Reversion.... am I ok?
 

I know I know... another question on reversion. Well ive studied very carefully the info from this site which had been very helpful, so I just wanna make sure I got it right before I hit the key! I'm building my new engine now, it's a mild 454 (462 now), and here is the setup I am planning on running, if it sounds like I'm doin anything wrong that could cause reversion PLEASE don't hesitate to speak up, thanks in advance guys! It's an 1989 original 330 horse 4-bolt block, bored 0.030 over, stock crank & rods (w/ arp bolts), 0.030 over speed pro hyperutectic pistons, L-29 vortec heads, (large oval ports) ported w/ stock size valves, HV oil pump, double roller timing chain, 1.7 crane aluminum roller rockers with poly locks, Weiand Team-G high rise single plane oval port intake (port matched) Holley 850 marine mechanical secondary carb, stock thunderbolt ignition. He're is the cam specs: Comp Cams Xtreme Marine Hydraulic flat tappet, 564/566 lift, 112° lsa, 272°/298° duration, 234°/237° duration @ 0.050, and is supposed to be good from 2500-6200, although I plan on propping it to not go past 5000-5500 so the bottom end will live. The excuse will be CMI sport tube headers, goin into dry tailpipes, ending right before the transom, and then connecting them to slash cut tips with internal flappers. Does this set up sound safe? (Yes the headers and tails have been pressure tested, they are ok) any advice or comments are greatly appreciated!

If you are going to dry tails the only way you are going to get reversion is from a leaky head or intake gasket. :D

Curious why you went through all this and kept a cast crank and pistons? Was cost the issue or did someone advise you of that?

Cost was the main issue. A majority of these parts were aquired through trading parts for parts, parts for labor, or stuff I already had. Im goin for a nice 500 horse on a budget, wasnt really expecting much more, it's a pretty heavy boat, so just wanted a well rounded engine that could get it up and movin alot better. Stock cast crank/rods figured were fine for 500hp with good bolts and not revving it to the moon, don't ya think? But you would say I'm good on avoiding reversion then?

You should be fine with the reversion issue with that exhaust system, but I'm not sure if you are going to make it to 500 HP with GM Vortec heads with the stock (2.06 / 1.72) valve sizes. These heads do have the larger oval ports, but if I recall correctly they also have the "ramps" in the ports to enhance swirl of the intake charge to promote atomization. They also have the smaller heart shaped chambers - what compression ratio did you end up with?

I'm thinking 450 - 460 HP is more realistic for this combination, but I may be wrong. Are you planning to dyno it?

I would not go past 5000 RPM with the stock 3/8 rods in that engine. You might consider poking around in Swap Shop. Bet someone has a set of the 7/16 bolt "dimple" rods that you could get for a good price which are much stronger. Not so much worried about the crank as I am the rods. Also, keep the CR down around 9:1 or thereabouts with iron heads.

If you can find it in your budget to upgrade to a hydraulic roller, by all means do it! You will make more power with much better chance of having the cam actually live for a while. Someone had some good deals on some pretty nice hydraulic rollers in the Swap Shop section recently. Even the GM ZZ502 roller cam would work pretty well in that engine with that exhaust, and those can be found pretty cheap. Crane 731 would be another solid choice, but bigger valves in the heads would be best with that one.

I have two sets of the good rods.

Also have two sets of 188 heads.

Thanks for the reply, yeah they do have the heart shaped chamber, pretty sure they are about 99cc, and with 0.030 flat tops (-6cc for the valve reliefs), and a standard compressed head gasket thickness of 0.039, I believe it put it right at about 9.09:1, so im thinkin I'll be good there. As far as the heads go, they do have that ramp in them, which is good for torque apparently in stock engines, but they flow a whole lot better if you machine them out and give them a good porting (without goin crazy with removing material tho) which is exactly what I plan on doing. You may be right on the 450-460hp tho, but I'm gonna try my best and see what it can do. As far as the valve size, I'm puttin new valves in it, but have done some studying and it seems like most people are saying that stock size valves are better for this particular head, As it helps unshroud the valve, possibly due to the shape of the chamber? I can put in bigger valves if it would be the better way to go, just heard so many mixed feelings that I haven't pulled the trigger on it yet.... what do you think?

Food for thought - Merc was building a 454 based version of the HP500 that they called the HP450 (I think), that had the same cam, heads, induction, and exhaust as the HP500. Obviously, they rated this engine at 450 HP or thereabouts. That's why I was saying that 450 HP is more realistic with your combo.

Do you already have the heads? Sounds like the guy who posted above me might have a better set of rods to use.

FWIW, I built a similar mill years ago, but ran the standard oval port heads and a slightly less aggressive cam. Heads were 820 castings, and had the larger intake valves installed and some pocket porting done in the bowls. Ran a Q-jet and stock exhaust on it. Never dynoed it, but betting I was around 380 HP or so. Boat ran about 61 on a good day - 88 Baja Force 235.

Oh ok good to hear. Yes, everything I listed is already in my possession, heads and block at machine shop already actually. And with my big heavy turd (Formula 242) only doin 51 in stock trim, I'm sure 450-500hp will leave my l me plenty satisfied until I upgrade to a bigger boat in the next few years, I just love the ride of mine so much (especially in the rough water), that I know I'm gonna be picky as hell on what I buy next, so i wanna enjoy it while I got it! Lol

I know you are on a budget, but you should have used the resources here before you spent money :D

Some things to keep in mind with your set up, don't push it too hard. The fact that you have a heavy load "wet" boat makes it even more crucial. I would lock the timing and be conservative on your AFR on the rich side and prop for 4800-4900 rpm. Those pistons will not tolerate much, if any detonation. And as stated above you will be limited on total rpm, but over propping and loading it down will increase your chances of detonation. You are running a fine line squeezing reliable HP out of that set up. Not saying it can't or hasn't been done, however it is not the ideal setup for those that have already learning the hard way.


On a side note there is a guy on my lake with a 330HP with a 177 blower on it, stock internals. Has been running 4.5 of boost for years with no issues, 10 mph gain. So....who knows :D