Dual quad tuning

[Sirshredalot]

Hey yall.

Cool new forum here.
So my monza is ready to hit the roadsand tear emup...only I got a problem.

Im running a tunnel ram (weiand street ram) with dual 600 single pump vac sec. holleys.
Both carbs are identical with the same jets, cams, squirters, and pumps.

Intake is heavily modified...so I know everything is working together.

But...I seem to be getting some problematic backfiring through the carb wheneverI stick my foot in it hard...this equates to a giant fireball through the carb followed by a mushroom cloud of black smoke...So i am assuming I need to replace the power valves.

but I dont think I have any vaccum leaks and I would think that 1200 cfm of carb wouldnt run lean anywhere.

Does anyone have any experience tuning tunnel rams?
Please help if you can.

PS: before you tell me that running one carb would be easier...this I know...but the harder it is to do...the cooler the results...soImsticking with the ram...plus I have about 20 hours of labor in the intake alone.

God bless
-Shred

[gerbsinmd]

What size Jets do you have in it. What can you tell us about the engine, comp ratio, cam, etc?

I would bet that the Jets would have to be a bunch smaller than on a single carb.

Black cloud of smoke says too much fuel to me.
Darrel

[greg72]

I ran a dual quad tunnel ram for 5 years on my Vega 355 ci engine. I started with 2 holley 390 cfm carbs , but they were too lean on the top end . So i went up to 2 Holley 465 cfm carbs . they worked perfectly. I also had a trick piece on each carb that holley used to make (probably still does) it was a cover for the vac secondary diaphragm that had a tube on it so I was able to connect them both together to equalize them .

I don't remember what jets i ended up with , only that i did not need to fiddle much with the 465s to get them to run right.

I ran an edelbrock tunnel ram the weiand ram's runners were a bit big and wanted to be sure that my power curve started @ about 2500 rpm .... and it did . The 355 had 10.25 :1 CR with GM camel hump 2.02 heads (hey c'mon it was 1984! ) and they had some porting work done. the cam was a crane hyd that made power from 2600 up to about 7k .

i used an MSD 6 box to fire it ,along with an Accel super coil and magnetic pick up distrbuter, the rear was 3:90 the trans a manual 350 and the converter was a bnm 10"

The car ran low 12's with a horrendous 60 ft time, on street tires.

I drove the snot out of the car put thousands of miles on it . than got stupid tubbed it, got married . had kids etc etc it has sat in the garage ever since .....but i digress.

I agree with you, a tunnel ram can live on the street .

Without knowing your specifics I would hazard a guess that you are dumping too much fuel.

I apologize for the long post , but i wanted to be sure to cover all aspects of the drivetrain....as with any application it should be matched. especially important when you are running someting more complex than a single vac secondary carb.

[Sirshredalot]

Sorry bout that...engine is a 327 with a set of HO 305 heads...1.84/1.5 valves.
Compression ration is roughly 10.5:1

Cam @ .50 is 222/222dur And 447/447 lift, 112deg. with 1.6 rockers on the exhaust side.
Springs are rated to .550 lift

Intake has lower runners epoxied and tapered to match the heads, upper plenum has been divided and the upper ports have been reduced in size to aid air velocity.

carbs both have 47 jets and 28 squirters.

An MSD 6a box lights the plugs up too.
TH350 w/2000 stall


I know the heads arent good for power past 5500rpm...but thats where I want the engine to stop anyway...I built the engine for streetable torque and the WOW factor...I love the pro-street look but am not a big fan of the drivability issues associated with huge duration cams and super steep gear ratios to be able to drive the car.
Also...I am a poor college student who is using what he had sitting around....haha.

I hope this gives enough info about the car to aid.
Thanks for the replies

God bless
-Shred

[greg72]

The work you have done to the intake sounds spot on for getting it to work better in a street application, getting greater velocity at lower rpms.

You are using 1200 total cfm on a 327 ci motor with small heads and a cam that starts making power about 2K, which matches your converter.

Everything else you have done seems to be a decent fit. That makes me think it is the carbs. My gut feeling is they are too big.

Hopefully there are others who have some experience with these intakes and they can share what they have learned. If nothing else many on here have carb tuning experience and as Darrel mentioned: black smoke usually indicates a rich condition.

[Elfmagic]

No one has mentioned the accelerator pump cam, just a thought but i agree that the carbs are probably too big.

[cosvega76]

Shred,

What size accelerator pump diaphragms do you have? There's a lot of volume to fill in that tunnel ram, you'll probably need the 50cc accelerator pump kits for those carbs.

Chuck

[gerbsinmd]

Check not only the accelerator pump cam, but the squirter size and accelerator pump size. 30 and 35 squirters were too much for for my dad's 383 with a 750 holley. I would think a pair of 28's (one in each carb) would be WAY to much for a 327. If you'r e running 47 jets, I would downsize the squirters a lot and see what happens.

Darrel

[Sirshredalot]

Hey...my mistake

I have 67 jets all the way around
All with 30cc accelerator pump diaphrams
9.5hg rated power valves

Thing is...I thought i was getting a lean pop and fire ball out of the carbs but I checked the plugs and they where horribly fuel fouled so I stepped up to a hotter plug....I was running R42ts' and switched to R44ts'
and gapped them a touch wider at . 040 over the 35 that I had the 42's set at.

Also someone brought up a good point that i might be running out of fuel because I only have one electric pump and 3/8 steel line to fill two carbs.
I know Ive got enough pressure but i think volume might be the problem.

Im going to try stepping the jets down to somthing like a 60 and throw another feed line onto my fuel cell with a second pump (one pump for each carb) and regulate them at the intake.

Im also considering using the electric pump as a supplementary pump and adding a high flow mechanical pump on the block...I just dont have alot of room down there to work with cause Im using the Hooker/TD style front plate mounts and I need a fuel pump that can be re-clocked to face the back of the motor.

I know its running rich because the plugs where fuel fouled pretty bad and when I removed the carbs I had a nicely atomized fuel/air fog in the intake just from trying to start the motor.

Please let me know what you guys think about the changes I have in mind...this is my first TR setup.
I know I should probably have 450's but those were not in the budget...cause the 600's where paid for...haha.

God bless
-Shred

[gerbsinmd]

If you have the means I would also take the squirters for the accelerator pumps down in size. I did that on my dads car and it cleaned it up a lot on the step in. If it is popping and stalling immediately when you stomp on it hard AND it is fuel fowled like you say, it is getting way too much gas. If you can ease into the throttle without any problems then the squirters are the first place I would look.

It sounds like you are doing the right thing with the Jets, I just wouldn't be afraid to take the size of them down a bunch more and try it.

Darrel

[starfire383]

With all due respect, I understand where you're coming from, but can't imagine a much more mismatched combo than 1200 cfm of carb on a tunnel rammed 327 with tiny 305 heads, and I think this is where your problem lies.

Here's my take- you're not moving air fast enough, and the backfire is a classic symptom of not enough fuel in the cylinder. But no amount of squirter shot will cure it, here's why

The small cubes of the 327, combined with the super small runners of the 305 heads mean that the air is not moving thru that intake at high velocity.

End result, the squirter shot has to travel thru a foot of intake runner to reach the valves, and it's doing it at a lazy pace. Air moves faster than fuel droplets (and they will be droplets, you'll never get good atomizaton with that much intake on a small motor with tiny heads) so when you hit the throttle, it gets a big gulp of air before the fuel reaches the valves.

Unfortunately, I can't see a good answer to your problem without changing the hard parts of the engine. Perhaps a solution would be a super high stall converter to unload the engine during the throttle stroke and allow it to rev without as much load.

Also, you're confusing tuning issues. Backfire on the throttle stroke is a lean spot 99.9% of the time. What's happening is the engine is running insanely rich at steady throttle due to having twice as much carburetor as it needs. But when you're stepping in it, instant lean spot. It will probably always run insanely rich with that much carburetion. Huge throttle blade area with little cubic inches means lazy air in the venturis. Which leads to poor atomization, which leads to rich mixture.

Bottom line, those black spark plugs aren't telling you anything about the backfire.

Good Luck!

[dwragon]

and dont use a mechanical pump,
it steals hp,
you cant put two on one block,
they leak into the blocks and wash out the rings and bearings.

[Sirshredalot]

I guess I should update my progress here.

carbs now have #35 squirters with white pump cams turned backwards...brings in fuel VERY fast...but I still have the 30cc pumps.

I also believe I put in a set of 8.5 power valves in place of the heavier pair....And the float levels are perfect.
I have removed the choke assemblies as well.

I have restricted my liquid feed line in the metering plates to cure the plug fouling at low rpm.

I still need to take vaccum readings but I havent got the motor all back together yet.
I just installed a set of pro-topline iron 180cc heads....I am having trouble getting my rockers to line up....I either need offset rockers or i need to have the heads machined...Im not sure which one is cheaper yet.
It sucks because i already have a great set of roller rockers...I believe theyre older erson rockers....really high quality.

But...Ive also got my headers installed (hooker 2129's) and my Mallory Unilite installed with my MSD 6A properly hooked up now.....Im still in the process of redoing my fuel system.

I will be running a holley blue pump regulated at both carbs with 3/8s steel line throughout.
I also have my vaccum gauge to monitor all the ongoings...I just need to cut another hole in the dash for it.

Id really like to run a mechanical pump in addition to the electric because I dont trust electronics....but i have seen the diaphrams blow out and fuel wash the oil....plus they cost near as much as the electric.

So im making progress in a positive direction.

God bless
-Shred

PS: If anyone has a set of offset rockers that they feel like getting rid of lemme know.
...I know...yeah right....but its worth a shot.
Im also lining up the toyota diff swap...so stay tuned for that.

[dwragon]

whats this with toyoto parts in a chevy? I just bought a 07 tundra. Im looking at the engine, and it loks like an aluminum chevy small block with Hemi heads on it, and it has a 6 speed auto hukd up to 430 rear gears. 350 ci, 381 hp, 413 torq. Had nightmare about putting it into a vega after being rearended. hope it doesnt come true. The blessed curse runs in my family. But dam it would move.