Cost difference when building a 306 vs. 347

[90mustangGT]

I am trying to figure out what extra things I will need to build a 347 that I wouldn't have to buy for a 306. So far I have figured:
Crank (cast will outlast the block right?)
Rods (I or H?) I will probally go with a DSS or SCAT kit.
Balancer (have romac SFI now, could sell to take the bite off)
Flywheel (wanted to go aluminum anyways)
Extra machining for rod clearances
Am I missing anything???

I am starting to plan on rebuiding the engine if the results of the compression and leakdown tests are not real good. 15 years and 156K miles, smokes, blowby, maby it is time. I have been considering after all is said and done the HP:$$ ratio would be worth it to go ahead and stroke it, not to mention the torque.

My engine combo now is the stock 302 bottom end, Thumper heads, B cam on 1.7's, a 70mm TB, Edelbrock Perfomer Intake, Longtubes, and other supporting components. I am aware that many components on my engine would not feed the 347, but I would probally still have more power over a 306, plus I can upgrade next year. I am on a budget, but won't halfass it either.

 

[85_SS_302_Coupe]

The major cost difference is going to be how you build it really...i've heard people say that strokers are strokers, and that mainly the difference in price is the quality that has to go into the bigger strokers for reliability. You could probably spend the same amount on a 306 as you do a 347, and just end up with a bulletproof 306. I'd personally go for the bulletproof 306....i think the 4.6 crowd has easily proven that cubes don't always make the most power if you've got good airflow and the right power adder.

 

[Daggar]

A bullet proof 306 vs. a moderatly built 331 or 347... Hmmmmm. I'm a big fan of the lowe end torque so I'd have to go with the stroker. What 85 SS is saying is absolutely true but one the things that sets the 302 apart is that low end grunt. Increase the stroke, you increase the mechanical advatage and also get a flatter power curve. With the same power adder and similar build on both engines, I'd have to go with the stroker.

 

[90mustangGT]

If I could find a stroker crank with the 50oz inbalance that would really cut costs. Another thing I am considering is that if I were to do the 306, once I tear into the engine I will have to have the stock rods treated crank pollished, that all cost money, might as well go ahead with the stroker crank and better rods.

I want to do all I can on motor, and a stroker will give me a lot more room to grow when I stack a big H/C/I combo down the road.

 

[Rick 91GT]

Any crank can be made 50oz balance, it is just a matter of removing material. It is better to turn the crank counter weights down instead of turning it into a piece of swiss cheese.

A good cast 306 kit will cost a few hundred less then a good cast 331 kit when all said and done...

 

[Daggar]

Seems like MM@FF did a n/a motor a year or so ago that was 485 hp. I don't remember the cost or much about the build. I'll keep and eye out for it (I'm sure I have it here somehwere) and post the combo when I do. It was a 347 kit in one of those articles on how you can do it but not break the bank. I think I remember a CHP rotating assembly and Holley upper and lower. I don't remember what cam they used. they built this thing up and tried both a carb setup and an EFI setup. I'll look and see if I can find it. I've been through a move since then.

 

[90mustangGT]

I was looking into the CHP kits also. I am not at that stage yet, not even sure what I am going to do.

I guess my question now is Would a stroker be my best bang for the buck mod? I'll pay a few hundred bucks for an extra 30+lbs tq.

 

[90mustangGT]

Another quesion; what would be a reasonable price of having my block machined. Cylinders bored .030 over and honed on a tq plate, mains align honed, clean/hot tanked, decked, and anything else I am missing.

 

[Mavrick]

STROKE IT!

 

[04-SVT]

Well, I am currently building a 331.
So far I have:
Eagle forged steel 4340 crank...
Eagle forged "H" rods...
SRP pistons (dished for 8.7 comp ratio)
JE full circle rings
King bearings
Maching shop cost $400
Total cost of parts listed: $1500

Keep in mind I wanted to build a bullet proof bottom end, so I did spend the extra $$$ for quality parts going with 4340 forged steel products. You could build a bottom end cheaper then what I am spending. I am doing all the labor myself, except for machining the block 30 over, stroker clearance, and having the valve springs installed and adjusted to correct height.

Before I decided I was going to build my 331, I was looking at just building and keeping it as a 306.
I was going to get the crank and block machined
Eagle "I" rods
King bearings
SPR Pistons (dished for 8.7 comp ratio)
Machine shop work $500
Cost for parts mentioned above $725

Although doing the 306 would be cheaper, I am building the 331 to be very reliable and the reason the compression ratio I want is 8.7 is for the 10 psi of boost I will be running from a Powerdyne unit. I would of spent the same building a bulletproof 306, cause I would of had to replace the crank to a stronger unit then stock to handle the boost and be reliable.

I dont know if I am helping you at all with my post, but figured some cost differences will help some.

 

[90mustangGT]

I dont know if I am helping you at all with my post, but figured some cost differences will help some.

It does help. I did a search and found prices from $500 to $1200. I am going to call the two reputable machine shops in my area. I plan on doing most of the work myself with the help of the master tech I work with that seemed excited about my plans. He has about every tool I need so really all I will need is the actual bore and honing, the rest we can do. From what I can tell, the only thing in machining you need to do with a stroker would be the clearing at the bottom of the cylinders for the rods. When reading all the posts in the search, I found people are spending too much money having the stock crank and rods worked. Why spend all that when for a little more you can get newer, better parts?

 

[Grn92LX]

90Mustang, your making a good choice on a 347. Your current parts obviously aren't the best, but like you said, you can change that later on. There was a guy on corral that made 299rwhp with a chip with a 347 and a set of thumpers fwiw. You are planning what I am, a nice 347 but reusing some parts you already have. I dont know about bang for the buck, but certainly that foundation can be improved down the road!! I wouldnt even waste my time on a 306 when a 347 shouldnt be too much more. Yes, a cast steel kit is more than enough. No reason for forged 4340 stuff in a stock block. Planning new combo's are fun, right?

 

[85_SS_302_Coupe]

A bullet proof 306 vs. a moderatly built 331 or 347... Hmmmmm. I'm a big fan of the lowe end torque so I'd have to go with the stroker. What 85 SS is saying is absolutely true but one the things that sets the 302 apart is that low end grunt. Increase the stroke, you increase the mechanical advatage and also get a flatter power curve. With the same power adder and similar build on both engines, I'd have to go with the stroker.

Agreed. If money werent a part of the factor, it's just like they say, you can't replace displacement. I was just saying that if he's on a budget, the stronger 306 might be a better option, since someday down the road he could have the cash for a blower or turbo, and then he'd have a stronger engine to handle the load.

 

[thumper460]

Actually guys... H beam rods for the 5.0 or the 347 are the same cost, new crankshaft.. almost the same cost ( cast Steel ) Forged or KB pistons almost the same cost.. Balancing.. the same cost, gasket/bearings, rings... all the same cost. Labor to build... differance here, the block needs to be notched, cams, t/chain, oil puml, pan.. blah..blah... all the same cost!! IF you do the engine assy and notch the block your self... your saving money!! Cool??

SOOooo.... 347 vs 5.0 ?? If your planning on building a killer 5.0... the cost for a 347 is REAL CLOSE!! You can use a quality ring set, gaskets, heads, and KB pistons ( 200 shot of juice) and savw more money... Just a thought!

But having a forged piston 5.0 core and just turn the crank, ARP the rod bolts and balance the assy... your way cheaper... cool?? and spray the 5.0 with a 250 shot... and your wiping the 347s nose all day long!! .... Unless the 47 is sprayed, of course..lol

Just me..........................

Thumper

PS. on a ported E7 heads and n/a in a fox body the 347s are deep in the 11's!! Just a thought...

 

[Grn92LX]

Agreed. If money werent a part of the factor, it's just like they say, you can't replace displacement. I was just saying that if he's on a budget, the stronger 306 might be a better option, since someday down the road he could have the cash for a blower or turbo, and then he'd have a stronger engine to handle the load.

The fully 4340 forged 306 will be NO stronger than a cast steel crank'd 347. An engine is as strong as its weakest link. In this case its the block. Why put 1000hp crank in a 500hp block????

If you can afford it, do the 347 and build it up as you can afford to. You will have a killer foundation as myself and others have said already. Now taking the money out of the bank is another thing, huh? believe me, i know how you feel. Its gonna be tough doing my combo but I should be happy once its done. Im waiting to hear from my cam grinder if he says I shoudl port the heads or not. If so, I will have that done first since I cant order a cam till the heads are done and flowed and wil order the shortblock at the time of the cam so it can be shipped to the shortblock builder and installed and degreed as part of his normal routine in the labor.

 

[tjm73]

If you are just looking at using what you have with more inches....

Above and beyond the machine work you should do to the block for the 306, a stroker will cost you how ever much this stuff costs, depending on what you buy.

Stroker kit
Balance for stroker kit
Damper for the balance you go with if other than 50 oz-in
Flywheel/flexplate for the balance you go with if other than 50 oz-in

Everything else you will need or do, you will do whether its 306, 331 or 347.

 

[90mustangGT]

90Mustang, your making a good choice on a 347. Your current parts obviously aren't the best, but like you said, you can change that later on. There was a guy on corral that made 299rwhp with a chip with a 347 and a set of thumpers fwiw. You are planning what I am, a nice 347 but reusing some parts you already have. I dont know about bang for the buck, but certainly that foundation can be improved down the road!! I wouldnt even waste my time on a 306 when a 347 shouldnt be too much more. Yes, a cast steel kit is more than enough. No reason for forged 4340 stuff in a stock block. Planning new combo's are fun, right?

I read your 347 ideas in your thread, I am with you, I like lots of torque on demand. Even if the motor is real good, I'll probally end up doing the 347 after all. The guy made 299rwhp, but I bet the low end torque required medical attention. Even if the 299rwhp 347 was paired next to a 299rwhp 306 combo at a drag strip, the 347 would have a clear advantage. Maby it would be closer on the highway. Maby peak numbers would be the same, put the tq curve on the 347 would be generally flatter through the rpm's and it would be much fatter at the bottom. To me it's not really as much peak numbers, I really don't care, it's about power through the rpm range I am in when racing. I also like being to accelerate easily w/o having to downshift. The main thing that attaracts me to the stroker is the expandability to get much higher output components. It is just too easy to over-cam and over-head a 3" stroke combo, unless you want to make it able to rev to 8K or put some boost on it. If I had the money, no doubt it would be a real nice turbo system, but after all is said and done, it will be close to $6000 unless I do a jy setup.

I am figuring I will be spending about $1500-2000 all togeather, I can pull that togeather by next spring. Then down the road I'll do another H/C/I and it will be like doing going form a stock 5.0 to a H/C/I all over again, nothing like being scared of your own car!!!

 

[90Notch]

The added torque from a stroker is well worth the money. As for costs the kits are pretty cheap now adays and it shouldn't be that much to assemble one but everyone here has yet to mention the added hidden costs associated with the increased torque (or atleast the ones I found when I switched to 331ci)...new clutch, trans rebuild kit and rear differential rebuild (all victims of spirited red light take offs

 

[90mustangGT]

Has anyone heard of C.A.T. products? They have some good prices and a local dealer stocks them.

 

[Grn92LX]

Has anyone heard of C.A.T. products? They have some good prices and a local dealer stocks them.

Stay AWAY. Look into scat, eagle or coast high. Those are all good kits that are affordable.