Rejetting Holley HP carbs on FEs?
 

Hey Carb/FE guys out there,


I know this is a general question, but I want to get some idea as to what some of you arrived at for your final jetting on single Holley HP (4150) carbs for your FEs. I run a 428CJ, 10.8:1 compression, with a fairly large cam.

Currently, my HP/4150 830cfm double-pumper with downleg boosters is running 86/86 jets squared. This seems pretty large for street driving. For WOT or on a track, its tolerable, but when getting stuck at a stoplight or two, it starts to load up. It requires a quick clear out, and its good til I get caught at a light again.

I am trying to decide if I need to keep the jetting squared, just going down a few jet sizes for primary/secondary from 86/86 to to something like 82/82, or if I can just step down on the primary. I'm not as familiar with the restrictions on an HP series carb vs. the normal street Holleys. I noticed the normal street Holley 830 runs 80/80 jets.

Any thoughts on possible combinations or step-down limit restrictions?.

There are a lot of variables when adjusting a carb. First off, you're on the idle circuit until approx 3000 rpms...you might try adjusting your idle screws. Always use a vacuum gauge and adjust for highest reading, both sides should be about the same number of turns off the seat. The only reason to run square jetting is that you're not running a power valve...otherwise the primaries should be about 10 sizes smaller than the secondaries. The power valve increases the jet size on the primaries 10 sizes when it opens. I always use a 2.5 power valve....that way it's not constantly opening in stop and go traffic and only open when you are at WOT. These are just a few areas that you can start tuning on...You can email me if you want further discussion on any of these areas....

It has a lot to do with the intake as well as how you are driving. What don't you like about what the carb is doing now? What do you hope to gain?

If you are running a dual plane manifold you can get away with switching to the smaller primaries.. But again, what is your goal.. I wouldn't do it if I were running a single plane.

Regards,

Re:
 

Hi SCOBRAC,

I'm running a dual-plane Ebrock. I hope to gain more crisp power in the 2,800 to 3800 rpm range. Anything above 4K is incredible as-is. I'd like to be able to not load up the car when "stuck" at lights idling rumpity rumpity for a minute or more. I will experiment with the primaries, but I was hoping to get it close within a few tries. 2,800 to 3,800 is the range I'd like to be in up in the twisty mountain roads, not having to rev to 4K all the time just to keep the motor cleaned up. I am comparing to my last cam (was lower lift/duration), in my last Cobra, which is probably not realistic either. If the rejetting does not work, I may even drop down a cam or so, but I want to give the jetting a decent try first. I was mostly concerned about dropping lower on the primaries only because this carb has two power valves, and they come factory jetted squared on the primary/secondary. I was told there is a reason for this, keeping them squared that is... I may drop two sizes on the Secondary, and three or four on the primary. Not sure yet, pending some solid feedback?

Jetting
 

I run an 850 Double Pumper with a single plane on my 427, I agree it sounds like you are a little on the rich side. I'll tell you my setup, but then play from there

80 in front / 88 in back
4.5 Powervalve in front / none in back

If I were to run 2 powervalves, I'd go 80/82 F/B

I'd start at that whatever matches your setup above, basically, 82 in front and then decide if you are running a powervalve in back or not, and pick the backs accordingly.

By the way, blocking a rear powervalve is OK, but not a front one. Its there so you can get enrighment at low vacuum, but still cruise with some sort of efficiency

Sounds to me that you are not only possibly overjetted, but maybe you have a bad or incorrect powervalve too. Take a vacuum gauge and see what yours has for vacuum at idle. Pic a powervalve 1.5-2 lower. SO if it idles at 8, go 6.0, however, I wouldnt go any higher in number than 8.5 or so, it'll open too easy.

The advice to go to 2.5 probably isnt good for a street driver, thats good for drag racing, but you are telling the carb to wait to enrigh until its flat out open throttle, you'll end up with a low end surge or hesitation. Or worse you'll have to run such big jets, you'll defeat what you are trying to do

Remember, pick the same PV and almost square jet it, little more in back, or block the rear PV and bump up the rear jets.

Re: thanks!
 

My427Stang,
cc: all,

Thanks! This gives me a little bit tighter range to focus my tuning in, and at least I know now that I'm not too far out of the ball park. I have 6.5 power valves F/R now. My other limitation of course, is my small K&N air cleaner in the Turkey pan. I've gone as large and tall as I can there as well for the looks/originality dept.

I'll be making some primary/secondary jet changes today. I'll try this first, but won't be doing powervalves just yet - that's round two. One other thing, I sure noticed a huge difference in my plug readings between 92 pump unleaded and 100/110 race gas. Wow. I'll not be mixing too much race gas in there in the future.

Thanks again.

Hotfingers-after reading your views on "square" and power valves,i have to ask-how am i running a 950+cfm dbl pumper/4 corner idle with 6.0 p-valves& 78 jets?:confused: :confused: :confused:

Cobrabill, what are you getting at?:3DSMILE: Carb tuning and jetting is trial and error. What works for one may not work on another's engine.

My answer on square jetting was given before I knew Duane had 2 PV's. I also run a 950+ cfm carb from C&S with one PV and my fronts are 78-79 and rears 83-84 with a 2.5 PV.

Re: Thanks to all...
 

Thanks to all for your feedback.

I considered various options and decided to drop down four jet sizes on primary, down two sizes on the secondary, lowered the floats just a tad for cornering, and howdy its much closer now.

I just took the car out for a fairly chilly one hour test ride after changes...

It seems to do a bit better now in the sub 3,500 rpm range now, more stable to drive, and crisper throttle response. From here I can play with idle mixture and discharge nozzles a bit more for the fine tune. I also learned that my 160 thermostat is not helping much in the winter, its running steady at about 160 degrees now, so I may go back to a 180 during the cold months. I noticed if I get caught at a light, and the temp goes up to 170, the throttle response cleans up. Its much closer now. Thanks!

Hotfingrs-thanks.Your earlier post seemed like a blanket statement,that's all.

Kountzecobra-even though there is a "number" where you're"supposed" to be(14.7-i think),the carb is gonna like what it's gonna like.

I agree cobrabill.

Duane,
Tom here,
Bring the car over and we can put a vacuum gauge on the motor at idle to figure out the best power valves. Like I said before, go down 2 jet sizes to start and then check the plugs. My guess is it will be around 82-83s that will be optimum!!
Thanks Tom Lucas

Boy's Take it to a good tuner with a dyno and use a sniffer to get the number about 13 to 1. We are in the 2000's not the 1960's

Re:
 

Hey Tom,

so far so good. I rejetted it yesterday, and I'm going to pick up a new vacuum guage soon. Its fairly close now. Plugs look much better with the 110 race fuel gone too! I left the 6.5 PV in there on both the primary and secondary. The throttle response is much quicker from 1100 to 2500 now too, and its a bit more driveable in the twisties at 3200 for short runs, but not for long runs. I'm testing lower dicharge nozzles now... but that is the easy part. Plugs are tan for the moment. If it starts going south, I'll give you a quick call but so far so good. Running the valves tighter with the aluminum heads made a noticeable difference. Gessford is running at .014 due to hot/cold constraint we discussed last week at Sears Point. Hopefully they have found their memory baseline now. At 750 miles now.

Thanks,
Duane

Re:
 

Cobra #42,

thanks for the recommendation. I have enough horsepower already, and like to get usable feedback. This post confirmed a few things, and I'm basically done now for the sub 3200 rpm tune.

FYI: I'll not make the mistake of letting someone on a dyno run the crap out of my FE for limited results and scratches on my fenders... I've seen how that goes already on a few of my buddies cars. Half the time these tuner guys on Dynos make big claims, spout off big nunbers, but most really don't know FEs - at all. Tom at FE specialties does a fine job, and he has access to dynos if needed. Tom builds FEs at 600hp for his higher performance builds, and I've seen the dyno sheets at 612HP+ for his radical builds - with less compression than my motor. When needed, Tom is my tuner when I need him... I'm just stubborn, and like to do some things myself. In this case, it worked! Thanks.

Decooney-agree on the dyno thing.And i'll add flow numbers to it.

I know a self proclaimed Pontiac expert whose motors consistantly dyno 100hp higher than similiar combos by other builders.:confused:

But cars with his engines are always getting thumped.Go figure.:LOL:

decooney, Sorry to hear that you haven't found a pro to work with, which will provide more than scratches and B. S. I'm lucky to work with one of the best, he deals only with high end stuff. One of his latest , 4 cylinder 1000+ hp honda set a new NHRA Hot Rod class record of 8.59. Try tuning that by looking at the plugs.

My point is.... most people don't have the equipment to read a plug nor even know what they are looking for. Unless you have a race track to take car and run your engine at max revs , run for a coupe of laps with new plugs, shut off the engine and coast to the pits, at best you are guessing. A dyno may not be perfect but track time at my local track is $5500 a day plus medical plus fire personnel. So I think a dyno is a great deal if you have the right shop.

Tip: If you see someone looking at a plug with one of those $20 plastic "Spark Plug Lights" he has no clue. The only way to truly inspect a spark plug is with a medical quality ear light, no exceptions.

Most people when reading spark plugs, only look at the color of the Porcelain insulator that is easiest to see, if this sounds familiar, I bet your running too rich. The porcelain is only one third of the equation.

You need to look at the deepest portion of the porcelain, not just the top. There should be a carbon ring at the bottom. The further that the ring extends up the porceain the richer the engine is running. The top of the insulator should be free of carbon..white, if you are running Champions ( and you shoud be).

Now look at the ground strap, you are looking at the color of the metal. The hotter it has run, the farther the discoloration will extend from the tip of the strap towards the threads.

Now look at the center electrode, what we are looking for is discoloration to see the amount of heat. The discoloration will run at an angle, the more the angle the hotter it has been.

You need to use brand new plugs for each reading, you cannot read old plugs. I know you guys don't need any additional horsepower as you stated but what about making your engine run cooler on a hot day. Never heard anyone tell me that their engine wasn't hot enough on a hot day. How about better milage for you guys running race gas at $5.00 a gallon.

Oh yea one more thing, if you keep a record of your tuning. Use a portable weather station and track all the variables, (temp, baro pressure, humidity, allitude, then you can easly change your jets to run best most of the time.

hopefully this makes some sense, L8r, db

The discoloration on the ground strap tells you about your timing...you want the discoloration at the bend of the strap...one way is too much total and the other way is not enough...and right now, without looking it up, I'm not sure which is which

Can I jump in here with a question? Just what is the race gas doing to your engine? I run some just to see the pipes turn that pretty gray color. Didn't think I was hurting it.

Just curious
Gary
ERA #291