6.2 Merc modifications
 

I'm in the process of modifying a 6.2 Merc Smartcraft engine for a customer. I thought I'd share some of what I've learned so far. It has a standard 2 bolt 5.7L block, GM powdered metal rods and an internally balanced forged crank. Not knowing what cam was in it, I measured it before disassembly. It is a hydraulic roller with the exact same specs as the Crane 104224 cam. 214/220 duration @ .050, .452/.465 lift. I have used this cam a lot in 5.7 and it works really well. I'll be stepping up to a little bigger cam for this engine. It has the Motorola ECU and uses a Hall Effect crank trigger. The distributor housing is made of plastic and it uses a rally trick flat distributor cap. I'm replacing the Merc EFI with an aftermarket system and FAST ECU. This, along with larger valves, some port work and headers should wake this engine up quite a bit. I'll post the results when finished.

Bob

Thanks for the info...
 

I was at Mercruiser school when the engine was new and they gave me a new products info book (printed in January 2001). I didn't have the camshaft specs, so thanks for posting them.
I will list the important things that are in the book;

4340 forged steel crankshaft, Kellogg forging machined by Lunati.
Special main and rod bearings are required because of the larger fillet on the main and rod journals.
Single groove crank key and single key.
The powder forged connecting rod is machined for camshaft clearance.
A special chamfered connecting rod nut is used for block clearance. Nut torque is 36 foot pounds.
Compression ratio is 9.0:1.
Sincerely
Dennis Moore

Be sure to post results, thanks Dwight

What are you replacing the merc stuff with? Thanks

I will be using a single plane 4 bbl. type intake with a 1200 CFM throttle body. Similar to the Holley commander 950 system. I'll use the existing Merc fuel pump system, 40 lb injectors and the Speed Pro - FAST ECU and wide band 02 sensor. The merc intake system is designed for low end torque and doesn't flow but about 600 CFM, so it can't support any real HP increases.

What will this cost and expected output verses putting on a Whipple?

Interesting question Marty. We had originally ordered a Whipple. But midway through the process found out that they had not sorted out the program for the Motorola ECU and it would be some time before it was available. So we cancelled the order and went to plan "B". I anticipate about 450 HP from this setup, opposed to 500+ with the Whipple. Cost is going to be similar. Seems to me the Whipple would be a better choice. However, it wasn't available at this time, and the customer decided he wanted to stay naturally aspirated...so here we go.

How will you utilize the O2 sensor with the water cooled exhaust? Is the mercruiser ignition set up adapted to the new processor? Sorry for all the ?s but I have been waiting for someone to take on a project like this. Thanks Dwight

There is a risk of water on the 02 sensor. You need to mount it in the top of the riser. There are several folks that have been running them successfully for quite a while now. The main use is for initial tuning. Once you get the base map just right the 02 sensor will be doing very little correction, so you could really do away with it. The intake is a Vortec intake. Holley also makes a Vortec EFI intake. The ECU is being set up specifically for the hall effect crank trigger and coil used on the 6.2.

Thanks for the info. By any chance are you going to run an oil cooler?. I was told that it is a very good idea to install one on this engine. I was wondering if the O2 is even needed with the map and coolant temp sensors. Is the fuel delivery going to be a throllte body injection or are you staying with port injection? Thanks again Dwight

Is the boat a 292 Formula? I read where someone was going to whipple one with the 6.2's.

It is a multiport fuel system. With the 02 sensor you can define the desired A/F ratio and it will correct to that reading. If the base map is right-on then the 02 sensor won't be doing much correction. But, it will give you the ability to get the map really close. As far as an oil cooler we don't have one planned for this boat. He runs on a small lake and will never see long hard runs. It is good insurance though. I may try to talk him into adding one.
Glad you brought it up.

You can put the desired mixture in and, the computer will adjust to it... I like that. Do you have any recommendations for an oil cooler? also what exhaust are you going to run? thanks Dwight

I can not remember all the answers to all of the ?s I had on this subject. I know I should have printed ot off.. What exhaust system are you going to use? Also was there any mods to the current system that you could see helping out? Thanks Dwight.

Whitey, we're using the Stainless Marine exhaust. I'm using a Comp Cams hydraulic roller, 218/224 duration @ .050. Quite a bit of port work and 2.02/1.60 valves for the Vortec heads. It should be pretty healthy once we're finished.

Bob

The cam does not sound allot bigger than the one in there already, does it have a much larger lift? I was also wondering why you did not go the carb route? I am a big fan of fuel injection but it seems as of right now, it is easier to make mods with the carb set ups. Dwight

Keep in mind I'm doing this for a customer. This is what he wanted and was willing to pay for. I would have gone to a carburetor myself and kept the EFI to reinstall later. Same on the cam. This is a family runabout and he requires a smooth idle. Any bigger cam would get lumpy. It leaves me in a dfficult situation of getting the package just right. He wants the HP, but none of the negative side effects of a modified engine. That's where a supercharger would normally be a better alternative.

I mentioned somewhere that a buddy of mine has his 292 formula at Hawkeye Marine in Dubuge IA getting Prochargers put on it.

Brian

I'd be very interested in how it turns out. Keep us posted.

bobl,
What type of set up would you personally do? Dwight

Once Whipple gets their system fully tested and a few in the field, that would be my first choice. I'm not crazy about procharger up to this point. Depends on how they do the fuel system in my mind. Just raising the fuel pressure like they were doing on the 454/502 setups is not a good method. Since Dustin is the only one that can reprogram the PCM555 ECU, I'm not sure how procharger is doing it. The engine I'm putting together will be a very dependable, good performer. It just won't make as much HP as a supercharger. Now, if you put the Whipple on with the modifications I'm doing you'd get some serious HP! Give me a few weeks and I'll post my results on this engine.

Bob

Thanks Bob I look forward to hearing about the results.