Rebuild, need advice....

SlowDropTop said:

Hey guys,
Its time for a rebuild....on a budget! My goal is low 13s for my vert, nothing crazy just fun, enjoyable and reliable . So heres what I was thinking:
The top end:
GT40-ported, and maybe milled-nothing crazy, I would like a 9.5 or 10:1 CR
E-cam (cause it came with the car when I bought it)
Not sure the intake-I was thinking ported lower but would that be enough?
Plus, 76mm MAF, 24lb inj, 65mm TB, Udp, FMS shorty headers, catted high flow h pipe, and dyno turbo mufflers.

ok now onto the bottom end, this is where I am COMPLETELY lost! I want a 306, you know bore it over, freshen up the cylinder walls. I would also like to use forged pistons, as in the future (a year or two) I would like to run a low boost application, I notice probe pistons seem to be used alot, but I have no clue on things like domed, notch, and all the other things. Also should I just use stock rods, bearings, and crank?

So here ya go, on top of those question....what the stock cumbustion Chambers on GT40 heads? What would I have them milled to to get desired CR? Does this all sound like a good combo for what I want out of my car?

And one final queston, haha, would I be better off just buying a preassembled long or even just a short block from a place like CentralCoastMustang.com?

Thanks guys
Ben

Sorry for the long post!

Click to expand...

First and foremost, you should decide now if you are going to go for boost in the future. If so, aiming for a 9.5/10:1 CR is kind of shooting yourself in the foot. You've got the chance to install low compression pistons now and you'll be able to run more timing with more boost while still avoiding detonation.

If you're certain you will boost it with those pistons, you will want to aim for dished pistons. Dome pistons are generally looked down upon because the dome affects the combustion pattern in the chamber... you want a smooth outward combustion that doesn't have to go over any hills.

As far as notching patterns, you'll want inline notches (AKA valve reliefs) for the heads you've selected. They make offset reliefs for the Trick Flow Twisted Wedge heads because their valves are offset.

For the bearings, you can use stock type like clevite, but your machinist will tell you want size to get depending on whether or not he had to grind the crank and how far. The general concensus is that stock rods will outlast the stock block, but if you've ever seen a thrown rod's results you'll think twice before hitting it with any serious boost.

Without a doubt I would just have the stock crank checked and possibly reground (polished at the very least). As I said earlier, your machinist will tell you what bearings to order.

For milling: SITUATION 1, you want high compression. If you're buying new pistons, there's no reason at all to mill your heads to achieve a certain compression ratio. I would only mill them if they look rough or are warped, and even than I would take off the smallest amount possible. When ordering your pistons you can tell them your valve relief cc size, head gasket thickness, and combustion chamber size and they should be able to give you flat top piston to get your compression up around 10.5:1 with a decent combustion chamber size. Unfortunately I don't know the combustion chamber size for the GT40's, although I think the GT40P's are 58cc and the GT40's are larger.

For milling: SITUATION 2, you want low compression for boost. Try to stay away from milling the heads as much as you can, especially since they're iron and more likely to keep a flat surface. Any milling you do will raise your compression ratio if you don't compensate with a thicker gasket or a deeper dished piston. When you order pistons, you can tell them what CR you're looking for, being low, and they'll be able to get your a dish for your desire.

I think you should save your port money for elsewhere. If you're going to go all out, go all out. If you're on a budget, stay in the budget mindset.

I think your "76mm MAF, 24lb inj, 65mm TB, Udp, FMS shorty headers, catted high flow h pipe, and dyno turbo mufflers." look good for your buildup. If you throw the equivilent of a Cobra intake onto this motor, you will basically have a Cobra motor. With boost, people have gotten pretty darned close to 400rwhp on a stock Cobra motor with very few supporting items. My friend's 94 Cobra with just exhaust is a force to be reckoned with, his low end torque actually pulled infront of my 293rwhp/327rwtq n/a vert pretty hard... I needed to get into RPM's before I passed him.

What brand MAF are you looking to get? I recommend Pro-M, in which case you'd aim for a 75mm. I've had 4 Pro-M meters with no problems.

For your final question... what are you looking to spend? Add up what you get in a pre assembled shortblock and compare that to the costs of maching and parts for the shortblock you want to build. Some places offer warranties on their shortblocks, you might want to consider that.

Good luck!

If you haven't done so already, call around your area and explain your situation and knowledge level. A good machine shop will have no problems helping you pick a good combo of parts. You can also call larger shops like CHP, DSS, F-P-S, and so on to get their opinions as well. There is so much to picking a good combo of parts, just make sure your engine builder understands your expectations. 347 vs 306

I've found that some machinists or shop owners do not understand the concept of wanting to stay within a budget. When I talk to them they actually give me a hard time for wanting to use a stock flywheel versus billet steel... or Windsor Jr Heads and not $1500 aluminum heads. I can understand if they try to steer me clear of POS Proform rockers which I have seen break, but if you can't drop $1500 on heads than you can't do it.

The ones I've found who will work with me are the ones who get my money.

Don't take this the wrong way, though. Expect your guy to tell you flat out if something is not going to work or if the part you are looking at is junk. But if you want GT40 heads with a letter cam and an Explorer intake, than that's what you want. Its not going to break, they're all durable reliable parts.

If you're not looking for top dollar, the summit rebuild kits can come with Speed Pro forged pistons and all of the rings/gaskets you'll need.

How much does your friend normally charge for portwork?

5psi on that compression ratio should be fine, but you will still be limiting yourself in the max boost area.