302 vs 306

1990_LX

1990_LX

Clubhouse Moderator
#1
#1
Well I'm looking into 306s and I'm getting come conflicting info. Some people say that it's not really worth the money if you don't need the walls bored due to deep scoring or even preparing to build a 347, ect. Others say that the extra volume has some kind of positive effect on the valves?(which made no sense to me) and then there is the age old argument "there's no replacement for displacement". I'm eventually buying a rebuild kit that comes with pistons and you can either get them in standard 4.000 bore or .030 over. I can get a fair deal on some machine work, how ever is it really worth it?:confused:
 
T

TERROR

Well-Known Member
#3
#3
4 extra cubes isnt worth it unless the cylinder walls are wiped out, even then i wouldnt bother stock 302 blocks are a dime a dozen
 
cobra20sc

cobra20sc

Well-Known Member
#4
#4
My undrestanding on the valve comment is that a bigger bore will help to unshroud the valves since they're close to the cylinder walls on bigger valve heads and help air enter the cylinder better. I think this is particularly the case on the afr heads for example.
 
AdirondackFox08

AdirondackFox08

Member Plus
#5
#5
I guess its really up to you. I know you're commenting about the post that dsblack93 posted yesterday with the stock cam and making 400 hp at the crank. I'm not sure how much .030" bigger pistons is going to help you out though, if there is much of a difference... I would just save the money for gaskets, bolts, and other odds and ends to put the motor together.
 
meanlx

meanlx

Well-Known Member
#6
#6
Don't bother with the 306, unless you're looking at running in a specific class and need to. If you want to stick with a stock block or 302 based block in general do yourself a favor and build a nice 331 or 347 (will make about 30-45hp more then the 302/306 with the same identical intake, heads,cam, etc). It really boils down to your goals and what your budget is.
 
1990_LX

1990_LX

Clubhouse Moderator
#7
#7
Well I just figured since you have a choice of what size pistons you can get with the rebuild kit I want to buy from Summit, why nit look in to it before I buy anything. Plus I have a connection at a machine shop so I can get much better prices then if anyone else were to just walk in. How much would it normally cost to have it bored out?
 
dsblk93gt

dsblk93gt

5.0 Moderator
#8
#8
Unless it needs to be machined, don't bother. Like stated above a 331/347 will gain you some power. I posted up a dyno of my old 331 before/after vs. the 302 for a comparison of the gains. Everything the same, just going from a stock 302 bottom end to a 331.

You need to figure out your budget or you will end up running out of $$ and then either not have enough to finish it or skimp out to get it done and have issues.
 
1990_LX

1990_LX

Clubhouse Moderator
#9
#9
I don't really have a set budget. I buy parts as I get money. I do not have savings I can dip into and pull out $600 for a build budget. I think I'll just get the block hot tanked, honed, rebuild it, and call it a day.
 
dsblk93gt

dsblk93gt

5.0 Moderator
#10
#10
1990_LX said:
I don't really have a set budget. I buy parts as I get money. I do not have savings I can dip into and pull out $600 for a build budget. I think I'll just get the block hot tanked, honed, rebuild it, and call it a day.
Click to expand...
Have it looked at then decide what to do from there.
 
Timspony

Timspony

Capital District Coordinator / Super Moderator
NYM Staff
#12
#12
The only true advantage to a 306 (bored over 30) is to slap in some Hi-compression pistons if you're going to built a stout NA engine (low comp. for a SC or Turbo)...Otherwise with the machine work, you're just spend $$$$ ... GL Jeff...
 
1990_LX

1990_LX

Clubhouse Moderator
#13
#13
That's true...thanks Tim and to everyone elses advise. I'll start with having it looked at but the walls look pretty good. Either way I'll have it looked at and go from there.
 
1990_LX

1990_LX

Clubhouse Moderator
#17
#17
Also, the crank out of the motor has some pretty good grooves in it, however the other 5.0 crank I have is balanced differently. If I just used a matching flywheel and balancer could I get away with using the older crank?
 
EHA Racing

EHA Racing

Member Plus
#18
#18
OK I want to give my opinion. If you are building an enigine you will at least have the cylinders honed with torque plates. Even if they dont need bored the piston to wall clearance will be greater than was recommended from the factory. The cyinders will most likely be slightly out of round. .030 over pistons are just as expensive as stock pistons unless you go with a flat top. Anyways, the key is the bore. Any width improvements to the bore not only add cubic inches it also improves flow and helps to unshroud the intake valve on any inline head, which will produce more power.
If you are that far deep, the extra $150 or so to bore the block is more than worth it.
In my world the bore is much more effective at creating power than stroke.
I'll give an example:
Take a 9.5" deck Dart 351W block and build a 427.
There are 2 ways to accomplish it.
4.1" Stroke and 4.060 bore (.060" ovebore)
OR
4" stroke with 4.125" bore

Which one will make more power, tune better and reduce piston speed?
The answer is 4" stroke with the big bore. Less rotating mass, more combustion volume area, less piston speed, more area to unshroud the valve, less windage, etc.....

Just a few things to think about.
 
1990_LX

1990_LX

Clubhouse Moderator
#19
#19
You raise a really good point there...never really thought about how even honing it will increase the gap. Like I said, the rebuild kit comes with a option for 3 different bore sixes, all at the same price, so really it comes down to how much it would cost at the machine shop. Also, I never though about a wider bore and shorter piston travel vs longer stroke but narrower bore. Over all what would you recommend? I'm not looking to make a race car, just something fun and the motor is rebuilt right.
 
EHA Racing

EHA Racing

Member Plus
#20
#20
A stroker is a good think, don't get me wrong. If you have the money I would build a 331. However, I would at least take the small step to a .030 or .040 overbore. It will only help and you said you good pricing at the machine shop. You should be able to get the whole block prepped and ready for around $450 or so. By prep I mean: tank, mag, bore, finish hone, line hone on the mains, parallel deck the block, soft plugs and cam bearings and final cleaning.
I built my brother's 306 with 10.5:1 compression, pump gas, twisted wedge heads, c4 with 4,500 stall. The car weighs over 3,200 lbs and will drive anywhere anytime, 100% street legal. It runs 12.20 on motor and went 10.54 last weekend on a 100 shot.
 
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