Overbore question

[Rusty67]

Ok, this is a stupid question but I'd rather ask here and get some good information then ask a parts house and get sold stuff I don't need.

I finally pulled the engine/trans out of my donor car last week and I've decided to spend money and rebuild the motor instead of just slaping it in. I figure if the drive line is definately good then thats 1 less thing to worry about.... for a long time at least.

Anyways, when you overbore a motor, you have to put in larger pistons and rings or do you just need bigger rings ?

While I'm here, anyone want to recomend what pistons I should use ? Its a late model 5.0/302 and I MIGHT go FI with it down the line...

 

[jadesville]

With a bored out block you'll need new pistons and rings.

You need to make the decision now if you want to go FI in the future or not since you will be rebuilding the engine. If you want to FI you'll be getting a lower compression piston, different ring gaps, etc.

 

[Rusty67]

By FI I ment Fuel Injection, not Forced Induction.

I figured I'd need new pistons and new rings... now to figure out which ones to buy...

 

[D.Hearne]

With a bored out block you'll need new pistons and rings.

You need to make the decision now if you want to go FI in the future or not since you will be rebuilding the engine. If you want to FI you'll be getting a lower compression piston, different ring gaps, etc.

Why would you suggest this? You want the highest compression regardless of induction. Unless you're going to supercharge it. A short block for FI or carburation is the same. More compression means more efficiency. There is a limit of course with fuel grade, but a 9-10 to 1 compression ratio is what you want with either for pump gas. You can get by with more too, depnding on other factors.

 

[NasaGT]

Why would you suggest this?

The original post said FI. I always though FI is usually short for Forced Induction, ie supercharging or turbo and EFI is Electronic Fuel Injection. I thought his post made perfect sense.

 

[jadesville]

Why would you suggest this? You want the highest compression regardless of induction. Unless you're going to supercharge it. A short block for FI or carburation is the same. More compression means more efficiency. There is a limit of course with fuel grade, but a 9-10 to 1 compression ratio is what you want with either for pump gas. You can get by with more too, depnding on other factors.

FI is a more commonly used term for forced induction. It made perfect sense considering he asked for what piston to use.

 

[SoCalCruising]

If you are not going to build a hot motor, just get stock replacement pistons, like the FRP slugs from Probe. Buy the pistons, take them to the machine shop with you, along with the recommended clearance (from probe; piston-to-cylinder-wall clearance) and the shop will get the bore/hone right. This is not absolutely necessary, but I do it for performance motors. You can take the rotating assembly at the same time for balancing (pistons, rings, pins, rods, rod and main bearings, crank, damper, and flywheel/flexplate).

 

[Rusty67]

Thanx for the advice SoCal.

I should have said EFI, my mistake. Once I realized I didn't put the E in there it was already too late, sorry about that.

 

[CochinoFilipino]

It can be read either way. Who's going to convert to mechanical FI?

Since you mentioned not wanting to be sold unneccessary parts, Do you even need to overbore the cylinders or need new pistons?

 

[D.Hearne]

FI, means Fuel Injection to me, shows how old I am.

 

[Rusty67]

Mechanical Fuel Injection would be kewl... did Ford ever make a setup for the small block ? I can only image it must be hell to tune if they did. I've seen a friends Porsche setup for it and it looks COMPLICATED.

Well, I'm sure since the motor has like 200,000 miles on it I'll need to hone the cylinders and I'm expecting to need to overbore it to clean it up. Altho I'll admit that the thing runs great compaired to my other motor with only like 90,000 miles on it. This one was a WELL cared for motor, unlike the last one.

I'm gonna tear the thing down and take it to a machine shop I trust locally and find out how much I need, the less the better IMO.

 

[Pakrat]

Before you do anything I would make sure that the block does even need to be overbored as Cochino mentioned. If your block has the standard bore still with less than .011 in. of taper from top to bottom than it can just be honed and still use the standard size piston. I tyhink people are way to eager to overbore their engine and they always seem to jump right to a .030 size. The first step can be a .020 size though which leaves you plenty of room for doing it again down the road all the way up to a .040 one day. I know alot of folks do it but i would never go .060 on a small block.

 

[Rusty67]

Actually, I agree with you. I am gonna take it apart and take it to the shop to find out whats up before I go buying parts. However, I am thinking I'm gonna want to put in new pistons anyways because I don't think the stock pistons in an 87 5.0 are what I want. I could be wrong about that, I figured I would at least want some pistons with valve reliefs in them incase I decide on going 1.7 rocker arm ratio. Besides, if nothing else, coated pistons last longer.

 

[CochinoFilipino]

However, I am thinking I'm gonna want to put in new pistons anyways because I don't think the stock pistons in an 87 5.0 are what I want. .

I think stock '87 HO pistons have valve reliefs and are forged. Guess you'll find out what's in there when you tear it down.

 

[SoCalCruising]

BTW, my suggestion of stock-type pistons doesn't fly if you use an intake valve larger than 1.90 in the heads. Just in case you were thinking of using performance heads ....

D.Hearne, I'm like you ... FI meant fuel injection. I remember talking about FI Chevy heads, which were the hot ticket back in the day for my 327.

Ford didn't need mech FI for the small block 'cause they offered the Weber conversion over the counter at the parts dept. That is very close to fuel injection and they make wicked power over most carb'd setups. Mine aren't even tuned, yet, and I'm still amazed at the power gain, all over, that I have now compared to the ported Stealth/650 HP DP setup I had. I go for tuning/dyno pulls Friday and will post results.

 

[D.Hearne]

When ordering pistons for it, watch the pin heights. You want a 1.610 pin height to keep the piston as close to the deck as possible. This means more compression for N/A applications, if you do decide to go F/I, then you can always tailor the boost to match or get a dished piston if you don't want to do that. The reason I suggest watching the pin height is not all 289/302 flat tops have the correct height for a near zero deck. There are many on the market with a 1.585 P/H.