Engine Tuning Issues

[Mr. Fixit]

5" of vacuum is the big clue, that is way low. My crate SBC idles at 20", with a stock cam. Your cam (do you have the part number?) is a bad ass street/strip item. Big cams kill vacuum, make the engine run rough, etc. Screwing with the carbs won't fix it.

Timing is not your problem either, but FYI I run 20 initial, 15 vacuum and 15 speed. A street machine really needs a vacuum advance distributor; it runs cooler and smoother, gets better mileage, has more power and better throttle response. It's a no brainer. Check the MSD 8394. It has electronic speed advance (no springs, bushings, etc) and vacuum advance, all adjustable with a screwdriver.

WHAT? :nono:

An engine is an air pump that uses fuel and and an ignition source to create power.

Stating that "screwing with the carbs" or that "timing isn't my problem either" makes no sense to me. These are the two major components to tuning an engine, right??? The type of distributor, or type of advance is chocolate and vanilla IMO.. The cam # is Comp Part 12-443-8

Thanks..

 

[PotvinGuy]

But you don't have a tuning problem. You have a cam that is street/strip, rough idle, per CC website, and it will have low vacuum. Now you can experiment with the timing and the carbs to minimize the roughness, and if that gets you to a performance (smoothness, mileage, power, response, temp) that is acceptable to you then you are good to go. But you are compensating for a cam that isn't designed to play nice. Now some folks like the lope, the roughness; I like my ride to purr like wifey after a box of wine. Pick your poison: int:

Re distributors and advance: I've run 2 MSDs and 2 Mallorys on my motor. All were quality pieces, but the vacuum advance was what made the big difference. And once you get the timing even close to typical numbers, you're OK for the street. I run the Mallory computer dissy, and have played with the curves at length; trust me, big changes are not to be found by tweaking.

My SBC idles cool and smooth at 900 rpm, 35 degrees advance (20+15), 20" vacuum. And if you want that, you can't get there with your cam. :wall:

 

[Mr. Fixit]

But you don't have a tuning problem. You have a cam that is street/strip, rough idle, per CC website, and it will have low vacuum. Now you can experiment with the timing and the carbs to minimize the roughness, and if that gets you to a performance (smoothness, mileage, power, response, temp) that is acceptable to you then you are good to go. But you are compensating for a cam that isn't designed to play nice. Now some folks like the lope, the roughness; I like my ride to purr like wifey after a box of wine. Pick your poison: int:

Re distributors and advance: I've run 2 MSDs and 2 Mallorys on my motor. All were quality pieces, but the vacuum advance was what made the big difference. And once you get the timing even close to typical numbers, you're OK for the street. I run the Mallory computer dissy, and have played with the curves at length; trust me, big changes are not to be found by tweaking.

My SBC idles cool and smooth at 900 rpm, 35 degrees advance (20+15), 20" vacuum. And if you want that, you can't get there with your cam. :wall:

Understood!

I must say that that she runs smooth though, not very lopey at all, but has lot of overlap. I have tried many settings and she is very sluggish at 20 initial and won't begin to wake up until about 25. She runs a solid 190-200 degrees even in the florida sun in traffic ever since I made the radiator shroud. I know I am getting closer to acceptable, I was just concerned about the higher idle in neutral. As for the so called milage, I think I am around 10, but burning effeciently with no smoke and nice looking plugs. :angel:

 

[PotvinGuy]

Understood!

I must say that that she runs smooth though, not very lopey at all, but has lot of overlap. I have tried many settings and she is very sluggish at 20 initial and won't begin to wake up until about 25. She runs a solid 190-200 degrees even in the florida sun in traffic ever since I made the radiator shroud. I know I am getting closer to acceptable, I was just concerned about the higher idle in neutral. As for the so called milage, I think I am around 10, but burning effeciently with no smoke and nice looking plugs. :angel:

Outstanding! Question: how was starting at 36 fixed, or at 28? Another advantage of a vacuum advance is that you can get easy starting at, say, 20, and then the vacuum will kick it up to a higher advance for idling (PotvinGuy must own a distributor company :flip: ).
Not sure why the idle changes so much from N to D. Normally that would indicate a tight TC, but yours sounds fine. I run a B&M Holeshot 2400, and the idle drops maybe 100 rpm.

 

[Mike]

I see you're now onto what PotvinGuy was saying to you.

I want to be sure I am correct in what I am saying. From the general gist of this topic, it seems you have been working at trying to get the car more responsive off idle. Yes?

The key word in that statement is 'idle'.

Take a look at your cam card. Look at the RPM range for the cam. 2,800 - 6,100 RPM. And you're trying to get the car to respond off idle?

Take a look at Weiand's recommendations on that intake manifold. 2,500 RPM and up. And you're trying to get the car to respond off idle?

You want things to work better? Then use the components as they were designed to be used. Get the car to the local dragstrip. Stage the car, get the motor all the way up against the converter and then let her eat. Those are race pieces, so drive the car like a race car. How well does the car respond in those conditions?

We used to build a lot of short-track IMCA Modified motors. We used a custom, mechanical tappet cam that didn't have nearly that much duration or valve lift. The LSA numbers were a lot lower, but we accepted the fact they were race cams and lived with it. Add the best part of 12.5:1 compression, Brodix Track 1 heads, HV-1000 intakes and 750 carbs. The guys loved them, because they would step out front on re-starts and pull all the way through 7,200 RPM (we used billet cam cores so we could run heavier springs). These were race motors, not street rod motors. They were outright slobbery up through about 2,600 - 2,700 RPM, but stand on it from there and they would rip your head off.

You're trying to use a bigger cam profile than that, along with a tunnel ram intake and two carbs no less, and make the combination transition well off idle? Hello??

You've never mentioned cylinder head chamber volume, but I'm betting it is way too high. The LSA on the cam will help a bit, but unless you're running a 305 casting or an aftermarket casting with similar volume numbers, your cylinder pressure is too low. Which will also contribute to a motor acting lazy.

When Comp Cams and Weiand are telling you to use their pieces at 2,800 RPM and higher, what are you hoping to find, nearly 2,000 RPM below that number? Whatever you're looking for, I can tell you it isn't there.

If you are married to what you have, then it's time to start looking into adding a band-aid or two. Was your cam gear drilled to accept bushings to change cam timing? If not, you'll need to drill it. Roll the cam up with a 2° bushing and check your piston to valve clearance. If you still have clearance, button her up and give it a try. Skip checking clearances at your own peril, because I'm betting you're already on the too-tight side of things.

That should help, considerably.

Get a couple fresh carb base gaskets and a piece of aluminum shim stock. Use your gaskets to cut the outline on your shim stock. Lift the back carb, drop on a fresh gasket, your new block-off and another fresh gasket. Bolt the carb back down. Give things another try. Rermember, you're back to just one carb, so your idle mixture settings are going to be in left field. How does that work for you?

If that works well, it's time to ditch that dual 4BBL top and replace it with a single 4BBL top. This will require a lot of money and a considerable amount of patience on your part, but take the intake base and single 4BBL top to a professional cylinder head porting shop. Explain what you're trying to use the intake on. Do your best to endure the laughter and explain why you need to use that particular intake. They can weld up the runners and stuff the plenum, to get them to a more reasonable volume. You are going to spend something in the vicinity of 8 times what the intake is actually worth, so be prepared for the expense to be high. Once everything is finished, bolt a 750 CFM vacuum secondary carb on top. You will want a selection of accelerator pump cams and squirters and a lot of spare time, but you'll likely be surprised at what you will be able to achieve.

You could find some improvement with a set of properly-built headers, but they will not come cheap. If something in the $2K range is within your budget, then that is another place to look. They will be designed to work, not to look pretty, so be forewarned. This would be the last resort step, in my not-so-humble opinion, so if you're not willing to spend time and money on the other suggestions, I wouldn't get too fussed over this one.

See? Playing with idle mixture screws and a timing light are not going to effect the kinds of changes you are hoping to find. If you want a lot of off idle throttle response, you are going to have to give the carbs a lot stronger signal than you are now. And it's not going to happen with that camshaft and intake manifold.

 

[Mr. Fixit]

Outstanding! Question: how was starting at 36 fixed, or at 28? Another advantage of a vacuum advance is that you can get easy starting at, say, 20, and then the vacuum will kick it up to a higher advance for idling (PotvinGuy must own a distributor company :flip: ).
Not sure why the idle changes so much from N to D. Normally that would indicate a tight TC, but yours sounds fine. I run a B&M Holeshot 2400, and the idle drops maybe 100 rpm.

Yeah, yeah, sounds like you have stock in MSD. :laff:

At 36 locked, no problem even all warmed up she starts right up. In order to get the 28 set up correctly, I had to open the idle speed some which explains the higher idle which also produced a much better throttle response off idle.

 

[Mr. Fixit]

I see you're now onto what PotvinGuy was saying to you.

I want to be sure I am correct in what I am saying. From the general gist of this topic, it seems you have been working at trying to get the car more responsive off idle. Yes?

The key word in that statement is 'idle'.

Take a look at your cam card. Look at the RPM range for the cam. 2,800 - 6,100 RPM. And you're trying to get the car to respond off idle?

Take a look at Weiand's recommendations on that intake manifold. 2,500 RPM and up. And you're trying to get the car to respond off idle?

You want things to work better? Then use the components as they were designed to be used. Get the car to the local dragstrip. Stage the car, get the motor all the way up against the converter and then let her eat. Those are race pieces, so drive the car like a race car. How well does the car respond in those conditions?

We used to build a lot of short-track IMCA Modified motors. We used a custom, mechanical tappet cam that didn't have nearly that much duration or valve lift. The LSA numbers were a lot lower, but we accepted the fact they were race cams and lived with it. Add the best part of 12.5:1 compression, Brodix Track 1 heads, HV-1000 intakes and 750 carbs. The guys loved them, because they would step out front on re-starts and pull all the way through 7,200 RPM (we used billet cam cores so we could run heavier springs). These were race motors, not street rod motors. They were outright slobbery up through about 2,600 - 2,700 RPM, but stand on it from there and they would rip your head off.

You're trying to use a bigger cam profile than that, along with a tunnel ram intake and two carbs no less, and make the combination transition well off idle? Hello??

You've never mentioned cylinder head chamber volume, but I'm betting it is way too high. The LSA on the cam will help a bit, but unless you're running a 305 casting or an aftermarket casting with similar volume numbers, your cylinder pressure is too low. Which will also contribute to a motor acting lazy.

When Comp Cams and Weiand are telling you to use their pieces at 2,800 RPM and higher, what are you hoping to find, nearly 2,000 RPM below that number? Whatever you're looking for, I can tell you it isn't there.

If you are married to what you have, then it's time to start looking into adding a band-aid or two. Was your cam gear drilled to accept bushings to change cam timing? If not, you'll need to drill it. Roll the cam up with a 2° bushing and check your piston to valve clearance. If you still have clearance, button her up and give it a try. Skip checking clearances at your own peril, because I'm betting you're already on the too-tight side of things.

That should help, considerably.

Get a couple fresh carb base gaskets and a piece of aluminum shim stock. Use your gaskets to cut the outline on your shim stock. Lift the back carb, drop on a fresh gasket, your new block-off and another fresh gasket. Bolt the carb back down. Give things another try. Rermember, you're back to just one carb, so your idle mixture settings are going to be in left field. How does that work for you?

If that works well, it's time to ditch that dual 4BBL top and replace it with a single 4BBL top. This will require a lot of money and a considerable amount of patience on your part, but take the intake base and single 4BBL top to a professional cylinder head porting shop. Explain what you're trying to use the intake on. Do your best to endure the laughter and explain why you need to use that particular intake. They can weld up the runners and stuff the plenum, to get them to a more reasonable volume. You are going to spend something in the vicinity of 8 times what the intake is actually worth, so be prepared for the expense to be high. Once everything is finished, bolt a 750 CFM vacuum secondary carb on top. You will want a selection of accelerator pump cams and squirters and a lot of spare time, but you'll likely be surprised at what you will be able to achieve.

You could find some improvement with a set of properly-built headers, but they will not come cheap. If something in the $2K range is within your budget, then that is another place to look. They will be designed to work, not to look pretty, so be forewarned. This would be the last resort step, in my not-so-humble opinion, so if you're not willing to spend time and money on the other suggestions, I wouldn't get too fussed over this one.

See? Playing with idle mixture screws and a timing light are not going to effect the kinds of changes you are hoping to find. If you want a lot of off idle throttle response, you are going to have to give the carbs a lot stronger signal than you are now. And it's not going to happen with that camshaft and intake manifold.

First of all, just to be clear in my own defense, when I bought the original car years ago and this is the engine that it had. I have not made any internal modifications to the engine and have learned through the school of hard knocks that this is not the most optimum combination of components for this use. Sure, it looks pretty cool, but may not proove to be as street friendly as I had hoped.

With that said, all of the timing adjustments and carb play has in fact made HUGE impact on the performance. It no longer stumbles off idle, runs very smoooth when accellerating and other than a slight stumble when I floor it engaging the second carb and secondaries on carb 1, does it hesitate a little and then screams (or maybe it is me screaming, not sure)

Sooo, to Potvinguy's point, "Now you can experiment with the timing and the carbs to minimize the roughness, and if that gets you to a performance (smoothness, mileage, power, response, temp) that is acceptable to you then you are good to go." I do believe that I am getting very close to acceptable with what I have. The fact is that I have a book of receipts and really dont know for a fact what lies inside the engine without disassembly, but I do know that that it is running stronger now then ever and is actually fun to drive.

As for your bedside manner Doc Mike, I learned long ago that if you don't have anything nice to say, well you know the rest... :snoot:

Thanks..

 

[Mike]

You asked. I answered.

For the record, I wasn't trying to be nasty or mean-spirited about anything. If that is how you perceived it, you have my sincere apologies. I calls 'em as I sees 'em and personalities have nothing to do with it. I just don't know a way to sugar-coat pointing out that cam/intake/carb combo is not the best for what you're seemingly trying to accomplish.

And I think if you take the time to implement some the suggestions I offered, you will find you can wake things up at lower RPM numbers. Rolling that cam ahead 2° will make a huge difference, but again, only if you have enough piston to valve clearance. You will be amazed at how much more bottom end it will have. Playing with pump cams and squirters can also bring some big changes. Have you ever moved the cam position on what you have? Look at the cam profile and look at what the move is doing to pump timing. You can get cams that will tip the pump in earlier, will bring the full pump shot in faster, etc. Your driving habits will have a lot of effect on what will work best, so there is no way to tell you what you should use. But moving your cam and comparing the results will point you in the right direction.

 

[Mr. Fixit]

You asked. I answered.

For the record, I wasn't trying to be nasty or mean-spirited about anything. If that is how you perceived it, you have my sincere apologies. I calls 'em as I sees 'em and personalities have nothing to do with it. I just don't know a way to sugar-coat pointing out that cam/intake/carb combo is not the best for what you're seemingly trying to accomplish.

And I think if you take the time to implement some the suggestions I offered, you will find you can wake things up at lower RPM numbers. Rolling that cam ahead 2° will make a huge difference, but again, only if you have enough piston to valve clearance. You will be amazed at how much more bottom end it will have. Playing with pump cams and squirters can also bring some big changes. Have you ever moved the cam position on what you have? Look at the cam profile and look at what the move is doing to pump timing. You can get cams that will tip the pump in earlier, will bring the full pump shot in faster, etc. Your driving habits will have a lot of effect on what will work best, so there is no way to tell you what you should use. But moving your cam and comparing the results will point you in the right direction.

Maybe my perception, but in any case, I appreciate your response.

Yes, I have played with the pump cams and made adjustments a couple of weeks ago which did help a lot. I do understand that my setup is not optimum for this appliaction, but it is like a bad marriage so we are staying together for the kids sake as they say. What made the most improvement was going to progressive linkage and using the rear carb just for power. With all idle mixture screws (both carbs) set evenly and primary throttle plates set to the most vacuum (8) it really runs very well and very crisp for what it is. With the scenario, she is idling at 1400 in neutral and 1000 in drive, but does come off of this so called idle nicely...

Thanks again...

 

[Screaming Metal]

Sorry, been really busy lately. Anyway, Yes, its best to run Vacuum advance on a street car where milage is a issue. But, you know what? Its not totally necessary. Look at motorcycles, no vac. advance and alot of them have 4 cylinders, and are very hi-perf. and get 35+ mpg! So, yes, it isn't necessary, but advisable.
On running alot of cam.....hahaha......You can get a street strip car, have everything set right, idle it down where it sounds really mean and bad.....go out to the track, do everything right, seems sluggish and loads up some. If you idle that same setup to where its idling a few hundred rpm higher, that same car can run up to 1 to 11/2 seconds faster in the 1/4 mile, just by idling things up.
If your running alot of cam and want to tame it, if its mechanical, just open your valve clearence a little. If its hydraulic, Rhoads lifters will help tame it if you don't want to change out your cam. Several other co's make those 'bleed-down' lifters.
Extra performance can be had by changing your rocker arm ratios. Usually on your exhaust side helps. You can only go so big on your exhaust valves, and once your set on your cam, increasing your exhaust lift and /or duration, will help you out sometimes.

The more cam you have the more vacuum goes away. Alot of all out motors that run on the street run vacuum pumps or possibly cans to store vacuun for acessories. Power brakes is a major concern with alot of cam.

Alot of cam usually calls for more compression, also, for it to work correctly.

 

[Mr. Fixit]

Sorry, been really busy lately. Anyway, Yes, its best to run Vacuum advance on a street car where milage is a issue. But, you know what? Its not totally necessary. Look at motorcycles, no vac. advance and alot of them have 4 cylinders, and are very hi-perf. and get 35+ mpg! So, yes, it isn't necessary, but advisable.
On running alot of cam.....hahaha......You can get a street strip car, have everything set right, idle it down where it sounds really mean and bad.....go out to the track, do everything right, seems sluggish and loads up some. If you idle that same setup to where its idling a few hundred rpm higher, that same car can run up to 1 to 11/2 seconds faster in the 1/4 mile, just by idling things up.
If your running alot of cam and want to tame it, if its mechanical, just open your valve clearence a little. If its hydraulic, Rhoads lifters will help tame it if you don't want to change out your cam. Several other co's make those 'bleed-down' lifters.
Extra performance can be had by changing your rocker arm ratios. Usually on your exhaust side helps. You can only go so big on your exhaust valves, and once your set on your cam, increasing your exhaust lift and /or duration, will help you out sometimes.

The more cam you have the more vacuum goes away. Alot of all out motors that run on the street run vacuum pumps or possibly cans to store vacuun for acessories. Power brakes is a major concern with alot of cam.

Alot of cam usually calls for more compression, also, for it to work correctly.

I appreciate all of the comments and will continue to play, and enjoy the car too. :angel: (That is if it will stop raining, going on 5 solid days with no let up)

Thanks..

 

[Mr. Fixit]

An update and a question. After much effort, (and a clear understanding that my set up is not at all a good choice for the street) I have come to the conclusion that I have gotten the timing and carbs as best as they can be for what they are and of course I am still not happy. While considering making a change to eliminate the Weiand Hi Rise set up with the two 450 Holleys and opt for a single plane and a single four barrel, I stumbled across this:

http://coloradohotrodparts.com/Real-Street-Ram-Kit-for-Small-Block-Chevy-RSR-001-CHEV.htm

Has anyone here ever seen this? If this setup really works as they are proclaiming, it sure seems like a good solution. They also sell just the top sections with the carbs as a kit too, so I could retain the Weiand manifold. Thoughts? Suggestions?

Thanks,

 

[roadmonster]

I think you have come to the correct conclusion that you are over-carbed and will never get really strong off-idle response. I started from scratch with crisp off-idle performance as the primary goal. A mild cam, small carb, and vac-advance ignition is the way to go for a T. I run a Comp 252, dual-plane Weiand with a Holley 600. Powerband is 800-4800, timing is 12+18+10, all in by 2000. Tight converter (by choice!) and it's a rocket. 3.00 rear end gets effortless wheelspin, 2nd-gear chirp, and often chirps downshifts. Tons of vacuum at all times makes it responsive and fun. This is a very tame setup but it's just what a T needs.

 

[Mike]

Has anyone here ever seen this? If this setup really works as they are proclaiming, it sure seems like a good solution. They also sell just the top sections with the carbs as a kit too, so I could retain the Weiand manifold. Thoughts? Suggestions?

They're trying to give you the best of both worlds, by giving you the look and reducing plenum volume, to try to keep the vacuum signal at the boosters alive. Will it work better than what you have? Without question. Will it work as well as the combination roadmonster described? There's the $1,349.00 question.

 

[Mr. Fixit]

I think you have come to the correct conclusion that you are over-carbed and will never get really strong off-idle response. I started from scratch with crisp off-idle performance as the primary goal. A mild cam, small carb, and vac-advance ignition is the way to go for a T. I run a Comp 252, dual-plane Weiand with a Holley 600. Powerband is 800-4800, timing is 12+18+10, all in by 2000. Tight converter (by choice!) and it's a rocket. 3.00 rear end gets effortless wheelspin, 2nd-gear chirp, and often chirps downshifts. Tons of vacuum at all times makes it responsive and fun. This is a very tame setup but it's just what a T needs.

Thanks for the detailed info, I appreciate it.

 

[Mr. Fixit]

They're trying to give you the best of both worlds, by giving you the look and reducing plenum volume, to try to keep the vacuum signal at the boosters alive. Will it work better than what you have? Without question. Will it work as well as the combination roadmonster described? There's the $1,349.00 question.

Well, actually it is $995 for the kit that I would need (upper manifold and carbs only) since I will retain my Weiand Tunnel. I have ordered this after several detailed conversations with Wayne (the developer of the product) and his assurance of satisfaction or money back which is clearly stated on his site as well.

In any case, I am anxious to get the items installed, hopefully have great results and report same to everyone.

 

[Mike]

It will be interesting to see how it goes for you. I suspect you'll be amazed what that big reduction in plenum volume is going to do for you.

 

[DIGGER1658]

Well, actually it is $995 for the kit that I would need (upper manifold and carbs only) since I will retain my Weiand Tunnel. I have ordered this after several detailed conversations with Wayne (the developer of the product) and his assurance of satisfaction or money back which is clearly stated on his site as well.

In any case, I am anxious to get the items installed, hopefully have great results and report same to everyone.

Can't wait to see the results! I recently found that Colorodo sight but have never seen or heard anyone using that setup.

 

[Mr. Fixit]

It will be interesting to see how it goes for you. I suspect you'll be amazed what that big reduction in plenum volume is going to do for you.

I hope to be amazed. I am tired of an awesome looking pig. Truly the definition of "all show no go"

 

[Mr. Fixit]

Can't wait to see the results! I recently found that Colorodo sight but have never seen or heard anyone using that setup.

According to the owner, this is very new and although only a small audience is using the setup thus far, the reports are great. More to come...