350 LOSS OF POWER

[LANCLJ]

I replaced my exhaust manifolds this past Spring, using the GLM manifolds with the matching 4" risers. I also went with thru-hull tips (internal and external flaps) for an additional power gain.<br /> Sad to say, that power output actually went DOWN after the exhaust changes. Now I know I was giving up some bottom end torque for the horsepower gain with the straight-thru open exhaust, but my results are terrible!<br /> Engine is a 350 Vortec, with an Edelbrock Performer air gap aluminum manifold, Edelbrock performer 600 cfm carb, Thunderbolt IV ignition. <br /> All engine adjustments are right on the money, carb, timing, advance, everything. WOT is all the way down to 3200 RPM, a drop of over 1,000 RPM. Boat has no bottom end jump or top end speed. <br /> ANY SUGGESTIONS ???

 

[Haut Medoc]

Re: 350 LOSS OF POWER

Welcome to iboats It sounds like you may have an exhaust restriction somehow....I would go through the system is see if your flappers are not opening fully........JK

 

[Bondo]

Re: 350 LOSS OF POWER

All engine adjustments are right on the money, carb, timing, advance, everything. WOT is all the way down to 3200 RPM

Well,............<br />Something is Obviously Not right on the money..................<br /><br />When was the Intake,+ Carb. added,.????<br /> <br />Was it at the Same time as the Exhaust,.????<br /><br />If Not,....... Did the motor make Good Power before the Pipes were added,.????<br /><br />The reasons I ask,.......<br />The Air-Gap manifold Isn't the best choice for the Vortec, In a Boat.........<br /><br />Was the Carb. Retuned for the new exhaust,.???<br /><br />If Not,...... That's where I Think things are Not on the money..................

 

[LANCLJ]

Re: 350 LOSS OF POWER

Yes, the flaps are working. (If the flaps were stuck, it wouldn't run at all, nor would it flow any water!).

 

[Bondo]

Re: 350 LOSS OF POWER

Originally posted by LANCLJ:<br /> Yes, the flaps are working. (If the flaps were stuck, it wouldn't run at all, nor would it flow any water!).

What About,.....<br />

Originally posted by Bondo:<br />

<br />When was the Intake,+ Carb. added,.????<br /> <br />Was it at the Same time as the Exhaust,.????<br /><br />If Not,....... Did the motor make Good Power before the Pipes were added,.????<br /><br />Was the Carb. Retuned for the new exhaust,.???<br />

 

[Haut Medoc]

Re: 350 LOSS OF POWER

Partially stuck would stiil give you a restriction.....JK If it's not that then look at Bondo's reply....Something is obviously not on the money....JK

 

[LANCLJ]

Re: 350 LOSS OF POWER

TO BONDO,<br /><br /> Everything was in place and ran great prior to exhaust change. I'm puting the exhaust back thru the prop, to see what happens. I'm thinking that maybe I gave up too much torque to spin the prop (21 pitch Stainless Mirage). Very frustrating.

 

[Bondo]

Re: 350 LOSS OF POWER

If you haven't Retuned the Carb. to compensate for the freer flowing exhaust,..........<br /><br />You're Probably running Lean,.. Atleast part way thru the rpm band,......<br />Maybe running Lean from Idle to WOT,.........<br /><br />I'm just trying to help you out here,......<br /><br />You asked the Question,.......<br />We answered with Questions,.......<br /><br />If We all work together here,.......Maybe,.....<br />Just Maybe,......<br />You'll get the Answers You Need............<br /><br />You Don't have to Yell to Me,.......... Just post the required Info,+ Somebody will have an Answer,............<br /><br />If You don't care for My Style,.... You Won't be the 1st,... And,.. I'll leave you to your Miseries........No Problem.............<br /><br />BTW,...... Welcome to the forums here at iboats.com....................

 

[LANCLJ]

Re: 350 LOSS OF POWER

TO BONDO:<br /><br /> Who's yelling ?????????????????? All I'm doing is replying back to your post where you asked if all the changes were made at once. Am I missing something here ?????????????

 

[tommays]

Re: 350 LOSS OF POWER

the CAPS is yelling in the internet world (TO BONDO)<br /><br /><br />tommays

 

[LANCLJ]

Re: 350 LOSS OF POWER

I don't know why this needs an explanation, but here goes:<br /><br />"TO BONDO" is nothing more than topic of my post, hence the caps. I put it there to make it obvious that I was replying directly "TO BONDO" with clarifcation to the solutions he was suggesting, and not to the general public.<br /><br />If I was "yelling", then wouldn't the entire message be in caps??????????????????<br /><br />If anyone is offended that I "yelled" out someone's name at the top of the post, sorry. I'll try to be more "sensative".<br /><br />... just looking for suggestions in getting the engine running properly. That's all.

 

[Bondo]

Re: 350 LOSS OF POWER

No harm done,+ No offence taken,........<br />So,..... In order to Fix your Issues,......<br />

If you haven't Retuned the Carb. to compensate for the freer flowing exhaust,..........<br /><br />You're Probably running Lean,.. Atleast part way thru the rpm band,......<br />Maybe running Lean from Idle to WOT,.........<br />

Just adding thru-hull pipes will Not reduce the Torque available to your prop,.........<br /><br />We're just trying to Find Why you can t make the power you were making,......<br />You don't have to address Any Answers to Just Me,..... This is a Forum,... Some of Us have to root out the Required Information so that Everybody, or Anybody can come up with a Reasonable Answer to Why you Can't Make Power...........<br />There are Many Great Techs that hang out here,+ are of the Highest Caliber,.....<br />And,... Ayuh,... I'm Not 1 of them,......<br />I'm just a pretty handy old Motorhead who's been playing with SBCs for Years,.........<br />I'm trying to get More Info from You,.. So They can Help You......<br /><br />If you want to switch your pipes back,... That's Fine.......<br /><br />If you'd like to Diagnois the Issue,+ Fix It,......<br />Then you've got to Help Us out,+ Provide the requested Info.............<br /><br />Anyway,...... I'll move on now,...... FreebeTony Needs My help with his Vortec Buildup........ <br /><br />Good Luck.........

 

[kenimpzoom]

Re: 350 LOSS OF POWER

Check the easy things first, was the throttle cable adjusted when changing manifolds? Are you sure you are getting WOT?<br /><br />What was the elapsed time between when it ran correctly and when it ran poorly? Did the boat sit a while? Anything else at all changed?<br /><br />Changing exhaust shouldnt make this big of a difference, something is really not right.<br /><br />Check you manifold vacuum while running. Also, are you certain the timing is advancing correctly?<br /><br />Are you sure you didnt damage a spark plug or plug wire when changing manifolds?<br /><br />Ken

 

[FreeBeeTony]

Re: 350 LOSS OF POWER

Hey Bondo........thanks for the honorable mention......glad I am in your toughts.<br /><br />Lanclj......just an observation........these guys ae the best on here (Bondo included).<br />I can't tell you how much help I have reveived and how much I have learned from this forum.<br /><br />You have to give as much info as you can and be as accurate as you can. Take it from me.....it can get very frustrating for both sides (you and the guy trying to help you) to try and pin down a problem......<br /><br />My 5.7 wouldn't go past 3200 RPM's either.....these guys will stick with you if you want them to. I have been working on my problem since June!<br /><br />My suggestion would be to make sure all 8 cylinders are firing when you are up at ~3000RPM's (under load). You could pull 1 plug wire at a time with a pair of insulated pliers to make sure its contributing.......

 

[rbezdon]

Re: 350 LOSS OF POWER

Tony, turely spoken from the voice of experience!!

 

[LANCLJ]

Re: 350 LOSS OF POWER

(NO HEADING) <br /><br />Believe me, I've been reading the posts on this board for months, making note of other peoples' similar situations and what worked for them. Only posted myself after running out of options.<br /><br /> Checked all the obvious culprits: <br />1. No exhaust restrictions.<br />2. Butterflies fully opening.<br />3. Advance in by +- 2,100 rpm.<br />4. Rpm's shoot right up in neutral and on land.<br />5. Plugs all good. No fouling.<br />6. No fuel delivery porblems.<br /><br />Considering yanking the carb and sending it out for a makeover. With the ignition checking out O.K. it leaves the carb as my only suspect.<br /><br />Since the problem shows itself only under load, it makes it a little "difficult" troubleshooting while moving along at 30 mph with the hatch open, which is what we've been trying to do.<br /><br />....going to attack it again this weekend. Want to get it fiqured out before it comes out of the water for the winter.

 

[Haut Medoc]

Re: 350 LOSS OF POWER

I would do a compression test now.....The engine will rev. up all day long in neutral but ....Under load is a whole different ball game, and if it performs well there....A leakdown test.....But first I would put a vacuum gauge on it....Easy test, and you can learn alot from the readings......JK

 

[FreeBeeTony]

Re: 350 LOSS OF POWER

I hate to say this.......but it sound too familiar to me.<br /><br />Go back and read my posts.......<br /><br />Check for cylinder contribution as I suggested above. At least then you will know all 8 are firing.<br /><br />Good luck<br /><br />The vaccum gauge is a very powerful and cheap tool.......