Liberator21

My new engine (383 Chevy), now has about 30 hours on it, and it’s running great, so now I’m thinking about more speed! Don’t ask me why, but when I built this engine, instead of going for a set of heads like the Dart Iron Eagles, I bought a set of stock replacements (DUH!). The heads I’m using are casting # 14096217. Here’s the description:
"10125377 Cylinder Head Assembly
This is a cast iron cylinder head assembly used on 285 hp 350 engine (P/N 12353641). This complete cylinder head assembly includes 1.94" intake valves, 1.50" exhaust valves, valve springs (P/N 3901068) and valve spring caps (P/N 14003978).
Technical Notes: This cylinder head has 64cc chambers. The cast number for this head is P/N 14101083 or 14096217. This cylinder head has 1987 and later inlet manifold bolt pattern. The center two bolts are at a 72º angle."
I had the heads pocket ported, gasket matched etc. Plus I put on Comp springs, and 1.5 roller tip rockers. I’m using the cast iron high rise Z28 style intake #14097494 and center rise exhaust manifolds (stock), with through transom exhaust, and Rex marine slip in silencers. Desktop Dyno shows a 50HP increase going to 2.02”/1.60” valves, but it also shows peak HP going from 4500rpm to 5500rpm, and peak TQ going from 3000 to 3500. Right now the boat will just touch 60mph at 4900 rpm when conditions are just right (cool dry day, one person in boat, ½ tank gas, good water). I want the boat to be in the 60 mph range with at least 2 people on board. Do you think switching to the Dart heads, and an aluminum intake, but retaining the stock exhaust manifolds will do it for me? (headers are too expensive). Aluminum heads are out of the picture because of expense. Also what size runner should I use? (170cc, 180cc, 200cc?). I figure it will be a good job for over the winter. Don’t tell my wife!

ACrooks69

iTrader: (1)

Well Liberator you are barking right up my alley. You have started doing all of the things I started out doing on my 185 Searay (20'2") When it was stock (260hp 5.7) in 91 the boat went 56mph at about 4600 RPM. The Edelbrock performer intake didn't bump up the top end but really aided in hole shot. Then the Comp cams 260H cam and roller tip rockers came. 62 MPH. Next a set of Kodiak Exhaust manifolds with stainless risers. 65 MPH. After that the stock center-bolt heads were worked over with some port work on the intake and exhaust along with port matching. 67-68 MPH. After that the 383 came with unported trickflow twisted wedge heads and a Comp Cams XR264HR roller cam with all of the other running gear. 73MPH (the builder said the motor was in the 410-420HP range. So what I figured along the way was 10hp = 1mph. Seemed pretty consistent along the whole mod process. I say you are going to need to put good exhaust on it despite you unwillingness to spend the money. By the way these figures were for a boat that was 2600lbs dry stock (less with all the alum parts now) and 3/4 take of gas and 2 people. At least you have thru hull exhaust, I finding out now you just can't put more than 400 hp thru the prop. The boat will actually slow down due to the excessive back pressure. If your diehard with doing heads only, the 383 should be able to handle 200cc runners no problem. How big of a cam are you running? Oh by the way the Kodiak manifolds ran me around $1400 8 years ago and I don't think they have gone up that much in price. Don't believe all the numbers desktop dyno spits out. Unless you can plug in all the airflow numbers those readouts will be off a bit. I also don't believe simply switching to 202/160 valve heads will move the peak power up 1000rpm. The cam will be more responsible for that. The XR264HR 212/[email protected] cam I mentioned earlier is no longer in the motor ( I went to a XM276HR 224/[email protected]) so if you have a smaller cam you may want to bump it up a bit (I'd give you a good deal on it if you would like it). Was a really good cam with the peak power around 5100-5200 RPM. I know I rambled a bit here, but what I did should steer you in the right direction. If you have any questions let me know or drop me an email.

Liberator21

I won't see the kind of speeds you're seeing with my setup. My boat's a little larger, and about 1000lbs heavier.I think I have a pretty good setup right now though. I've got the scat stroker kit with 6" rods, a 4 bolt main truck block, SRP forged pistons with a CR of about 9.6:1, Total seal gapless rings,and a comp cams xtreme marine xm262h. It's 218/224 @.050". The engine is real strong now, but it just seems to run out of steam at the top. As far as the Kodiak manifolds go, they're aluminum, which is out of the question for me. The boat stays in salt water all season. I was thinking about stainless headers, but the price!!! Ouch! What about the GLM manifolds? I've read good things about them, but I also found some guy trashing them. Check it out: http://www.boatfix.com/forums/topic.asp?TOPIC_ID=48904
Apparently the resident "Expert" of that site doesn't like them.
Know anyone with a set of small block headers for sale at a good price???
I'm still thinking the heads are probably the way to go. As far as the Desktop dyno numbers go, I take them with a grain of salt. I don't have actual flow numbers for my heads, but I do have them for the Dart Heads. Using all my data, and the stock head with pocket porting selection in Dyno 2000, it showed 360 hp @4500rpm with torque in the mid 400's @ 3000rpm. With the head flow file for the darts, it showed 405 hp 1000rpm up from the stock heads, and a bit more torque 500 rpm up. I'm just using the numbers for comparison purposes. I know the're not totally accurate, but they will get you in the ballpark. Dyno 2003 showed slightly lower numbers. One other question, What kind of carb are you using?

ACrooks69

iTrader: (1)

I'm using a JET modified Qjet. You're HP estimates are pretty good, and the numbers you are expecting to pick up with the Dart heads are pretty reasonable. Now that you list the cam size I can see why Desktop dyno moved the Hp band up. That cam will like to live around 5200-5300 RPM. I see you're reasoning for staying away from the Alum manifolds now. All I can tell you is that I don't think the stock manifolds will flow as you want them to. It's going to be the barrier to a lot more HP. In fact, I don't think that motor will see 400 hp with the stock manifolds. Just my opinion. I keep getting my eyes opened up to how important it is to have good exhaust on the boat and when I expect my jetting problem will go away with the addition of the thru hull exhaust I'm preparing to put on, along with some more speed With the Dart heads I wouldn't be surprised if you pick of 2 or 3 MPH. If you don't pick up top speed I'd say you really need to get some better exhaust. So I'm still sticking with the better exhaust. I don't know about any of the SS headers. You are right though they are expensive. But step up and get them. You'll be happier in the long run.

Liberator21

I didn’t know Jet did Marine Q-Jets. I’m using a Me modified Q-Jet (did it myself).
It works quite well. What jets and rods are you running in it? I figured the stock manifolds were the bottleneck. My heads were ported by a friend of mine, who has been doing it for more than 10 years. He’s got a nice flow bench setup, and a good reputation for his heads making serious power. The reason I’m shying away from the big ticket headers is because I’m hoping to sell the boat in about 2 years to move up to a 24’ with a big block (I like big blocks). But who knows what will happen in 2 years? I’ve already got an engine which I’m in the process of collecting parts for. I’ll probably stroke this one too. I read an article in a boating mag, where they did a manifold swap from stock center rise to the GLM center rise. The boat picked up 3 mph. This was on a stock 260 Mercruiser in a 21’ sport boat. I wonder if they’ll help me? I could always do a little work on the inside of them, and clean up the passages a little. Those are around $500 for the set. I’m thinking about doing exhaust first just to see what happens. Maybe that will give me the little extra I’m looking for. Besides, I’ll probably be due for manifold replacement by next year anyway. If that doesn’t do it, and I end up keeping the boat a little longer, then maybe I’ll do the heads.

chriscraft240

Lib- I'm running the same base motor you are in a camaro. I went from chevy 882 heads to the proline-200cc. Midrange to 5500 rpm much more noticable, I'm also running headers though. Get heads its worth it! Check 383strokerkits.com

ACrooks69

iTrader: (1)

Can't remember the primary side but the secondaries are AX rods. These are pretty rich rods and I have a feeling I'll have to go back to the DAs when I get my exhaust opened up. I came up with that it is so restrictive that the exhaust can't get out of the cylinder at high speeds causing a severly lean mixture (very white plug) and even pinging. When the AX rods failed to correct the problem I looked at the exhaust and I think I hit the nail on the head. Just pretty dang hard to pump 450hp through the prop of an alpha drive I guess.
I had been eyeing those Proline also, but I do not believe the spark plugs will clear the stock exhaust manifolds (someone key in if they will). That is what kept me from doing the trick flow heads on the 350 because of the revised plug angle. Not a problem with the Kodiak Manifolds. You mentioned you might get rid of the boat in a couple years anyway. Just get the heads then. If you just want to be consistent at 62 then that should be fine. If you decide you want to keep boat in 2 years then throw the exhaust on it. No point spending money to make it go a lot faster if you don't plan to keep it right. And if you do keep the boat then you can expect a pretty good performance leap when the manifolds are done since they will be choking the combo.
On another point. Couldn't you get the water passages of an alum manifold coated for corrosion protection? Like what edelbrock puts on the water passages of their marine intakes. Just a thought.

Liberator21

Isn't the water passage of the Edelbrock manifold brass lined? Can't do that. I experimented with powder coating the inside of a new thermostat housing. The water still found a way through, and rust started. That only buys a small amount of time. Has anyone else had any experiences with running aluminum exhaust manifolds in salt water??
I saw the Kodiak manifolds on the Rex Marine site. I think the kit was $1020.00

ACrooks69

iTrader: (1)

I would think there is some sort of ceramic coating they could apply. I would do an internet search on that and call up some dealers.

TomZ

iTrader: (2)

Why don't you just try the GLMs in iron? They look good from the inside. I don't think exhaust is going to be as important on the small block than it would be on the big block. I think the GLMs will do more than well for your combo.

I would put more money in the heads than the exhaust... your center risers along with thru-transom exhaust will do well enough as is.

By the way... that 4 Winns is going to be a lot heavier than you think. We basically have the same boat, and I'm pushing 430 HP with with a 383... still right around 60 MPH. These hulls just don't have enough to run above that. I have too much of the speed bug right now so I'm just enjoying her for what she is. I'm saving up to get into a more conventional go-fast boat. I'll still keep my 4 Winns for cruising but I know she's never going to give me what I want.

Tom
Virginia Beach