|10-23-2007 08:00 PM|
|NXS||sure hasn't but if he still hasn't got it lined out 4 years later...I don't think he will.|
|10-23-2007 06:48 PM|
|10-23-2007 06:43 PM|
|NXS||have you looked at the date?|
|10-23-2007 06:37 PM|
You need more accelerator pump volume
you need way more timing at idle
you need to hook up a functional PCV and vent the other valve cover.
you need way more rear gear
you need a minimum of a 10" 3500stall converter.
Remove both carbs and flip them over and look at the throttles.
Reset all the throttles so that the idle transfer slots are just barely exposed under the throttle blades on all 8 barrels. (.015-.030")
Reinstall the carbs don't upset the throttle preset.
Hood up a PCV hose to the base of one or both of the carbs hook op the PCV to one of the valve covers vent the other valve cover.
Lock out the ignition timing mechanical advance curve so that you have 36deg of timing at idle and all the time.
Set the timing at 36deg BTDC at idle.
Should idle at 800rpm when fully warmed up.
You should not have to touch the throttle idle speed setting from the baseline preset (all throttles the same with just a slight bit of the idle transfer slot exposed under the throttle blades) . Re adjust the idle mixture screws slowly and evenly as nessessary for best idle.
You can now use ported or full manifold vacuum for vacuum advance. Limit the vacuum advance to 12deg.
you will need larger accelerator pump shooters (.035" or bigger) and maybe even larger 50cc pumps. jetting my need to be adjusted.
get a 4.10 or 4.56 ratio rear gear and a minimum 10" "3500stall" converter.
your idle speed and quality and throttle response will be much better after doing all these changes.
|10-23-2007 09:39 AM|
i have a 73 nova 350 4 speed with a tunnel ram, 450 Holley's. i had the same bogging problem. i found some answers in a Chevy high performance mag. aug 2006 in performance q&a sec. it says to use some stainless steel mechanics wire put a small piece in each main circuit air bleed, located in the venturi area above booster. make them long enough to bend down the outside of the carb. idle air bleed is located toward the out board side of carb,the main is toward the inboard side. i use my vacuum advance and my timing is set at 37 total with vacuum advance off and plugged. they give a complete setup in the book. i would call and order that issue. or i could e-mail the article to you.
|12-25-2003 08:57 AM|
|12-24-2003 07:05 PM|
Don't compare yourcar to your friend's, BECUSE ITS NOT THE SAME, you already found that out. Pro's can't even build two engines that are the same, how can we? Everyone is giving you good advice, take this information and study it, ready some good tech articles, ask some more questions, get some more advice and decide on a plan of action. Only change one thing at a time and note the results.
Consult with the cam manufacture as to what stall, gear ratio, tire size,l etc that he recommends for that grind. Re-read the advice that was given to you today and see how that equates.
|12-24-2003 06:01 PM|
You can make that tunnel ram work. It is not ideal for street use but can be made to run.
Your power band should start ~3200, I would think a stall in the 3000 range would be a minimum. 3.73 gears would also be minimum.
You said you upgraded to a larger acc pump, right? Did you change the acc cam as well? If you didn't you really haven't changed anything. You will have to find what works for your combo as far as with acc cams. Your bog is cause by a lean condition (as described above). You may need to change your squirters as well. It would take a lot of typing to explain the whole tuning process. Does the suggestions above make sense to you? I don't know how much carb experience you have. I don't want to get to carried away.
With your stall you need to understand, that those long runners (tunnel ram) make very little torque down low, this means a converter that would stall at 2500 behind a non tunnel rammed car may stall only at 1800 behind the tunnel ram. Add a tranny cooler if you don't already have one and increase the stall to at least 3000-3200 (if you are buying off the shelf stalls).
You have a relatively small engine so it will be a little more crucial to get tings just right if you want it to be fun to drive. With a larger engine and a tunnel ram it is easier/less finicky, more forgiving. They make more torque so it covers up some of the downfalls of the tunnel ram.
One last thing, I think a solid flat cam would have been a better choice for this application. To make any power you are going to have to spin that 350 and the hyd roller is not the best type of cam for that. Your effective power-band will be from 3500-6200 if everything is tuned perfect. With a solid flat tappet you could stretch that power-band out to 6700 (maybe more). Tunnel rams are made for higher RPM operation.
Hang in there this is part of hot rodding, make it work.
OH, one very important question, what kind of compression are you running?
Let us know how it goes.
|12-24-2003 12:10 PM|
You should recurve the distributor. Run it with 18o distributor advance and 16 initial. I would get a Mallory Unilite with mechanical advance also. Look on Ebay, they are cheap. You might need more accelerator pump shot as well.
Gears will help too. They aren't that expensive, and will make a big difference.
|12-24-2003 12:02 PM|
it idels around 1100-1200-and im not sure of the initial timing.
i dont have the vaccum hooked up to the distributor,im going to run it with it unhooked. i never liked it hooked up. my friend runs his unhooked. my stall is around 2600-2800 i belive, i was running a 488/510 cam now its 560 lift so i believe my stall should be ok but im planning on going to around 3200-3500 soon
my trans is a 350 automatic, i have 2.73 gears and yes i know i got to changed that lol .. my tires are 295/50r15 my friend runs the same size tires as i do, and yes it kinda spits when i hit the gas going around 50 or so, thanks for all the advice guys, robbie
|12-24-2003 11:17 AM|
That is classic performance for a racing manifold used in off-idle service. When you hit the throttle, vacuum in the manifold drops, charge velocity falls drastically and the gasoline that was being carried as a mist/vapor condenses and falls out of the stream. The usual way of overcoming this is to overkill the accelerator pump and dump in a huge amount of gas to compensate for the bog. Not the best way to do it but it works. Forget gas mileage, there won't be any!! Also sounds like you need a higher stall speed torque converter. If you don't have at least a 2000 get one. Better yet for your rather radical combo, get a 2400. Also, you MUST use vacuum secondary carbs - if you have double pumpers, you simply have WAY too much carburation for the street.
One thing you might consider is to reduce the volume of the tunnel ram, especially if your car is mainly a Sonic Drive-In cruiser. Get some Devcon epoxy putty (the industrial stuff, not the hardware blister-pack tubes) and fill the box so there is only a small volume below each carb plus a small (1") crossover between the two plenums. Look at Chrysler's old cross ram manifold they made in 1960-61. Long runners, two carbs and small plenums on a production, street driven car. Reducing plenum size will vastly improve street-ability and won't affect the top end power that much. The power increase from those manifolds is primarily from the length of the runners. There is no need for the huge plenum volume, other than ease of manufacture.
Here is some reading material on the subject.
Cross Ram maniold for a Chevy
Chrysler Cross Ram
More Chrysler info
More Chrysler info
Ram induction theory
|12-24-2003 11:06 AM|
|Crazy Mopar Guy||
I have run dual quads on almost everything I've ever owned, even my daily driven work truck had a warmed over 440 with a tunnel ram.
I found that certain carbs worked in certain conditions, and the tuning made all the difference. I ran two Holley 450 carbs on the work truck in the picture, it ran better than any single 4bbl I know of, cold starts, driveability, everything was pretty damned good.
The keys to MY tuning were using stock springs in the distributor for the advance, running 36-38 degrees total timing, and no vacuum advance lines were hooked up. I never had any troubles whatsoever.
I ran over a dozen small block Chevs with tunnel rams, and- with the exception of my two present cars, had most of my street cars I've owned with 2X4bbls for the last 15 years.
It's the combination you need- parts combination and tuning combination, and once you get it you won't go back, IMO...?
|12-24-2003 10:38 AM|
Are you running an automatic in that thing? If you are and are using the stock torque converter that could be your problem. The stock converter will work against the engine that you have in there, until you get into your power range (2800 - 8000). One of the other thing that you might try doing is adding a little more air into your idle circuit by drilling a 1/16 hole in the primary butterfly of the carb ( I'm assuming that your running a Holley). Changing the pump shot should also be considered. Just a few considerations to make, hope this helps.
|12-24-2003 10:34 AM|
Need more info.
What is your idle RPM?
What is your initial timing set at?
If you have vacuum advance, are you connected to the Ported or Full vacuum fitting?
What stall speed are you running?
What trans are you using?
What rear gears?
What diameter rear tires?
When stomping on the "Go pedal" at 50-60 does it spit back thru the carbs or just fall on it's face?
|12-24-2003 10:24 AM|
need help????with tunnelram set-up on sb350..
I have built a 350 sb with a tunnelram. The problem im having is after i start it up and it warms up,it wants to bog when i start to go,and when i put in in gear its wants to cut off at time. now i know alot of you guys are going to say that running a set-up like this aint for the streets but a friend of mine has one and his runs good.,but he cant offer me no advice cause the guy that helped him has moved so im turning to ya''ll. his car is almost the same as mine, both are novas, and we have the same tunnelram from summit with 2-440cfm carbs. but with his, he changed the nozzles in his carbs and changed the accelerator pumps from what came in it to 50cc diaphragms. we both have 64cc heads,mine are cast iron,his are aluminum with the same kind of vaules. he went with a 6oo lift roller hyd cam,i went with a 560 lift roller hyd cam.. after i started the engine i set the timing at 36 total advance ,it will idle perrty good. i have checked my vaccum with the car in gear and it was between 8-9. i changed the power vaules . it had 8.5 so i went with 5.5. i was told that was good. well any help would be great before i start changing parts, here is my set-up.
tunnel-ram with 2-450cfm carbs(rpm range 2800-8000)
hyd-roller cam 288/286-230/230-560/560 lobe 110
part number 12-450-8 comp cam(rpm range 2500-6000)
64cc sportsman heads
flat-tops piston with 4 eyes
high flow fuel pump
msd distributor part#8360
its not skipping ,it just falls on its face when i hit it. even when im running about 50 or 60 it will stummble when i give it mor gas.