3.73 to 4.10's worth it?

[westsidek20]

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.

[Lt.Del]

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.

[westsidek20]

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?

[ehjorten]

Sounds more like a mis-match of engine components than a problem with gearing.  Just my humble opinion.

[454Man]

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.

[zieg85]

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...

[westsidek20]

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?

[westsidek20]

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?

[454Man]

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.

[thirsty]

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.

[zieg85]

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.

[454Man]

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:)

[westsidek20]

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!!!

[454Man]

What cam do you have in mind?

[Engineer]

+1 on the cam swap....