Help with 383 Build

[pennyduke]

I'm doing a 350 Stroker to a 383 using a 94 block .030 over and 96 Vortec 64cc heads. I'm trying to find a balanced Scat rotating assembly with 5.7 rods that will get me at or near 9:1 cr. I have been using Gregs thread as a go by and noticed that he used 23cc d dished pistons. But I can't find them in any of Scats Kits. All i see in 18cc piston in the kits. Does anyone know anyone that sells complete kits that will get me close to 9:1 cr. I don't want to get the kit with the 18cc pistons then have to buy the 23cc pistons and pay for having it rebalanced. The block is at the Machine Shop ready and waiting for the Assembly. Thanks

 

[Tail_Gunner]

Re: Help with 383 Build

Nie to see your own thread...Give it a few there's a boat load of these threads...

 

[greg82255]

Re: Help with 383 Build

Best of luck with your build!

If the block is already at the machine shop, why not work with them to get a rotating assembly? I was always told that you want the machine shop to have the pistons before they do any final honing of your cylinders so they can fit each piston to each hole. I used Speed Pro -23cc pistons (that's why they aren't in the Scat kits ), a Scat cast 383 crank, Scat 4340 forged I-beam rods, and moly rings made by Hastings I believe. I'd be happy to get out the invoice and give you all the part #'s I used if you would like, but I also gave my flywheel to the machine shop and had them balance the rotating assembly.

 

[wca_tim]

Re: Help with 383 Build

I used these pistons... http://www.summitracing.com/parts/SRP-139629/ SRP made by JE for mild turbo or blower apps, -16cc dished, forged pistons made of a low expansion alloy. The man siad they were important if I wanted to run the snot out of it and have it hold up... so far, so good...

Orriginally built engine with 64 cc world products sportsman 2 heads. forged scat crank and H-beam rods, (externally balanced), block blueprinted and zero decked for a tight quench, ran great with no detonation at all on permium pump gas (93 octane). had 190-195 psi cranking compression on all cylinders. If I remember correctly, static compresion came out to just about 10:1 with the head gaskets we used. The tight quench is the key to avooiding detonation...

Swapped to CNC competition AFR 195 heads with 75 cc combustion chambers. cranking compression down to 150-160, can run any gas and still makes more power than before, toying with the idea of a procharger... or perhaps a whipple... in the not too distant future. I can dig up other specs if you like. Hope this is helpful.

 

[pennyduke]

Re: Help with 383 Build

I gave the machine shop the heads and block about 3 weeks ago. The heads are done with new springs, Keepers, Retainers, Screw in Studs, and Valve job. They have been waiting on me to get them the Rotating Assembly for about a week. He does want to measure each piston before final assembly. He also wants to preassemble it so he can deck it at zero. I was just searching for a complete kit that would put me at 9:1 with the flex plate and balancer included. I did find a kit last night with -21cc pistons that will put me at about 9.2:1 cr. I think I may order it today if I can't find one with the -23cc pistons.

 

[chizwizdiz]

Re: Help with 383 Build

**subscribed

 

[John_S]

Re: Help with 383 Build

I gave the machine shop the heads and block about 3 weeks ago. The heads are done with new springs, Keepers, Retainers, Screw in Studs, and Valve job. They have been waiting on me to get them the Rotating Assembly for about a week. He does want to measure each piston before final assembly. He also wants to preassemble it so he can deck it at zero. I was just searching for a complete kit that would put me at 9:1 with the flex plate and balancer included. I did find a kit last night with -21cc pistons that will put me at about 9.2:1 cr. I think I may order it today if I can't find one with the -23cc pistons.

What head gasket thickness are you using for your calculations? Gaskets can be had that are 0.051", and think even to 0.060".

 

[wca_tim]

Re: Help with 383 Build

John, are you thinking of moving compression ratio up a little with thicker head gaskets? I would bet that the machinist is planning to choose head gaskets that will yield a quench of something like 0.040' - 0.045" - which helps a lot with detonation. With a cam that gives even a little bit of overlap to drop dynamic compression (but not so much as to open the door to reversion issues), you can easily and safely run 10:1 one on pump gas (92-93 octane), probably 9.5 with 87 octane. 9.2 ish should easily be fine. My understanding is that the quench is much more important in staving off detonation than the relatively small amount of compression you lose by going with a thicker head gasket. make sense?

 

[pennyduke]

Re: Help with 383 Build

Im trying to stay with a 0.042 head gasket, 4.030 bore, 64cc heads, zero decked, 3.75 stroke, and -23cc pistons. The problem i'm having is finding the -23cc pistons in a complete balanced scat kit. My other option is to buy the 18cc scat kit and switch the pistons to the -23cc pistons bought seperatly. Then try to sell the -18cc pistons somewhere. If I do that, I will have to have the entire assembly rebalanced. Unless someone knows a better way to go. If I use the -18cc pistons I will be at 9.8:1. I do plan on goingwith a mild Cam. The same one in the HT383 by GM Performance.

 

[Tail_Gunner]

Re: Help with 383 Build

I trying to stay with a 0.042 head gasket, 4.030 bore, 64cc heads, zero decked, 3.75 stroke, and -23cc pistons. The problem i'm having is finding the -23cc pistons in a complete balanced scat kit. My other option is to buy the 18cc scat kit and switch the pistons to the -23cc pistons bought seperatly. Then try to sell the -18cc pistons somewhere. If I do that, I will have to have the entire assembly rebalanced. Unless someone knows a better way to go. If I use the -18cc pistons I will be at 9.8:1. I do plan on goingwith a mild Cam. The same one in the HT383 by GM Performance.

Id hold on that cam...There have been so many improvements on cam design its crazy to go with a old smog cam. To make this short post the spec's on the can and lets take a look at duration time..Or overlap

 

[pennyduke]

Re: Help with 383 Build

I have another cam in mind also. Comp Cams 08-416-8. But I would like to get the Rotating Assembly ordered first. I may just have to order each part individualy and forget about the kit.

 

[wca_tim]

Re: Help with 383 Build

for off the shelf cams, it's hard to beat the comp marine series... xm 270H, 276, etc..., the specific choice in that series depends more on your planned exhaust and intake (especially exhaust) set-up than anything else. The only way to do better is to have one custom ground by one of the couple of guys that specialize in custom grinds for marine engines. you're much more likely to have problems with grinds designed for cars...

 

[John_S]

Re: Help with 383 Build

John, are you thinking of moving compression ratio up a little with thicker head gaskets? I would bet that the machinist is planning to choose head gaskets that will yield a quench of something like 0.040' - 0.045" - which helps a lot with detonation. With a cam that gives even a little bit of overlap to drop dynamic compression (but not so much as to open the door to reversion issues), you can easily and safely run 10:1 one on pump gas (92-93 octane), probably 9.5 with 87 octane. 9.2 ish should easily be fine. My understanding is that the quench is much more important in staving off detonation than the relatively small amount of compression you lose by going with a thicker head gasket. make sense?

I wasn't thinking about quench. Just getting the comp ratio to near what the OP wanted. If he drops the compression ratio to the low 9's, quench is not going to make a big difference.

The HT383 cam is the same as the roller cam that is used in the 5.7L mercruisers. Certainly can run a little more than that.

 

[Scott Danforth]

Re: Help with 383 Build

I agree, cam choice will be dependent on exhaust choice. either a Comp Cam, or a custom grind from Elgin

 

[pennyduke]

Re: Help with 383 Build

I went ahead and ordered the complete Balanced Scat Rotating Assembly from Summit. They price matched Jegs and saved me a few dollars. The kit has the -18.00cc pistons. I will ask my machine shop if they think I should switch to the -23.00cc pistons to get me closer to 9:1 cr. I really don't think they do many boat engnies but I will see what he says. If I do switch to the -23.00cc pistons it will cost me $319.92 for the pistons and would have to have it rebalanced. Then I would try to sell the -18.00cc pistons on Ebay. Summit sugested running this kit and using a higher octane gas. The link for the kit is listed below.

http://www.summitracing.com/parts/SCA-1-91100BIE/

 

[Tail_Gunner]

Re: Help with 383 Build

for off the shelf cams, it's hard to beat the comp marine series... xm 270H, 276, etc..., the specific choice in that series depends more on your planned exhaust and intake (especially exhaust) set-up than anything else. The only way to do better is to have one custom ground by one of the couple of guys that specialize in custom grinds for marine engines. you're much more likely to have problems with grinds designed for cars...

Agreed i have one in a v6 and no reversion what so ever..Cant tell you the exact power gain but the 4.3 acts like a two stroke now

 

[wca_tim]

Re: Help with 383 Build

I have an xm-270-H12 grind comp in a 383 and although I kind of wish I had been more aggressive, it has great manners and would be perfect for most folks purposes... it would likely be really close on reversion with stock manifolds, the next one down in duration (specific cam depending on whether using hydraulic roller or flat tappet) would be fine with stock exhaust and would still make a good bit more power than the other cams being considered. If you wanted to use aftermarket risers or manifolds / risers or even add extensions to your risers to put the water a bit further back and allow you to run the 270 for a nice step up in power. (reversion is where the overlap between intake and exhaust valves being open creates a little suction in the exhaust and draws water back into the engine - not good).

running the -18 cc pistons, you MAY have to run premium gas or retard your timing a little bit for cheap gas to avoid any detonation, but it should be no problem at all running premium. With that kit, your heads, an xm-270 or similar cam, ideally with 1.6 ratio rocker arms, edelbrock airgap rpm and an edelbrock or holley 750 cfm marine carb, you should wind up with 375-400 horsepower with a peak at 5000 - 5200, have a tame enough idle around 600 rpms to keep from trashing your drive and an all around great running package. It's a tried and true combination of parts...

look up posts by mkos1980 on vortec heads and related builds too, good information and a sharp guy from what I can tell.

If you decide to have a custom ground cam ground, word on the street is and has been for years - Bob Madera at Marine Kinetics is "the man". Period.

http://www.marinekineticsonline.com/index.html

Cheers!

 

[pennyduke]

Re: Help with 383 Build

I need to give you guys some information about my boat so we can talk about the right cam. It is a 1993 Bayliner 2452 with a broken 5.0L mercruiser in it now. The outdrive is an Alpha 1 Gen2. I really don't want to go too far over 300hp and hope I dont blow the drive. I will be using all the parts I can, oil pan, pullys, coil, ect form the old motor. I have an Edelbrock Performer Intake and the Vortec heads have been redone with upgraded springs and a valve job. I guess the next thing I need to order is a Roller Cam, Roller Lifters, Push rods, and roller rockers. I really like this boat for fishing and sometimes get up to 6 friends out at the same time. That 5.0L never had a chance with my heavy boat and I would have to move people forward to get it on plane. Now how do I select the correct cam?

 

[Tail_Gunner]

Re: Help with 383 Build

I need to give you guys some information about my boat so we can talk about the right cam. It is a 1993 Bayliner 2452 with a broken 5.0L mercruiser in it now. The outdrive is an Alpha 1 Gen2. I really don't want to go too far over 300hp and hope I dont blow the drive. I will be using all the parts I can, oil pan, pullys, coil, ect form the old motor. I have an Edelbrock Performer Intake and the Vortec heads have been redone with upgraded springs and a valve job. I guess the next thing I need to order is a Roller Cam, Roller Lifters, Push rods, and roller rockers. I really like this boat for fishing and sometimes get up to 6 friends out at the same time. That 5.0L never had a chance with my heavy boat and I would have to move people forward to get it on plane. Now how do I select the correct cam?

You need to be very spefic when talking heads and spring's..AKA are the redone heads 305 head's or 350..The spring's what type....the retianer's what type...were the heads machined for increased valve lift..were they shaved..More than few get caught in a little ..Opps. Were the studs apr stud's... is this a roller engine..It's a simple upgrade if done to the letter.

 

[John_S]

Re: Help with 383 Build

I need to give you guys some information about my boat so we can talk about the right cam. It is a 1993 Bayliner 2452 with a broken 5.0L mercruiser in it now. The outdrive is an Alpha 1 Gen2. I really don't want to go too far over 300hp and hope I dont blow the drive. I will be using all the parts I can, oil pan, pullys, coil, ect form the old motor. I have an Edelbrock Performer Intake and the Vortec heads have been redone with upgraded springs and a valve job. I guess the next thing I need to order is a Roller Cam, Roller Lifters, Push rods, and roller rockers. I really like this boat for fishing and sometimes get up to 6 friends out at the same time. That 5.0L never had a chance with my heavy boat and I would have to move people forward to get it on plane. Now how do I select the correct cam?

I think you are correct with trying to stay in the low 9's compression. You don't want the high-test bills for that boat. No need to run higher compression and having the "perfect" quench. Mercs 383's don't, along with that HT383, and any production motor. I wouldn't zero deck it, and choose a head gasket that gets you close as you can.