305 upgrades?

[Gmc-76]

Originally Posted by motornut

yup both trucks are true duals,but (79-305) has an H pipe,both @2.25,no Ejunk really

Is there really a noticeable difference in the power? I know my tuck has all the emissions junk, a cat, a muffler with single in dual out, and I don't know if I were to put true duals with flow-masters and ditched most of the emissions crap if that would affect my back pressure.

[motornut]

Originally Posted by Gmc-76

Is there really a noticeable difference in the power? I know my tuck has all the emissions junk, a cat, a muffler with single in dual out, and I don't know if I were to put true duals with flow-masters and ditched most of the emissions crap if that would affect my back pressure.

It seems better to me but I drove it home with the muffler rubbing on the drive shaft lol,
I was told 2.25 is better for a stock engine on duals.
Bigger pipes can pull/scavenge to much .
I compare it to a trumpet, gotta blow a certain pressure , to get " the sound".
the " rat tat tat"...
And it works for me, even crush bent 2.25 would breath better then stock.
Then add in a plugged cat , on that stock system.
I bet it's even louder with the soft top!

[50seven]

IMO that little truck motor needs all the tourque it can possible make to turn that 2.73 diff. Block off the EGR with just a simple piece of sheet metal between the flanges. Easy to make yourself. Check for vacuum leaks. Get rid of that clogged cat.

You can even run smaller diameter tires on the back give that 2.73 less leverage to have to turn.

As I said before get another diff. Most jimmy/blazers came with better gear ratios. Cheap easy fix you can do in a day pbbly for less than a couple hundred dollars depending where you get your diff and if you have a place to do it.

There really isn't much more you could do. A 700r4 is still going to be a dog with 2.73's in the back. The transmission might rarely get into 4th gear and pbbly won't want to stay there if it did.

2.73 aren't even fun in a 455 powered Trans Am

[Gmc-76]

Originally Posted by 50seven

IMO that little truck motor needs all the tourque it can possible make to turn that 2.73 diff. Block off the EGR with just a simple piece of sheet metal between the flanges. Easy to make yourself. Check for vacuum leaks. Get rid of that clogged cat.

You can even run smaller diameter tires on the back give that 2.73 less leverage to have to turn.

As I said before get another diff. Most jimmy/blazers came with better gear ratios. Cheap easy fix you can do in a day pbbly for less than a couple hundred dollars depending where you get your diff and if you have a place to do it.

There really isn't much more you could do. A 700r4 is still going to be a dog with 2.73's in the back. The transmission might rarely get into 4th gear and pbbly won't want to stay there if it did.

2.73 aren't even fun in a 455 powered Trans Am

would a 3.08 be ok? or a 3.73? I still need to be able to ride down the highway and keep up with traffic. Im forced to have to keep my th350 for a while.

[50seven]

GMC76

I had a Nova with 3.08 in it and a 700r4 it went down the road doing 50/55 mph at around 1700-2000rpm. It was way out of power range for the 350 in fourth. But got decent mileage. I calculated it out with the gearing of the trans having a deep first gear the 3.08's where like having 4.11 and in fourth O/D it was like your 2.73's going down the hwy. My numbers are off the top of my head so don't roast me if they aren't exact you can calculate all this on paper it is worth doing to get what you want. I wasn't overly impressed with 700r4. The early 700's are weak. I tore up 2 of them. The 700's got better in the later eighties

Got good at changing 3/4 clutch packs........

There is a bit of playing around to get the lockup to engage disengage brake switches and wiring but not that bad. It is all on the net just not a bolt in and drive type of install. It would not be the first thing I would be doing to your truck.
That diff is still going to be there after a trans swap

[50seven]

Sorry GMC 76 I didn't answer your question about gear ratios on what diff you should go with.

That is something you are going to have to determine

What do you want from this truck? Keeping the 305? Eventually changing to a 700r4? You say you want to drive hwy speeds. Here is what I would do.

Decide what rpm you want going down the hwy? Pbbly 2000 rpm?
What speed do you want to travel down the hwy at?
Using your final output ratio of your trans in high gear 1:1 or 0.73:1 depending on which trans.
What size tires are you running or plan to run?(so you can determine the circumference - how much distance the tire travel in one revolution)?
Calculate from that information what diff you should be looking for?

You will pbbly decide to go with 3.08 3.23 or 3.42's.

A little time spent on paper saves a lot of frustration.

[bdiamond]

First gear gets pretty short with anything much lower than a 3.42.

[Gmc-76]

Originally Posted by 50seven

Sorry GMC 76 I didn't answer your question about gear ratios on what diff you should go with.

That is something you are going to have to determine

What do you want from this truck? Keeping the 305? Eventually changing to a 700r4? You say you want to drive hwy speeds. Here is what I would do.

Decide what rpm you want going down the hwy? Pbbly 2000 rpm?
What speed do you want to travel down the hwy at?
Using your final output ratio of your trans in high gear 1:1 or 0.73:1 depending on which trans.
What size tires are you running or plan to run?(so you can determine the circumference - how much distance the tire travel in one revolution)?
Calculate from that information what diff you should be looking for?

You will pbbly decide to go with 3.08 3.23 or 3.42's.

A little time spent on paper saves a lot of frustration.

I want to keep the 305 and th350 for a little while. I plan on swapping in a 350 with a 700r4 sometime, for now I plan to stick with the rally's and the 235s. I feel a 3:42 would work??? But yet again highway. most of my driving is highway and I plan to do hopefully 60mph.

[bdiamond]

Most newer 1/2 ton trucks (88-98) have a 700r4/4l60e with a 3.42 rear axle.

[Tom]

When I sold my 79 I pulled the vortec 350 and put a stock, old 305 in its place that I picked up cheap. Ramhorn manifolds, dual 2.5" exhaust, edelbrock 600 carb, MSD HEI were all that got left performance wise on the engine. It had a 200-4R with a 2300rpm stall convertor and 3.08 rear gears. The dam thing had no power. I couldn't imagine driving it on a daily basis like that. I literally could not use overdrive as it didn't have enough power to maintain speed and this was in a 1/2ton shortbed.

[Gmc-76]

Originally Posted by Tom

When I sold my 79 I pulled the vortec 350 and put a stock, old 305 in its place that I picked up cheap. Ramhorn manifolds, dual 2.5" exhaust, edelbrock 600 carb, MSD HEI were all that got left performance wise on the engine. It had a 200-4R with a 2300rpm stall convertor and 3.08 rear gears. The dam thing had no power. I couldn't imagine driving it on a daily basis like that. I literally could not use overdrive as it didn't have enough power to maintain speed and this was in a 1/2ton shortbed.

I cut the stock exhaust right underneath the cab, eliminating the cat and muffler(full of holes and soot) and bought a cheap thrush muffler and a turndown and welded it all together up underneath the cab. It sounds better and it has a little bit of a noticeable difference in power