.30 Over

Xterminator03 · Jul 26, 2008

I wanted to know Houw much does it cost to bore the block .30 over. What can I expect as a power gain. and where can I get this done in or around NY. i also want to raise my compression up. As High and as safe as I could.

Foxfan88 · Jul 27, 2008

boring cylinders our shouldnt be looked at from a performance standpoint, boring them out is to clean up and get a square and perfectly round hole.

if it can be avoided i would do that. making the cyl walls actually makes them thinner and weaker.

and for performance you would never feel a difference just boring the block out.
the way i look at it. if you have an engine making 1 horse per cube, and going .030 over (on a 302) will net you 4 CI (306)throughout the engine engine. if you kept everything the same you would see 4 horsepower.

boring holes out would also increase compression but i am sure it wont be nothing worth mentioning at all. chamber size, gasket thickness and piston tops are going to make the biggest differences on compression, stroking and engine keeping the same heads gaskets and pistons also increases compression. while boring it out affects it also. like i said the difference is almost negligable.

on the price. i dont know for sure but i think the standard is about 25-30 bucks a hole to get machined out.

5spd GT · Jul 27, 2008

Keeping everything the same, the larger bore will increase compression roughly ~ .015:1 points. It deals with the larger swept volume.

The good thing with boring/honing the cylinders is to get a new cylinder wall. It also allows you to pick a higher compression piston design (flat to dome).

Expect around $200 for an overbore, of .015" on each side (.030" overbore).

Xterminator03 · Jul 27, 2008

If I get the block bored I will need new pistons I have heads that give me a 64cc in the chambers. Im not to sure what compression that gives me now. but im looking for something like 11:1 or higher. Not to sure if thats to high, or what problems it may cause.

Foxfan88 · Jul 28, 2008

thats quite a bit of compression, you will need to run premium gas for sure. and probably some octane booster if you want to make alot of power.

for the street you could really retard the timing and run it rich to make it run without boosters but you will be missing out on alot of power.

bmo37 · Jul 28, 2008

SemperFIGOD said:
I wanted to know Houw much does it cost to bore the block .30 over. What can I expect as a power gain. and where can I get this done in or around NY. i also want to raise my compression up. As High and as safe as I could.

Depends boring a block is a couple hundred dollars, the real work is balancing the parts and assembly of the short block. If u have the money might want to consider a stroker kit rebuilt if your going to have the block bored and redone, As far as compression the easiest way to raise it would be domed pistons in your rebuild but u must make exceptions for valve clearance. Also the more compression u make the more hp u get but at what cost like already stated unless ur cars a trailer queen only ur going to need high octane gas, really good tuning and I might even say locwire headgaskets. Personally I wouldnt go to overboard if you plan on adding boost later ur going to wish u stuck with a lower compression engine.

Xterminator03 · Jul 30, 2008

Ok if that is to high of a compression what would be a resonable number where its still streetable. I wont boost the car But I will Juice it. At the same time I dont want to be stuck ussing anything higher than 93 Gas unless im running the car at that point race gas is not a problem for me.

Xterminator03 · Aug 4, 2008

What's as safe High Compression Ratio to run on a street car. and with Heads with a 64cc Chamber what pistons would be good?

85_SS_302_Coupe · Aug 4, 2008

5spd GT said:
Keeping everything the same, the larger bore will increase compression roughly ~ .015:1 points. It deals with the larger swept volume.

The good thing with boring/honing the cylinders is to get a new cylinder wall. It also allows you to pick a higher compression piston design (flat to dome).

Expect around $200 for an overbore, of .015" on each side (.030" overbore).

That about sums it up. .30 over doesn't really give you much if any gain...the gain comes from fresh rings, better cylinder compression and the new pistons you'll be using which will likely increase compression ratio. Boring .30 over gives you roughly 1/2 cubic inch per cylinder which is barely enough to matter by itself.

As for how much is safe...that depends on what grade gas is available to you and how good your tune is. My buddy's 347 is around 11.4:1 and he runs 93 on a dyno tune and he could drive it DD if he wanted.

bmo37 · Aug 4, 2008

I'm 12:5:1 ratio and under boost i've seen guys into the 13:5:1 ratio on a NA combo but thats with race gas. For street ur not going to see much fuel ratings much higher than 93 octane with a few exceptions, and buying octane booster as a fuel addative each time u fill up a daily driver is going to be really expensive. Again with a good tune you can achieve a CR of 12:5:1 or 13:1 with no issues no 93 premium gas.

MaxTheHooker · Aug 4, 2008

uhm, am i missing something or is 12.5 to 1 WAY WAYYYY too high for a boosted application?

oz · Aug 5, 2008

There is no hard and fast rule about static compression ratio because what matters is dynamic compression ratio. This is most effected by the cam. If you have a lot of valve overlap, your dynamic compression will be much lower and therefore you can get away with a higher static number (like 12.5:1).
Your best bet is to come up with a proposed combination (cam and compression ratio) and then throw it out there on the forums an see if anyone uses a similar combo.
I've heard of 13:1 engines running on regular because they had a lot of overlap and I've heard of 9:1 engines having problems on premium due to lack of overlap so it's not really about the static compression ratio - it's more about the cam specs.

Regarding hp increase - I'd say 2-3 hp for .030" over.

Bore .030" over = $120-150. You'll need them to hot tank the block, assemble the new pistons and rods, turn the crank and install cam bearings also at a minimum. You could also have them tap the oil plug holes and istall the plugs. If there is any concern over block integrity, they should check that before they start cutting it.
Balancing the rotating assembly is mandatory for any performance application as well. Expect to spend $200-$300 for that. You will need to give them everything that rotates - balancer, pistons/rods, crank, flywheel. If they don't ask for the flywheel, go somewhere else.

bmo37 · Aug 5, 2008

MaxTheHooker said:
uhm, am i missing something or is 12.5 to 1 WAY WAYYYY too high for a boosted application?

its boarder line but i'm running low boost 6-7lbs and its on a 347 stroker engine. Yes if i were to run really high boost than i would have went with a lower cr, 8:5-1 or just around 9

Xterminator03 · Aug 5, 2008

oz said:
There is no hard and fast rule about static compression ratio because what matters is dynamic compression ratio. This is most effected by the cam. If you have a lot of valve overlap, your dynamic compression will be much lower and therefore you can get away with a higher static number (like 12.5:1).
Your best bet is to come up with a proposed combination (cam and compression ratio) and then throw it out there on the forums an see if anyone uses a similar combo.
I've heard of 13:1 engines running on regular because they had a lot of overlap and I've heard of 9:1 engines having problems on premium due to lack of overlap so it's not really about the static compression ratio - it's more about the cam specs.

you can see my setup in my signature

And by the sound of things an 11:1-12.5:1 Compression Ratio would be in the range of what im looking for as long as 93 octane fuel is sufficient.

.30 Over

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