Monz

Hi!

I have a carburated (Q-jet) 350 Mag and having some trouble finding the specifications for this engine. The engine is from around 1988.

How much hp does it produce in stock configuration (at what rpm)? Is it supposed to use through transom exhaust?

Do all carbed Magnums have roller cams and lifters?

Should the flame arrestor be bigger or higher on the Magnum than on the std 260 hp?

The ignition module is the old type aluminium box, but I can’t find any id code on it. What is the most likely total advance this module will give?

How many degrees advance should the ignition have at idle? It’s set at 10 degrees now.

I would appreciate any information!

Iggy

I have the same engine.
I'll try to answer your questions.

Mine is a 1988 350 MAG
All information given will pertain to my engine.

HP is 270

Max RPM is 4200-4600

Exhaust? I doubt every application had thru hull. Mine does.

Roller cam? Maybe, some do some don't. 1988 was a transition year from flat to roller lifters. It depends on when in 1988 it was built. The engine block is a roller type.

Larger flame arrestor? Don't know. Mine is as big around as the carb it self.
As for height, all 350 MAGs use a cast iron version of the high rise 1969 Z-28 intake manifold. It would be higher than a "standard" 350 engine. Cast into the intake on top of the front runner is the GM part number. The high rise part number is 14096242. Look to see if it matches.

Your ignition sounds like an older type. Mine has the small black module mounted on the exhaust riser.
Are there any markings on the box at all?
Maybe some one can enlighten us as to what type it is.

10 degrees at idle sound about right. What you should do is find what the total amount of advance is at 3000 rpm. Look for about 32-34 degrees. You'll need a timing light with an advance function or a fully degreed balancer to do it.

Hope this helps.

BAD-HABIT

I found the part# of the TBolt IV box on the underside of a yellow sticker on the box....I think it was a warning sticker of some sort...I couldn't find the number anywhere so I took off the stickers one day to re-paint the box and there the numbers were...Check on the underside of the stickers. (sounds funny I know but the numbers on mine were NOT on the box only on the sticker) I think the timing was supposed to be 8degrees....Get Denniss Moores book a.s.a.p. It will help you alot...

BH

Monz

Thanks Iggy for your answer!

270 HP is not more than 10 HP over the “standard” 5,7 L 260 hp. I’ve heard that only the high rise intake would give 15 HP. Could 270 HP be propeller shaft horsepower?

I’ll guess I have to pull a push rod and measure the length to learn if I have a roller cam. Or is there an easier way?

I know I have the high rise intake. The flame arrestor is not more than an inch high. I’ve seen arrestors that have been at least twice as high. Iggy, it would be interesting to know the height of your arrestor?

My ignition box has been painted, but I’ve tried to scratch it of. Only information so far is “Thunderbolt IV”.

Does anyone know how much torque it produces and at what rpm?

Thanks again!

jaroot

mercruiser rates their motors at the propshaft, add roughly 30 hp for crankshaft hp.

GM transitioned to roller camshaft technology in the sbc in 1987 - 88... i don't believe mercruiser made the move in the marine motor until the mid 90's.

1988 350 mag was 270 pshp

if you want to check to see if you have a roller just remove a valve cover look down past the pushrods into the lifter valley and see if it has the tiebars round the lifters and spider holding them in place... can't miss it.

Monz

Thanks guys!

//Monz

89mach1

I have an 1989 350 magnum on the air cleaner it says Lh drive, does that mean I need a LH prop. Is this a common rotation in a single engine boat? I need to re prop 24' mach 1 that is running a 14x 19 quicksilver prop and turning 6000 rpms @ 37 mph.

thanks
Bob

Scott72

My last boat had a 1988 350Mag in it. Timing on the old box was 8 degrees if I remember corectly. I've heard that the normal 260HP 350's back then are really putting out closer to 225HP.

pullmytrigger

On a Thunderbolt IV the timing is controlled by the module, the last two numbers stamped on the module will tell you how much it will advance the timing, in my case it has the 24 degree module (twin 1989 350 mags) so you add 24 to your base timing and come up with your total advance......stop what your doing and go get Dennis Moores book ,it goes through all this and how to check timing correctly and everything else..........doug