Help with 383 Build

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joewithaboat

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Re: Help with 383 Build

pennyduke said:
I think it's too late now. I'm stuck at 9.7:1.
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As long as you are tuned well and dont overdo the timing Im sure you are going to be fine. That bigger cam is going to help you out here as well.
 
Tail_Gunner

Tail_Gunner

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Re: Help with 383 Build

joewithaboat said:
Unless you are using "file fit" rings the "as is" gap on run of the mill rings are usually double what the minimum would be.
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Jowie your a funny guy i am absolutey convinced you spent you sometime in a shop..However the shop did not do heavy duty cycle motor's..Reading this thread where did you come up with filing rings.... when keeping CR ratios in a high stress engine at 9.5 and above were ok....Are you bench racing....
 
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John_S

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Re: Help with 383 Build

joewithaboat said:
As long as you are tuned well and dont overdo the timing Im sure you are going to be fine. That bigger cam is going to help you out here as well.
Click to expand...

Yes, he needs to calculate the dynamic compression with his cam selection.

IMHO, the build is leaning more toward a performance build vs an extreme towing application, which this is more equivelent to. I don't think it has reached the point where it will absolutly be an issue, but having a powerband that won't be fully utilized is just a waste in my eyes.

If he is running T4 ignition or a T5 with no knock sensor, has a good likelyhood of not hearing the detenation until it is too late. In a car/truck with the motor in front of you, it is much more apparent. Back in the boat engine compartment, (buried on a cruiser), along with wind noise, etc, not so much.



FWIW: The Merc 377 ring gap spec is:

Top & 2nd Ring: Production: 0.016 - 0.026 (0.40-0.66), service: High limit +- 0.001

Oil: Production: 0.010 - 0.050 (0.25- 1.27), service: High limit +- 0.001
 
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joewithaboat

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Re: Help with 383 Build

Tail_Gunner said:
Jowie your a funny guy i am absolutey convinced you spent you sometime in a shop..However the shop did not do heavy duty cycle motor's..Reading this thread where did you come up with filing rings.... when keeping CR ratios in a high stress engine at 9.5 and above were ok....Are you bench racing....
Click to expand...

Gunner...

We did lots of different stuff at the shop i worked at. Including "heavy cycle motors"

I think you mentioned adding .002-.003 to the ring gaps correct? Checking ring gaps is SOP for assembling an engine and is good advice. Especially because Ive seen them packaged wrong. What I'm saying is the ring manufacturers all error on the high side of the recommended gaps as to not ever run into problems with pistons locking up on folks that dont check them. Adding additional clearance would usually only come into play if one were using file fit rings, hence my comment. This got me thinking tough, if i remember correctly... KB Hypereutectic's use unusually high ring gaps, especially in forced induction or heavy load applications so O/P make sure you check their charts for recommended clearance.

EDIT/ADDED http://www.kb-silvolite.com/kb_car/clearance_pop.php
looks like KB recommends .032 for the top ring in this application

A 9.5 to 1, 350 horse, small block is in my opinion not really high stress. As i said before If it has proper fuel, oil, good spark, cool air, it will run like a raped ape... all day long.


John,

I agree that this is probably pushing the performance end of things vs a tug boat. But i dont the o/p has crossed the line. It might need premium fuel. It will definitely need to be propped correctly as to not lug it down. Maxing out the C/R will make the most power and be the most fuel efficient. Will it be easier to make a mistake and burn up than a 8.5 to 1 engine ? Yes...

The thing most people over look in an engine pushing the C/R limit is lack of fresh cool air.
 
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John_S

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Re: Help with 383 Build

The engine efficiency gained from the compression ratio, I doubt will offset the cost of running premium. Usually, filling 100gal tanks hurts the pocket book enough without the premium surcharge. The OP seems OK with the added cost, though. Most cruiser owners I am familiar with are dialed right in to their engine and spending the least $ to get to X location.
 
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pennyduke

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Re: Help with 383 Build

UPDATE: Well the bottom end has been finished for about 2 months now. I'm just getting back to where I can work on the motor now. I still need to pull the 305 from my boat so I can get some parts off of it.

My next step is to get the top end put together. I need to order the Head Gaskets now. But I'm not sure which ones to order. Greg used felpro 1003. When I look at these on the Summit site is says bore size 4.166. What exactly does thet mean?
 
Tail_Gunner

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Re: Help with 383 Build

Penny welcome back. this is where your machinist should come in, he know's what's been done to the head's milling.. shaving or whatever. Once again i would urge you to keep the compression to 9 or below...when we are fooling around tinkering and building engine's in here there for go fast boat's that have very little load on them when running fast..not like your boat which is more of cruise,but a nice cruiser...:cool: Lots of load on the engine and 9/1 will not be any performance loss.
 
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pennyduke

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Re: Help with 383 Build

Thanks for the help guys. The machine shop never told me what the deck height was. He did say it looked close to zero. Should I have him measure it before I choose the head gasket or is this something I could measure? If it is at zero deck that puts me at 9.65:1 using the 0.041 inch head gasket. if I choose a thicker gasket I believe that will hurt my quench.
 
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joewithaboat

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Re: Help with 383 Build

pennyduke said:
Thanks for the help guys. The machine shop never told me what the deck height was. He did say it looked close to zero. Should I have him measure it before I choose the head gasket or is this something I could measure? If it is at zero deck that puts me at 9.65:1 using the 0.041 inch head gasket. if I choose a thicker gasket I believe that will hurt my quench.
Click to expand...

Pennyduke,

You can measure the deck height pretty well with the short block assembled with just a strait edge and feeler gauges.

If the shop didn't have the ability to actually blueprint the deck to the crank center-line it is unlikely that they would try to get it to actual zero.

If the valves and seats were reground the chamber size likely a little bigger than 64cc.

If you were to actually to measure everything critically i would bet you are more like 9.25, tops.

The only thing that would throw this off is if heads that were heavily milled.

You could probably get away with using a thinner gasket.
 
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pennyduke

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Re: Help with 383 Build

The heads were not milled. I will check the deck height tomorrow like you described. Do I need to check each piston or just a few? I almost want to measure everything to see what my CR really is. Or should I not worry about it?
 
Tail_Gunner

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Re: Help with 383 Build

pennyduke said:
The heads were not milled. I will check the deck height tomorrow like you described. Do I need to check each piston or just a few? I almost want to measure everything to see what my CR really is. Or should I not worry about it?
Click to expand...

Yes worry a bit now. Be cautious Penny your done with the build..you have spent the money..your tooling down the river and you have a problem....9/1 takes that part out of the equation and your machinst will know what gasket's you need to get there..Give comp cams a call give them your cam.. lifters... and induction. Tell them you want tourqe at all rpm level's and see how they repsond to CR. Maybe the 270 live's well above 9/5.
 
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pennyduke

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Re: Help with 383 Build

What is the opinion on using a High Volume Oil Pump on a 383 Marine Engine? I have seen many different posts but can't decide which way to go. I'm getting closer to the end. Thanks all
 
Scott Danforth

Scott Danforth

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Re: Help with 383 Build

I used a Melling pump, pickup, and pump shaft when I changed cam and heads. it flows about 20% more than stock. I have done it to every SBC I have ever pulled the pan on and never regretted it once. In my mind, good insurance.
 
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pennyduke

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Re: Help with 383 Build

What do y'all think about using guide plates with roller tip self aligning rockers?
 
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pennyduke

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Re: Help with 383 Build

That's what I was thinking. I ordered the non self aligning rockers by mistake. I have to order the self alinging ones today. I used an adjustable pushrod and checked the rocker position to the valve with the marker test and it looked real good.
 
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