[ksims1868]

I know the saying..."there's no replacement for displacement", but I want to know how much better a 350 really is.

I've had 350 chevy's for years, but it was always a REALLY hopped up 350 in my truck or car. NEVER in this heavy @ss K5.

I have a 1984 K5 Blazer and I think I want to ditch the 305 and install a 350, but 1st I want to know if it will really be worth the swap.

My 305 is bored .30 over, has a mild cam, headman headers, Holly 650 carb, and runs EXCELLENT. It has 26K miles on it and it is a VERY dependable engine. I just feel like I need more power.

I can't even spin the tires on dry pavement. Can a 350 spin 35" tires on a K5 Blazer while on dry pavement?

I am considering installing a mild 350...nothing too radical.

 

[kling-on]

what would you want for the 305 ? since its a slow junky motor I dont know the answer to your other question

 

[Rastus]

Sounds like you need to go with lower gears. what is your current gear ratio?

 

[S.A.K-5]

keep the 305, a few more ponies wont really help unless the k5 loses a few thou sand poundspopcornn

 

[ksims1868]

keep the 305, a few more ponies wont really help unless the k5 loses a few thou sand poundspopcornn

Okay - so it really isn't ever going to feel "snappy" like my old Chevy trucks did. I can accept that, and it is kind of what I expected. I remember I had a Chevy truck with a "bone stock" 305 engine that felt pretty quick and had no trouble spinning the tires, so I figured it was just the extra weight of this fat K5 that made it feel sluggish...not necessarily the engine itself.

The gears are stock as far as I know. Whatever that is.

 

[kling-on]

probley 307 swap in some 410 or even 456 if you have a o/d you'll get the snap back

 

[S.A.K-5]

1funny1 jamminzz

 

[Lifted78Chevy]

Keep the 305....if it ain't broke why fix it.....u want to get power....just save up for that fat bigblock to drop in the blaze....that'll diffrently light um up....so keep the 305 till your ready to put in a "Real" motor.....but with more power comes more broken parts so maybe keeping the 305 is saving you money in the long run.

 

[mrhoes]

i agree i have a 305 in my k5 and i am going to run it until it dies. i have a 350 sitting in my garage that will go in there next. when i ran 31s i had 3.42s and it wasnt that great on the road it ran at 1500-1700 in OD. gears would probably help put more power to the ground and it would take off quicker.

 

[4x4Freak]

Definitely put some gears in it. You will benefit from that more than anything.

 

[ksims1868]

Okay...gears then. So...stock gears (what I probably have) are 307. I've had 342 and 410 gears recommended.

Should I just swap the rear gears or do I have to do both diffs? I want to still be able to drive (comfortably) on the freeway at 70-75 mph...wouldn't 410 be a bad choice for freeway driving?

I had a 373 rear end in my 71 chevy, but it was more for drag racing...THAT was a bad ass truck!.

So my best bet sounds like a 3.42, but now I need to know if I need to swap both diffs, or if it will just work if I have it installed it in the rear.

 

[Rastus]

4x4 = both axles. 3:42 ain't deep enough. go with 4:10's at least.

 

[4x4Freak]

If you have a th350 go with the 4.10s, if you have a 700r4 go with 4.56s.

 

[wheelerjb]

If you have a th350 go with the 4.10s, if you have a 700r4 go with 4.56s.

?por que? is that because of the 5th gear in the 700r4?

 

[American]

You guys are smokin crack...

A 305 has a 3.736" bore compared to the 350's 4.00", both use the same 3.48 stroke. The issue here is not JUST displacement but rather how much air/fuel the 305 can flow. The cylinder heads have a smaller combustion chamber for the smaller bore of the 305 and as a result must use smaller valves.

For example, the 601 (last three digits) castings with a 58cc chamber use a 1.77 in and 1.5 ex, and have a small kidney shaped chamber similar to the 'double hump' 64cc heads used on the 327 & 350. This casting comes on the 267 and 305 and flows terribly. You could go with a 416 casting (yes, there are others) that has a larger chamber, usually found on the 305 it was also used (poorly) on the 350. This head uses 1.84 in and 1.50 ex valves.

I have built some decent flattop 305's and with a little headwork they run ok but you will see far better results with a similarly built 350+.

One of my best combos was a 350 with hyperutectic flattop pistons (cheaper than forged and will tolerate NOS well), a mild cam with around a .492" lift and 280 deg duration. Some clean, match ported 76cc heads with a 1.94 Intake and 1.60 exhaust will work nicely. Keep it together with a double row timing chaing, high volume pump (I always liked the Melling M-55HV). Use a decent dual plane intake manifold for good low rpm torque and don't over carb it, if you can't use some sort of FI then go with a good Carter or Rochester build... a Holley if it's setup just right. Overcarbing and camming an engine are the number one mistakes.

Parallel deck the block, they are all uneven. Align bore the mains and balance the crank assembly. I have built more of these than I can count and you would be surprised how many big blocks I've outrun merely because they were over carbed and cammed...and put together poorly overall.

 

[4x4Freak]

?por que? is that because of the 5th gear in the 700r4?

No, because of the 4th gear.

 

[4x4Freak]

You guys are smokin crack...

Care to elaborate?

 

[American]

Nah.. it was humor. I was just giving you guys a hard time. I've just always subscribed to keeping the gearing streetable...where you can actually drive 70+ without revving the crap out of the engine.

If you are building something that is strictly off road so be it.. but if you are driving it on the street, like most of us, 99% of the time I'd rather have a strong engine.

 

[Jeepndav]

But since he went to larger tires, wouldn't getting "larger" gears get everything back closer to stock? Then he could keep the 305 stock and still do the 70 mph without reving the crap out of the engine.
















Now where did I put that crack pipe? smokin

 

[American]

Good point for sure.