I have been looking at increasing bore and compression for boost in power over the winter,

Yes I konow I will not know mh0ow much it is worth w/o some solid runs this year. Few more chances to get that info left,

Going from 3.250 bore to 4.310 or maybe 4.375 with compression increase of 12:1 to 15:1. According to desk top dyno before pc died it is worth 60 to 70 hp. Rather I go with a .250 bigger crank is up in air since requires new rods and the ones in motor are about new. At 150o a set i rather not do both. I could reinstal old rods with 128 runs but that was my change-out point for those in blower motors.
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So question is agree or disagree with power gain from bore anhd increase in compression?

I do not like to run over 15 to 1 compression for several reasons. I think the horsepower gains are minimal and it makes safe tuning window smaller. Just not worth it to me.

As for increasing bore that is not a bad idea especially for Chevys because it gives more room around the valve for air flow. Hemi is better there. Still your gains will be minimal if you can tell at all and only you and your checkbook will know if it is worth it to you.

So to answer your question, yes it would help a little you could probably get bigger gains with right tire, gear ratio and chassis tuning.

Very basically you make X amount of horsepower per cubic inch....So whatever cubic inches you increase you should pick up that amount of horsepower....That's figuring for the increase of engine size only...many/most upgrades will also increase HP for other reasons...
Now going from 12 to 15 compression in one jump is not a wise, or even good, idea imho....I understand you're blown alky but....everybody loves to go fast(er) but in reality we only need to have the best package to win....Static compression and boost are the same thing....only different...you can change pulleys all day/every day and find a "happy" spot....
But I know you well enough to know you're going to do what you feel like doing, so good luck with your project my friend,,

quote:

Originally posted by imakehp:
Very basically you make X amount of horsepower per cubic inch....So whatever cubic inches you increase you should pick up that amount of horsepower....That's figuring for the increase of engine size only...many/most upgrades will also increase HP for other reasons...
Now going from 12 to 15 compression in one jump is not a wise, or even good, idea imho....I understand you're blown alky but....everybody loves to go fast(er) but in reality we only need to have the best package to win....Static compression and boost are the same thing....only different...you can change pulleys all day/every day and find a "happy" spot....
But I know you well enough to know you're going to do what you feel like doing, so good luck with your project my friend,,

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Combination of how I stated it and understanding of it. Car is not blown alky. Just injected. The blown was in reference to changing out rods if run bigger crank I would need different rods. I have several sets out of my blown alky stuff that have 15 to 20 runs which was the point that rods got pulled and new set went in.

Agree if had blower pulley swaps are quick easy and cheap and when have a wall full of pulleys it is really cheap. Well Let's say I can go anywhere from 40 to 75% od before having to but a pulleyt or belt. Just not going blown with this deal. I would not think of 15:1 eith blower even in a Hemi

This message has been edited. Last edited by: wideopen231,

Bore increase will be 14 ci(4.310) or 28 for (4.375).

As for helping unshroud. If you think Chevy has valve close to cylinder. You need to look inside cylinder of Hemi with heads on and flipped over while rotating assembly and watch valve opening. Although very short time the low lift inake is all but hi9tting sleeve, Evewn with .125 over it will be close for first .150 to .200 .I Have bunch of gastes that show valve clipping the edge iwth minimal wear in guide.
If you look ate intake seat it is under the o-ring seat so close you can not change seat w/o damaging it. That is why they have Fat heads, which I do not. Well not yet. But fat heads require new pistons, new rockers(2300), new valve covers(1000) new headers (300), and pushrods(400). Oh did I mention another 5k for the heads? All used prices. So a good start on building a BBC.
Not happening anytime soon.
While Hemi's design has some great stuff going for it . Like any engine, it has room for improvement.

Looks like I should be able to find out the difference.
ordering pistons I was told should have them by March. Hopefully, rings will be available sooner.

Funny side note when asked the machine shop about boring it out. They said would have to have pistons. Told them nope you bore it to 4.378 and pistons will fit. He should he would check to see if could find a boring plate. After three calls he called me cussing( known for a long time) me for not telling him I had one and that the 3 he called had used mine for a job, Seems hemi;s are not the most commonly built engines around here.LOL

So if I can get everything ready I should be able to get a run or two before new pistons arrive, Figure to just use my other repaired block and swap parts out when ready, giving me chance to get few runs on low compression. Still will not know which makes the bigger difference since compression and ci both going up.