powerplay230

I had the guide tops and spring pockets machined and new springs installed .I also had the intake and heads gasket matched. What sucks is if i have the valves done i will have damm near as much in these heads as a set of alum heads. Has anybody gone from the smaller valves to the bigger ones and if so what kind of gains did you get

MOP

I did the whole thing at once, 383 and big valves! I have great torque through all ranges, a 383 likes to breath. I am running a fairly mild cam, I make a tad over 375hp and about 400lbs torque. Run a 650 for good all around power and 750 for a tiny improvement at WOT.

Phil

aj1101

Phil,

Can you share a little information on your setup? I have an 86 Scarb 22' with a 300 horse vortec 5.7 liter crate motor. We have to pull the motor because we are having an oil pressure problem. I am thinking about stroking the engine while it is out but dont know if simply stroking the engine, putting in the bigger valves in the vortec heads and running the factory wet exhaust will be workable/worth the money in terms of the hp/tq gains I might get. If I need to replace the heads and exhaust I dont think I would want to drop that kind of coin on this boat.

Couple of questions:

What kind of exhaust are you running?

Did you replace the heads or the valves and springs?

Could you share some of the specs for your build?

Thanks.

yikes

Like AJ says "Can you share a little information on your set up?" What cam are you using? Is it internal or external balanced?
My motors rusted from the outside in so I will be starting from scratch. Planning 4 bolt blocks with aluminum heads and exhaust. Air gap manifold with a holley and MSD.
It's a rare old school boat and I would love to add another 230 HP. It was runnning in the low 60s with prop exhaust and i hope a jump from 520hp to 750hp would put me well into the 70s.
Thanks

powerplay230

My block is bored 40 over. Im running a scatt crank and scatt 6'' rods. U get a little more dwell at tdc with the 6'' rods versus the 5.7'' which i was told will make alittle more power plus theres less side force pushing on the pistons which in this build are forged SRP. Im also running summit racing vortec heads 1.94in 1.50ex, vortec rpm air gap intake,edelbrock750 carb , glm alum manifolds and risers,thunderbolt iv ignition and comps xm276hr cam. C/R is 9.35 to 1. I have found out though that this cam is to big for this ex. which is basicly stock as far as were the water enters im getting reversion. I have since talked to crower cams ,told them my problem, they asked questions about my motor and exhaust and are grinding me a cam specifly for my motor and told me if it didnt perform to my liking to send it back and they would fix the problem which i thought was pretty cool

motorz

The new Merc 383 400HP SB is using High-Flow Iron heads with 2.08in 1.60ex . The 383 350HP SB is using Gen+ Iron heads with 1.94in 1.50ex.

powerquest208

I bought my 383 from Blueprint engines & it dynoed @ 405hp. They give you 1 yr warranty. I bought the long block for about $3300 2 years ago. I run it hard & it still holding up. Need to take a look at them.

wtfo

I would make the investment in a decent exhaust set up, emi imco, etc... it's worth it.

and Ryan's right on the money and knows his stuff as apparently do some of the other posters. Good information.

I've been running a 383(5) with an xm-270h, ported 200cc intake runner world products heads 2.02 / 1.6 valves and 64 cc chambers (cast - I spend time in brackish), block zero decked with a tight quench,.040 over, -16 cc dished forged pistons H-beam rods 4340 crank, etc... for a compression ratio of 10:1, thunderbolt distributer with a v6 module and crane fireball cd ignition, around 32 degrees total advance, imco powerflows with long risers. it pulls hard from idle to 6000 rpms and idles well enough to pull kids skiing, etc....

I've recently heard some folks around here having great results with the brodix head intake combos that are cnc ported and port matched with the intake, but that's not cheap. I do agree that you're better suited with a decent set of aftermarket heads rather than bigger valves in the ones you have. You won't have any issues with power down low running bigger valves and quite a bit larger intake runners. I've been running a single plane intake with plenty of power out of the hole...

A lot of the power is in the heads - you have enough cam to make a good bit more if you get the heads, and then the exhaust manifolds flowing better. Better heads in particular will wake that motor up.

note also on exhaust, that it's more than just the riser, but also what comes after - what do you have after the risers? Mine go out above the rub rails...

Just my experience.

doggiedave

At any thing below 4000rpm the difference in power will be negligable as opposed to cost. also the vortec head was designed to create high velocity/swirl for a better combustible mix also the vortec chamber design intended same. plus was intended to create better flame travel.a good pocket port and gasket match will equal any gains from bigger valves without the port work. needs to be done gently (don't hog out the ports) the low end torque should help you get on plane faster it all depends on your budget. the vortec heads will also be a little more tolerable with compression as opposed to the older style combustion chambers that even some of the newer aftermarket heads still use. ( old habits die hard) jmho