73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: westsidek20 on April 05, 2012, 10:40:55 am
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Hey guy's, its been a while since i had a chance to do anything, its good to be back.
Well i got under the truck knocked the differential to check out my gears and turns out to be 3.73.
Now i have a freshly built 383 (thumpr cam), as i stomped on it, wasn't really pleased with the result, i thought i could get more kick out of it.
So here's a little info, its a 78 K20 with a th400, my tires are 16.5x33x12.50 , i would like the truck to respond faster from a stop, so i was thinking bigger gears? would swaping 3.73 to 4.10's make the difference or do i need more?
This truck is just for fun, i would like to be able to burn some rubber, some offroad (not a rockcrawler) and no towing.
Any info., ideas or suggestions would be greatly appreciated.
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i have a 383 w/ an rv cam to take advantage of the lower rpms. i dont know what a thumpr cam is, but my '79 will burn the rubber off the tires w/ my 3.08. those 383's have loads of torque.
You have taller tires and they are quite wide. a 4.10 will be an improvement. Narrower tires will make a difference too. Make sure your timing is good and engine well tuned.
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Thank you Sgt., Thumpr cam is just something that is supposed to be "performance" and gives the engine a ruff idle with more of a rumble sound to it, its by comp cams, by the way i DONT recommend it to any one, it does make it loud but it lacks performance, as i have unfortunately found out.
Now i know that my K20 is not meant to be a street performer and i cant expect to much of a boost with a heavy truck like this.
My concern is going from 3.73 to 4.10 enough? is it that much of a difference? or should i go for more?
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Sounds more like a mis-match of engine components than a problem with gearing. Just my humble opinion.
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What carb are you running? Sounds like the carb is too small or not jetted right for the combo you have. I'm in the same boat and am about to send off my 76 800cfm qjet to everyday performance for a rebuild and mod to suite my cam and engine combo.
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My $.02 is that a 383 should get up and go quite well with 33" tires. I know several folks that have really kicked themselves for getting a thumper cam and while they sound good idling through a car show they do lack performance. I would do a cam change before re-gearing, you could go all the way to a 5.13 and I still think you wouldn't be satisfied...
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Well im running a 600cfm Edelbrock performer, i did the carb calculator thing and it suggest around 680cfm, its just that my pockets went thin after the engine build, and the 600 edel was a steal at 100dlls.
Do you think swaping the carb would make the truck move faster from a stop?
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Thanks Zieg, the idea has crossed my mind.
So you think the 383 has enough power to burn the 16.5x33x12.50 tires on a 3.73 gear ratio?
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I do think the carb is small. Those carb calculators aren't always correct. On a 350 it would like a 750 or 800 cfm carb. I will let you know how my carb goes from everyday performance. The shop is spot on with qjet rebuilds. You give them your engine specs and they build it to suite your engine. For less than 200 bucks can't get any better than that. Most out of the box carbs are "generic" and still require rods and jets, power piston springs and such to get things running right, so you endup coming outta pocket 300-450.
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I would change the cam first also. If it doesn't make any power at lower rpm then changing gears isn't going to make the engine create power off idle and at low rpm. Changing gear ratios in a 4x4 is more expensive than changing your cam too. I have always gone with the rv style cam in 4x4's.
It's funny this comes up now. I opted to go with an spare circle track motor in my build. It was new with low street miles in a C10, never was used on the track. I'm working on tuning it now. I am regretting not changing cams before I put it in. At first I thought I don't need all the low end I can get out of it. Now I am thinking that I will hate it once I get to drive it.
I do think the carb is small. Those carb calculators aren't always correct. On a 350 it would like a 750 or 800 cfm carb.
I'm from the other side of the fence on this. I think a 600cfm is enough for a 383.
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Thanks Zieg, the idea has crossed my mind.
So you think the 383 has enough power to burn the 16.5x33x12.50 tires on a 3.73 gear ratio?
My tire burning days are over especially at roughly $200 a pop but it should be a very responsive and be able to move on down the road right nicely. My 454 is completely stock with 134K miles and if I get into it to much will brake the tire loose just trying to get moving and I am not talking dumping the clutch either. I have a 3.21 out back. I fairly built 383 ought to have close to the torque of a completely stock 454 I would think. My tires are the tall stock width LT235/85R16 with knee deep rubber.
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I would change the cam first also. If it doesn't make any power at lower rpm then changing gears isn't going to make the engine create power off idle and at low rpm. Changing gear ratios in a 4x4 is more expensive than changing your cam too. I have always gone with the rv style cam in 4x4's.
It's funny this comes up now. I opted to go with an spare circle track motor in my build. It was new with low street miles in a C10, never was used on the track. I'm working on tuning it now. I am regretting not changing cams before I put it in. At first I thought I don't need all the low end I can get out of it. Now I am thinking that I will hate it once I get to drive it.
I do think the carb is small. Those carb calculators aren't always correct. On a 350 it would like a 750 or 800 cfm carb.
I'm from the other side of the fence on this. I think a 600cfm is enough for a 383.
Totaly here ya. If his truck was in dallas, tx id give him a chance to see what a well built qjet can do:) with the longer stroke and larger hp and tq id think a bigger carb will bring up the power. Now I am with everyone on the cam profile idea because the thumper cams are ment for sound. Heck ill have a lope with my high energy 260 and still have bottom end and it has only 212 duration. You just have to figure out the cam degreein then ignition timing and then carb tuning:)
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Its hard to admit it, but it looks like swapping the cam is going to be my next move. DARN!!!! Just went i thought i was able to enjoy the truck :(
This Thumpr cam totally lacks power, and i know they are meant to make the engine rumble, but seriously its too loud, makes the cabin rattle and all the car alarms go off. Annoying.
I wish i can put a big sign on the site for all members to STAY AWAY FROM THUMPR's!!!
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What cam do you have in mind?
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+1 on the cam swap....
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I would look first at your carb. You bought it used but do you know how it is calibrated? I had a HUGE difference in part-throttle performance once I dug around in my carb and changed some things. First thing I found was one of my accelerator pump nozzles was plugged. Fixed that and went with the next step up one. Then I adjusted the hole that the pump arm was using, that also made an improvement. Then I bought an Edelbrock carb tuning kit and found that my carb had the lightest springs in it on the metering rods, which also choked power. Before I bought my truck the guy tried to get it through emissions so I think they totally leaned it down. I stepped up the springs and went one size thinner on the rod and my truck is a different animal now. And it's way easy to do on those carbs. Changing the jets is a bit of a pain as you have to remove the top half of the carb but not a huge deal. Look into that and where your timing is and you might see great results.
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So i posted a few weeks ago about changing 3.73 gears to 4.10's, and most of you thought that i radder swap the thumpr cam (i don't recommend to any one!) to something that gives me more torque, to be able to move faster from the stop... my truck isn't able to smoke the tires!!
Its a 78' K20 with a 383 has 170cc runners, 67cc World S/R Torquer heads, 2.02/1.6 valves, Roller tip 1.52 rockers, 600cfm,
Flat head pistons, Edelbrock RPM intake, MSD ignition system, 14 FF Rearend with 3.73, 16.5x33x12.50 tires.
So now that i made the mistake of putting a "thumpr" cam, its soo slow from a stop, i beg for your input on this, i want to get the right cam for the truck, i want it to be faster from a stop, mostly street driven, light offroad, no towing.
I filled out the Compcams Camshaft recommendation Request with all my info, and they suggested the XE268H, Xtreme energy Hydraulic Flat Tapped Cam, the specs:
RPM Range 1600-5800
Lobe sep 110
Lift@.050 224/230
Intake Centerline 106 Valve lift .477/.480
Does any body here have any experience with this cam? or comment on it?
Any other suggestions??
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comparing that cam to My cam I'm gunna buy(I'm getting a extreme 4x4 from comp) your cam you listed is just a lil bit better than mine.and they said mine is good for low to mid range torque witch will get you moving....So id say that would be an alright one to go with
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There are only a few people here that have built alot of engines. Do you have a speed shop or racing shop near you.
You are asking for specifics from most on here who have 1 or maybe 2 differnt try's at different componets in a engine. A speed shop or racing shop who have built hundreds and done the experimenting would be able to help you better, then you should ask questions on here about what they recommend.
I don't build engines, but that is what I plan on doing when I get to the engine on my build, I am looking for a specific engine to do a specific job, so I figure talk to the ones who do it for a living, then ask advice from the hobby crowd. Just my thoughts.
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So i posted a few weeks ago about changing 3.73 gears to 4.10's, and most of you thought that i radder swap the thumpr cam (i don't recommend to any one!) to something that gives me more torque, to be able to move faster from the stop... my truck isn't able to smoke the tires!!
Its a 78' K20 with a 383 has 170cc runners, 67cc World S/R Torquer heads, 2.02/1.6 valves, Roller tip 1.52 rockers, 600cfm,
Flat head pistons, Edelbrock RPM intake, MSD ignition system, 14 FF Rearend with 3.73, 16.5x33x12.50 tires.
So now that i made the mistake of putting a "thumpr" cam, its soo slow from a stop, i beg for your input on this, i want to get the right cam for the truck, i want it to be faster from a stop, mostly street driven, light offroad, no towing.
I filled out the Compcams Camshaft recommendation Request with all my info, and they suggested the XE268H, Xtreme energy Hydraulic Flat Tapped Cam, the specs:
RPM Range 1600-5800
Lobe sep 110
Lift@.050 224/230
Intake Centerline 106 Valve lift .477/.480
Does any body here have any experience with this cam? or comment on it?
Any other suggestions??
Back when I was dreading for a truck I can across a truck with that cam.sounded pretty good, but it had a 2000 stall convertor in it, thing got off the line darn good
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As I was reading your description and the motor details I thought to myself "Hmm, the XE268H that I have would probably work well for him and then I see that's what Comp recommends! I really like that cam and the 268 grind has been a workhorse for Comp. It seems to work well in most milder street applications. I have a 3.40 rear end but shorter tires but otherwise a somewhat similar setup to yours. My truck before the cam, heads and rear end change could barely do a brakestand. Now if I am rolling at about 15 mph and stomp on it, it will light up the tires and spin them into 2nd gear too. My truck being a 2wd shorty is lighter than yours but even still, your combo with that cam and a well-adjusted carb and distributor should get the tires spinnin'!
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First, Why start a new thread on the same issue with the same ride? Second, you say you have a thumpr cam which tells us absolutely nothing specific about the cam. You need to post the specifications and how you installed the cam (timing).
Now before you do anything else, tell us about your ignition system and how you have your timing set.
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sorry for starting a new thread, its just that i thought that the initial post isn't the topic anymore, and wanted to get as much feedback as possible.
The thumpr cam's specs:
Operating range 2000-5800
227-241 at .050
471-456 at 1.5:1
107 lobe
I do have a B&W torque master 2000 stall in it.
The ignition system is MSD Streetfire dizzy, 6AL ignition box, wires and plugs.
I appreciate all your help.
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No need to be sorry but if there's more information available then keep it together.
Your whole set up doesn't sound like it's a good fit for your truck. What transmission do you have? You may want to put the stock converter back in. Where is your timing set at?
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What kind of a torque converter do you have? What stall speed? That can make a big difference in how the truck responds from a stop.
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Sorry for the late response, but i will update once i figure it out, thanks for all your comments.
For now i will take it to a pro shop, first thing i will have them check out the tranny (TH400), from then maybe the cam.
You are right Vile, im guessing that the set up was wrong, when im going around 70mph is when i feel the power and it got scary at around 95 mph (imagine the 33's on the K20 with the trampoline bench jumping around) but its not that good from the stop, thats why i might swap the cam.
I was thinking about posting a video of the truck in action, so you guys can see.