HELP with my 454 heads

« **on:** December 19, 2008, 05:22:50 PM »

Ive been reading all the great posts on these boards and have found that I need some direction on an engine. I bought my first jetboat this last summer and was so excited to get it home and run it that I didnt bring a compression tester with me for the exchange. Needless to say, if I had brought one and done some testing I would have found three dead holes. Anyway, engine turned out to be well worth what I paid for the boat. Block is #399289 4 bolt mains, heads are #3964291 and intake is #3963569. The block was a factory replacement for an LS-6 Chevelle stamped #T0618CRR. Crank is cross-drilled nitrided forged steel.

Now what I am needing some direction is on the heads. The heads are closed chamber 108cc. The pistons I bought are forged domes that should bring me to around 10.5:1 CR.

Should I.....
A. Try them out with a thicker gasket to decrease the CR.
B. Sell them and buy a set of oval ports with open chambers to bring my CR to around 9.78:1.
C. Leave them just the way they are and run 91 octane forever (if that will even work)

And btw I had the heads completely redone to the tune of $950 so the money has already been spent on them.
Did I miss anything? Jet is a berkeley "C" with unknown impeller. More than likely an A.

« **Reply #1 on:** December 19, 2008, 06:23:30 PM »

I sounds like you got a good combination of parts. I don't have the answers you need, but I'm sure there will be many good recommendations coming soon.

Welcome to the site, and don't forget WE LIKE PICTURES!

« **Reply #2 on:** December 19, 2008, 06:37:54 PM »

Quote from: crewchief22 on December 19, 2008, 06:23:30 PM

Welcome to the site, and don't forget WE LIKE PICTURES!

Pictures.... Here are some of what I found when I took the heads off

A bit blurry but you get the just of it.

Boat is a 1976 18' Sidewinder

Interior. Anyone got a shag carpet rake they want to sell?

« **Reply #3 on:** December 21, 2008, 12:45:34 PM »

Wow, I didnt think I had asked that difficult of question! Come on guys there must be someone out there that has an answer

« **Reply #4 on:** December 21, 2008, 01:10:11 PM »

Tear it down and remachine the entire short block and rotating assembly along with some new pistons to get you the compression you want . I've never really cared what the compression was in any motor , I always ran 91 so I would try and shoot for as much compression as you can with 91 . 10:1 is about it .

The obvious : One pistons looks fuked .

-beerjet-

« **Reply #5 on:** December 21, 2008, 03:04:53 PM »

I would have a porter rework the heads, help out the combustion chamber, lower compression a little, but mainly to make it a more efficient burn. Sounds like you got all the right stuff to make a stout motor....

BTW, I've always like sidewinders, never seen one with that interior configuration though, mi gusta

« **Reply #6 on:** December 21, 2008, 06:15:52 PM »

You are asking a question but dont really give us a basis to offer you an answer. Why do you want lower compression? Is it to save n fuel costs or some other specific reason? You would have a burn a ton of fuel to recoup your cost saving of usuing a lower grade fuel! I also always use the higher octane fuel myself becasue we are putting a quite a load on these engines when we run them at high a RPM.

Joe

« **Reply #7 on:** December 21, 2008, 07:26:02 PM »

Quote from: SkyHarborCowboy on December 21, 2008, 06:15:52 PM

You are asking a question but dont really give us a basis to offer you an answer. Why do you want lower compression? Is it to save n fuel costs or some other specific reason? You would have a burn a ton of fuel to recoup your cost saving of usuing a lower grade fuel! I also always use the higher octane fuel myself becasue we are putting a quite a load on these engines when we run them at high a RPM.

Joe

My question has nothing to do with fuel quality. It has to do with 10.5:1 compression and running the risk of detonation. With the head/piston combo that I have now I will be at 10.5:1 or greater. If I use a larger chambered head I will be at 9.78-10.0:1. Easy for 91 octane.

« **Reply #8 on:** December 21, 2008, 07:53:03 PM »

it appears that you already know the answer to your question...everything works off of everything else its just a cycle of life or jetboats...my question to you is how fast do you wanna go?

« **Reply #9 on:** December 21, 2008, 07:54:19 PM »

Quote from: Mr Plow on December 21, 2008, 07:26:02 PM

My question has nothing to do with fuel quality. It has to do with 10.5:1 compression and running the risk of detonation. With the head/piston combo that I have now I will be at 10.5:1 or greater. If I use a larger chambered head I will be at 9.78-10.0:1. Easy for 91 octane.

The problem is the open chamber 9.78:1 heads might detonate as easy as the 10.5:1 closed chamber heads..... maybe it's time to get that quench thread running again

« **Reply #10 on:** December 21, 2008, 08:10:14 PM »

The primary cause of detonation is poor fuel quality for the given compression ratioo. If you are willing to pay for the porper fuel that your engine spec calls for you will be fine. The way I see it, your question is 100% about fuel quality/cost!

Joe

« **Reply #11 on:** December 21, 2008, 08:16:41 PM »

Quote from: SkyHarborCowboy on December 21, 2008, 08:10:14 PM

The primary cause of detonation is poor fuel quality for the given compression ratioo. If you are willing to pay for the porper fuel that your engine spec calls for you will be fine. The way I see it, your question is 100% about fuel quality/cost!

Joe

Theres alot more involved in choosing the correct octane for your motor than just the calculated compression ratio....

« **Reply #12 on:** December 21, 2008, 08:27:47 PM »

You are very correct! I never said there wasnt! Bottom line, You have to pay to play! If the rest of his ngine is speced right AND he is willing to pay for the required fuel this is not an issue!

Joe

Quote from: pw_Tony on December 21, 2008, 08:16:41 PM

Theres alot more involved in choosing the correct octane for your motor than just the calculated compression ratio....

« **Reply #13 on:** December 21, 2008, 08:29:47 PM »

Actually your Dynamic compression ratio is much more impportant then the static compression rati.

Sorry for all of the typos there is a problem that I cant see what I am typing as I post it!.

Joe

« **Reply #14 on:** December 21, 2008, 09:05:02 PM »

Soooooo , no one else saw the fuked piston

-beerjet-

« **Reply #15 on:** December 21, 2008, 10:01:33 PM »

He said he bought new pistions and has no idea of the preious history of the boat so who knows what caused that damage to happen. I bought a boat one time that ran perfet and een start perfect but on the lake under a load it would blow the sparkplugs apart. I finally put a timing light on it and it had 55 dgees of initial advance! How that boat could start so easily is beyond me!

Joe

PS The domes of my postions showed detonation on them as well but that was because the PO had no idea what he was doing!

Quote from: beerjet on December 21, 2008, 09:05:02 PM

Soooooo , no one else saw the fuked piston

-beerjet-

« **Reply #16 on:** December 22, 2008, 05:30:43 AM »

Ok let me turn this thread slightly, I was told by a buddy of mine that I should go with the oval port open chambers because they will flow best for what the boat needs. Are ovals really going to help me in any way shape or form?

Quote from: 1980Nordic on December 21, 2008, 07:53:03 PM

my question to you is how fast do you wanna go?

As fast as that hull will allow me. I know I wont be breaking any records with it. We use it for skiiing, tubing and para-sailing.

« **Reply #17 on:** December 22, 2008, 09:07:31 AM »

Yes , dig up some 049 oval port castings . Great heads for making torque and will still breath to and above 5K RPM when your right foot calls for it .

-beerjet-

« **Reply #18 on:** December 22, 2008, 09:09:41 AM »

And you dont want to go fast in that boat . Ski and tube your bains out .

-beerjet-

« **Reply #19 on:** December 22, 2008, 09:16:27 AM »

Quote from: Mr Plow on December 19, 2008, 05:22:50 PM

Ive been reading all the great posts on these boards and have found that I need some direction on an engine. I bought my first jetboat this last summer and was so excited to get it home and run it that I didnt bring a compression tester with me for the exchange. Needless to say, if I had brought one and done some testing I would have found three dead holes. Anyway, engine turned out to be well worth what I paid for the boat. Block is #399289 4 bolt mains, heads are #3964291 and intake is #3963569. The block was a factory replacement for an LS-6 Chevelle stamped #T0618CRR. Crank is cross-drilled nitrided forged steel.

Now what I am needing some direction is on the heads. The heads are closed chamber 108cc. The pistons I bought are forged domes that should bring me to around 10.5:1 CR.

Should I.....
A. Try them out with a thicker gasket to decrease the CR.
B. Sell them and buy a set of oval ports with open chambers to bring my CR to around 9.78:1.
C. Leave them just the way they are and run 91 octane forever (if that will even work)

And btw I had the heads completely redone to the tune of $950 so the money has already been spent on them.
Did I miss anything? Jet is a berkeley "C" with unknown impeller. More than likely an A.

Mr Plow ,nice looking little boat , bummer re your motor 10 + to 1 compression should run readily with 91 octane if you limited the timing back and all the other "factors" are in order , if the jet is stock and the boat came with a BBC the Impeller is most likely and "A" Heres some info on those heads which seem to be quite the "prize" check out the various links on the search Call or email if you need help Tom
http://www.google.com/search?hl=en&q=3964291+heads&btnG=Google+Search&rlz=1W1GCNV_en&aq=f&oq=

« **Reply #20 on:** January 31, 2009, 02:19:16 AM »

Wow! I would dump those heads and get some 049's! (oval ports) Also I would have a reputable engine/head guy cc the heads BEFORE you buy any pistons. Also check deck height. Just trying to help, good luck

« **Reply #21 on:** January 31, 2009, 06:52:32 AM »

Plow,
781 heads are equally as good as 049, both open design, and maybe a bit easier to find. Using closed chamber heads also reduces your piston selection/availability...but large oval ports are definitely the way to go.

p-jet

« **Reply #22 on:** January 31, 2009, 09:00:35 AM »

If you've already spent the money on the heads, I say run 'em! My 468 runs on 91 octane all damn day with 11:1 compression. The RPM range your boat (or any jet for that matter) is going to spend 90% of it's time calls for a nice flowing, well designed head, outside of a set of aluminum heads, the heads you have are just about perfect.

« **Reply #23 on:** January 31, 2009, 09:59:22 AM »

Fix what ya got, maybe a fat gasket if it makes ya sleep better. Run the 91 like everyone else. Tune it correctly and LETS GO!!

« **Reply #24 on:** January 31, 2009, 10:07:48 AM »

sell the pistons and get a set of flat tops, will work good on the cloaed chamber head, and you can run 36 degees in timing and get power out of the motor with 91 octane

Mr Plow

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