350 Engine advice--GOOD UPDATE!

[MikDee]

Re: 350 Engine advice

Re: 350 Engine advice

V6 Vortec: Mercruiser Service Manual #25

V8 Vortec: Mercruiser Service Manual #24

Oh Yeah?,,, What page?,,, like I have those laying around
nevermind

 

[John_S]

Re: 350 Engine advice

Re: 350 Engine advice

Lying around? No, those just take up some bits on the HD. You can view them yourself at: http://forums.iboats.com/showthread.php?t=251571

 

[MikDee]

Re: 350 Engine advice

Re: 350 Engine advice

Lying around? No, those just take up some bits on the HD. You can view them yourself at: http://forums.iboats.com/showthread.php?t=251571

Well how about that, I didn't know these were saved? I remember awhile back when it was mentioned this info disappeared from the internet. Well a Hearty belated Thanks to Don S. for archiving that great info, and a Thanks to you John for directing me to the link, I feel like a kid with a new box of toys ,,, I guess my busting on you is all in vain now :redface:

 

[MBAKER]

Re: 350 Engine advice

Re: 350 Engine advice

As far as head gaskets and pushrod lengths go....pushrod length does matter even though you have adjustment in the hydraulic lifter, any time you change the head location either through decking the block, different head gasket or milling the heads, you are 'possibly' changing the required pushrod length. That being said no more than it will change with a simple milling or decking operation, a stock pushrod will prob work, especially with a mild cam, but the best way would be to check for proper rocker geometry once the head is on and get the correct length pushrod as needed. The more you deck, mill, change gasket thickness etc, the more pronounced it will be.

 

[John_S]

Re: 350 Engine advice

Re: 350 Engine advice

mbaker,

The amount that the pushrod is seated down in the lifter stays the same. The rocker arm will need to be tighten down slightly more to get to zero lash. The stock gaskets are already rather thick, so you would be very limited in how much you could increase it, anyway. Most of the time, people are going the other way, as you mentioned milling, thinner gasket, etc to raise compression. It that case the pivot point is slightly raised. There is allot of adjustment range with the stock design. I think you are talking some radical changes before you need to change pushrod length. The rocker arm is probably not the bottleneck either, it might be the pushrod clearance in the head.

 

[MikDee]

Re: 350 Engine advice

Re: 350 Engine advice

mbaker,

The amount that the pushrod is seated down in the lifter stays the same. The rocker arm will need to be tighten down slightly more to get to zero lash. The stock gaskets are already rather thick, so you would be very limited in how much you could increase it, anyway. Most of the time, people are going the other way, as you mentioned milling, thinner gasket, etc to raise compression. It that case the pivot point is slightly raised. There is allot of adjustment range with the stock design. I think you are talking some radical changes before you need to change pushrod length. The rocker arm is probably not the bottleneck either, it might be the pushrod clearance in the head.

This was exactly my thinking as well, when I said with adjustable lifters: "Then theoretically pushrod length shouldn't really matter"

 

[MBAKER]

Re: 350 Engine advice

Re: 350 Engine advice

I know there is a lot of adjsutment in the stock pieces, but just adjusting the rocker up or down doesnt mean its right all the time. There is more to rocker geometry and pushrod length than whether or not everything just fits together. Along with the milling/decking/gaskets, how much the valves have been ground, or the seats ground etc affect how everythign goes together, and just adjusting the rocker nut as needed doesnt necessarily keep the same geometry in the valve train as it was designed for. I guess what im saying is it may work, but may not be ideal.

I agree most of the time you arent varying enough from stock, that it will probably matter. But it doesnt hurt to check. On a highly modified or race engine, it should always be checked.

 

[MBAKER]

Re: 350 Engine advice

Re: 350 Engine advice

Back to clarify my first post about the pushrod length.... post #45

It was in response to the post saying pushrod length doesnt matter with adjustable vavletrain. I agree it isnt as critical as with a non adjustable valvetrain --BUT-- my point was you wouldnt want to throw in a pushrod .050 shorter or longer than stock into the vavletrain if you didnt need it. Sure you might be able to adjust for it and get it all to fit, but it would likely have the tip of the rocker running off to one edge of the valve, or throw the rocker geometry through motion off which affects you cam lift curve.

I know nobody here was talking about changing out for non stock pushrods, but it doesnt hurt to check if you have the thing apart or changing heads, rockers etc. For all the tolerance in stock pieces, a stock pushrod will prob work most of the time, but on the other hand with all the tolerance stacked one way you never know there might be something out there that is better.

 

[MikDee]

Re: 350 Engine advice

Re: 350 Engine advice

MBAKER, Good info, point taken, you should always check!

To stroker, IMO the 252 cam is not quite enough, I recommend this cam: http://www.compcams.com/Cam_Specs/CamDetails.aspx?csid=2&sb=1

This is a mild tried, & true, proven orig. equip. hi-perf. Chevy design updated by Comp cams. It is a plug, & play bolt in, that uses all the orig. valvetrain parts with a safe amount of extra lift, and a safe amount of extra duration to make it worthwhile without going crazy, but quite a bit better then the stock "plain vanilla" http://www.compcams.com/Cam_Specs/CamDetails.aspx?csid=1&sb=1common cam (used in almost all stock chevy small blocks ) not to say this is a bad cam, it's smooth, and will provide 300hp in a 10:00X1 compression (double hump head), 4bbl, dual exhaust 327! I know I had one! But, the 151 cam above, will give you a 25hp boost, with no other changes in that same 327! So, you can guess what it'll do for your 355!

I had this 151 cam as well, in a different engine, you might find a slightly lopey idle, but it will pull strong from off idle to about 6k rpm, you'll probably have to prop down to 4600-4800rpm with it.

Heads I can't help you with, but I know the Vortecs are the best stock heads, but may require extra matching parts, or machine work to fit.

 

[n2ostroker]

Re: 350 Engine advice

Re: 350 Engine advice

Oh the choices to make. Car, boats, whatever it is I'm cursed. Just like anything , you play with it then the modifications just keep coming....


Anyway, for an update.
it was popping and backfiring real bad. Then it would smooth out, then get worse. Timing didn't matter, anywhere from 4-10btdc. It finally pulled beyond 2k rpm and I got a speed and rpm reading though it still had a backfire consistent but random if that makes any sense... Took the foil off and handling was much improved, didn't get pushed around or feel like the stern was digging in in rough water anymore. Smart tabs in my future I believe...

Don't know if I was smoking something the last weekend or if the foil caused some prop slip but this time it hit 4000rpms top rpm. Speed was 45mph on GPS. Prop is a stainless steel 15 1/4-21 pitch. That shows about 10% slip. This was trimmed out as perfect as I could get. Any higher and it would spin and loose a couple of mph. Still the whole time I was backfiring at higher rpms too. The top end test was enough to get rpms maxed and trimmed, get a reading, slow back down to not hurt anything.

Checked everything over and over. Pulled the dizzy cap and there were 4 hairline cracks going from terminal to terminal. No telling if there were more I couldn't see. Picked up a new dizzy cap and will try again this coming weekend unless I can make it before then.

About the 256 cam. I'm probably going to go with the 262 or the 270. Price is the same or close across the board. Not to knock the 151, I'm sure its a great cam for a car. But with the single pattern and looks to be 114 lobe sep I'm not putting it in my boat. There are much better choices for a marine application and Comp Cams has the xtreme marine series for a reason. Just look at the lobe differences between the 270 and the 151.
151- 342/342 -at .050" 222/222
270xm- 270/286 -at .050" 226/236

Those old muscle car cams had huge lobes. You're stick at mid/low lift a lot longer instead of getting the valve open. The roller cams get the valve open even quicker.

As for aftermarket heads, don't think I hadn't considered them. But the vortecs even after modding for higher lift I'll have a lot less money into. If I decide to keep the boat for a long time I can most likely get my money back out of the Vortecs and upgrade. I'd thought about just finding some 1.94" 76cc heads and doing some home porting and cleanup then through in a decent valve job and let it go till I decide what to do with the boat later next yr.

 

[John_S]

Re: 350 Engine advice

Re: 350 Engine advice

If the dist cap doesn't fix your popping, you can be running lean. Recommend checking for vacuum leaks and then tune carb.

 

[Uraijit]

Re: 350 Engine advice

Re: 350 Engine advice

I second that. If you're getting backfiring, your heads are not the issue. If the cap doesn't sort you out, you're running lean.

 

[MikDee]

Re: 350 Engine advice

Re: 350 Engine advice

Oh the choices to make. Car, boats, whatever it is I'm cursed. Just like anything , you play with it then the modifications just keep coming....


Anyway, for an update.
it was popping and backfiring real bad. Then it would smooth out, then get worse. Timing didn't matter, anywhere from 4-10btdc. It finally pulled beyond 2k rpm and I got a speed and rpm reading though it still had a backfire consistent but random if that makes any sense... Took the foil off and handling was much improved, didn't get pushed around or feel like the stern was digging in in rough water anymore. Smart tabs in my future I believe...

Don't know if I was smoking something the last weekend or if the foil caused some prop slip but this time it hit 4000rpms top rpm. Speed was 45mph on GPS. Prop is a stainless steel 15 1/4-21 pitch. That shows about 10% slip. This was trimmed out as perfect as I could get. Any higher and it would spin and loose a couple of mph. Still the whole time I was backfiring at higher rpms too. The top end test was enough to get rpms maxed and trimmed, get a reading, slow back down to not hurt anything.

Checked everything over and over. Pulled the dizzy cap and there were 4 hairline cracks going from terminal to terminal. No telling if there were more I couldn't see. Picked up a new dizzy cap and will try again this coming weekend unless I can make it before then.

About the 256 cam. I'm probably going to go with the 262 or the 270. Price is the same or close across the board. Not to knock the 151, I'm sure its a great cam for a car. But with the single pattern and looks to be 114 lobe sep I'm not putting it in my boat. There are much better choices for a marine application and Comp Cams has the xtreme marine series for a reason. Just look at the lobe differences between the 270 and the 151.
151- 342/342 -at .050" 222/222
270xm- 270/286 -at .050" 226/236

Those old muscle car cams had huge lobes. You're stick at mid/low lift a lot longer instead of getting the valve open. The roller cams get the valve open even quicker.

As for aftermarket heads, don't think I hadn't considered them. But the vortecs even after modding for higher lift I'll have a lot less money into. If I decide to keep the boat for a long time I can most likely get my money back out of the Vortecs and upgrade. I'd thought about just finding some 1.94" 76cc heads and doing some home porting and cleanup then through in a decent valve job and let it go till I decide what to do with the boat later next yr.

Aha, a bad distributor cap! I told you there was something else going on with your engine back at post #7

On the cam I'm sorry, apparently, I was referring to a different 256 cam then the one you meant (the automotive cam), if you meant this one XH256H marine, it would be Fine! You could go for more, but why? then you'd lose some low end, & fuel economy.
http://www.compcams.com/Cam_Specs/CamDetails.aspx?csid=98&sb=2

 

[n2ostroker]

Re: 350 Engine advice

Re: 350 Engine advice

The plot thickens....

New cap and the idle got better not that I thought it was bad just a little stumble. Didn't think anything of it. Haven't had it on the water but something just wasn't right.
Pulled the carb and the floor of the intake was soaked with gas.... I'd noticed what I'd consider high fuel consumption. like 10gal in 35-45 minutes of mixed driving to try and find problems. One of the phillips screws in the bottom of the carb was 2-3 turns loose. When I separated the lower body of the carb everything was soaked with gas. Lower carb body gasket, bottom of primary plates, bottom of secondary plates. Mind you I'd already turned the carb over and emptied it before ever disassembling.

As far as I can tell the only difference in the 305 to 350 carbs is the secondary metering rods. I guess I try to find those while I'm in there. looks like it should go from a CL to a CH(roch# 7045779). Anyone have a suggestion where to get a carb kit and the correct metering rods?
The sec rods I can change later if need be(can't get them quickly), correct? Just unscrew the top secondary linkage screw and pull out and replace? Also does anyone know what the float height should be or if I should even mess with it?

Oh the carb number is a 17080565 1366.

Back to work....

 

[wca_tim]

Re: 350 Engine advice

Re: 350 Engine advice

I'm currently running a com xm270h cam in my 383. It pulls great, idles as low as 500 rpms (with a little lope of course) and pulls great from the bottom ent all the way to aroun 5300 rpms. It is actually a bit tame for my taste in this motor, but I can imagine it would be a great match with 1.52:1 com roller rockers on a 350 with decent heads... (so long as you do something wit the exhaust)

The cam grind is mild enough that I'm seriously considering stepping up some this winter. maybe a comp xm278h, xm290h or a crane in the same lift / duration range. guess could also order a set of afr heads and bump the compresion up a halp a point while at at...

what were you saying about cursed? choices? etc...?

 

[MikDee]

Re: 350 Engine advice

Re: 350 Engine advice

The plot thickens....

New cap and the idle got better not that I thought it was bad just a little stumble. Didn't think anything of it. Haven't had it on the water but something just wasn't right.
Pulled the carb and the floor of the intake was soaked with gas.... I'd noticed what I'd consider high fuel consumption. like 10gal in 35-45 minutes of mixed driving to try and find problems. One of the phillips screws in the bottom of the carb was 2-3 turns loose. When I separated the lower body of the carb everything was soaked with gas. Lower carb body gasket, bottom of primary plates, bottom of secondary plates. Mind you I'd already turned the carb over and emptied it before ever disassembling.

As far as I can tell the only difference in the 305 to 350 carbs is the secondary metering rods. I guess I try to find those while I'm in there. looks like it should go from a CL to a CH(roch# 7045779). Anyone have a suggestion where to get a carb kit and the correct metering rods?
The sec rods I can change later if need be(can't get them quickly), correct? Just unscrew the top secondary linkage screw and pull out and replace? Also does anyone know what the float height should be or if I should even mess with it?

Oh the carb number is a 17080565 1366.

Back to work....

Wow, loose screws! glad they didn't end up in the engine Sounds like you got the right idea about changing the metering rods. A carb kit will tell you the float level, being as you should really get one now,,, Be sure to check the main primary power valve that it works freely, it controls the primary metering rods. Also, check the accelerator pump plunger, these are 2 important items to check on a Qjet. After fixing all this your boat should do about 60 now! Just don't overrev it

It sounds like WCA_Tim has had good luck with the 270 marine cam in his 383engine, so you have something to consider now.

 

[John_S]

Re: 350 Engine advice

Re: 350 Engine advice

It could be just that loose screw and new gasket, but check surfaces for warping. Do a search on "q-jet epoxy well plugs" and you should find lots of info.

I'll send PM on possible kit.

The "17080565" matches mercruiser service manual #17 for a MCM 5.0LX. Along with the CH rod difference, the 350 version has a tighter spec on the air valve spring wind-up.

305 = 70-90 grams
350 = 75-85 grams

The manual calls for a special gauge, but I used nickels (5 grams each) and straightened paper-clip to focus pressure.

Float level is 15/64.

See DonS post for online service manuals: http://forums.iboats.com/showthread.php?t=251571

 

[n2ostroker]

Re: 350 Engine advice

Re: 350 Engine advice

Alright, I'm defending myself by being a Ford guy....

Got it 90% straightened out. Haven't had it back on the water yet but it's running much better.

Got the advice from an old GM mechanic. Dad mentioned the problem to him and the first thing he said was adjust the valves they're too tight.

They were too tight..... Even slightly bent a pushrod. Good thing they're only $1.50 each. When I pulled the old motors cam and lifters I cleaned all the lifters cause they were full of a oil/water mix. I never soaked them with new oil. I put everything together and went 0 lash then another 3/4-1 turn past. Well that was too much. I pulled the valve covers and adjusted them with the motor running and had to back them all off a full turn or about 2 threads on the stud. It runs great now. Regained control on the idle screws and had to take them 4 turns out. It seems a little lean and has a pop when you punch the throttle but no more pop/crack/backfire/fireball out the carb.

Think I'll pickup a power piston spring kit for tuning on the water. Might need to bend the accel pump arm to get a little bigger shot too. I had to back the air valve tension down to around ~60grams. Once I get it on the water I'll really be able to test it and tune things better. But with no load it leans a little so I would think with load on it it'll be amplified a little.

Anyway, lesson learned. :redface:

Thanks for all the advice.

 

[wca_tim]

Re: 350 Engine advice--GOOD UPDATE!

glad you got it going! Enjoy getting it dialed in and playing on the water... love this time of year.

 

[n2ostroker]

Re: 350 Engine advice--GOOD UPDATE!

So life has been busy and I missed a few things when I put everything together. It's all straight now.

I had 3 plug wires out of order.... Just put them back on like they were on the original motor without checking, assuming they were correct. I was wrong.

Got the valves adjusted right and the carb dialed in pretty good.

Found the HO305 heads I have flow about the same air as as the 260/5.7 of the same year just a smaller combustion chamber, few cc smaller runner, and the intake valve is a 1.84". They still run good and I think I'll just do some porting and 1.94" valves this winter and deshroud the valves accordingly. Along with either a Performer or Performer RPM intake. Also going with either the XM256h or the XM262h marine cam while I'm at it. Thats it for the motor this winter.
New impeller for lower unit, replace bellows, grease everything, fluid change on the list for lower unit this winter.

I have a buddy who's going to loan me a 23 and 24 pitch prop to try out in the spring. I'm also going to put on some smart tabs to stabilize the boat a little better on the top end.

Anyway, after all that....
The boat runs excellent now. Excellent throttle response, no bog or hesitation. Mileage is much improved. Runs good on 93 with the 8* initial timing with the high compression. No spark knock. It planes almost instantly. Shove the throttle and before you can back off its on plane(hence wanting more prop). It ran 54mph on GPS with 3 people and 1/2 tank of fuel at ~4800rpm. I can cruise at ~3800rpm around 43-45mph all day long and its smooth as glass. Very happy camper right now

Thanks for all the help