mrhorsepower1

How much boost do you have right now? 8 PSI? If you decide to add more boost then you will have to jet back up a bit. I have a 540 package with an 8-71 blower that makes 950 HP with 9 PSI on pump gas. With you compression ratio on pump gas I would stay around 9 max. If you run 104-108 octane you can go to 12 PSI. The unleaded fuels are getting worse and worse. I am getting more and more competitors "pump" gas engines coming in with pistons out of them. Gee I wonder why?

tomas_wallin

Dean,

I went out for a couple of hours and a total of 70miles yesterday and I never saw the AFR above 10.6 from 1500-4000rpm. The EGT is at 1200F at 4000rpm in the SM Gen III end pipes.

The transom gets real black so I need to raise the AFR quite a bit.

I never dropped the two numbers because of lack of time but I guess I should drop a bit more than that with the 10.6 AFR, right?

The vacuum drops to 5mmHg quite early in the rpm range, like 1500+ rpm so the PV opens very early. Shouldn't I give it a try and change to 3.5's instead of the 6.5's?

Turbojack

With it being boost referenced I think that will be a good start with the 3.5. Be on the safe side with the jetting and only go 2 steps at a time. You go too much, motor goes lean, you will be doing more then just changing jets. What side is your O2 sensor on, even or odd. I have been told the odd side will run leaner then the even side.

tomas_wallin

I changed from 86/96 to 78/89 and went from 10:1 to 11:1. I assume the reason for the afr to go down to 10.6:1 is that the engine got alot warmer this time?!

Is the PV comparable to about 10 jet sizes? If so, 3.5's should probably make things a bit better.

The O2 sensor is on the even side. I do see a slight difference in EGT between the two banks and if I remember correctly the even side is a bit warmer (but not much).

mrhorsepower1

I agree with TurboJack, drop the PV to 3.5 this will open later. The other thing that most likely needs to be done is to take the carbs entirely apart and drill and tap the high speed air bleed circuit for an adjustable air bleed. The Holley carbs that are not an HP Series will tend to go dead rich starting at about 4000-4400 RPM range . If you have a precision pin gauge set , check the high speed bleed orfice size. It is located directly next to the bowl vent tubes and will be the smaller of the to holes. Let me know what it pins. They have varied from Holley. The power valve is worth about 6 numbers .

tomas_wallin

I had a couple 2.5's I put in and went for a 60+ miles ride today. At 4000rpm with 160F oil temp it's now at 11:1 and at 5000 at 11.3 with 180-200F oil temp.

Still during drive break in so staying out of too much boost. about 2-3PSI at 5000.

I will give it a try with 3# lower in prim and sec valves before I end this season. It's LATE in fall here in Sweden now... Airtemp's about 45-50F on a good day.

Smitty

iTrader: (1)

Tomas

Give Bob Madera a call and discuss with him the AFR's you have been seeing.

Smitty

Turbojack

At 4,000 what vacuum or boost are you seeing. What is AFR at 3, 000 and vacuum or boost?

tomas_wallin

I have just about zero vac/boost at 4000rpms. At 3000 I have 10.6-11:1 and a couple mmHg vacuum.


I have a wicked slip with this labbed 31 bravo, that's why the boost is so late. 30%@4000 and 20%@5100... It looks like it should be pretty good for wot though with the falling slip numbers. I will make a few wot test before I put it away for the winter. So I know wot rpms, speed, AFR etc etc.

RumRunner

Did you change the slip links on the carburetors to 1:1 or are you still using the standard progressive linkage?