High compression heads

[sparkroost]

I am in a quandry.. I have the 1973 115. High compression heads(the highest there is). My machinist relieved them at the sides where the piston can come in contact. In trying to find a good head with no scratches or pits, I came up dry. Had one person contact me wanting 60$ for one. I then talked with the machinist doing the work on my block and he recommended the next compression down from them. 40$ for both, re-surfaced and relieved. upon inspection of the heads he provided, one of them has some pits in the flat area near the spark plug hole. Dayum I hated to see that! So now I contemplating using the high compression heads but am afraid of pre-detonation. <br />If I reduce timing, how much would I have to go? Would I run premium gas?(pump gas)<br />How much power would be lost reducing the timing? <br /><br />Is there a way to run the 26 degrees without pre-detonation? (please don't respond with 103 octane fuel) <br />Is there an additive that will increase motor octane?<br /><br />Sorry for all the questions.. but I need to get this right the first time

 

[JB]

Re: High compression heads

Is the make of your engine some big secret?

 

[sparkroost]

Re: High compression heads

gulp... evinrude 1973. 115393M Model #.

 

[ledgefinder]

Re: High compression heads

I think OMC and Sierra both make a fatter head gasket for the 3.5" bore V4s, specifically for the purpose of dropping the compression (this is in addition to their regular thickness model). If you don't see it at iboats.com, give a yell.

 

[denniz]

Re: High compression heads

Pre-detonation.....???? does anyone else find this funny??? Sorry, to clarify its pre-ignition that causes detonation.

 

[sparkroost]

Re: High compression heads

Rod,<br /><br />Not really, but I see why you would think it's funny.<br /><br />pre=before<br />detonation=explosion<br /><br />It makes sense. You just have to have an open mind.<br /><br />Obviously you understood the question, didn't you?<br /><br />Try to be objective <br /><br />Is there not another way to take advantage of these heads?

 

[sparkroost]

Re: High compression heads

Pre-ignition causes detonation???<br /><br />Detonation is an explosion, pre-ignition does not cause it. sheesh.<br /><br />Compression, air, fuel, exhaust causes detonation.<br /><br />he he

 

[sparkroost]

Re: High compression heads

Course, ya gotta have fire

 

[sparkroost]

Re: High compression heads

ok, now you have me confused, he he. pre-ignition can cause detonation, but detonation is supposed to be timed so that the fuel does not explore under pressure before it's time to detonate...<br /><br />When I think of detonate, I think of it as it happening on time. To pre-detonate is to detonate before it is supposed to.<br /><br />Pre-ignition is to ignite before ignition is actually triggering the explosion.<br /><br />That is not correct? sheesh..

 

[denniz]

Re: High compression heads

preignition is the main cause of detonation. Ill send ya a manual if you need one. Ive got some old merc tech training manuals that explain it in great detail.

 

[bret walters]

Re: High compression heads

the fuel air cahrge in an internal combustion engine is not supposed to detonate, propper cumbustions is a controlled even burn of the fuel charge. detonation is the uncontrolled explosion of the fuel charge al at once. this uncontrolled explosion is often cause by preignition.

 

[denniz]

Re: High compression heads

AH sparkroost, your a engineer... THAT explains why your confused.....

 

[badasselectric]

Re: High compression heads

Worse, an engineer with tools.

 

[sparkroost]

Re: High compression heads

I can't grasp the concept. Detonate IS explode. Even charge? More like the explosion must happen at the right time to be effective. If it happens to early all the force of the explosion will work against the piston.<br /><br />Pre-ignition comes from the fuel exploding under pressure in an uncontrolled manner, before it is time. This can be from hot spots or incorrect timing.<br /><br />We want detonation, just not before or after it is supposed to detonate.

 

[denniz]

Re: High compression heads

your brain will exploid (detonate) in 60 seconds

 

[denniz]

Re: High compression heads

Hey sparkroost, you can detonate from having a pack, cd, or other component double firing.

 

[sparkroost]

Re: High compression heads

Where is the gremlin holding his finger up.

 

[bret walters]

Re: High compression heads

it is combustion not detonation. dynomite is detonated. fuel is burned. when fuel detonates the combustion chamber pressures spike and cause damage to the piston tops and heads. if detonation continues the engine dies. it is not a hard concept to grasp.

 

[denniz]

Re: High compression heads

Im trying to help I offer to send you one of my old training manuals didnt I?

 

[sparkroost]

Re: High compression heads

It sounded to me like you were being sarcastic. I did not major in small engines, but I know how they operate. You are using termonology against me. <br /><br />Combustion is what you say the fuel is supposed to do. You are taking "combustion" and using it as an all in one meaning. To explode on time or in a controlled manner. Now you want to say that detonation is not supposed to happen. Yes, you light dynomite and it explodes.. You also electricaly ignite the mixture, and it detonates.<br /><br />Either way you are creating an explosion.