mxcrazed

Hey everybody on TGO, it's been a long time since I have posted on the forum since I parted out my bird long ago but I still have a sbc in the family. Some of you may have already assumed it was in a boat due to the pistons I described, in fact it is. I have a 86' volvo aq225 (225hp) 5.0. I'm planning on keeping the boat for one more season and I want to get a little more out of it. The engine runs very well and has good compression numbers so I decided to look into head/cam combos to jack up the output. What I know is that I have full dish pistons an 8.5:1cr 1.84"in and 1.5ex valves and I will need to keep it iron because it is raw water cooled. I don't yet know the actual castings of the heads but I was planning on calling the dealer Monday since the boat is in storage and I haven't been able to cross the pn from volvo. Once I know the casting I will have a pretty good idea what -cc my pistons are and what heads to use to bump my comp to around 9.2:1. I have owned a set of 081 heads in the past so I know the 416 heads will flow pretty well if they will work well with the "full dished" pistons and I figure I can have them decked if the cc is too big.

I know that there are plenty of marine forums available but I have spent a lot of time on google this past week and many of my searches bring me back to TGO so I figured I would stop here first. Any input is welcome and appreciated, well besides telling me to go 5.7l

305sbc

iTrader: (3)

416s will flow well after a thorough porting, which is quite time-consuming.
You can save a lot of time by just porting the bowl/seat area and still get at least 80% of the flow gain.
You may also increase the valve-sizes by converting to 8mm LSX guides/valves.
If you do this then I'd do a mock-up to make sure the intakes clear the bores. I've never had one not clear, but you never know.

They can be decked, but the decks are pretty thin even before decking, so you want to be careful to prevent overheating. These castings are prone to cracking.
Don't let that scare you. Barring some weird event you should have no trouble running them hard for at least a year.

The aftermarket iron 305 replacements cost more but are much thicker and the ports are cast better from the start and require less porting work.

mxcrazed

I see you know what your talking about 305. My engine runs at about 155* operating temp would this help prevent cracking with a thinner deck? How much is it safe to shave them? I assume I would need to have the valve seats replaced to use these larger valves? I don't foresee going too big with the cam because I need to keep the idle low around 800 so I don't damage the outdrive when shifting. Can the ls1 springs/retainers support .500" and 5200rpm? How much spring pressure should I use for a cam in that vicinity?

305sbc

iTrader: (3)

It all depends. Cracks can form from overall heating and warpage, or localized hotspots around the chambers, or from just a factory defect in the casting causing a weak-spot. A casting may never crack, or you could do everything right and it still cracks. I don't worry much about it. I just try to avoid overheats, and also avoid abuse that causes detonation or pre-ignition. I really doubt you would have a problem in your application. It happens more often in trucks & vans that haul a lot of weight up hills.

You can sometimes shave a lot off. I currently have a set that has been cut around 0.060", but that is from several resurface operations. I think it's best only to resurface as much as necessary to true the surface and no more. 416 chambers are pretty tight already.

With the factory cast iron heads you simply cut the seats out a little bigger for the bigger valves. The aftermarket iron heads often have hardened seat inserts that can either be re-cut or replaced if you are needing to cut a lot of material away. With the factory head the only danger in opening up the seat a lot is running into the water-jacket around the chamber when blending the back side of the seat into the short-side radius.
I put in the LS1 2.0"/1.55" valves, and I radius the valve edges so they are actually a few thousandths less than that. I open the seats up to 90% of the new valve diameter, and I have not hit a water jacket so far, but there are imperfections in some castings, so keep an eye out if porting them.

With the lighter LS1 valves the factory take-off Z06 beehive springs ($50 on ebay) are more than enough and only require around 100 pounds on the seat for most street applications. The small retainers used on the beehive springs gives a good bit of extra clearance for lift.
For bigger cam applications I would use the Comp918 beehive springs, but they cost more.

To use the 8mm LS1 size valves you would need to install the 8mm valve-guide inserts and re-spec your valve seals so they fit both your guide-top and your new valves.

If using stock size sbc1 valves, then you probably want to see around 120 pounds on the seat, and you might need to run thinner retainers for lift clearance, or machine the guide-tops down some.

mxcrazed

I have takes the boat out of storage and removed the valve covers to learn that it is already equipped with 416 heads... What I have decided to do is add roller rockers since I am replacing the lifters (one or two are bleeding down) with new Delphi lifters. What do you guys think about this style self aligning rocker arm http://www.ebay.com/itm/261211072377?redirect=mobileI want to get the boat in the water ASAP so I'm not interested in doing any major work. I'd like to go to 1.6 arms and I like the valve train stability and hp available from this mod. The valves already have double springs and I plan to check for clearance issues and current lift with a feeler gauge and dial indicator. Please let me know if I am setting myself for a bad day.