expensive) springs to make it all work together.
In 99% of cases you will be better served by the factory rocker. If it makes you feel better, just upgrade the trunions and have billet stands made. It makes for a killer setup.
These are facts. I am obviously not selling anything here as I had nothing to do with this build. Just trying to spread truth from experience.
Shane
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I am going back to stock now thanks to yalls help and it doesn't bother me at all. My 383 setup that had 503rwhp with the big G5X4 cam had stock rockers and did just fine. I figure they might be a little noiser but that doesn't bother me either. Talked to LG and they were of the same opinion about going back to stock as yall are. Picking up a set today.
As far as headers go, I found a good deal on a pair of Pacesetter coated 1 3/4" (I know, 1 7/8" would be better) headers for $200 bucks so those will go on tonight as well as the new Comp 921 springs (came with the car) and stock rocker setup. Going to build a y-pipe using the Flowmaster collector (2x3" into 1x4" pipe) and use a 4" electric cutout under rear seat. Cat-back will be a restrictive but quiet setup for nice evenings out.
Should be down to finding an intake by tomorrow. Thanks for all the help so far gentlemen. I'll keep you posted on progress.
As far as headers go, I found a good deal on a pair of Pacesetter coated 1 3/4" (I know, 1 7/8" would be better) headers for $200 bucks so those will go on tonight as well as the new Comp 921 springs (came with the car) and stock rocker setup. Going to build a y-pipe using the Flowmaster collector (2x3" into 1x4" pipe) and use a 4" electric cutout under rear seat. Cat-back will be a restrictive but quiet setup for nice evenings out.
Should be down to finding an intake by tomorrow. Thanks for all the help so far gentlemen. I'll keep you posted on progress.
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From: Princeton, Texas
Thread Starter
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From: Princeton, Texas
You will need MUCH shorter pushrods with the Comp R's. It is possible to run them without adjustable rockers but your preload should only be .002"-.003", yes really, only 2 to 3 THOUSANTHS. This would mean you would perform the check I described above but you would want about 1/16th of a turn from zero lash with an aluminum block/head combo. You could get as close as possible with pushrod length then use shims under your rockers to fine tune the preload. You can shim the factory rocker stands up to ~.075" without killing rocker geometry. I would get the proper length pushrod then shim as little as possible to get the proper preload. If you need further help, PM me. I can give you a number to reach me by.
Thanks,
Shane
Thanks,
Shane