muggsyjack

I have a 750 Vac. Secondary carb on a 305, open headers, long dur. cam and torker manifold. Th-350 Trans, 4.10 rear gears and 3500 stall converter. Car has run 8.6795 in 1/8th mile. 81+ MPH. After runs, plugs look fine. Light tan electrode.

Question #1

How do I know if secondaries are opening correctly? Car seems to build RPM slowly, I am guessing the lower vac. caused by cam is delaying full secondary operation. There is no miss or anything, it seems like car gradually accelerates in both 1st and 2nd gear.

Question #2

The is an off idle hesitation at times. is this related to idle circuit issues? It will hesitate very momentary and then recovers fully without backing off. It is most noticable at lower rpm launches.

I have bought a tuning manual. I now see where transition slots may prevent clean idle circuit operation. I have already put a 65 power valve in because my idle vacum is 13.

Any insights would be helpful.

__________________
1992 Camaro RS
350 cam, headers, manifold, 750 d/p carburator. Th-350, 5400 stall TC, Moser 9", 430 gears. Boxed LCA's, adjustable panhard bar, air bags.
Red Car (mine)
Best 350 ET: 7.18 1/8th mile 95.0 MPH. 1.52 60'
Best 305 ET: 8.01 1/8th mile. 85.45 MPH. 1.72 60'
Black Car (son)
6.88 1/8th mile 98.5 MPH 1.44 60'
6.41 1/8th 107.6 MPH 1.41 60' (125 N2O)

Chickenman35

You have three things effectively killing bottom end torque. Long Duration camshaft...what are the specs? Open headers ...kills bottom end torque. And the Torquer manifold.

There is much better technology than a Torker available today. A Torker kills bottom end grunt on a 350...let alone a 305. Old, old technology.

On a 1\8th mile track I would recommend a Dual Plane such as a Performer RPM .

If..and only if the engine is built to the nuts with lots of compression and good heads, would I consider going to a Single plane such as a Victor Junior. If you can pull 7,000+ RPM out of your 305..then go with a GOOD single plane. A Torker is not a good single plane. It's time has come and gone.

Run a full muffler system. You need TORQUE with a 305. Open headers kill it.

You should be able to run a fairly soft spring on the secondaries. A long yellow would be a good starting point. Attach a paper clip or rubber O-ring to the secondary rod off the diaphram. Then you can tell how far the secondaries are opening. Don't be surprised if you see no more than 1\2 to 3\4 opening on the secondary. That is not an indication of a problem. It's probably only how much air the engine will pull.

What accelerator cam are you using and what size shooter? More details on your engine please. Such as timing. compression, head specs, camshaft specs etc.

muggsyjack

Cam is 235 duration @ .050, .488 lift. Using 1.6 roller rockers. Carb is 750 Vac. secondary. Timing is 20 static w/38 full mech advance @ 3000 RPM. Compression is 10.5 to 11.0 to 1. Cranking compression test was 220 PSI.

Heads are weak point. Stock 305 HP heads w/1.94/1.50 valves and 3 angle valve job. Milled to improve compression. Minor relief around valve to unshroud.

Ignition is Accell dist w/300 series box.

Send me your E-Mail and I will forward video of car on single pass. Engine runs clean just does not wind out as quickly as I would expect.

Is not a dog, 8.6795 @ 81+ in 1/8 th mile.

Chickenman35

Ok...sounds like a fairly potent 305. Is that .488 lift with 1.5 ratio rockers or the 1.6 rockers. Just curious.

Sounded like you were complaining that it was weak in 1st and 2nd. Quote: There is no miss or anything, it seems like car gradually accelerates in both 1st and 2nd gear

What RPM do you launch at? What spring do you have in the Secondaries now. What Pump cam and Shooter size do you have?

I still think that the Torker and Open headers hurting you. I tried a Torker on a fairly stout 350 years ago and it just killed my bottom end performance. Car was lazy just as you described. What RPM do you turn?

A Performer RPM will pull strong to 7,000 but has a slightly fatter torque curve than a Victor JR. In side by side Dyno tests there is surprisingly little difference in the HP figures between a Performer RPM and a Victor JR.

Circle Track tested both the Victor Jr and a Performer RPM a couple of years ago and found they were neck and neck. The Perf RPM made a bit more Torque on the Bottom end and the Victor Jr made a bit more HP on the Top. The Difference was something like 12 ft\lbs of Peak Torque gain with the RPM vs about 10 HP Peak gain to the Victor JR at the top end. Mind you this was on a very well built ARCA series motor...350 cubic inches. A 305 is going to be lacking in Torque compared to a 350....so I still swing to an RPM


The open headers aren't helping you either. A proper full lenght dual exhaust, with an H or X pipe and Dual mufflers such as Flowmaster's would really bump your bottom end torque and cost you nothing in HP. In fact you would probably pick up a bit of HP. Proven time after time in dozens of articles....

Not saying that the car is a dog...just that you could have a better combo. Carb tuning may help...but you still have some basic problems with your setup.

However...simple things first ( and cheap ) ...so post the info on the carb, launch RPM's , shift RPM's etc... and we can go from there.

Chickenman35

BTW...cam duration and vacuum readings have no affect on the opening rate of the secondaries. It is entirely dependant on airflow velocity.

Holley's have a very sophisticated VS circuitry ( Much better tha the Demon's but that's another subject ) . Initial opening is controlled by a Pitot tube that is connected from the Primary Venturie to the Vac Diaphram. There is a an air bleed in this circuit that balances the circuit to ensure a smooth operation and to ensure that the Vac Secondaries will close.

Once air velocity in the Primary Circuit reaches a sufficient value, enough vacuum will be applied to the Vac Diaphram to start the Secondary opening. On the Secondary side there is an additional opening that is connected to the Vac diaphram and to the Primary Vacuum circuit. The Secondary feed provides two basic functions.

1) Provides a stronger signal to diaphram as the secondary throttle blades open.

2) Acts as an an additional air bleed when the Primaries close. Along with the Main air bleed this ensures rapid bleed of of vacuum to close secondary throttles rapidly

Chickenman35

A couple of suggestions off the top of my head to get you going. These may change once you post back with the info requested.

) Secondary spring. I'm thinking a long yellow spring should be a good starting point. May be a bit light. Get a quick change cover kit if you don't already have one. Check opening amount with the paper clip trick.

2) Pump shooters. I'm thinking you'll need at least a #35 shooter with the Torker. Try a Blue cam in the #2 hole. Get a hollow shooter screw.

3) Transition slots. No more than .040" exposed on the primary side. Open the secondary side a bit more if necessary to close the primary blades a bit.

muggsyjack

.488 is with 1.5 rockers. Closer to .520 w/1.6. Thought this may help compensate for heads. Carb is out of box except for 65 power valve.

Launch is at 2000 RPM. Anymore and car tries to creep, brakes won't hold. Shifting at 6500 RPM. Have tried lower points to no great impact. Fifteen passes total, all in 8.67 to 8.78 range. MPH remains somewhat constant.

I would post vid of single pass but is too big for board upload. Considering testing dual plane and/or 1.5 rockers.

Chickenman35

RPM range certainly within that of a Performer RPM.

Still need to know what shooter, and cam you have. List number of carb would help a bit...although a physical check is best.

I think I'd try 1.5 rockers on the intakes only. If ET drops then an indication that the engine want's less cam.

Video's hard to tell ( unless something grossly wrong ) what the ngines actually doing. What looks great on video can feel like crap in the car. You're the best judge of what works.

What do you have in the back for brakes? Drum or disk? Drums will actually hold better against the convertor than disks. Drums have a self-servo action. Disks don't.

Either way an adjustable proportioning valve will help you out. Crank more brake Bias to the rear.

muggsyjack

Carb is 3310-3. Power Valve was changed to 45, not 65. I also have a 35 if needed. Otherwise it is same as delivered. choke is wired open. Running 5 PSI per gauge. Using in tank TPI pump w/Mallory regulator. Cannot run pressure higher because gauge bounces. Installing new gauge on cowl to verify pressure during run.

Drum brakes in rear w/new shoes. Cylinders good, m/c good. Rear tires start pulling free between 2200 and 2400 RPM.

Looking at spring specs w/assortment. Stock spring may be issue. Will try long yellow and straighten transition slots/idle plates.

Should I order a trick kit for cams or are they separate?

muggsyjack

I may be chasing ghosts to a degree. Last time I raced it was a dragbike running 10's.

muggsyjack

Also have one inch spacer under carb. Used single plane in expectation of nitrous addition at some point.

Chickenman35

OK..3310-3 comes with a #25 shooter out of the box. Tech specs don't list cam, but it probably came with a white or a red cam. Either way not enough initial shot. Your 3,500rpm stall convertor helps mask some of the problem.

Order the cam assortment. Always nice to have the different profiles to play with.

I'd still recommend the Blue cam in #2 hole. As for shooter...try a #31 and then a #35. See if that gets rid of your tip in hesitation.

Rear brakes. Drums should be able to hold the rear wheels. May take a while for shoes to bed. Do you have a line-lock on the rear drums or do you do the two foot shiffle?

Either way I'd recommend an adjustable proportioning valve to crank in some more rear bias. That should do the trick. Premium lining are a must.

Stock secondary spring is a silver or "plain" spring. Fairly stiff on a 350. Definately too stiff for a 305.

Power valve has little affect in Drag Racing. As long as it's at least 2 points lower than vaccuum reading at idle in gear it will be fine. Power valve tuning has more affect in Road Racing.

Having a re-think on your Torker....your high stall convertor ( 3,500rpm ) and 4.10 gears are probably masking it's poor low end performance. Convertor allows the engine to flash past the weak point of the manifold. Still...there is better technolgy out there. I'm thinking a Victor Jr might give you a bit more HP over the Torker. Still a lot of manifold for a 305 though...

Brilliant thought!!!! Why not give Edelbrock's Tech line a call? That's what they're there for. I've had pretty good service from them. The odd time that I got someone that was in over their head ( New guy ), they immediatley switched me over to a senior staffer.

BTW..I've used Nitrous on a dual plane before...no problemo. Just check the spray bar orientation before purchase.

Chickenman35

Couple of other tips. Remove the choke assembly entirely. Install a K&N stub stack...this will really help flow through the carb. Might be worth a tenth all by itself.

Pablo

Stick with the single plane, 95% of the rpm your car is in is where single planes build more power. Dual planes only give more signal to the carb on low end by making it appear smaller, I think the longer runners giving more low end perf. is neglible. I have run FI on my single plane and I have low end to spare, so i think its mostly vac. signal. The runners are tuned for low rpm anyways. With a dual plane youll also have 1 half of the engine with a much bigger plenum than the other and more disparity between runners.

Now if you have the ORIGINAL torker i would suggest you get rid of it it is an X manifold and they are pretty terrible. The Torker II isnt bad though, I have one and as you know i trap a hair away from 105 with a 305 with full exhaust, and smaller cam.

If you are going to swap manifolds id definately go with a victor junior. I think you should put some more work into the heads though before you think of anything else, just removing all the casting irregularities from a set of 416s has to be a huge gain.

muggsyjack

Have cams and squirters ordered. Already swapped spring. Will try your recommendations. May not get to track until next week.

Appreciate the help.

icebird_1981

with VS the car is suppost to gradualy accelerate smoothly, u r not suppost to feel the secondarys open and if u do that means they r opening to soon.

muggsyjack

changed spring, replaced nozzle and cam..... Engine runs crisper, response is improved. Will be going to track next Friday night to test...

Chickenman35

muggsyjack

Special thanks to Chickenman.....his tuning tips helped to drop best time down to 8.3559 @83.03 in 1/8 th mile.

Chickenman35

Wow...over 3\10's in the eighth mile and nearly 2MPH. That is good...Excelllaaaant

muggsyjack

Tonight ran an 8.3445 @ 83.26 MPH w/1.8936 60' time.

The next question is: I have the long yellow spring in and there is no bog present or any indication of secondary opening. Should I try next lighter spring in secondary?

Plugs look great, light tan w/little sap buildup on outer ring.

Chickenman35

Go for it. Your Et's will tell you if you went the right direction. You should not be able to feel any secondary opening. If you do, it usually means the spring is too light. At that MPH and ET you can be assured that the Secondaries are opening. Note: they do not have to open all the way....opening rate is more important than amount. A 305 at 5,500 RPM with a 780 VS may only pull the Secondaries open 3\4 of the way. That's fine. That's all the air the engine needs.

What happens is that you get a slightly lean condition if the secondaries open too soon. Not enough airflow to start the secondary boosters flowing properly. This lean condition is very subtle...you may not be able to feel it...although a dyno should show it...both in HP\Torque production and A\F mixture.

Doesn't last long, but when you finally get enough airflow through the secondaries, the boosters start flowing and that is the slight " kick" that you can sense. You've passed through this slightly lean area and now are getting a correct booster signal.

Dragstrip a very good way to set up VS carbs. The ET and MPH will not lie.

83 Z28 HO

Hmmm, on my stock crapajet I can BARELY feel the secondaries open with I floor it from a stop or slow roll. Odd. But I'm getting a 600 or 650 and disconnecting the computer so.

bidle98

I had a holley on my 406 and I had the same hesitation sometimes and I did have slow rpm build up. I figured out that my converter was not big enough and to play around with the power valve and squirters.I havve just a little bit bigger cam then you do but same mite apply.

F-BIRD'88

your 1/8th mile ets amd mph convert to 13.10@105.4mph

not bad at all.

I'd try increasing the initial timing to a full 35deg.
remove the mechanical advance springs and weights and tie wrap the mechanism fully advanced. reset timing to 32-36 deg.

This motor will make maximum hp at near 7000rpm.
This car needs more rear gear ratio to use all the motor up in the quarter mile. I'd move up to 4.56's... 4.10 are not enough gear.

The cam may respond to being advanced a few degrees.

The old edelbrock torker is infamous for a pesky off idle stumble.
Carefull tuneing of the shooter size, pump cam and initial timing setting will get rid of the flat spot.

The 750VS secondary opening rate can be further tweeked by
using a Quick fuel technology lower vacuum diaphram housing with the adjustable vac bleed rate screw (looks like a idle mixture screw on the lower housing). But will take carefull tuning
as to much opening will cause the car to bog.

220PSi is a lot of cylinder pressure for street pump gas.
Try some race gas. (110 octane)
Try some 12-18" long collector extensions to enhance the torque ...

Chickenman35

Weakest point in the combo is the heads by far. Huge HP to be gained with better heads. AFR's would be my choice...although the Edelbrock RPM's are nice as well. Valve train on Edelbrocks not up to the task though. Too wimpy of springs for your combo. I went to Isky 8005a's on my motor with a Comp Cams 236\242 @.050" and .575\.590" lift ( with 1.6 ratio rockers ). I'd definately go with Aluminium.

Edit: With your current heads no point winding the motor up. They just can't flow enough air. Just about anything would be better than the stock 305's that you have. I would choose some good quality Aluminium heads such as AFR, Holley or Edelbrock with a suitable combustion chamber to keep your 10.5 to 11 to 1 C\R. Keeping you C\R around 10.5 to 1 with Aluminium heads will enable you to use a good quality pump gas no problem.

Edit: Intake? I'd go with a Victor JR. No use changing intakes till you do something about the heads...they are the cork in the system right now. But you probably already know that.

Note editing!! Got in late last night at 2:00AM Got your post confused with one above and thought you had a 406

Heads still the weak point...but not nearly as bad on a 305 as on a 406 LOL!!

muggsyjack

Per Chickenman suggestions, we made carb changes and car responed well. Flat spot/stumble gone. Car will now light tires if you stomp from an idle. Using new 12" wide Goodyear Nascar slicks off E-bay. Traction is an issue at present.

Current best time is 8.3345 @ 83.74 MPH w/1.89 60' time. Tach shows 5000 RPM at the finsish line in 3rd gear. We know the heads are weak point. Currently have them off to match gaskets, open as much as possible and remove casting flash. Current best is arrived at by shifting at 6200/6300 RPM. Tried both higher and lower and car slowed.

Hoping current effort allows improved breathing. Anything would probably help. Also adding shift kit and 90/10 shocks to improve transfer and gear change. Son says 200 to 300 RPM lag before shifts.

The 305 was originally intended as a throwaway motor for me to become more familiar with tuning and son to get used to car/drags. Did not really expect it to respond as good as it has. All components are lower grade. Especially the heads. Could not use original swirl port models as they would not breath above 4000 RPM. Cam is Summit cheapo. Springs are off brand (they are strong as I keep bending my spring compressor removing them). Heads were milled to hell and back. The manifold is a $40 Torker2 off e-bay. The engine had been rebuilt prior and only had 20k on it. New bearings, rod bolts and high volume pump is only bottom end investment. Even dumped original hyd. roller setup as the valvetrain weight would be too much for stock diameter springs.

Overall engine runs good, enough so that no one believes it is a 305 2 bolt POS. I like sound of open headers and it is loud. Most guys are running some type of muffler. I have 45 degree turn downs to keep exhaust from heating fuel lines and trans.

We would like to see 12's N/A before adding nitrous. Since the car is running last part of 1/8th in weaker band, 1/4 mile should be in the high 12's.

How much gasket matching, general opening and cleanup will help I cannot even make a guess. I have all the tools required from racing two stroke triples years ago. Any improvent will show.

I had originaly installed 1.6 rockers to help heads breath better. Maybe I would have been better using 1.5? Any comments?

I appreciate any input as I am relatively green on current trends. I am more familiar with AFB's than Holleys.