355 Vortec Tuning. Watch the videos.
 

I built a 355. Flat top pistons, vortec heads, comp 262 xtreme marine flat cam, RPM air gap intake, GLM manifolds. I put on a Sea Demon 750 double pumper and new ignition. I am not quite happy with my tuning.

The first video is 12 degrees at idle, 32 all in. The carb had the idle set at 800 with the mixture screws about 1 1/4 out.

http://i880.photobucket.com/albums/a...h_IMG_0112.jpg

the next one is same timing but I played with the idle eaz and mix screws more. It Idled at 1000-1100. I felt it was too high but ran the best.

http://i880.photobucket.com/albums/a...h_IMG_0116.jpg

The last video ran at 750-800 but didnt sound as healty.

http://i880.photobucket.com/albums/a...h_IMG_0118.jpg

This is the first motor I have ever worked on that was carbed and not computer controlled. What do you guys think?

Don't beat yourself up...the fact that you probably never got the motor up to a decent operating temperature might have something to do with tuning. LOL

It reached 150. I have a warm water outdoor spiqet so i had the water luke. The air was still 36 though.

wait until it warms up like mentioned..the AF screws you have out 1 1/4 turns,,put those at 1/2 turn and no more then one full turn...but first screw one of them all the way in,,if it still runs then you will have to reset the front throttle blades to stock spec..always leave the front one alone and raise and lower the idle with the rear one..

Just adding some other info on top of to make sure your using a current gas blend. The RVP (Reid Vapor Pressure) of gas is totally different than it is in the winter months compared to summer months. My point is use current gas from the pumps since your weather is 36 degrees out trying to tune your motor. Some states change their gas blends & RVP 7 times a year because of climate change.

We have boaters quit using their boats after July in which is 110 degrees and then bring them in when its starts to freeze at 32 degrees for winterizations. A lot of times their engine will not start because the summer gas blend will not even light off or if it does start the engine runs like timing is way off or misfiring constantly.

Anyways maybe a pointer for someone trying to tune their motor in the winter months on what gas was left over in the tank from summer. Hawaii is the only state who does not change their gas blends or RVP because they have almost the same constant temps all year round. RVP or Reid Vapor pressure google it if you want to learn more about what the hell I'm talking about..

I'd put a wide band on it and take out the guess work.

whatta do with a wide band and carb? just read it on the laptop and adjust?

I had no idea they had different blends of gas. I knew diesel has winter blends but thought that all gas was the same. My fuel is from mid October. I think I will just wait till it warms up a bit.

the proper way to adjust the air/fuel ratio at idle speed is to open all adjusting screws one and one half turns, then put a vacume gage to read intake vacume,then start engine and let it run until it is warmed up and the choke is open,now you adjust the screws evenly to achieve the most vacume.you might need to adjust the idle screw that controles the closed position of the throttle blades.this information is just as it is written in the holley tech section.i forgot to mention this is done with the car in gear so in the boat the drive needs to be in gear in the water.

i dont know how to do that,can you please explain the procedure.

Tune it on the water. Put a load on it. Sometimes you think you got it all set on the trailer, and you get to the lake, shift it into gear, and it will stall. Idling at 1100-1200, is no good for the drive you have there, when shifting in/out of gear....

Idle Air bleed size, idle feed restrictor size, and that BG idle Eaz deal, all can play a part in where you're mixture screws will need to be. Theres a reason they are adjustable and not fixed. Not all engines require the same settings. :helmet:

Install the wide band to get the AFR readings. That will take the guess work out of that aspect. No computer needed. Many wide 'kits' come with the sensor and gauge so you can monitor the AFR real time.

I'll warn you right now, shifting that Alpha into gear over 800, especially over 900 will break it. I've broken a few at 900 and 1000 within a half dozen shifts or so.

Just a big FYI.

recommended idle is 650 to 700 for alpha drive in the water. Dog clutch hates higher idle while going into gear.

Is there a chance that is to much carb for a 350 ??



John jr

Although I've found 650s are more responsive on small blocks, 750s are doable with a little tweaking and jet work.

My question is almost the same but:

Is there a chance the flat tappet cam wasn't broken in yet with this carb fooling around?

BTW: In cold air and non-warmed engine that air gap intake will make it t idle not worth a chit. It will probably want a handful more initial timing.

I thumbing thru an ''Engine Masters" magazine a little while ago. They had a 500HP small block chevy. They tested 4 carbs.

Holley 4776 600 Double pumper.

Holley 750 Ultra HP

Holley 950 Ultra HP

BG 600

They dynoed each carb on the engine. From 2500-6500RPM. Not only did the 950 Ultra make more peak power, it made more torque than the rest of them, even in the low rpm range of 2500-3000.

The entire point they tried to make in the writeup, was that back in the 70's, bolting on too large a carb just didnt work well. With modern carb technology today, a larger carb, properly setup, can be very responsive, efficient, and work well. A modern 1050 Quick fuel, is a far cry from an 80's 2 circuit Dominator.

We dyno'ed my big blocks and actually lost alittle going from 750's to 850's. But, having said that, the 850s were Demons the dyno guy sitting there and weren't set up for my motors. We were running at 107%VE and he wanted to see if he could get more air. Didn't work/