350, Merc, Voretc, timing advance? 95 octane, Edelbrock 600 cfm/Airgap RPM
09-19-2009, 05:16 PM
#1
Registered
Thread Starter
Join Date: Apr 2009
Posts: 13
Likes: 0
Received 0 Likes
on
0 Posts
350, Merc, Voretc, timing advance? 95 octane, Edelbrock 600 cfm/Airgap RPM
Dear Gentlemen!
I was recently repowering my 21 foot Chaparral with a brand new Mercruiser 350 long block with Vortec-heads. I decided to ad an Edelbrock 600 cfm marine-carb (#1409) and an Airgap RPM intake (#7501).
I have calibrated the carb at "rich" (going up then down on the mix-screws) with standard jets (Primary .098, Secondary .101; Metering Rods - .068 x .047; Step-Up Spring - orange 5" Hg).
It all works great and runs at smooth idle 600 RPM topping at WOT 4500 RPM/54 mph.
Now to my question/questions. I have understood there is a standard Thunderbolt V ignition system and I am also aware how to adjust it (white/purple cable to earth), I am running on 95 octane (Sweden, standard).
How far could I advance my timing given that 95 octane is a bit more that the US-87-89 octane?
Since the Thunderbolt V advances automatically, were to I measure the advance? at Idle or at what RPM?
What would you recommend to obtain maximum HP, still not frying my heads, I am mostly cruising at 3000-3500, however my friend has recently bought a big-block, and it would be so great to still be able to overtake him now and then…..
Many thanks in advance for your thought…/Lars
I was recently repowering my 21 foot Chaparral with a brand new Mercruiser 350 long block with Vortec-heads. I decided to ad an Edelbrock 600 cfm marine-carb (#1409) and an Airgap RPM intake (#7501).
I have calibrated the carb at "rich" (going up then down on the mix-screws) with standard jets (Primary .098, Secondary .101; Metering Rods - .068 x .047; Step-Up Spring - orange 5" Hg).
It all works great and runs at smooth idle 600 RPM topping at WOT 4500 RPM/54 mph.
Now to my question/questions. I have understood there is a standard Thunderbolt V ignition system and I am also aware how to adjust it (white/purple cable to earth), I am running on 95 octane (Sweden, standard).
How far could I advance my timing given that 95 octane is a bit more that the US-87-89 octane?
Since the Thunderbolt V advances automatically, were to I measure the advance? at Idle or at what RPM?
What would you recommend to obtain maximum HP, still not frying my heads, I am mostly cruising at 3000-3500, however my friend has recently bought a big-block, and it would be so great to still be able to overtake him now and then…..
Many thanks in advance for your thought…/Lars
09-24-2009, 07:13 PM
#2
Registered
Join Date: Mar 2008
Posts: 176
Likes: 0
Received 0 Likes
on
0 Posts
only advance the timing as far as you need to to make max horsepower for your setup - I would guess somewhere around 33 or 34 degrees btdc?
most merc v8 modules are 22 or 24 degrees advance and in before 3500 rpms. if you set initial starting at 8 and add a couple degrees at a time; when you stop picking up rpms at wot, back off a degree and you're about there.
You can also watch the "timing line" on the plug electrodes. You want it to be a little below (closer to the plug) the bend in the electrode. closer to the base indicates too much advance, further away indicatesyou'll make more power with a little more advance.
the name of the game isn't getting as much advance as you can, it's getting the fuel burnt as uniformly as possible and putting the maximum cylinder pressure at about 10 degrees atdc...
or so goes my limited understanding...
most merc v8 modules are 22 or 24 degrees advance and in before 3500 rpms. if you set initial starting at 8 and add a couple degrees at a time; when you stop picking up rpms at wot, back off a degree and you're about there.
You can also watch the "timing line" on the plug electrodes. You want it to be a little below (closer to the plug) the bend in the electrode. closer to the base indicates too much advance, further away indicatesyou'll make more power with a little more advance.
the name of the game isn't getting as much advance as you can, it's getting the fuel burnt as uniformly as possible and putting the maximum cylinder pressure at about 10 degrees atdc...
or so goes my limited understanding...
Last edited by wtfo; 09-25-2009 at 09:21 AM.
09-25-2009, 11:19 AM
#4
Charter Member # 55
Charter Member
That 95 European octane rating is not the same as US octane ratings. You need to find out the equivalent US octane rating before you start changing stuff.
I have also read that Vortec heads do not like a lot of timing.
I have also read that Vortec heads do not like a lot of timing.
