So I'm building a 455 marine motor I snagged for a thousand dollars to replace the olds 350 gas motor that my grandfather put in after the olds 350 diesel died. So far I've broken it down to the short block.
here's the specs I know so far or are at least semi confident are true.

High compression dished pistons ( not sure if these are factory or what yet but the are the shallow dish variety)
1 G head 1 Ga head big valve heads with hardened seats. Both are being ported by a friend (spent about 7 hours last night drinking and porting one of them lol)
Edelbrock Performer aluminum intake
Lunati Voodoo cam with the following specs Advertised Duration (Int/Exh): 256/262; Duration @ .050 (Int/Exh): 213/219; Gross Valve Lift (Int/Exh): .485/.499; LSA/ICL: 112/108; Valve Lash (Int/Exh): Hyd/Hyd; RPM Range: 1000-5300
new timing chain and gears, new lifters and springs and retainers all from lunati
800 cfm quadrajet that i plan on ordering from Sean Murphy once i nail down all the specs
1 3/4 headman style headers for a cutlass 3 in primary into 2.5 true duals with turbo style mufflers
stock oil pan
and all new gaskets during the "rebuild"
Pertronix HEI from the current 350 and all the accessories from that engine (hoping they all bolt up, but that's a problem for slightly later)

Am I making the right decisions here as far as cam / compression / and general stuff. The motor as we have torn it apart looks good however it sat for 7 years with marvel mystery oil sprayed into the cylinders and the oil drained. Lifters look almost brand new, you can still see reaming marks inside of the valve guides.

the truck has a Th400 that may or may not have the original diesel converter and governor setup in it, and 2.76 rear gear with a 275/60r15.

Main use for the truck will be a daily driver, I want something that will idle on a 100 degree day in traffic, tow whatever i think the rest of the truck is capable of handling. and maybe if i'm lucky be able to do a low 13 second pass in the 1/4 so it'll at least be fun. OH and massive burnouts for when you just want to be stupid, the current 350 has trouble turning over the 275 wide tires.

 

I would recommend you measure the heads, piston dishes, and piston-to-deck clearance to determine the actual compression ratio. That camshaft seems fairly small for a high compression 455 engine. Too much cylinder pressure and you'll be fighting detonation issues.

 

funny you mention that, as when i ordered that cam I was worried it would be too big, (didn't realize at the time what the CR would be)

I figure I'll just run some thick head gaskets to bring it back down some if need be. Going to measure how far the pistons are below deck tommorow. Ideally in my head I would wind up with and actual ratio of around 10 - 10.25:1 i figure that will be safe on 93 and make plenty of torque.

 

10-10.25:1 with that cam will be a detonation machine. With that much static compression, you would want more like 236 @ 0.050" on the intake side to tame the static compression and run it on 93 octane. I have about that compression with a 236/242 @ 0.050" roller in one of my 455s and it is fine on 93.

 

With that cam what's the max cr you would run on the street on pump?

I put it at TDC today and looks like it's pretty damn close to zero deck. Going to do the math and see where exactly I'm going to fall.

 

The cam mentioned in your first post is really small for a 455. 9.0:1 would probably be pushing it.

 

Engine is going in a truck with 2.76 gears and a stock converter. Wouldn't a larger 230 degree cam not be happy in an application like that? Any specific cam recommendation then? Lunati hasn't shipped the cam yet. ¥c

 

I think it’s time for some of the cam experts to chime in on specifics. Mark Remmel would be a good one to ask (cutlassefi).

 

A single pattern would be best, something like a 220/220@.050 on a 112. That should give you a good mid range as well.

 

IceCold4x4, let us know where the actual measured static compression ratio ends up. Cam choice is a toss up until that is an actual known quantity.

 

came out with 9.7:1 assuming the heads haven't been touched and i run a standard .027 head gasket, they currently aren't in my possession. (i doubt they have been milled as the intake didn't look to be milled. but even if they are down to like 70cc from the 80 that they are supposed to be i can still drop that down to 9.66 using a .080 cometic gasket.


cutlassefi that single pattern isn't really much more duration would that little bit really help with the detonation (and ballpark what lift am i looking at with one like that)? I have no problem running it on 93 pump gas. It's going to be my daily and if that's the price to pay for the bottom end grunt so be it.

 

Most big block heads are around 82-84cc but you need to measure them to be sure what you actually have.

 

will do as soon as i get them back.

 

This cam has a fair amount more “off the seat time” so it will release some cyl pressure. However the single pattern will retain good drivability.

 

finishing the heads up this weekend. and looks like the factory chambers are intact as we CC'd them out at 81. Putting my comp ratio with everything else at 9.68:1. (give or take .1 there was some carbon on the pistons and the deck hadn't been cleaned yet but I can still adjust with a head gasket down from there.)

I plugged some numbers for a ported G head into one of those computer dyno models and I'll admit yes I think the cam i picked is too small, however playing around with different cam settings (this does seem a bit like black magic), your suggestion of a 220/220 single pattern looked like a good curve and should allow the use of regular gas without detonation being a severe problem. Looking like if my assumptions on what the porting will give (about 75 percent of a edelbrock aluminum head) this thing should be north of 500 TQ. might even crack 400 depending on how the intake flows and how much of a hindrance a couple of 3 inch turbo style mufflers are.

Got an exact recommendation Cutlass efi? (i'm about sick of looking at cams and punching in numbers at this point LOL)

 

A 455 is a torque monster but if that is the stock diesel converter, it might stall super low, like 1200 rpm. Must regular TH350 converters flash at 1600 to 1700 rpm. My 94 Olds 350 powered Z71, the 4L60E stalled at 1500 rpm. Go do some launches and see where your tach needle jumps to. I would go 2000 rpm on the stall. My 78 1/2 ton also had 2.76 gears. An Olds 307 Vin Y was actually a big improvement, Olds 350 better again over two sbc 350's with that tall gearing. A 455 will be smile city and cruise nice low rpm with stock tall tires.

 

I want to say that it stalled around 1500 with the small block olds. Was hoping the big block might loosen it up a bit to 1800. Really I'll stick with this gearing or a set of 3.08's maybe until I go for a gear vendors or try a 4l80e swap. But if I go 4l80e I'll probably build a 598 off a blueprint short block.

 

Why screw-up your quench/squish distance? Crappy piston-to-head distance CAUSES detonation problems when between about .050--.100. Larger gaps make for an "open" combustion chamber--lazy, slow-burning, needs lots of advance for power, but might not detonate.



If that's a "lakewater-cooled" marine engine, I sure hope you popped out all the core plugs, and sonic-tested the cylinder wall thickness in about a thousand places. Marine engines are known to corrode the cylinder walls from the water-jacket side.