I was running a 2 1/4 dual exhaust on with my 502 and we switched to 3" dual and it made a HUGE difference. It was like she was happy to breathe. I do know that you should work out the compression problems first since there are back pressure to think about. Too much or too little it won't run right. Good luck.
Not sure really why. . . .i did a compression test about 12k miles ago, it was 128psi on the low cyl and 132psi on the high they say for these eninges 125psi is good so i must have a healhty one than. . .
I have totally rebuilt the carb since then. . . but hell if i'm putting the cheap stuff back in it again. . .
Would building a set of header's for it make enought of a difference to bother ?
Well for one thing, to get that kind of compression you would need custom built pistons which are not cheap! Wisco makes some and there is one other company that does. You need deep pockets for them. Even the 502 Chevy big glock pistons are just .010 shy of the 4.562 coffee can size bore you have. However if you can get .020 or .030 over size pistons for a 502 and then they would fit the bore and give you roughly 9.25 with some milling of the head and decking the block. I would keep it under 9.0:1. If the wrist pins and connecting rods fit then you would have a high performance engine. You would have to check it out first. It would be cheaper than custom pistons. Those ole' V6s were made for pulling and not high rpms. Cheap jap engines don't pull well but rev high. Thats why they come with 4.10 or 4.30 gears to make them pull somewhat. Those GMC engines were rugged made though. Last for many years taken care of. Personally I would build it stock and do the two things you suggested, decking and shaving the head, and have it balanced with some porting and polishing. You may have to fabricate a 4 bbl manifold for it. It there is room you might be able to bore the two back holes in it for the carb. Twin 2 1/2 or 3 inch Magnaflow exhaust would also help out the performance. I have 3 inch Magnaflow on my truck with the long muffler and it sounds great and not too noisy. Has a deep sound. Also you might get some custom headers made. Justr a thought on that. Too high of compression and you would have to run racing fuel in it. At about $7.00 a gallon I think that would not be a good idea. If you go from 7.5 to 8.5 or even 8.75 you will like it a bunch. Your mileage will increase as well. Add MSD ignition, K&N air filter and synthetic oil such as Texas Refinery Moly Pro Spec III like I use. Or Amsoil 10-30. It is doubtful that roller rockers are available unless they interchange with a known GMC or Chevy engine. If so, you want stainless steel, NOT aluminum. With the expensive cheaply made gas you relly don't want high compression. You want high torque which is what they were made for. Remember, HP wins brags and torque wins drags! Also check out www.doubleyourmiles.com. I have one for mine once I get it set up. Every little bit helps. I wish you well on your venture.
If you have good compression, and have rebuilt the carb, then you have 2 of the 3 "ingrediants". How about the ignition? Vacuum advance (if it has one) working? Distributor plates stuck? Coil and condensor matched for impedence? Wires and plugs correct (not both resistive)? Timing where it should be? Also, correct thermostat installed and working? That engine should run great on 87 octane.
Jon.
Good carburetion is fuelish hot air The most expensive carburetor is the wrong one you attempt to modify. If you truly believe "one size fits all," try walking a mile in your spouse's shoes! The Carburetor Shop
1. OIL: As fare as oil goes a run amsoil sae60 truck should have strait weight 40 but i figure 60 in synthetic should be about the same thing truck fire's up and has instant oil pressure even at -35*F fire's right up oil pressure shoot's right 65psi same as the summer time the cold dose not effect the flow rate at all a cording to the mechanical gauge as the needle don't delay and rapidly shoot's to 65psi year round if till took a few second to start building or the psi climbed slowly i would run thinner oil but it's almost instantly hit 65psi hot idleing it sit's at 55psi just tap the throttle shoot's right up to 65psi atfer driving a long time it will fade back to 57psi from 65psi. . .
I will never use an oil thinner the 10w-40 in anything especailly a synthetic. . . 10w-40syn flow's just as fast if not faster than 5w-20 standard oil. . . the GMC,M123, B61, amx, and all my summer only collector's and heavy duty truck's get the 60w... everything else get's 10w-40 in the winter 20w-50 in the summer I found my engine's last longer that way. . .If i had time i would list all the engine's i had die with 5-30 and 10-30 that got rebuild again! then ran 10-40,20-50. or 60w oil's and lasted 3 to 5 times longer and still going. . .heavy oil work's for me. . .
2.COMPRESSION: I don't see how raising the compresssion ratio is going to make it a high RPM engine, diesel's have 18-22:1 C/R's and only run 1800-3250rpm. . .
Back to subject:
I want a brute force low ender pulling up to mid range. . .
start pulling at 1250-1500rpm rpm die off at 2750-3250 rpm, but currently it will pull till about 2200 than it fade's off fast all done by 2500 but i still gotta run it out too 2700-3300rpm to keep it from lugger out in the next gear. i would like about 380TQ instead of 280TQ . . . the truck is a doggy glutless wonder from 2200rpm on up when you hit the on ramp and are pulling into 72mph traffic at 50mph! truck should whined up to 60mph easy in the length of an on ramp with 8-19.5 34" tires 5.13 gear's granny SM420 trans lot's of low end torque should jack rabbit off the line. . . let me show ya what i got and what i'm looking for would be best i guess. . .
STOCK OUT PUT:
190hp@3600rpm.
280TQ@1600rpm.
Wanted out put:
175-225hp@3750rpm. << plenty of HP rev's could be lower. . .
380-420TQ@1750rpm. << low rev's big torque. . .
still able to cruze at 3,000rpm like it dose now. . . i would be happy with 175hp if i had 380-420FTLB torque to back it up with
truck only dose 62.5mph@3,000RPM and takes it time getting there empty i don't load it any more darn collector plates but when i did the extra weight didn't slow it down thank GOD! once rolling up to cruzing speed of 3,000rpm it didn't lug down any even in the hill's loaded to 14,000lb ocasionaly 16,000lb< has been that high a few times oop's dead empty if should getup and go faster than dose i think. . . if it's going to be slow i want it to get up to speed fairly quick . . .
i don't want lot of horse power i want Gob's of mad TORQUE! ! !
I have been told if i want torque keep the rev's low and the compression high. . . high compression 9.2-10.5:1 low duration cam with high lift, big 2bbl carb has more torque than a 4bbl i'm told. . .
If you have good compression, and have rebuilt the carb, then you have 2 of the 3 "ingrediants". How about the ignition? Vacuum advance (if it has one) working? Distributor plates stuck? Coil and condensor matched for impedence? Wires and plugs correct (not both resistive)? Timing where it should be? Also, correct thermostat installed and working? That engine should run great on 87 octane.
Jon.
it may have been so crappy gas I won't run the cheap stuff in this truck anyway. . .so high compression requiring 93oct won't really matter. . .
"I don't see how raising the compresssion ratio is going to make it a high RPM engine, diesel's have 18-22:1 C/R's and only run 1800-3250rpm." You've got 2 completely differently operating engines, there. A Deisel doesn't run on the same principles as a gas engine. The high compression is necessary to raise the combustion chamber temp to allow the feul oil to fire and burn, as there is no spark in a Deisel. In a gas engine, generally speaking, a high compression allows for higher octane feul, and they generally are high RPM high horesepower performance engines. Raising the compression isn't going to fix the problem, and most likely will cause more problems than it will cure. Namely, if you have the heads millet, the intake and maybe even the block might have to milled as well just to make things bolt back up. Plus you have to consider the pistons, milling the heads could cause issues with the valves hitting the piston. I would suggest trying to find out why it won't run n 87, might be as simple as a timing issue.
I don't rightly care about it runnning 87 truck won't be seeing anymore of that stuff any how. . . I could run on 87 till issue it had back 9 year's is solved but then it'll go right back to 93oct.
Truck hasn't had regular gas in 9+ year's. . .I tired regular the first week i had it didn't like how it ran tryed some premium within 75 miles truck started running like new never went back. . .so what ever the issue was 93 corrected it or atleast put a bandaid on it. . .
I'm sure this engine is doing all it can it's just an out dated relic from long gone era and i'm expecting to much from a 6.2L V-6 guess...
I would just think a V-6 that big would alot more gutsy, I guess 40 year's ago these were the 5.9/6.7's, 7.3/6.0L's, and 6.5L/6.6L's of the time. . .
How i wish it was diesel. . .you can make a 50 year old diesel engine scream like a late model with very few altertions. . .
My B61 had 180hp in 1959 that same diesel now is running 315hp all day long ! all they local diesel shop did was add a turbo charger and adjust the fuel. . .tho now i got a non turbo diesel compression ratio with 25psi of boost slamming at it but they say engine should still live 250,000+ mile's just gotta keep it in tune. . . I did sorta alter the triplex and basicly made my own I took the modneren 5spd mack tran's that has OD put a 3 speed behind it so i got low split direct split and high split so it has 2 OD's but now it run's 72mph@2,000rpm instead of 58mph@2250rpm so it's still a 2 stick 15 spd still gotta slit every gear but now i get some road speed strongest/fastest thermodyn on the road well... prolly the only thermodyn on the road most opted for the 237 maixdyn swap than tuned it up to the 250hp version popular in cement truck's of the 70's and 80's. . . the 300 econodyn had an after cooler that wouldn't allow it to fit in the butterfly hood tombstone radatored truck now the B70's and B80's it fit barly as they had more squared out front end. . .
Back on subject sorry for that off shoot:
why can't this old V-6 Be updated just like that ? alter some thing's for more power ?
Engine run's perfect as it is now fires right has good oil pressure don't leak don't burn oil, just dosen't have the power I would expect for it's size. . . I guess i should listen to everyone else " if ain't broke don't FIX IT! "
Hmmmm... LOL !! Sounds to me like it would make a " Good boat anchor. . ." or maybe a good mailbox base, scrap it and put in a 350 "best engine GM ever made"
Some people are like Slinkies, Their not really good for nothing... But they still bring a smile to your face when you push them down the stairs.
If i wanted a 350 in it i would have have done it by now there Hoss got love Yahoo's. . . yea i guess 4 out 5 blowing up, Yup I would put the 350 in my TOP 10 of GM's greatest mental malfunctions. . .I used to think it was only 3 of them blew but a buddy of mine reminded of the old k-5 that spun 3 bearings i'll give that some credit it never came apart. . . sounded like 3 pool ball's tapping each other tho it ran around the yard for almost 3 year's with 75W-140 and pucket of wheel bearing holding together . .so i guess only 3 out of 5 acctually put rod threw the block. . .all 4 engine had #7 rod bearing spun. . . so it was a reaccuring issue. . . 1 in my 92 GTA tran's am ran almost 4500miles with the spun bearing. . . 1 int eh old k-5 ran 5 year's with 3 spun bearing's, and 2 new GM crate 350's went threw my 66 C-30 chevy tho original 350 that came in it ran just knocked i won't count it. . .
If i wanted a 350 in it i would have have done it by now there Hoss got love Yahoo's. . . mike
Hoss ??? Chill out there Gomer... Im only messing with ya... If ya cant take it dont dish it out, THIS AINT NO PI$$ING CONTEST.... It was a joke DUH ?? Yer right ya gotta them YAHOO'S!! Ah Huh ! Todd
Hey Gomer !! "See Signature Below"
Some people are like Slinkies, Their not really good for nothing... But they still bring a smile to your face when you push them down the stairs.
OMG! ! ! relax Guy. . . I usually start everyone out as "gomer" than bump them up to "hoss" some time i use girl name like DR COX on the show scrub's. . . I gave ya a head start geez barbie. . .
I knew you were giving me hell cause i gave it to you I was just explaining my bad luck with the indesructable 350 chevy. . . I'm sorry if it came of pissy I thought is was just making my case with some sarcasim. . .
My uncle ran 350's in his fleet of tow truck's for 25+ year's mst of them went 250-300K mile's with out an issue. . .
I had bad luck with my first handful of them. . .so I quit using them. . . I like the 400 better I haven't had any issues with 400 chevy's all tho I did build everyone I had my self. . .Hmmm maybe it wasn't the 350 as much as me buying them instead of building them. . .I would take 350TBI over any 350TPI anyday any time every time. . .
Anywho I'M SRRY for any hurt feeling's guy!
Mike. . .
now what about getting some more pep in the step of this good old solid Brick they call the 379M-V6. . .
No hurt feelings bro... just jazzin ya "barbie" LOL !!... But I would like to see that 379M-V6 it sounds cool Ive never heard of or seen one got any pics ?? Todd
Some people are like Slinkies, Their not really good for nothing... But they still bring a smile to your face when you push them down the stairs.
I did have some on my phone till i left in the truck with the windows down a few inches and some critter chewed it up. . .I'll be getting some good photo's at some point soon as i'm hopping to drop the new cab on it this summer. . .it's badly rotten but i still drive it every summer almost all summer really. . . it's normal season is mid april to mid october. . .
Ed
RRY for any hurt feeling's guy!