Gev IV 454, modern fuel and timing
08-24-2015, 04:18 PM
#1
Registered
Thread Starter
Join Date: Jun 2013
Posts: 6
Likes: 0
Received 0 Likes
on
0 Posts
Gev IV 454, modern fuel and timing
Hello all,
I have a 1983 Gen IV 454 mag engine in my boat now, the book calls for 10* initial timing, is that still a valid setting with today's gas with ethanol? I run 89 in it with the 10% ethanol. When I can get it, I run 100%, gas sometimes its 87 others its 89. I was thinking about bumping the timing to 12*, it definitely idles better there, I have not brought it up on plane at 12* however.
Also would any one know what the total advance is on the thunderbolt 4 amplifier Merc part # 15248T02 (current number) 390-7804A3 original number? The sticker on mine had been painted over so I don’t know if its 20 or 24* total advance. I'm assuming its 24, but we all know what happens there...
Thank you for any input
--clawless
I have a 1983 Gen IV 454 mag engine in my boat now, the book calls for 10* initial timing, is that still a valid setting with today's gas with ethanol? I run 89 in it with the 10% ethanol. When I can get it, I run 100%, gas sometimes its 87 others its 89. I was thinking about bumping the timing to 12*, it definitely idles better there, I have not brought it up on plane at 12* however.
Also would any one know what the total advance is on the thunderbolt 4 amplifier Merc part # 15248T02 (current number) 390-7804A3 original number? The sticker on mine had been painted over so I don’t know if its 20 or 24* total advance. I'm assuming its 24, but we all know what happens there...
Thank you for any input
--clawless
08-24-2015, 04:51 PM
#2
From another OSO member, can't remember who.
Assuming you have the aluminum module (big square aluminum box bolted to the exhaust manifold)
390-9607A3=22 DEG @3500
390-7804A3=24 DEG@3750
390-957A1-20 DEG @3000
Hope this helps.
Assuming you have the aluminum module (big square aluminum box bolted to the exhaust manifold)
390-9607A3=22 DEG @3500
390-7804A3=24 DEG@3750
390-957A1-20 DEG @3000
Hope this helps.
08-25-2015, 07:36 AM
#3
Registered
Thread Starter
Join Date: Jun 2013
Posts: 6
Likes: 0
Received 0 Likes
on
0 Posts
Exactly what I was looking for, thank you!
Any thoughts on upping the timing 2*? I have the 24* box, giving me 36* all in, provided no one changed it over the years, no reason to think anyone did. I feel I slight surge at around 3700rpm so I'm assuming that's because it goes all in there.
thanks!
--clawless
Any thoughts on upping the timing 2*? I have the 24* box, giving me 36* all in, provided no one changed it over the years, no reason to think anyone did. I feel I slight surge at around 3700rpm so I'm assuming that's because it goes all in there.
thanks!
--clawless
08-25-2015, 04:20 PM
#4
Charter Member # 55
Charter Member
No reason to increase it and no gains to be had running 36* on a stock 454Mag.
The module you listed has 24* of advance. Leave it at 10* base timing for a total of 34*
That surge is probably the secondaries on your carb opening. The timing advance increases in small increments every 100rpms from 1000rpms to 3700rpms.
The module you listed has 24* of advance. Leave it at 10* base timing for a total of 34*
That surge is probably the secondaries on your carb opening. The timing advance increases in small increments every 100rpms from 1000rpms to 3700rpms.
08-26-2015, 07:17 AM
#7
Registered
Thread Starter
Join Date: Jun 2013
Posts: 6
Likes: 0
Received 0 Likes
on
0 Posts
OK ill stick with the 10*.
Unfortunately the three marinas around me only have E10, closest one with 100% is kinda far but on the way when I take long weekend trip, they are starting to get to know me
I swapped a bad 330 for the 370 of the same year range, was the 370 not considered the mag?
--clawless
Unfortunately the three marinas around me only have E10, closest one with 100% is kinda far but on the way when I take long weekend trip, they are starting to get to know me
I swapped a bad 330 for the 370 of the same year range, was the 370 not considered the mag?
--clawless
Last edited by clawless; 08-26-2015 at 07:31 AM.
08-27-2015, 12:23 AM
#8
Registered
370 Cyclone was made 1978-1987. Others in it's family were the 400-420-440-460 Cyclones. Does the guy got any more he wants to trade for junk 330's!!!
Last edited by picklenjim; 08-27-2015 at 02:29 AM.
08-27-2015, 07:22 AM
#9
Registered
Thread Starter
Join Date: Jun 2013
Posts: 6
Likes: 0
Received 0 Likes
on
0 Posts
Ok Cyclone it is!
Sorry, by swapped I mean replaced a shot 330 with a fresh rebuilt 370. Everything transferred over except the intake. The power steering bracket had to have its holes made bigger. Also had to tweak the carb, I found the original internal setup on here I believe. This is the engine the boat should have had to begin with.
--clawless
Sorry, by swapped I mean replaced a shot 330 with a fresh rebuilt 370. Everything transferred over except the intake. The power steering bracket had to have its holes made bigger. Also had to tweak the carb, I found the original internal setup on here I believe. This is the engine the boat should have had to begin with.
--clawless
Last edited by clawless; 08-27-2015 at 07:36 AM.
