I will be installing a new Holley 750 vacuum secondary Model 3310, on my freshly rebuilt 355 which is in the works. I will have trick flow heads, 10.3:1, headers. crane 278 cam (222/222 467/467). Turbo 700r4 with 3000 stall converter and a 4.10 gear.
What changes should I make to the carb before trying to fire it up?
Feb 1st, 03, 06:40 AM
YOu will need to set/check the float level, that is really the only thing you can do before starting the car (if you have an electric fuel pump), if not you will even have to do that with the engine running.
1. Set the float levels.
2. Adjust idle speed.
3. Adjust idle mixture (either use a vacuum guage or adjust for highest idle speed)
4. Adjust your idle once again to set it where you want it.
I think that should get you in the ball park, of course once you start driving it, you may (probably will) need to make some adjustments, to get the best performance out of it.
Feb 1st, 03, 07:38 AM
I don't advocate tinkering until the engine is running but will suggest a like path to the one above. Find out what the factory setting are susposed to be and check them on your carb and make any necessary corrections. You should be able to pull the float bowls without damaging the gaskets. You can adjust the floats dry or at least verify the floats are proper from the factory. This is also a good time to to replace the factory gaskets with the blue reusable ones. Once you are up and running "out of the box" then you can bench mark and then note results of any changes you make.
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Feb 2nd, 03, 04:36 AM
I agree with Dennis, but I personally have tinkered wit the O-3310 enough on small blocks to know it will most likely be too rich out of the box for your 355 (have never seen one too lean on a SBC). With your combo I would start with #70 jets in front and a 9.5" power valve (comes with #72's and a 6.5" PV). Then while you have it apart just install the good blue rubber Holley bowl and metering block gaskets.
Once you fire the engine, get the timing set at 36* total and do the float and idle mix / speed adjustments like Royce said. I don't know what plugs you are going to run, but my 383 likes the Delco FR3LS (2 ranges hotter than the FR1LS in the TFS directions).
I mention plugs because when you go to check plugs to see if you are running rich or lean, too cold a plug will make everything look rich and add to the confusion.
Hope this helps.
Feb 2nd, 03, 12:11 PM
Thanks for the info, I'll start with the 70 jets and the 9.5 power valve. I was just going to run the Holley 600 I had on it, but I've had this 750 for a while and figured it might give me some more power now that my combo might be able to handle it. I haven't bought the plugs yet, so the plug advice is welcomed.
Feb 7th, 03, 10:11 AM
I've been digging back through some of your posts on Holley 0-3310 tuning. It appears like you've had the most success with primary jetting in the 69-70 range and the secondary jetting in the 72-76 range. Are you running a secondary PV with that jetting?
Feb 7th, 03, 02:19 PM
No - the O-3310 does not have a secondary PV. I found 70F/74R or 70F/75R works best on my combo. I've changed my combo around a bit over the last few years and have tried various jet settings - I've gone as lean as #69 in front but I found you really need to have a PV that is right on the money if you do. If you run a #69 and the stock 6.5 PV it will cause a flat spot (lean under light throttle) when you roll into it.
Feb 8th, 03, 07:01 PM
Thanks for responding. Here's my dilemma. I've got a 4053 DZ carb that, out-of-the-box, runs rich at WOT on my 302 (11.5:1 A/F ratio on the dyno). I realize it's not a 3310, but it's probably pretty similar (same throttle bore diameter, metering blocks, etc.). I've been working on the primary side of the carb and have gotten the best driveability by replacing the #68 primary jet with a #70. If I go from the stock #76 to a #74 secondary jet, that gets me back to the original total jet/PVCR area, which I'm thinking will give me a similar 11.5:1 A/F ratio. So, with 70/74 jets, I've still got the extra 8 or so jet sizes of fuel coming through the secondary PVCR which goes a long way to explain why I'm so rich at WOT.
In your experience, how many jet sizes can I reduce the secondaries before I need to start looking at reducing the size of the secondary PVCR instead of leaning out the jetting? For example, if I get to 70/70 jetting and it's still rich, do I go to 70/68 jetting or back to 70/76 jetting and block the secondary PV?
Thanks for your insights. -Neil
Feb 9th, 03, 04:50 AM
Sorry to poke my nose in here but, I run the 750 Holley with my GMPP 350HO with no problems. I tried it with the 72jets, then to 70 jets (due to rich condition) and then back to 72 jets after figuring out that I had a huge vaccuum leak. And I am at 5,000 feet altitude btw.
Neil, there is no PVCR on the secondary side. The PVCR is only on the primary - it is not drilled on the secondary. If there is no PV there is no PVCR.
11.5:1 A/F ratio is pretty rich IMO - you want to be much leaner than that IMO more like 12.5 - 13.0:1. If you start with #72F/#76R and wanted to keep total jet area the same but lean out the primary you would go to #70F/#78R. But why would you want to do that --- you'd still be too rich at WOT?
I'd try #70F/#74R with a power valve that tips in pretty quick. For example, if your lowest steady vac reading in gear is 11" try a 8.5" PV. If you are running a manual trans, take 1/2 of the vac reading in neutral --- if you have 15" in neutral, use a 7.5" PV.
You can also run a long line from your carb to a vac gauge inside the car (go in through the window or something). Then watch it while you are cruising. From a normal cruise speed (like 50 MPH in high gear) slowly roll into the throttle. When you are into the gas just a little more than what you normally use to make minor speed adjustments (more like 1/4 pedal) look at your vacuum gauge, this is about where you want the PV to be rated at. Basically, you want the PV to start opening when you go from cruising to medium acceleration. In case I confused you here, just hook up the gauge and go for a drive, you'll see what I mean.
IMO you need to open up the primary PVCR on a vac secondary carb when you have to go real lean on the primary jets for the right cruise mix. then if when you nail it you have trouble getting a smooth transition on the back barrels, you might need a bigger PCVR opening. You can also play with the diaphram springs and accomplish pretty much the same thing (when adjusting secondary transition). But I have never needed to drill one out and chances are that if you DO need to drill one out you have the wrong carb to begin with. I think class racers that are stuck with factory carbs are the ones that have to go through this "drill" the most (pun intended) http://www.camaros.net/forum/biggrin.gif
[This message has been edited by Eric68 (edited 02-09-2003).]
Feb 9th, 03, 08:45 AM
My stock jetting was 68/76. This is the jetting that produced the 11.5:1 A/F ratio on the dyno. I have had to go richer on the primary side to solve some driveability issues (lean surge at light-throttle cruise). So going to 70/76 jetting has only made me richer at WOT. 70/74 jetting would get me close to the original A/F ratio (still rich). I'm trying to figure out how lean I'm going to need to go on the secondaries to get best HP. What I'm noticing is that you and others have built small blocks that run well with 70/74 jetting and no secondary PV. Right now, I'm at 70/76 jetting AND a secondary PV. That would make me a ton richer on the secondary side. I'd also be interested in hearing from other DZ302 guys on this one, as most of them seem to be running 72/76 jets with both PVs. I'm just trying to have my act together for the next dyno trip.
Feb 9th, 03, 10:13 AM
Neil, sorry about that --- it just clicked and now I realize you are not talking about the run-of-the-mill O-3310 and that you DO have a secondary PV. My bad.
The nice thing about having the secondary PV is that it helps with the secondary transition. When the secondaries start to open with a standard O-3310 mixture goes lean for a split second until there is enough signal on the secondary venturi to start pulling fuel. The O-3310 runs the primary on the rich side to compensate for this.
With your secondary PV the carb will add fuel to the secondaries when you start hitting the gas hard before or just as the secondaries start to open - but I don't know if the primary and secondary PVs are set to open at the same time or if the secondary is staggered and open later.
I would just richen up the primary to a #70 or #72 like you mentioned and then lean out the secondary to compensate. If you are 11.5:1 now, you are over all too rich, so I would lean out the secondary if you fatten up the primary. Since you have a secondary PV (depending on the size of the PVCR) you mighht run best with the fronts pretty darn close to the rear - like #72F/#72R
the bad thing is if you race it the secondary PV can be uncovered under hard acceleration. That's why none of the "big boys" run sec PVs and use jet extensions.
You could always try plugging the secondary PV and try running #70F/#76R. Just an idea.
Pls let me know how it goes on the dyno - I'm interested to learn about how the secondary PV setup works for you.
Feb 9th, 03, 03:10 PM
Thanks for the tips Eric. I'm probably going to try 70/74 and 70/72 on the street and then set up some more dyno time. The factory PV's were staggered with 6.5 primary and 8.5 secondary. I've dropped both to a 3.5 at Holley's recommendation because my cam pulls 7" at idle. The car runs better than ever with the 3.5 PVs and 70/76 jetting, but I know it's going to be fat at WOT due to the prior dyno testing. I'd love to squeeze a few more ponies out of my combo. I'll let you know how it goes.