548 compression ratio ?
 

Hi guys, looking to finally do my motor build. If some of you may know I was preparing for a procharger build last winter. Well the charger deal fell through and I really only need 650 hp for my boat. So I'm going to go N/A with a 548.
I have for this year a set of 320 cast iron Pro Topline or RHS heads. Going to run the Scat center C/W crank and h beams and
Mark IV bow tie block.
Question's
Should I run the arp 2000 bolt for this NA set up?
What compression should I top at at I can get 93 most anywhere I boat.
What intake would be ideal
And should I stick to a large 4150 body carb instead of a dominator ?

Thanks Bill

Bill I would think 9:1 would get you there. As far as Rod bolts go anything you put in it would be over kill. A 850 cfm 4150 would also do the job. Just don't use a Hp500 carb. Holley, QFT or something similar is all you need.

A flat top piston with 120cc heads . .041 thick gaskets will give you 9.25:1 comp ratio. 1050 dominator will get you between 675-700 hp . Of course there is a lot more to consider , cam, intake , rockers, push rods.......
Plan the entire build so all parts work with each other

Thanks, BB and BillyB for the replies, I have a machine shop / builder telling me that 10-5;1 would be OK and the cam grind cam offset the compression and make it run good on 93,. then if there is an issue to pull some timing out of it. I am questioning that because of a lot of reading i did last year on this site as guys don't seem to go over 10-1 NA in marine apps on 93 octane.

my heads have a 118CC chamber and i will be having cam ground for this application. I want to go no larger than a 660 lift as the heads dont flow much better any higher then this and i want to be easy on Valve springs.

Does anyone have any good duration recommendations for a 548 to make that power from a past build ?

10.5 is too high in marine world . Yes you can bleed off compression with a late closing intake valve , but why? 540 builds have been done for the last 20 years. There are plenty tried and true combinations. Also no need to over think the cam by planning a "custom grind". Like I said previously, that engine has been built so many times that every cam company will spec you an off the shelf cam.

totally agree, shelf cams are plentiful and leave the guesswork out, if I did mine again I would have used a Crane 651 or 741 cam...

Unless u go aluminum I wouldn't for any higher than 9.6:1. You put the right cam and decent flowing heads 650 will be easily achieved. 540's with dart pro one 310's and custom comp grind will do it. Rhs heads are decent but may have to get a set or two before you get two good heads. If your going cast you can find some good deals on dart 308's otherwise those EQ heads. 320cc int runner at the most. 310cc is what I'd shoot for. Hyd Comp Cam 244/248-647/637 on a 111, dart intake, 850 or 950 Holley. There's a bunch of combos that will get you there but this one is just one.

I already have the heads and they are the older Pro Topline cast Iron 320cc Assie heads, before RHS aquired them. All set up and ready to bolt on. Maybe a spring change depending on the cam as i use to run the 731 crane in it.

I found a couple sets of FT pistons between 9-1 and 9;4-1 Manley @9;2-1, CP bullet series @9;3-1 and Diamond's @ 9;1-1 and are the 2618 material pistons.

Then u have the Mahle Power pak at 9;4-1 and SRP 's at 9;5-1 in the 4032 Material which can be run tighter and less noisy,

What would be the better route for the NA marine engine.? i know the 2618 material is better for the blown application but wondering if the 4032 material would work for a NA marine deal..

I ran 9.7:1 on my old iron Merlin heads for a few years on premium with no issues.

Most flat tops have a -3cc valve relief, and the top ring down close to the same distance. I take those manufacture's compression ratio suggestions and throw them right out the window.

You need to figure out your own compression ratio, based on several things. Actual CC of the heads, not the advertised CC, how far the piston is in the hole, how far the top ring is down, the valve relief/dome/dish volume, headgasket thickness and diameter, and so on.

This is a nice calculator to use.

http://www.diamondracing.net/tools/

How far is the piston siting below or above the hole?

I'd look at the profiler sniper JR intake, Holley Ultra Gen 3 950cfm dominator, 9.5:1 range, and Lunati's voodoo marine camshafts.

They have a 240/245 112 LSA, or if you wanna turn it a little harder, 245/250 112. They are a nce line of camshafts, that are proven lobes, stable, without excessive lift, or excessive exhaust duration. The 651 crane is a nice cam, but with 244/256, it works better in a boosted combo with mediocre exhaust flow.

Just my opinion.

Can't remember if you mentioned racetec or autotec pistons in earlier post but you may find the right cc for your combo there also. I just went through the same ordeal. Good pistons and reasonable. Just thought I'd throw that out there. They had exactly what I needed for my 565's.