blown 350 wont pull over 4000rpm
 

ok heres the parts list.2010 block 030 over 4 bolt main ,9.5:1hyperuetectic pistons,world products sportsman 2 heads 72 cc ,es1095m cam450/461 lift 224/224dur, 1.6 alum full rollerrocker,hi perfomance welded push rods,gm performance nodular iron cast crank,kodiak alum headers, dean nickerson 750 carb. timming set at 30 deg all in, carb rebuilt blocked off power valve ,jeted 80s all around .best i can get is 4000rpm even when over trimed ,:eekdrop:b&m 142 blower

Prop pitch/drive ratio? The hyperpistons dont make the best blower pistons, I have broke the Gm zz4 ones in a non blown 350 small block so watch the boost, timing and don't torque load it (which is what you might be doing right now), Smittty

Ring end gap is critical on those hyper-u pistons . Too tight and you tear the top ring land off .

Compression seems high for a blower motor. Is it detonating?

How does the AFR look?

lower the sparkplug gap to .028 and see what it does..may be blowing out the spark..

If there is no PV in the secondaries, then the secondary jets need to be about 10 sizes bigger than the primaries. Did Nickerson build this carb for your engine????

I had a similar set up in a street rod and the engine pulled hard to 6000rpms+.

The cam is kind of small. I would think something closer to .490 lift would have a lot more power up top.

How much boost????

bought engine as is runs extremly rich with 90 in secondary,5 psi boost,cant find any info on cam. probly pull it out and go with a lt4 hot cam.

plugs are a nice tan color,look goood

no detonation,pops or backfires starts great ,idels great,runs great, just wont go past 4000

Prop? Drive ratio?

15dia 22 pitch 4 blade /1:50 but it will do the same with a 13.750 23 3 blade.

15" diameter is a lot to swing for a small block, even with a blower. I'd try a 21" or smaller 3 blade or a 20" or smaller 4 blade.

Having #80 jets squared with no PV in the secondaries makes no sense. If its rich with 90's in the secondaries, then the primaries must be rich with 80's.
You probably need something more like 74's and 84's.

With todays clean burning fuels, the porcelain on the plugs should be almost completely white. Too read the plugs, you need to look at the base circle coloring.

thanks griff ill give that a try this weekend and see what happens

I wouldnt run any supercharged boat without a wideband a/f and a fuel pressure gauge,, otherwise you are playing russian roulette with your engine

fixx
 

does not matter what the plugs look like,,the boost will blow the spark out after a certain amount of rpm,,i have seen this before,,the boat will still run but it wont have enough spark to ignite all the fuel and will smell rich when it blows all the unburned fuel out the exhaust..4000 rpm is usually the magic #..

Good point, what ignition system? Plug gap?

fixx
 

dont know if its the same gut i talked to a few weeks ago but he said he had the plugs at .040..

What Ignition? Stock HEI? Might need an ignition upgrade, cam appears on the small side, which would explain a lot, but definately throw a WB O2 on 'er, and keep that thing rich or you're going to be melting pistons...

How does she act when the power falls off? Any breaking up or misfiring? Or just feels soft when the power builds? Could be spark or fuel, double check both before changing anything internal...

I agree with staying Hyd Roller, but not sure if the hot cam is the best choice with boost.... If everything else checks out (spark, air, fuel) add more cam...

Good luck...

thunderbolt IV ignition plugs gaped at 035

plugs gaped at. 035

pulls strongup to 4000 just hits a wall,no no breaking up or,misfires

pulls strong up to 4000 just hits a wall,no no breaking up or,misfires thunderbolt IV ignition 8 psi fuel pressure at idel to wot.

I hate to tell you this, but the entire build is all wrong for reliable marine engine. The pistons are not what you want for a blower engine. The hyper pistons are marginal for a performance engine, the comp ratio is about the max you would want for a naturally aspirated engine and 9.5 is certainly too high for a blower engine. A forged crank would be much better. The cam is small, but is being cheated by using 1.6 rockers instead of standard 1.5's.
It really sounds like this was pieced together with a bunch of leftover parts.

Truth be told .

Prop down to a 19" prop and see if the same thing happens. 15" diameter 22" pitch is a lot for a small block. A prop change is an easy non-invasive test.

does the same thing with a 13.750x23 3 blade the 350 mag would spin it at 5200 rpm . but seeing that boat season is pretty much done here .going to go ahead and pull the motor out and reuild it this winter. ditch the hyper pistons, go with flat top forged pistons ,any suggestions on cam size while i got it tore down ?

I find it hard to believe a stock 350 Mag would pull a 23" prop through a 1.5 drive to 5200 RPM. I have yet to see that done in any SBC except in a very light boat. That equates to a 67 mph with 11-12% slip on a stock 350 Mag. I just don't see that happening.

The numbers are off somewhere.

fixx
 

really? :eekdrop: i swing a 26'' prop to 6200 with a 355 through a old volvo penta drive with a 1.62 ratio..mild small block..

Blower or N/A?