What Compression Ratio to shoot for

[Bow Tie Omega]

Well, everything is coming together with the BTO. Some bad luck with the motor has turned into some good luck. I am re-thinking my compression ratio numbers, as I am having to buy new pistons for the motor. Anyone who has done a project knows that whatever you have is never good enough. I had set up the motor to have a 9.32 compression ratio. This motor is a cast Iron 2 bolt block with Iron 119cc Oval ports which have been mildly ported and polished by myself with a clean up via the local motor shop. The motor will have Lightening Headers, with a Scat forged steel crank, Eagle H-Beam Rods courtesy of Flat Broke, a Comp Cams Extreme Marine Cam (can give numbers if necessary), a Weiand X-elerator manifold with a Holley 850 . I do not want to cross the 600 hp marker because it is a 2 bolt, but I do want to get close to it. Any suggestions, can I go for 10.0 to 1 or should I stay at 9.32, as I know as is, it will be a sound motor. Thanks for your time...Joe
PS... I do not want to turn this block into a 4 bolt at this time, I will be looking at new blocks after next Summer.

[396_Z]

I know you said that you don't want to go with a 4 bolt block just yet but if your planning on going that route at all now is the time. Get a set of splayed main caps from summit, hav them fitted to the block and go like a sum-bitch. 600 hp is a weak rating for splayed caps.

[sgdiv7]

something to think about, when have you ever heard of someone pulling a crank out of a two bolt main block? I have been running a bbc with hp some where around 800 for three years now in a flattie and my crank has not pulled out. In my opion the crank doesn't take the initial shock like on a car and I have had both and the question is have I just been lucky? Three years of testing now and its still in there and oil psi still the same filter is still looking good on the inside from after everytime I get back I cut it open and take a look. Im waiting for it to blow up so I can bulid a bigger one and It won't.
Bill

[sgdiv7]

Oh ya sorry, this was a compression ratio question. put 10.5 in and run 91 oct gas.

[Bow Tie Omega]

396, It is purely a budget issue, I have put over $15,000 easily into the boat in the last year, as the boat is a stringer up restoration. The wife's face starts getting all contorted and she makes these scary noises every time I even mention the boat anymore. This was supposed to be a $5,000 project

[flat broke]

Joe,
I can't remember if this is a jet boat or not (matters for how much cooling water you have access to), but if it is, I would say you could run up to 10.25 with proper attention payed to your cooling system pressures and a requirement. If you were running aluminum heads, you might be able to push it further, but for 91 on iron heads I think 10.25:1 should be safe.
Check on the pricing for the splayed main kit and labor while your here. Not saying you have to do it, but if you're planning on upgrading the top end at a later date, you wouldn't have to pull the motor again.
As important as the compression is, its the attention to your cam grind that is going make or break the motor's performance. Look for a nice hydrualic roller grind that works with your compression ratio and airflow and things should work out well.
Chris

[cstraub]

I would go for around 9 to 1.
Chris

[OMEGA_BUBBLE_JET]

there are alot more 2 bolt blocks running down the track then 4 bolt blocks. just something to think about. I have never seen a 2 bolt main cap broken. anyone???
If you are truly that concerned stud the 2 bolt block and you should be good for 1000 hp.
Omega

[Hotcrusader76]

You need to figure out your DNC (dynamic compression ratio) with the cam you're going to utilize before working the SCR (static). Often times pump gas and an early IVC (intake valve closing) can warrant more compression ratio than your normal to seeing.
Also consider how the motor was built; IE deck height and quench. Very important factors to the DNC
~Ty

[Bow Tie Omega]

Thanks for the posts everyone!!:)

[SUNSATION540]

WOW what a bunch of stuff !!! you didn't say do you have stock valves in the heads or 2.19/1.88 it changes your comp volume i build a 9.25 454 with a crain 560 hyd cam that dynos 510 hp based on a 454 mag you are in a wishing tree 600 plus takes big heads big hyd roller large cfm carb and the right ported heads. 2bolt blocks puke at 750hp... pump gas will suport static comp ratio of 10.25 w alum heads or 9.75 with iron @140 temp with .45 brake spcf of 13.8a/f super cat engine world champ twice:yuk:

[1BIGJIM]

Good english:rolleyes:

[BrendellaJet]

Originally posted by SUNSATION540
WOW what a bunch of stuff !!! you didn't say do you have stock valves in the heads or 2.19/1.88 it changes your comp volume i build a 9.25 454 with a crain 560 hyd cam that dynos 510 hp based on a 454 mag you are in a wishing tree 600 plus takes big heads big hyd roller large cfm carb and the right ported heads. 2bolt blocks puke at 750hp... pump gas will suport static comp ratio of 10.25 w alum heads or 9.75 with iron @140 temp with .45 brake spcf of 13.8a/f super cat engine world champ twice:yuk:
First off he said close to 600, not 600 plus. And Ill ignore your lack of gramar for now. Generally someone with 3 posts doesn't bring a lot of clout to the table-especially with all of the gear heads on this thread already. Instead of knocking his goal of CLOSE to 600 hp, why dont you slow down and qualify your statements instead and help a jetter accomplish something. If you want to get all technical without backing anything up, do it in the bench racers forum.

[cstraub]

I'm interested in the "Compression Volume" of 219/188 valves over stock......
What we have found with 2 bolt main BBC blocks with either studs or bolts, the caps start to walk around 600 with bolts and 700HP with studs. They will take it but I don't recommend it. IF you want the 600HP range, I would stud the mains and dowel locate the 3 centers, this will help with the "walk".
As hot pointed out, the camshaft can manipulate the engine to "thinking" it has more compression. I have to do this all the time in spec engine classes with compression ratio limits. Cylinder pressure can be a friend or enemy.
Chris

[Bow Tie Omega]

Originally posted by SUNSATION540
WOW what a bunch of stuff !!! you didn't say do you have stock valves in the heads or 2.19/1.88 it changes your comp volume i build a 9.25 454 with a crain 560 hyd cam that dynos 510 hp based on a 454 mag you are in a wishing tree 600 plus takes big heads big hyd roller large cfm carb and the right ported heads. 2bolt blocks puke at 750hp... pump gas will suport static comp ratio of 10.25 w alum heads or 9.75 with iron @140 temp with .45 brake spcf of 13.8a/f super cat engine world champ twice:yuk:
Who are you and were you drunk when you wrote this???:rolleyes:

[Bow Tie Omega]

Thanks for all of the posts, once again. After some thought, I decided to stay with what I originally planned to go with. The rebuild was planned around the cam I purchased and it does not make much sense increasing/changing one aspect of the motor without doing the same to all of the others as well. As most of us know , that costs alot of money, which I have already spent once without even trying things out yet. I will save my new ideas for the next project down the road. Thanks again..Joe