engine proformance question

--------------------------------------------------------------------------------<br />1]..befor my 454bb 7.4L engine was rebuilt my vacuem guage reading was 15''+_ . now it reads 10''+_. would a hotter cam reduce vacuem ?

Re: engine proformance question

yes, it most certainly will depending on the type of cam installed. Maybe consult the cam manufacturer to see if you are inline with what they would expect.<br /><br />There may also be a vacumn leak. Possibly the carb or intake is loose?<br /><br />Justin

Re: engine proformance question

the carb rebuilder noticed every time my carbs come in, the curb idle was to far in.he said my carbs were always flowed, 20''vac. the curb idle were pre adjustment/ set by him.he said thear's a problem with the engine if i had to increase the idle.i always have to increase the idle to keep the engine runing. would the hotter cam do this as well.

Re: engine proformance question

I could be wrong....But I think that a normal vacuum reading should be 17-21# regardless.....At idle,out of gear....JK

Re: engine proformance question

Do some reading here: <br /><br /> http://www.centuryperformance.com/vacuum.asp <br /><br />It shows how to diagnose engine problems by looking at a vacuum gauge.<br /><br /> It also says "Normal reading (usually 17-22" Hg. in stock engines) Race engines vary "a lot" and in most cases will be considerably less."<br /><br />I was hoping it would say specifically that a bigger cam causes lower vacuum, but I'm pretty sure if you do some more research you will find that to be true. I believe the more radical you get with the cam, the lower the vacuum at idle.<br /><br />Regardless, if your carb guy set up the carb on the boat while running you shouldn't have to be changing anything. So It does sound like there is a vacuum leak somewhere.<br /><br />Justin

Re: engine proformance question

thanks for THE link J.J.W

Re: engine proformance question

man o, a big cam will definately give you a low vacuum. The spedifics depend on how big the cam is. Comp cams web site has a little info.

Re: engine proformance question

the cam thats in the engine right now was the original cam that came with the boat.when i had the crankshaft bearings replased i also changed to a new cam.i told the michanic to match what ever the old on was.he put in a comp cam 1000 to 5000 rpm marine.the engine proformance was never the same . that is where the 15'' of vacuem came from. now this last rebuild i told him to put back the original cam the engine came with ,the old cam was fine he said, now my vacuem reading is 10''.i never checked the vaccum when i first got the boat so i dont know what the readings should be.

Re: engine proformance question

2] how would the engine preform if water was driping into #5 the exhaust manifold?..... Would i hear a popping /clack,clack noise coming from the exhaust? <br /><br /> 3]my rubber booth that goes to the spark plug was touching the exhaust manifold,the booth split right up, exposing the metal lick clamp to the plug, the clamp was grounding on the manifold.would that hinder the proformance.<br /><br />when im done fixing this boat ill be a pro and move to ALASKA.

Re: engine proformance question

Man o war, I can not believe the fundamental and simple problems you keep finding. To find the plug issue after 3 and now 4 complete rebuilds is unbelievable. YES, a grounded plug will hurt performance. The 8 cylinder engine is running on 7. YES, the low vacuum is bad. It is possible it is your intake then. Read my post on your intake 2 mm shift. This would create such a poor vacuum condition I would be surprised if the boat ran at all, let alone idle. Now on top of that it had only 7 active spark plugs. I am amazed you ever got it started and idle enough to get in gear let alone get on plane. By the way, the grounded plug can not contribute to gas in the oil.

Re: engine proformance question

unless that's a typo, a non-firing cylinder (caused by a grounded sparkplug wire) will contribute to gas in the oil. The cylinder isn't firing and is sucking in and expelling raw fuel, it will wash down the cylinder and get past the rings and into the crankcase.<br /><br />Dropping a cylinder on a big v-8 at no load and not at real low rpms, say > 800, can be not that noticeable so it probably isn't and should not be the cause of a 10" vacuum reading.<br /><br />First check the obvious, then figure out if the cam was degreed properly. That can be a cause of poor vacuum reading and may even require carb adjustment to maintain idle. Depending on the integreity of your mechanic that info, or mistake as it may be, can be covered up if you just ask him to check it during the teardown. But in answer to your question, yes camshafts (hot cams) which are designed for power at high rpm, typically have poor vacuum at idle and require more air at idle by either adjusting the idle set screw to open the throttle blades more, or by drilling holes in the throttle blades.<br />I don't have specific knowledge as to what cam specs and cam timing give what idle performance and expected vacuum readings, a google or visit a camshaft website would give you the best idea.

Re: engine proformance question

man-o war, get this for your mechanic. Teaches how to set up (degree) the cam and properly install it.<br /><br /> http://www.powerandperformancenews.com/store/merchant.mvc?Screen=PROD&Product_Code=190&Store_Code=CC

Re: engine proformance question

i did ok removing and installing the heads on the engine ''LAST WEEK SATURDAY''at night after the michanic re sealed the valves. 1 or 2 mistakes .I did drill that hole in the throttle plate A VERY SMALL HOLE.ill start the engine tomorrow to see if the idle problem is fixed.is it ok to run a PVC system with a proformance cam?