Mercury 3.4 l Formula EFI Outboard

[rdmerhar]

I consider myself lucky to find a beautiful Apache 10 meter Warrior with twin 3.4 formula EFI outboards. Did some engine repair, took off the speedmaster 14.5 x 24 props (was chewing exhaust since its conception in 1983!) and installed some 14.5 x 22 correct props (center exhaust) and went for my maiden voyage Nov. 30, 2006 on good ole lake Erie. Other than the trim gauge being reversed (thought it was going to roll over as soon as it went on plane!) I had a great first experience. Had a GPS with me that showed 49mph at 4K. Didn't dare to go any higher because I had pump gas in her and thats what the previous owners problem was, lots of detonation.

My question is, Is there any EFI buffs out there that can come up with some good recommendations other than "buy new motors, saying it politely!"

I want to know things like: Reshape combustion chamber to this volume and that deck height and this squish width. or You should tweek this or that, reprogram the blackbox, make this modification, remove this rev limiter wire, etc.

Hope to have a lot of fun this summer with the new toy and hope everyone is going to do the same!

I own a small Marina in Rocky River, OH called Rocky River Bridge Docks and there always a free visitor dock waiting for you if you mention you saw this on Scream and Fly! We have a starter site up at www.bridgedocks.com (Now just parts and accessories since closing the marina in 2014) An e-mail I can be reached at is rick@accu-mix.com

Hope to hear from you, about visitor questions and mainly how to keep my engine covers on all year!

Rick Merhar 1-440-356-1202

[mercpunk]

3.4 efi's are rare but apperantely not as rare as i thought there isn't that many out there so advice might be slender If I am right there were only six 3.4 EFI's everbuilt goodluck with them .

[Raceman]

3.4 efi's are rare but apperantely not as rare as i thought there isn't that many out there so advice might be slender If I am right there were only six 3.4 EFI's everbuilt goodluck with them .

There were a couple of configurations of 3.4's with EFI. There was the 3.4 EFI, which it sounds like is the case here. It wasn't common, but not ultra rare either, and could be ordered from High Perf without a lot of restriction. These engines were available 20" and presumably in 25" also, although I've never seen an XL version. They had throttle adjusted timing, a shiftable gearcase (same as the std. 3.4 gearcase), and the large diameter alum. flywheel and Ford passenger car starter just like the std. 3.4. They were steel sleeved however as opposed to the chrome bore of the std. 3.4. The engine that's probably being confused here as being so rare is the T4. Some people have said that there were only about 8 T4's built, but I believe there were more. There was an unlimited boat built with three of em, (Texoma) and in 1978 Merc showed at St. Louis with either 2 or 3 team boats fitted with em. They had an EFI powerhead also, but had a small alum. flyweel like the other V6 Mercs and a std outboard starter rather than the huge Ford piece. The flywheel is the easy way to spot the T4 compared to the 3.4 EFI. Also, the T4 had the timing locked just like all of Merc's V6 engines that were factory equipped with Speedmasters and were on a 12" Champ mid, similar in dimension to the Champ stuff of today. The Speedmaster, a #8 was specific to this engine. Both the 3.4 EFI and the T4 had lift off one piece cowls as opposed to the clamshells on all the other 3.4's.

I have multipe T4 AND 3.4 EFI powerheads and also own the one that someone referred to as being on the 22velocity300promax boat. I bought that powerhead when Frank put a Promax on that boat, probably 5 or 6 years ago. The one on that particular boat was actually a factory T4 Powerhead that had been converted with adjustable timing and some other mods to regular 3.4 EFI specs.

Gene Triechel at G Force Technology was working at Merc High Performance during the T4 program and is knowledgeable on the engines. (disclaimer: I haven't had pleasant experiences in my dealings with Gene and would recommend his services be limited to advice, rather than actual work on an engine). I believe that John Sherlock, who posts here regularly as Sherlock would be a good source of recommending someone who could offer sound advice on running the engines on pump gas. I don't think you'll find re-contouring the combustion chambers to anything other than hemispherical shape to be a worthwhile mod, but would think that putting std. 3.4 heads on the engine might give you a pump gas friendly compression ratio. I'd guess the heads wouldn't be hard to find, but I don't know about availabilty of head gaskets. A lot of the 3.4 stuff has been NLA from Merc for a long time. A couple more things............ the engines are VERY dependable when used within their design limits, but if you try to twist em you'll grenade em. Otherwise, I think the gearcases are the weak links. Also, the 3.4EFI and T4 are steel sleeved as opposed to chrome bore, and the rings for them are non-existant as far as I've been able to tell for at least the last 10 years. I have another powerhead that's scattered that would be another complete drop on if I could find rings for it.

[mercpunk]

Raceman You Are Right I Did Have The T4 And 3.4 Efi Mixed Up Thanks For Clearing It Up And Explaining It Better. As Far As Head Gaskets I Think They Are Still Produced In Aftermarket.and Rings I Have Only Been Aware Are For Chrome

[rdmerhar]

Your right on the money with that great explanation of T4 vs. EFI. I actually have one T4 on the Starboard. Is that smaller flywheel actually the same as other models? Its machined down with a smaller ring gear, starter mounts are hand fabricated, welded on to the block, very nice to see this workmanship, almost hand-made. I've been so busy with the Marina I haven't had time to have fun, YET! A little more experience and reading my post about chopping exhaust, well now I know about venting, slip and other prop facts. I was having some problems getting on plane with the 22P standard props, hit around 8K in my cavitation frenzy. Ended up twisting the prop shaft and the drive shaft! Trying to get a fresh one on this week to test my new 28P Bravo Ones, should go real good. Wish I got right back to you, would like to talk about picking up some spare parts if you'll let them go.

[Raceman]

I'm still curious about exactly what your engine is. In the first post you said "removed Speedmaster" and something about center exhaust. All T4's had the champ/formula 1 length mid, which is a FULL 10 inches shorter than a 20" mid. I don't believe Merc ever sold a T4 powerhead on anything but an F1 type mid. Sure would like to see some pics of that motor.

[Dd24skater]

I used to work on that Apache in the 80's....Is it still all black? The engines were difficult to get parts for then....I can't imagine what it's like 20+ years later.

The power head covers said 3.4 EFI, but what the engines were I don't remember. The boat was rigged at a very exclusive High Performance shop so what they are exactly would require an expert.

Very cool boat!!!!!

[rdmerhar]

I'm still curious about exactly what your engine is. In the first post you said "removed Speedmaster" and something about center exhaust. All T4's had the champ/formula 1 length mid, which is a FULL 10 inches shorter than a 20" mid. I don't believe Merc ever sold a T4 powerhead on anything but an F1 type mid. Sure would like to see some pics of that motor.

[rdmerhar]

The Apache was originally fitted with the EFI Offshore units, not T4 powerheads. The T4 was found several years later and still on the 25 mid hanging on the boat, coming off soon for a go thru, hoping to hit the water soon! Here's some serial numbers from the two Ebay motors I found a few years ago, they start with what looks like T2, now isn't that confusing! Happy Easter!

[rdmerhar]

3.4 efi's are rare but apperantely not as rare as i thought there isn't that many out there so advice might be slender If I am right there were only six 3.4 EFI's everbuilt goodluck with them .

That is most likely not true that only 5 were made, if so I have all 6! Here's a pic of the T4 block showing the added finger port

[Capt.Insane-o]

You are going to find parts extremely hard to find for those engines. Treat them well. Brucato could probably come up with an ecu for them. Raceman has a powerhead or two as well. That sounds like a cool find and it would be neat to see some pictures.

[Triple J]

See if you can contact 22velocity300promax via this site. He had one of those on his Velocity.

[shawnjetton]

why were ther so few produced?

[1BadAction]

T4 efi race motors are the rare motors, not the formula 3.4 efis. although there isnt many of the formulas around anymore either.

[Rajin Kajun]

I just aquired a 3.4L cozworth. It has a 25in. mid , std. lowerunit, cyl. are steal, 6 carbs. . This a strange motor! It has a red flywheel litewieght, It saids 250 on the split casing. It is a black max