Lower Unit Help Please

[Captain Chaos]

just had this from seller:

"Hi Lawrence

The standard comp. for a pro-max is 135 lbs according to Mercury service manual. It probably has high comp. head gasket installed."

[JamesM]

I dunno about 60 thou but I know that 150psi is fine on 95RON unleaded, you dont really wanna take it much more than that though.

[Captain Chaos]

Matt,

thats superb....i think i've sorta talked myself into this!!

it may all be imaterial the way the price is going!

I got my maths wrong in the PM btw!

fingers crossed!

[JamesM]

normal unleaded is 95RON
Optimax Super and BP ultimate unleaded are all 97/98RON

150psi will be fine on the standard 95RON unleaded we have over here.

[jw.]

Originally posted by Matt
...It's important to realise detonation is not the same as pre-ignition or pinking. It's similar, but the flame front is still under control, it's not an explosion. ...

Well yer nearly there...

Preignition is caused by something other than the spark at the plug igniting the mixture prematurely. Pinking is a pressure rise faster than you might want and it is verging on detonation. It may contain a wee explosion within the burn. As you say, detonation is dangerous.

Retarding the ignition timing, to start the burn later and avoid too fast a pressure rise, will be necessary if the compression pressure has been increased.

[Captain Chaos]

Originally posted by Matt
Go with yer gut feeling.

Erm, thats got me 4 student loans, a girlfriend, an estate car and a couple of nights in a police cell!!! I'll stick with using my brain....what i ahve of one

QUOTE]Originally posted by Matt
you were told the motor is stock, and it clearly isn't. [/QUOTE]

Actually (shame i deleted original emails!!) i was told as far as he was aware it was "as it left jerrys marine in 99"....he does clearly mention in the add "With the compressions, Mercury recommends to use only premium fuel (92 octane or higher)" just bellow where the compression are stated.

also from another perspective buyer:

Q: Hi TX. Is motor original? Any powerhead work done? Has ECM been read by dealer? What oil was used? Who serviced motor? Why are you selling? Thx for your time and help. RoyP

A: Roy - The motor was originally bought from Jerrys Marine in Sulphur, LA. I believe the only defect that this powerhead has had is an intermittent trigger assembly which was replaced. The outboard has been serviced by and stored for approx. 2-1/2 yrs at Taylor Marine in Orange TX. I do not know if they read the computer, but they told me it was in excellent condition. To the best of my knowledge, it has been run on Merc oil and serviced by Taylor Marine. Thanks.. Glenn

the guy also has 500+ positive feedbacks!

[JamesM]

I allways thought that detonation pinking and preingnition where all the same thing. The way I understood it was that the fuel air mix was ignited prematurely and the flame front (energy wave) hit the piston before TDC which is nasty as its trying to push the piston back down whilst its still traveling up, as oposed to after TDC therefore pushing it in the direction its allready traveling in. More octane slows down the flame front thus allowing the piston more time to reach and pass tdc, hence why you can run more ignition advance with more octane. A slower burn will also push the piston for longer and will there for still be pushing when the crank is at a greater angle w.r.t to the conrod and thus give beter leverage and therefore more torque. This is how nitrous works as it has a very slow burn compared to petrol alone

[Captain Chaos]

just working that out.................coz if it is........i'm already fecked.....what a dissapointment.

hold of going to bed and i'll let ya know in 5!

[Captain Chaos]

not enough burgers!

ta

in answer to question.....i reckon mastercard will let me squeeze a wee bit more than that!

[Captain Chaos]

oh well...it exceeded my maximum!

off to bed.....back to drawing board tomorrow

bollix!

[hutchy]

Originally posted by Captain Chaos
just had this from seller:

"Hi Lawrence

The standard comp. for a pro-max is 135 lbs according to Mercury service manual. It probably has high comp. head gasket installed."

must be using rice paper to gain that much psi

[Jon Fuller]

Originally posted by Johnny Boat Dude
This is how nitrous works as it has a very slow burn compared to petrol alone

Nitrous itself doesn't burn at all, the Nitrous, when heated by the ongoing combustion, releases Oxygen, which allows the extra fuel you've intoduced through aditional jets/injectors, to burn.

As the Oxygen is liberated from the Nitrous by the heat of combustion in a fairly controlled manor, it's relatively kind on the motor. I think the process of liberation of Oxygen, cools the charge, which also helps.

At least this is how I understand it.

[Jon Fuller]

Originally posted by Matt
one of the google ads is for a Whipped Cream Charger!

[JamesM]

Originally posted by Johnson
Nitrous itself doesn't burn at all, the Nitrous, when heated by the ongoing combustion, releases Oxygen, which allows the extra fuel you've intoduced through aditional jets/injectors, to burn.

As the Oxygen is liberated from the Nitrous by the heat of combustion in a fairly controlled manor, it's relatively kind on the motor. I think the process of liberation of Oxygen, cools the charge, which also helps.

At least this is how I understand it.

So its not a slower burn as such just a longer burn because your burning more fuel?

Also how far off the mark was I with the pinking, pre-ingnition or whatever thing?

[Hydrostream]

if youre that bothered about the high compression retard your timing a bit, but 150 psi is ok on our premium unleaded.

BTW, if you don't mind me asking, how much were you quoted for shipping for i?

Alan

[Hydrostream]

Captain Chaos: just found this on S&F...

http://forums.screamandfly.com/forum...threadid=66986