mercruiser 7.4l mpi crank position sensor

[cnotecherry]

You think I will loose torque I thought I would gane there is about 30% more air flow compared to stock either way I think it is a better set up for marine I should be pushing some pretty high numbers with the edlebrock heads and high comp pistons anyway

 

[alldodge]

Currently having my 502 built by Young Performance, and was planning on going with the holley efi system, then Eddie Young said if I did I would loose some low end torque, but would increase high end HP at WOT. My cruiser weights in at 10K+ so I need the torque to get me up, don't need more speed. You should gain some HP with your setup

 

[cnotecherry]

I think I will have plenty of get up for my 24ft 5000lbs so the high end power might be better for me anyway cant wait to dyno this thing and see what its pushing

 

[alldodge]

I think I will have plenty of get up for my 24ft 5000lbs so the high end power might be better for me anyway cant wait to dyno this thing and see what its pushing

Totally agree :thumb: and if it's in the budget add some bungs in the exhaust tubes and retune your ECM for optimum power

 

[cnotecherry]

Nothing is really in the budget but I do it anyway Bring On Another Thousand how do you retune the ECM is it done on the dyno is it expensive?

 

[alldodge]

Nothing is really in the budget but I do it anyway Bring On Another Thousand how do you retune the ECM is it done on the dyno is it expensive?

Any laptop can retune the ECM with the MEFI burn software (Mefiburn.com and Mefituning.com and others). Dyno time is a bit high but you can really see how changes effect the over all power curve. It would be worth asking around your area to see what it would cost and if the tuning is available.

 

[alldodge]

BTW what are the new stuff your building the engine with? Edelbrock head part numbers, piston type part numbers and any other items not stock?

 

[cnotecherry]

Elelbrock marine performer rpm heads 110cc chambers part # 61459 with 10cc domed pistons about 9.5/1 comp ratio bored .03 over new but stock mercruiser camshaft I wanted to go a bit bigger camshaft but was told it would not work with the ECM new but stock rods and stock crankshaft after I put my aluminum exhaust and water pump on I probably shaved 150lbs off and the engine shop predicted 430hp 450 ftlbs but I think there a little high how are you building your 502?

 

[alldodge]

I'm coming up with a compression ratio of 9.64
Rod length 6.135
Stroke 4.00
Bore 4.280 (bored .030)
Deck height 9.78 true (spec 9.8)
4/2= 2 , 2+6.135= 8.135 , 9.78-8.135= 1.645 Deck height

Dome pistons -10.00 volume, compression height 1.645
Head gasket 0.039

Now I am using the 1.645 piston compression height because I don't know the piston part numbers your using. If your height is different your compression will be different. Same goes with the .039 head gasket I am assuming your using.

I have built all my engines until this one. Decided to let the professional do this one to see how it goes. Here is my thread
http://forums.iboats.com/forum/engi...129-formula-27pc-complete-power-plant-rebuild

Keeping the heads, intake (but modifying), crank and valves, everything else is being replaced. Only reason keeping the valves is I replaced them a few years ago with Inconel.

 

[cnotecherry]

Yes your calculation is corect Im suprised your keeping your heads how much to modify them? I thought it was cheaper to just buy out of the box bolt ons not to mention wieght reduction and being able to go with a higher comp ratio how are you going to get 500 hp? Big cam and retune the ECM? I thought you couldnt go to big of cam lift because of sucking in water or can you go big lift and les duration what are your cam specs and comp ratio going to be

 

[alldodge]

Yes your calculation is corect Im suprised your keeping your heads how much to modify them? I thought it was cheaper to just buy out of the box bolt ons not to mention wieght reduction and being able to go with a higher comp ratio how are you going to get 500 hp? Big cam and retune the ECM? I thought you couldnt go to big of cam lift because of sucking in water or can you go big lift and les duration what are your cam specs and comp ratio going to be

You can get high compression out of cast iron about as easy as aluminum. The plus on cast is it is more durable in a marine environment, even more so with open cooling. Unless your building something which requires more air flow then cast is the way to go. Compression builds by decreasing head gasket thickness. shaving the head, reducing deck height, piston volume and bore. Easiest way to build HP is increase compression but the other side is the cam.

Your previous post shows your using oval port heads instead of rectangular port, so your keeping air flow down. You could have gone with rectangular port heads and eased air flow. With remaping the ECM you could go with putting 502 heads on your 454.

My build should come in between 500 and 525HP (started as 415). The cam will be custom grind higher lift and less duration, and since I'm not running dry exhaust we cannot get to wild with duration so reversion should not be an issue. I'm going from a MEFI1 to MEFI3 ECM, intake top portion of runners cut down, fuel rail will be custom modified with return line to tank. Number 7 injector will be opened up and the VST will be changed out for cool fuel.

 

[cnotecherry]

I know you can get high compression with cast heads I was told it was not good because of detonation because cast doesnt dissipate the heat as well as aluminum. I went with oval ports because there flow was more than I needed and was planning on using the stock intake and rectangle heads dont go with oval intake I believe it works the other way around though

 

[alldodge]

Detonation is mitigated by quench and keeping it around .040 for the most part. I'm by no means an expert, that's why I decided to let a professional do my engine for me this go round. Eddie could have decided to use iron or aluminum and it would be OK with me, he chose to use iron and explained why. Boat different then cars in temps and enviroment
http://www.hotrod.com/how-to/engine/1311-ideal-quench-height/

 

[cnotecherry]

Alldodge so I am having problems with my idle again the IAC doesnt seem to be closing as much as it should its idleing at 8-900 rpm and timing is 8-10* retarted when put my finger over the idle air intake it goes down to 600 and the timing is 8-10* BTDC is this something that you retune the ECM to or is it a vacuum problem I dont see how I could have a leak its a new IAC and it bottems out fully closed and resets when I turn the key off like it should but doesnt close enough when idleing I thought the ECM would just close it on its own

 

[alldodge]

Is your timing set correctly, meaning, was set at 8 BTDC while in base timing mode?
Have you measured your vacuum, and if so what is it?
http://www.northerntool.com/shop/to...Ux8jEDcpLjqoZk7vR7kdbJj-wT0iBoT27RxoCc1rw_wcB

The ECM would not be retuned to fix the idle issue, and the ECM with the IAC does control the idle.
It was idling fine and now the idle has increased , correct?

 

[cnotecherry]

Yes the timing was set properly I have not checked vacuum presure I do not have a gauge I think I will go grab one right now but wont I get a faulse reading because my IAC is not working properly could it be my TPS maybe teling the ECM I am throttled up a bit does the IAC open or closed when throttle up

 

[alldodge]

If your TPS has an issue then this could cause your high idle. The vacuum should still be steady and 15 in Hg or so. Trying to figure out what is happening and the only way I know of is with tests. Would be great if there was a scanner to use

 

[cnotecherry]

So just bought a vacuum gauge it reads 14-15 in-hg steady at idle I unpluged the TPS and idle went down pluged it back in and it stayed down does this reset the TPS? But my timing still seems out its still a bit retarted at idle and just backfired when I throttled up I have checked the timing a number of times in timing mode it is 8* BTDC in timing mode have you checked timing on one these engines not in timing mode at idle?

 

[alldodge]

So just bought a vacuum gauge it reads 14-15 in-hg steady at idle I unpluged the TPS and idle went down pluged it back in and it stayed down does this reset the TPS? But my timing still seems out its still a bit retarted at idle and just backfired when I throttled up I have checked the timing a number of times in timing mode it is 8* BTDC in timing mode have you checked timing on one these engines not in timing mode at idle?

The 14-15 reading for a new rebuild is low, you should be at least 15 and would feel a lot better with t least 16 at idle. A low but steady idle in most all cases is incorrect ignition timing or a vacuum leak.

Unplugging the TPS can cause other issues and cause fault codes to be set in the ECM, but this should not reset the IAC. The IAC is controlled by the ECM in taking in readings from the TPS, MAP and Temp Sensors.

 

[cnotecherry]

I dont see where I could have a vacuum leak I think it is my timing like I said earlier my timing light is an advanceible one I wonder if the advance could be out I will check all my vacuum hoses for cracks or holes to be safe other than that maybe my TB gasket