TomZ

iTrader: (2)

Currently, I'm running the factory Merc Q-Jet with Edelbrock parts and so it has been OK in terms of performance, however. I'm thinking that some of my problems in the past have been due to the carb and now that I have a replacement I'd like to get some "safe" jetting tips.

Once again, engine specs are:

383 CID
10.3:1 compression
Vortec heads, ported, polished, 2.02/1.60 valves
Comp XE-274H 230/236 @ .050 .487/.490 1.5 rockers
Performer Vortec intake (switching to a Performer RPM Airgap as soon as funds allow)
Timing set @ 32* at 3700 RPM
Cast iron center-riser manifolds (Marine Power, larger than the Merc stuff)

The new carb is a 4010 vacuum 750 that is box stock. I'm not sure about what it came with from the factory jet wise (Mortec.com says that stock it has f-73's and r-75's with a 6.5 pv). I'm looking for a good "safe" place to start. I'm running on the ragged edge of detonation at this point and a lean condition could royally screw me so "safe" is better than all out top performance.

Thanks!

Havasu Hangin

...your motor is very close to mine, I just have a little less duration, a little more lift on my cam...I took my "out of the box" 750 to a carb guru...this is my current setup:

Idle- 1 1/2 turns
Primary- 75
Secondary- .086
Power Valve- 6.5
Nozzle- .033
Secondary spring- .063

Timing- 18 initial; 36 total

They also did a 800 conversion...although I don't think I'll ever need those CFMs. The big problem with my "out of the box" 750 was that my engine was having trouble pulling enough vacum to open the secondaries at the right time.

It runs a little rich...but like you say, better safe than sorry. Other than that, very crisp, and big on the top end...

TomZ

iTrader: (2)

Wow, that's a pretty big jump on the secondary side. I need it to pull like a train on the top end... I'm hoping that the Holley will fix me up... I think the Q-jet starts to run out of fuel on the top end (need to modify the bowl to hold more fuel... but why bother though... I like the Holley better ).

What cam are you using and what kind of exhaust do you have? I trying to get an idea of the differences so that I can compare the setups and adjust from there.

Thanks!

Havasu Hangin

Crane hydraulic roller 222/230 .509/.528
Edelbrock Performer RPM Heads (71cc)- ported & blended
TRW 10-1
EMI Thunder Exhaust
Holley Street Dominator Manifold

Like I mentioned, that purple secondary spring really woke the top end up. I think you'll really like that Holley. I don't have much experience with that Q-Jet, but my Holley hasn't disappointed me yet on my 383.

My engine also LOVES alot of timing...

TomZ

iTrader: (2)

I'm hoping that the Holley will wake it up.

Using the Vortecs, the timing is a little more conservative, though I think there's some room for more. I'll have to test it out once I have things situated a little more. That could be where I'm missing out. I'm close on the detonation front though, so if I want more timing I have to start mixing my gas. Most Vortec head engines like the timing around 32*.

Are you using those heads with a closed cooing system? I've contemplated using aluminum heads, but I'm afraid of having to replace them due to corrosion (replacing the intake is one thing... half hour operatoin to do it all. Heads would be a different story.).

What kind of boat do you have this setup in and how does she run?

Later!

JON242

I'm running a Dart 421" small block, 9.0 compression, GIL dry exhaust, Performer RPM Air Gap, Holley 750 w/mechanical secondaries. 75 fronts, 82 rears, 6.5 PV. Great throttle response and just a little bit on the rich side.

Havasu Hangin

Well Tom, no closed cooling system, but I have the luxury of fresh water boating. Around here...iron rusts, and aluminum corrodes, so pick your poison. Edelbrock is marketing marine heads now, so they must have some confidence that they will last awhile.

The boat is an old daycruiser (look under "my webpage" for some pics) that I brought back to life. For a heavy boat with a small block, she does pretty well.

No GPS, but the best to date is spinning a 23' SS 3-blade around 5K RPMs...and I've still got some tweaking to do.

Good luck!

patrick22309

TomZ,

Who did your head/engine work in the NoVA area?

Thinking of getting about 300 ponies for my Stingray in the for of head/exhaust work and need a recomendation.

I was thinking of refreshing the entire 260 engine and just add a set forged pistons, factory vortecs, and decent exhaust to get me in the 300hp range. I cannot go much higher because of my Alpha and the fact that 300hp should put me over 70mph and a 20ft boat gets very light at that speed.

Patrick

TomZ

iTrader: (2)

My stuff was done at ARU Racing down in Summerduck. As of right now though, you'd need to have given them a motor to work with last fall in order to have it done by now. They are OVERLOADED! They build circle track stuff and it keeps them beyond busy.

With that said... why don't you try your hand at doing it yourself? The Vortec heads alone will get you 300 horses with nothing else. If you wanted to try your hand at doing it yourself, I'd be more than happy to help you with it. You could get the heads and intake, and we could have it hauling buns in a weekend!

Later,

patrick22309

How would the complete vortec out of the box handle a marine app? I hear all these exhaust valve horror stories, but I am not a poker runner and normally cruise at 3500 on the river.