EZZZE

iTrader: (14)

As many of you know, I have an '88 coupe mustang with a carb'd 5.3. It has a custom Pat G cam, milled 243's, long tubes, th350 with a PTC 4K stall and 4.10's. I have a vic Jr with an out of the box Holley 850 dp with choke horn, etc. Anyway, I have an Innovate air fuel gauge and seeing as how the track was closed, I was trying to get the afr close by doing 3 to 4 second bursts on the street WOT in 2nd gear. I was getting between 10.2 and 10.7 to 1! I know I should be around 13: 1, right?

My questions are: Is the 850 too big for my 5.3, and should I just go ahead and get a Holley 750 hp? If I do try to keep the 850, how many jet sizes should I go down to try to get the afr to 13:1? Also, I have a custom curve in the 6010 box, but I haven't got to look at it yet. Should I check the timing curve before messing with the carb?

Thanks for any help.

Pop N Wood

iTrader: (1)

850 is most likely bigger than you need. Doesn't mean it can't be made to work, just means it will be a little harder to get tuned right.

The wideband will make it pretty easy to get the WOT jetting right. Just go down two sizes at a time until you are at your desired AFR.

Timing won't really affect the carb settings at WOT so much. It is getting the car to drive smoothly when cruising and normal driving that the carb and timing interaction comes into play.

EZZZE

iTrader: (14)

Thanks for the reply. Would you keep the primary and secondary jets squared and move down two at a time?

Pop N Wood

iTrader: (1)

What do you mean by squared? If you are running a power valve then hopefully you don't have the same sized jets front and back.

Adjust the primary and secondary jets independently. You can even disconnect the secondaries to get the primaries right first.

EZZZE

iTrader: (14)

OK. Thx

Paul57

Unless your 5.3 is putting out 500+ hp then an 850 is overkill for sure.

EZZZE

iTrader: (14)

Naw. I'm gonna say around 350 - 360 rwhp. I believe the 850 is too big too, but I got it with the car. I'm gonna jet it down this weekend and try to at least get the WOT AFR dialed in. If worse comes to worse, I can get access to a Holley 750 hp to test as well.

Thanks

Paul57

FYI...a vacuum secondary is a better choice for most applications. Your car will feel a lot "snappier" with a 750.

speedtigger

iTrader: (16)

Paul, the OP has a 4k stall, 4.10 gears and has transplanted an LS motor into a Mustang. I think we can safely assume he is not "most applications".

The general rule is: high stall (3000 or more) go mechanical secondaries. Vacuum carburetors do not operate efficiently in cars with high stalls and high numerical gear ratios. Mechanical secondaries perform far superior in these applications.

Vacuum secondaries are good for mild applications where you have low stall or stock torque converters and/or low numerical final drive ratios and heavier vehicles.

Paul57

I see your point... especially with a 4k stall (I missed that part).
Basically, I am advocate of vacuum secondaries on a car that is "more street than strip". But, I do not know the OP's intent. I was always under the impression that an adjustable vacuum secondary could be tuned to work properly for a given situation. Is that not the case??

EZZZE

iTrader: (14)

My car is driven on the street, but it is definitely more oriented toward the strip. It has a spool, large cam, and a large stall. However, everyone's definition of streetable is different. I feel it drives better than my old '99 T/A with 6.0 and 4K converter.

Anyway, I got the msd 6012 hooked up and looked at my timing map. It had something like 20 degrees total timing with the map sensor supposed to kick in more. However, there is no map sensor hooked up! I started with a very conservative map: 12* @ 0 rpm, 15* @ 200 rpm, 18* @ 800 rpm, ramped up to 29* all in by 3000. Even with the AFR still super fat, the car felt worlds different. It roasted the 28 X 11.5 M/T ET Street bias plies on the 1-2 shift for about 5 feet. I am going to the track Friday and keep adding more timing and ramping it in sooner until I slow down or get detonation.