WHAT WAS THE DOWNFALL OF THE 3.4/300 MERC??

[Instigator]

Anybody know the inside poop on that motor??
I believe it was a Cosworth block that was cast in England.
How close did it actually come to 300 HP's?? And why did it die??
All of a sudden I'm starting to see these things turning up for sale and wonder if it would'nt make a neat project for one of you Merc guys??
Just curious.
Instigator

[Raceman]

They were basically work horses that people tried to make into race horses. They were good engines when treated properly although the early gearcases weren't up to the task. Only the later 3.4 was the Cosworth block, early ones all Merc. The T4 and 3.4 High perf longshaft had an undeserved bad rep as a grenade. When the T4's were run on sprint boats and turned relatively hard for a big motor, there were some upper bearing issues, but they could have probably been solved. I've got an old carb 300 hp 3.4 on a 26' deckboat and it's been flawless. I've been hopin' for several years the damn thing'd blow so I'd have a good excuse to stick one of the EFI powerheads on. The 3.4's were also available as 275's and I've been told 250's also, but I've never seen one. They are heavy and they are thirsty.

[22VelocityProMax300]

I ran a 300hp 3.4 for 10 yrs on my 22 Velocity with relatively few problems other than normal maintenance.My biggest headache was trying to find parts for it.the six carbs could sometime act up in real hot weather.For one season I ran one of the 3.4's with the EFI units.Great top speed,However with a 16 amp alternator I barely had enough amps to run the electric fuel pump and ecu box.I was fortunate I had Gene Treichel of G Force technology work with me to dial in that engine.He was with Merc Hi performance originally and he built the motor.It was a cool experience.

[jimmyb]

raceman did a great sum up of the motor...

It was definately a big motor and it ran well in race form... it was mercury's response to OMC's V-8

wasnt there a max displacement rule or something that was put into effect for tunnel boats or something that finally killed the 3.4L race motor?

[Instigator]

I thought they were in response to the V-8's but seemd like they dissapeared about as fast as they arrived?
Anybody know how many years of production??
Saw a guy locally, last season that had a 24' (I think) Mate with a 3.4 275 that was all original! He said never been down, and I believe was one of the Cosworth blocks.
Just thought their would have been enough market to keep it around if it ever got dialed in??
Were'nt they close to the weight of the V-8 as well??
Almost think they would be rare enough to add to a collection??

[yellowallison]

Both L-25" good condition. Let me know if anyone is interested!!

[Firestarter]

22 VelocityProMax300, I am curious as to the performance difference between the olds and new.

RT

[22VelocityProMax300]

Firewalker,the old stock 3.4 litre 300hp merc,the fastest speed that I ever ran with my Velocity was 81 mph on Lake Winneabago.Jim Merten Jr drove it using one of his own 28" 4blade cleavers.Just like his famous father,Jim jr.can really drive a boat,It took me about two more years and bigger Kahunas to reach his numbers. The 350 Hp EFI motor ran 85 mph at 6400 rpms.I may mentioned before,according to Gene Treichel,Mercury only made about 10 of the 350 efi,s.I was able last summer to get 84mph out of my current pro max 300.using a 27"spinelli.Mercury racing currently is using a Velocity 22 as a test mule,with a 300x on it.I talked last week with the Merc engineer that is using it.He is using a 24"Trophy turning 6900RPMS at 76MPH.They are not trying to pull top speed figures but rather various other tests.Mercs boat has no setback.It needs at least 12" and a 26"Trophy.I am running about 400lbs lighter with the layup on my 22.Sorry for the long post.

[Raceman]

You were out abusing that T4 powerhead like that before you sold it to me huh?????? I think you told me you only used it to get back and forth to church on Sundays.

[22VelocityProMax300]

Hey Norris,good to hear from you again. Merten and I were trying to make a church service on the other side of the lake.Didn't want to miss the collection ya know!!If you get the chance,I don't have a picture of that t-4 block. I have had a few of my friends asked what it looked like.The only pictures I have is with the stock 300 cowling on.Thanks Frank