RGMEPP

In the build process of 403. How much compression can I handle at the various octane levels ?? 87, 89, 92 ?

F8L Z71

You cant really put a fine number on it because static CR is only part of it. Your cam is going to dictate your dynamic CR which is by far more important.

RGMEPP

Lift 295 @ cam w/ 1.8's for 531 at valve
Dur. @ 050 200 int. 208 exh.
supposedly extreme low end/midrange, good for heavy loads.
403, stock 317's, unblown.

Yelo

That cam is WAY too small for a 403.....think more along the lines of a 224/224 or a 228/232. That motor is gonna make killer torque even with a big cam due to having such a large displacement, go with a bigger cam and you'll make ALOT more power (possibly over 100hp more) than you ever will with that 200/208 and you'll still be able to keep the revs under 6300

Flyer

iTrader: (1)

Yelo, that's still small for a big motor. I would say the 228/232 would be a bare minimun. Putting a 200/208 in a 403 will be a total waste of cam and motor. You would get more power out of a stock 6.0 and come out MUCH cheaper.

How are you coming up with 403 anyways?

Yelo

I was trying not to scare him off by suggesting a 239/242 .608/.612 114 (that WAS my original cam choice), Hell...if it was me I'd be running a T-ReX or G5X4 in a motor that size (I'm actually considering doing so in a stock-displacement 6.0 )

I think the 403 comes from a 4.005 x 4.00 (cylinder clean-up honing only)

Flyer

iTrader: (1)

That's more like it.

treyZ28

Its dependant on so many things its impossible to put a number on it.
Cam, bore, heads, exhuast, load (towing? weight? gears?) gas quality, piston design, power expected, valve quality/type, piston shape/cut etc...

at my old job, you could tell exactly when the winter blend gas came around. All the boosted cars started knocking.

If you are towing a ton, high compression is bad.
If you drive through mountains at 80mph for hours at a time (like me) and have tall gears, you dont want much compression.
If you polish your heads and have nice smooth, flat pistons and Na filled valves- you get away with more.
Big bores get away with less
If your tune is awesome, you wont be building up a ton of carbon- get away with more.

RGMEPP

4.00 Stroke, 4.004 Bore, 71cc heads = 403. Probably a little small on the shaft, but its sitting here new. also, gets used as a TRUCK, can't get to racy. 3.73's. GVO in the future as it sees some long highway. Therefore the cruise range of any shaft needs to take this into consideration. Any sugg.'s welcome. Kinda pushin it on time got to go, will post more detailed spec.'s later if any have an interest.

02sierraz71_5.3

iTrader: (2)

The highest I would go is 10.5:1 with aluminum heads, proper quench area and 93 this is considering a heavy truck with towing purposes.

Honestly I wouldnt go over 10:1 towing anything, I think you would be able to make more power with less compression and a little more timing while towing.