5.7 TBI build questions
I picked up a very well maintained 1997 Cobalt 20' with 180 hours on everything. Its in very good shape and everything works as it should. Right now with 4 passengers, half tank of gas and all its running gear it will top out just above 50mph at 5000rpm. The motor is a 220hp non vortec 5.7, outdrive is Alpha 1 with a 19p prop.
I would like to do some motor work on it, but the TBI has me a bit leary. Initial plans were to do a set of aluminum heads (looking at BluePrint 195cc), Comp cam xm270 cam and a dual plane intake. I'm worried about tuning TBI and it not flowing enough for the build. I spoke with Ben at MefiTuning today and was told to do a full tune in the boat would cost 1700+ or 495 for a canned tune. I contemplated tuning it myself, but I would prefer a professional to do it. 1. Am I pissing in the wind building a TBI motor? 2. Would this motor combo work well? 195cc aluminum heads, Comp Cam XM270, and a dual plane intake. 3. How are people using a TBI on an aftermarket intake, would an adapter plate work to mate the TBI to a 4brl intake? 4, Should I ditch the TBI for a Holley Sniper self tuning kit? I realize the alpha 1 is only good to 330ish hp. It will have a drive shower and high quality oils. The boat is used on small lakes in Nebraska with the occasional river run. |
I'm old school and would ditch the tbi in a second. Keep it simple....
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I like the two pumps and a shoulder roll technique. Ask my wife. :)
, , , , , , , , , , FYI: carbs usually take to quick small pumps and a shoulder roll to start cold. |
Been there done that. I switched my carbs to big block TBI units with a Holley adapter. I used a TPI ecu.
It works fine and has good fuel economy. Even with the bigger throttle bodies, I would say they are flow limited to about 330hp. If you want to make more than that, I would go with a carb or port injection. Jeff |
The e TBI is your stumbling block. It will potentially limit airflow and injector selection will be problematic. With a TBI I'd swap out to a Holley system. IF you had a MP Merc EFI setup I'd tune it myself. You are going to have to spin the motor faster for more power and thats where the TBI will hamstring you.
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Tbi is good for emissions and gas mileage. I have 2 big 2 inch 454 tbi units. Complete with injectors and the big water filled OEM adaptor to a q-jet base. If your TBI is working, you could swap throttle pos sensors and IACS and mebbe give one of these a try. I have no idea what the injectors are like. The adaptors alone sell for 50 bucks. I will do a whole tbi with adaptor for 50 plus 25 to ship it. And I will probly profit about a buck fifty on ahipping. THEN you can get hold of harris tbi chips on ebay who still does a lot of tbi Eprom work. (These ecu are really old school. But they work.) But your best bet is run it as-is till you get a better setup. Now, an alpha with power. The lighter the boat, and the longer pitch the prop, the more likely the drive will hold up. You put a 454 in a old alpha sundancer and hit the gas with a big 17 inch prop, that drive will last about 5 seconds. You got a hot 383 in that cobalt with a 25 inch prop, it doesn't have the low gear bite to snap shafts like a short pitch prop does.
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Question. Does the ecu look like a car ecu? Or sealed like marine stuff?
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Toss the TBI,. Go with an Edelbrock air gap dual plane and a 4bbl. carb.
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stock OEM back then used MEFI 1 for 1997.
Your set up is not up for making more than 300 hp Not worth spending 1000 s on. Out dated fuel delivery system and a really outdate ECM. . Stock exhaust very poor as well. The risers and the riser gasket are the exact same used on 180 / 190 hp V 6. I would play with props and weight and or take weight out of the boat. - Stock Cobalts are fairly heavy built boats. I would leave it stock And when one goes to sell a Cobalt runabout - they are worth more stock than one that's moded. Most Cobalt owners would buy anther Cobalt. |
Originally Posted by BUP
(Post 4586118)
stock OEM back then used MEFI 1 for 1997.
Your set up is not up for making more than 300 hp Not worth spending 1000 s on. Out dated fuel delivery system and a really outdate ECM. . Stock exhaust very poor as well. The risers and the riser gasket are the exact same used on 180 / 190 hp V 6. I would play with props and weight and or take weight out of the boat. - Stock Cobalts are fairly heavy built boats. I would leave it stock And when one goes to sell a Cobalt runabout - they are worth more stock than one that's moded. Most Cobalt owners would buy anther Cobalt. |
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