I aquired a BIGS 950 Stage 5 Holley today, and was interested in tuning inputs for my 10.4:1 iron headed 464 engine. My cam measures 233/248 on a 112 LSA installed at 108. With the old 850: - It makes about 525HP and 550TQ, I've been shifting at 5800 rpm but could go higher, SP1 intake. - I've got about 12 psi vac. at 950 rpm, a little less maybe 11 psi in drive at 750 rpm. My full weight Skylark has a 3.42 gear and a 3200 rpm stall converter. Here's the spec. sheet from BIGS, carb originally purchased in `05 or `06. This carb. was originally tuned for a street/strip 427 Chevy, with manual transmission. It looks close I think. I have not had any luck contacting BIGS.
I have a BIGS (QuikFuel Technologies) 950HP. I run the largest airbleeds that can be put in. I also run a 4.5 power valve, I believe. My jets are 82 primary and 88 secondaries. This setup works pretty well for me. We have similar engines. My cam is Poston's 113A cam. Also, make sure you have jet extensions in the secondaries. On takeoff, they'll be sucking air if you don't.
Wouldn't you know it, I called Jesse at BIGS and got him this morning. Very helpful guy. Here are his suggestions: Change jets to 78 primary and 83 or 84 secondary. Then run at the track and watch mph. Jet up until mph falls off. Stagger of 5 or 6 (78 minus 83)without PV in the rear should be close with the billet metering blocks. Whan compared to the 850 that I have he said the 950 is a much smaller carb. due to venturi size and taper. I should have better throttle response and not nose over and go rich like the 850 does now. Cold start-up and idle should be much better as well. Should be interesting....I'll likely install this thing this weekend.
Did the 850cfm carb run the 118mph in your sig? If so what model 850cfm was it and how was it configured? That is a great MPH for your listed combo.
Yes, that run was made with the 850 (#4781). Before I put the engine in the car, at the dyno, we progressed down to 78 jets in all four corners and the air bleeds were drilled/increased to .028 front and back (start of dyno they were 0.026" and jets were 80's). Shooters were 25 front and 35 rear. The AFR curve was going more rich in the upper rpms. Both PV's were 5.5. BSFC started off at .38 and progressed to .45 by 6K rpm. Total timing was 35. We discovered one of the emulsion tube passeges was enlarged on the secondary side but could not do anything about it. After the dyno and before any drag strip runs I replaced the secondary metering block, drilled front and rear air bleeds to .031", upped all jets to 80's and upped the primary shooter to a 31. I also changed both pump cams, front to a pink installed in the #1 position and rear pump cam to blue installed in the #2 position (bigger shots both front and rear). These changes were made in an attempt to help the occasional stumble off idle. Timing was reduced to 32 total. I also lowered the idle about 200 rpm, this eliminated the occasional run-on issue. Many of these changes were made after seeing average cranking compression of 213 psi.:shock: Throttle response and cold starting is better, but not as good as I'd like even with the mechanical choke. I'm hoping these areas will be noticably improved with the 950.
I have the CNC Bigs 950. I need to run bigger idle air bleeds like Phil does but otherwise pretty close. Biggest difference is running 6.5 power vavle in the front. Last time I checked the front mains were 80 and the rears are 88. Just got this cool AFR guage so I will be keeping a lot closer track of that. I do not know where Phil got that Bigs is the same is Quick Fuel though. Last time I talked to Jesse he was complaining about having to send sub standard parts back to Holley. Bigs is in WI and Quick Fuel is in KY. But I have been wrong before, just ask my wife :laugh:
O.K. Jet extensions, check Possible larger idle air bleeds, how large is large (I've got .070" now)? Are your butterflies drilled, if so which ones and what diameter? Good inputs guys! Doug, I've been thinking about an AFR gauge too. Are you going with Inovative LM-1 or LM-2?
Just checked on my setup and it is identical to Craig's. It came with 79/86 on the jets and I did go up to 88's. The idle air bleeds were 70 and changed to 73 and it had no effect. My goal was to be able to have more than 1/2 a turn out on the idle adjustment screws. So I think I need to make a big change there or go smaller on the idle feed. This is not to say the carb is not working well just that search for perfection. I got a good deal on the AEM guage. Does not have all the bells and whistles of the Innovate but it was a good price. I think I am going to mount it in an a-pillar pod with the vacuum/boost gauge. The fuel pressure gauge will go in the right pod of the instrument panel. I think instruments under the dash are useless. The butterflys are not drilled.
The 950 was installed a few days ago. First drive was yesterday, after it warmed up it seemed to respond nicely and idle smoother than with the 850. I had 79's primary and 84's seconday with no PV in the rear. I changed it tonight to 80's in all four with 6.5 PV's (I'll drive it tomorrow). Cold starts are a little better but still not where I'd like. Senario (same as before) If I pump it with the pedel lightly I can ~usually keep it running (500 to 1100 rpm range), after two or three minutes it will idle by itself. If I pump it a little too much it will knock off, if I pump it significantly more it will run but then I'm at 2000 plus rpms, neighbors love that. Squirters are 35/35. Trying to be somewhat quiet during those early morning neighborhood starts is still not easy, any suggestions?
How many turns out did you have to go on the idle adjustment screws? Mine only needs a 1/2 turn out. I think our Buicks are not as happy as they could be with the idle setup. We could use a little more air in the mix in my opinion. The idle air bleed deal is nice BUT you cannot buy the things in anything less than a set of 10! I think we may be asking too much of the carb to idle cold. That's what they made chokes for. Hoping to have my AFR guage on this weekend and see what it looks like on the startup. Maybe Phil will jump back in and tell us what size air bleeds he is using and we can order a set and split them.
When I had the rear butterflies at the minimum position (square slot exposed) I had about 1/2 turn out. I adjusted the rear slightly more open and now have about 1.2 turns out. Fronts are about 1.4 turns out. I went back with a PV in the rear so I've got 80's in all four corners with 6.5 PV's. This is how the old 850 was set-up, and ran good WOT, except it had the primary butterflies drilled about .125" or so. I have not changed anything else on this 950 (bleeds, shooters, pump cams) carb. I hear Holley has a new wideband setup, saw it in latest HR mag.
I'm also trying to tune a HP carb. Mine is a 1000HP # 80514-1. Having a heck of a time. Combo is Stage 2 alum. heads, 240/246 on 110 lsa, 108 int. centerline. Perf. intake with above carb (to fit under stock hood). 4 speed car. The carb came equipped with 84 jets front, 88 jets rear, 6.5 PV, idle air bleeds at 73 and High speed air bleeds at 32. Front squirter at 31 and rear at 36. White cam in the #1 hole primary with a 30 cc pump. Brown cam in the #2 hole secondary with the 50 cc pump. .125" holes drilled in all four throttle blades. Burning rich, black plugs. Idle vacuum is 8" and idle mixture screws had little effect. Made sure primary throttle blades were mostly closed and transfer slot showed about .020". Secondary blades closed. Changed jets to 80 front and 84 rear and still has black plugs. Changed to 4.5 P.V's havent' run it since that change. Need to get timing figured out to get idle vacuum up where it should be in the 11" area. Running an MSD 8552 with NGK BPR6ES plugs if I remember the plug number correctly. If its still rich I'm thinking of dropping rear jets back to 80 also. Really need an AFR meter at this point. I may be in for a group swap of air bleed if you guys are going that route, so count me in. Any other suggestions? Not trying to hijack your thread, seems we're in the same boat though. Thanks
Your advice is very welcomed here Dave. Well, with the 950 installed, my corrected times fell off by .1 yesterday at the track. Guess more tuning is needed. I should have taken the 850 with me..... but didn't. Based on some advice at the track (thanks Rick) I removed the rear PV and put the plug in to avoid possible lean situation on take-off. Under acceleration you could uncover both the rear jets and PV. I had not thought about this before but I did have jet extensions for that same reason. I jetted up 6, giving 80's front and 86's rear. This did help some. Now, I was using the PV in the rear on the 850 however. I also dis-connected my front sway bar for a couple of runs, had not done that before. The front really comes up noticeably more/easier when I do this. I did not get any good runs out of it for those two runs however. I need to ditch the air shocks I think.
Craig What elevation are you running at? I have Biggs 950 that was run in Ohio at around I believe 300' I will be running at 2500'. It has 90 in all four corners, and I am really new to this type of carb. Thanks Rick
Elevation is right at 100', yesterday the pressure altitude was 180'. Try this site to tune your jets http://bgsoflex.com/auto.html Scroll down and click on Holley Carburetor Jet Program on the left.
Dave, You definitely have something wrong. With the jets I run (80/88) on the 950 my plugs are white. You have better heads and more cam. Wish I had some quick answer. Anyone near you can switch carbs with? I tend to think it is something else. Good luck. Here is a question for all. What kind of 60 fts do you have to run before power valve gets uncovered? Two years ago I was using carbs from my oval tack buddies to see how a Holley would work on my Buick. These came off of 800 HP super stock cars that are incredibly quick. Both of the carbs I tried had rear power valve. They both worked great and I ran 1.70's 60 ft with both. I know the cars they came off accelerate harder than anything my car will ever do. As far as my Bigs950 it is working very well. I think the idle circuit is a touch off and could be a little better. The main issue is there should be a bit more air in the idle mixture. Takes a few minutes to warm up but what do you expect from a race carb? Once warm it is good for the day. Hope to have it to the track this weekend and have the AFR hooked up. Will let you know what the numbers look like.
I agree, you can have a fair/decent 60' with PV (1.745 my best). When I install a PV in the rear I take note where the PV windows are and try to make sure one opening is between the 5 and 7 o'clock positions. Now I have heard that once you are under 2.0 you ~could have a brief lean condition on takeoff o No: A lower float level could also make this condition worse. I think it's time for a chassis dyno to test both the 850 (configured where I ran my best runs) and the 950 (play with tuning). I'd like to see the fuel curve of each and see how the AFR's compare.
Just got my hands on a new 4781-8 850cfm dbl pumper. It is set up kind of strange from the factory. It has 80 pri and 78 sec jets with a 50cc sec pump. I am going to give it a try this weekend for some street duty.
Davis, mine ran good at the track with 80's and PV's and 50 cc pump in the rear. I drilled out the outer air bleeds to .031 since it was going a little rich up top.
