pontiac 461 e85 dual quad carb setup

[pontiacpower]

Hello bangshifters. Im currently undergoing my first engine build and im running e85. My engine is a pontiac 400 stroker= 461, My original plan was to stick a single q jet on top after having someone who knows them drill every orphus out. I came across a edlebrock dual quad manifold for 230 bucks and im curious If two stock q jets could feed the motor enough alcohol. I hear that e85 needs to be somewhere between 30to 50 percent richer than gas so in my mind this might be a cool addition and maybe an economical one in terms of less permanent modification? all you guys runnnin e85 what do you think?

[cstmwgn]

In my opinion - you still need alcohol jets even if you have 8 carbs. It is the ratio of fuel to air going through the throttle body that is important. SO yes having a dual quad high riser might be cool but you still need to have the carbs set up for E85.

[silver_bullet]

be careful with gas station E-85... the percentage is often several points below 85%... http://www.afdc.energy.gov/fuels/ethanol_e85_specs.html

Vapor Pressure, psi	D5191	5.5-9.0	7.0-9.5	8.5-12.0	9.5-15.0
Ethanol Content, vol%	D5501	51-83
Methanol, vol%	D5501	0.5, maximum
Higher Alcohols, vol%	D5501	2, maximum
Sulfur, ppmw	D5453	80, maximum
Acidity, mass%	D1613	0.005, maximum
Washed gum, mg/100mL	D381	5, maximum
Unwashed gum, mg/100mL	D381	20, maximum
pHe	D6423	6.5-9.0
Inorganic Chloride, ppmw	D7328	1, maximum
Water, mass%	E203	1.0, maximum
Inorganic Sulfate, ppmw	D7328	No Limit
Potential Sulfate, ppmw	D7328	No Limit

[pontiacpower]

I understand that the levels do change from batch to batch and there is a winter blend as well. I plan to buy a drum and test each batch before i fill it. I have a truck so whether i get a 55 gallon drum or an even bigger cell that sits in the bed getting the stuff isnt an issue. This was something that thumpin455 set me on. I like the fact that it is a renewable energy source and it burns clean. I also like the fact that i can use higher octane too. One other reason is that i think that we should do something to lessen our dependance on oil. And also the fact that its just different.
Now i do know that the carbs will need work but the idea that makes me wonder if dual carbs would work is that research is showing i will need somewhere between 30 to 50% more fuel compared to gas. With one 4 barrel carb all the orphuses would have to be drilled out to flow more fuel but If there is 2 carbs feeding the engine than could i dial both of them down and be able to use jets and parts that i can buy as opposed to fabricate/drill?? I dont mind fabrication but Im only knee deep in this hobby yet and lovin every minute of it, Just not comfortable inside a carburetor yet. i do know this will be expensive to convert the carbs to run e85 too
This car is going in a 71 lemans. my tranny is a t350 built supposedly. I know it was rebuilt but i dont know how bulletproof it is. The rear is a 2.88 i believe and a peg leg for the moment. so far since buying the car i have done hotchkis shocks and sway bar up front, HEI with springs and stock weights. right stuff disc conversion up front with new booster and prop valve(these brakes arent much better than the drums btw) Brake lines all the way around. alternator, ball joints, Rear hotchkis sway bar yet to be installed.

My 400 is bored and align honed for 4 bolt mains and cam bearings installed. I have forged scat crank rods and kb pistons just have to put the short block together when i get the block back.
I have a set of 68 #62 heads that are bare castings from like a 68-69 gto. they have 2.11 1.98 valve holes but like i said they are bare castings.
I do have a stock q jet manifold from 70-72. with two q jets one front inlet the other is a side inlet. some jr headers prolly more but
i have about 2k left to spend currently and some of it is going into control arms and spindles along with a steering box and the rest of the valvetrain (cam, lifters, pushrods etc) Doubt ill have anything left over after that but i dont mind saving for a bit, ill be happy with the motor alone to wake up the ol girl. The stroker should entertain me more than enough but if not than 2 or 3 years from now maybe ill throw a turbo on or something and get creative.

[Thumpin455]

Over 70% it doesn't matter much for tuning, and the only time you will have problems is if you are over 14:1 or lots of boost, because the gasoline will cause a ping issue. More alcohol means more power, more gasoline means more chance of ping/knock. Ethanol can run incredibly rich and still make great power, so the winter vs summer blend isn't as much of a problem as people make it out to be. My 455 doesn't really care if it is winter or summer blend, the Qjet leans out a little is all. No big deal. Guys who fight with it thik they know more than they probably do, and keep messing with things trying to get more. Forced induction is a different world than NA, and with a hair dryer or belt driven intake it matters quite a bit more. NA the engine doesn't give a damn unless you have very high compression and are trying to get every last ftlb and hp out of it.

I have the Offy two 4 intake, and it fits two single feed Holleys on it easily. Much easier to convert than Qjets, and getting two Qjets to run together might be a bit too much fun. I have the intake to try it, and I am not doing it, and I know Qjets very well. What's that tell ya about it? Converting Holleys is simple, a set of numbered drill bits (mine cost $80 from CarQuest) and a normal Holley jet selection that comes in the white box and ranges from 60s to 110 or so is about all you need to convert a Holley. Might end up swapping boosters, but really it depends on the carb. The straight boosters in the single feed Holley's are easy to drill, down legs need replaced if they can't flow enough to hit the AFR for the power you want. The Qjet you only need the drills, and its best to have a wideband O2 with no exhaust leaks to see what the changes actually do. So you're talking like $300 for stuff you can use other than for one carb.

Here is how the carb works. Air flows through a venturi which speeds it up creating a low pressure area. If you have ever been between two buildings that are a few feet apart, or had an opening hangar door with fast wind as the gap appears and slows down as the door opens farther, you know exactly what its doing with a slight breeze becoming a furious windstorm until the gap opens more. Ok that low pressure has an orifice that is connected to the float bowl. The bowls are still seeing atmospheric pressure, you know around 14psi at sea level. So lowering the pressure at one end of a tube, atmospheric pressure will force fluid out of the bowl through the tube to the low pressure area. You can do it with a fast food cup and a straw sticking out the window of your car. Get the angle right and you can suck all the liquid out of the cup with nothing more than wind.

The boosters are the smaller circles in the throttle bores, they are a smaller venturi placed in part of the big one to get the best signal, or air velocity. Some are higher, some are lower, the Qjet has two of them in each primary bore. They help pull the fuel faster from the bowl and give you the best signal, the Qjet has tubes hanging in the secondary side, no boosters because it relies on the secondary opening rate to maintain the velocity required to flow the fuel at the right time. They use the huge bores as the booster with the air valve on top.

The jets dictate how much fuel enters the air stream once the main circuit is open, at idle the main isn't seeing enough low pressure to pull the fuel out yet. That is why float level is so important, too low and it takes forever for the fuel to get to the venturi, too high and its dripping fuel at idle. Change the vacuum of the engine and the float level needs changed as well, so factory settings can cause problems in some cases. Its also why a big carb is less responsive than a smaller carb on a small engine, or with a big cam that produces minimal vacuum at idle. Not enough low pressure from a high velocity air stream to get the fuel flowing. A bigger hole has less velocity than a smaller hole, all else being equal.

The idle circuit with the screws only works at idle and slightly above it. It doesn't normally affect the rest of the carb operation. You aren't changing much by turning the screws, just how much your eyes will burn at idle.

Ok, so you have a low velocity condition with the throttle blades closed at idle. You whack the throttle, and what happens? The air starts moving faster, but there is a lag time for the fuel to flow. Without a shot of fuel at the right time, you get a big bog like secondaries opening too fast. That is where the accelerator pump comes in. It shoots some fuel in to make up for the lag time required for the fuel to get pushed out of the bowl and into the low pressure venturi. Its a bit of extra fuel so the engine sees seamless power when you open the throttle quickly, do it very slowly and its not an issue, but who opens the throttle like Granny going to church? With Holleys you can change the squirters, and cams to make the shot bigger, smaller, longer in duration or shorter depending on what the conditions are you have with the vacuum and everything else. Qjets have the long and short holes in the arm, that is pretty much it, the least tunable part of the Qjet.

Ok now we get to why you do not jet down a big carb on a small engine, and why it doesn't work leading you to sell me your great carb that you screwed up for cheap so I can rejet it and make great power. Chevy circle track guys do this all the time, so I like to farm them for stuff they don't understand to get good stuff cheap. Carbs are about moving air, and adding fuel to it. They aren't about moving fuel and adding air to it (well part of it is, but that is not the point I'm shooting for). If you put tiny jets in you are simply leaning the mix, not limiting the airflow at all and gasoline doesn't like to run lean, but at the right amount will make good power. You put jets in that are too large, you richen the mix and on gasoline that is a problem, because it makes less power and runs like shit when pig rich. You aren't limiting the air flow, only how much fuel gets to it, and carbs are all about air, they are primarily air valves, not fuel valves. Think air first, not fuel when doing carb stuff.

Two carbs will flow a certain amount of air, they will only add as much fuel as they are tuned to add for a given vacuum. Two carbs bog because on a low compression engine, especially a small one like a 305 chevy, there isn't enough vacuum to pull the fuel, which is why they tend to idle like crap in some cases. By adding the second carb, you are adding more air, sometimes more than the engine could ever use, which results in a very low vacuum. More compression and larger engines can use more air and will pull more vacuum for a given cam timing. (haven't even touched on cams yet) and can utilize the increased air flow. That is why most engines make more power with a single 4 vs dual quads, and pro stock engines use a bunch of two barrel Dominators cut in half.

With ethanol some things change, like how much fuel you need for it to run, how much fuel will make max power, the range in AFR that will work best. It will still run with gas carbs, but will be down on power because its too lean, and run like crap all around. More O2 in the fuel means you need more fuel to feed the air going in the engine. Since there is more O2 in it, you can run it very rich and make lots more power. Double the AFR is best power, but it will run great quite a bit leaner. Simply running more carbs does not address that, you need to open them all up to flow the right amount of fuel for the air going through them.

That is generally speaking, there is more to it, but that is the basic understanding you need to do this stuff for yourself.

[pontiacpower]

I understand that the q jet is harder to tune in every situation. single 4, dual 4s. I have been told by almost everyone ive ever talked to that the q jet is very meticulous and tough to work on because of how much more complicated the insides are. I happen to have two of them so should i just sell them and go holley? or keep them and run one as a test dummy and the other as the final carb on my setup? I still plan on running e85 no matter what happens because i dont want to be spending more money to dish the pistons and open up the combustion chambers. What is it that is stopping you from trying to run 2 4s on your setup? from what im getting out of the few conversations that we have had about this is that you cant go wrong tuning e85 as long as you stay rich. I know you said that dual 4s dont do shit until you get to big inch motors that draw a lot of air but what defines big? Am i in that category at 461 cubes because i know theres guys that run over 600 cubes on this site in the drags. i have been researching guys that run duals on their engines and so far the only stuff ive found is for sbc 400s. i watched a test about running 2 4s on a chevy 400 bored like 30 over and on the other end a single 4 netted at least 20 ponies and 40-50 ft lbs. Point being that 2 4s makes less power on smaller/ish engines (wheres the line between big and small though) Does the demand for air vary between oversquare and undersquare or is it strictly the amount of cubes drawing air.
also when it is said that a carb flows 750 cfm does this refer to air + fuel or strictly air?
I know you focused the topic of carbs being air first. Would 2 q jets flow the correct amount of air that my 461 could use? is there some math i can do to figure out what cfm i need?.

[Thumpin455]

Qjets are great carbs, easy to screw up by the unknowing, but they work great when you know them. Only way to know them is to run them and learn.

Setting up two carbs to run on the same engine is harder, you have to do everything multiple times. I will run two Holleys any time, even though it means pulling a carb off just to do the jets on the rear carb. I tried dual Qjets, but you need two that are very close in calibration, then you need to adjust them at the same time, and decide which one will be primary or if both will handle the idle. With multiple carbs you want simplicity.

Getting a Qjet to run well on E85 takes more than a jet change, its involved and you are in the carb a lot until its done. Doing two at the same time, well the thought makes my brain hurt. Yeah it can be done, but the reason I run Qjets is for power and economy. If I am running a dual quad intake, I really am not concerned with economy as much, so it will be Holley on it. The Holley is simple and easy to work on, converting them to E85 is very easy and straight forward with minimal changes outside the meetering blocks.

Vacuum secondary carbs like the Qjet will only ingest as much air as the engine wants, as long as the secondaries are adjusted right so they don't open too fast or slow. The small primary bores of the Qjet mean it can be used on small engines, like the 4.3 v6, and the spread bore design was used by many OEs including BMW on small engines(2.5L to 3.5L). The basic design was the same as the Qjet on the BMW, but of course it was somewhat different. The huge secondaries with an air valve means the same carb can be used on a large V8 with high or low compression, lots of vacuum, or low vacuum, and that is why the Qjet is so unique. It isn't too big or too small. People are running 9s in drag cars with Qjets, and they came on almost every V8 from GM from 67 until the advent of EFI.

This is my Offy intake and the carbs I plan to use on it. Its not going on for max power, but to complete the look on my 65 LeMans that is getting a straight axle and lexan windows. However much power it makes is fine by me. I'm not going to run Qjets on it due to the complexity of getting it running right.

[pontiacpower]

well i guess ill take some time to switch the 350 over to a 4 bbl when i get the lemans out. use that as carburetor lesson number 1. Do a basic rebuild and try to figure out how to tune the thing. I have Ruggles book so im sure that will be a good enough manual to get me through for a gas rebuild. I appreciate the help todd and if you ever need a healthy set of hands let me know. I would gladly come up to Marquette to learn a thing or 2 from the Pontiac guru

[fatguyzinc]

I is there some math i can do to figure out what cfm i need?.

cubic inches x max rpm / divide by 3456.

at 461 x 6000rpm divided by 3456 i get 800.3472222.
of course this is just a GENERAL sizing, some motors
( 455 buick, 460 ford, 454 chevy, and yes 455 pontiac, etc ) want
more than normal, others (small block chevy, small
block ford ) like a little less.....

[pontiacpower]

Im right in the ballpark between 650 and 700. Would e85 affect anything in the equation? I feel that this would make the engine more efficient because all the e85 gets burned as opposed to gas where you can see carbon deposits on everything. If my calculation is true than to 750s on a dual plane qual quad would be way to much to feed this thing