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Discussion Starter #1
I would like to see a good "how to tune your engine" thread posted at this forum. There are many discussions about picking the right camshaft, pistons, heads etc etc. But I havent found any particular post that gathers info about "how to get the most out of your engine". I guess there are people out there who is cussing engines that runs poorly, simply because they werent tuned the right way. Certainly there are many "unrevealed" horsepower out there! So, please c'mon now every experienced engine builder. Share some valuable information how you tune your carbs, ignition, valves, cams, etc etc... Maybe Paul could lead the way?
Matt
 

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that sounds like a great idea for something that could become a stickie. Even starting with the basics, like the order in which to do basic stuff. A simple guide for newbies, could even be hands on FAQ with some pictures. it is hard to learn how to set up a carb with nothing but a haynes manual.
 

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Hey Mike and Paul, here I see an opportunity for you guys to answer the question once, and then move to the best of tech for future reference.


Mike, since you work with a dyno all day, I will bet you have the best tuning tricks.

I'm with the other guys on this one. I have picked up a tidbit here and there on the subject of tuning, but it would be really helpful to have a nice compilation of good methods for proper tuning.

Randy (shutting up to listen now) :shh:
 

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Well, the first step is making sure you have the right parts in the first place.
For example low compression, big cam engines are hard to tune except for wide open throttle and run a like a sick, 3 legged dog on the street.

The second step is to be sure the engine is in good condition.
The difference between a crisp running, tuned engine and a tuned but lazy engine is directly related to pressure/vacuum sealing. Do not underestimate this fundamental concept.


For example these make tuning difficult if not impossible:

  • Poor ring to bore seal
  • poor valve to seat seal
  • burned valves/sticking valves
  • worn cam/lifters
  • Loose timing chain
  • vacuum leaks
  • slipped balancer ring
  • faulty plugs/wires/cap/rotor
  • loose distributor shaft bushings
  • sticking advance mechanism/ruptured vac advance diaphram
To diagnose and tune it is imperitive you have the correct tools:
  • Timing light
  • hand held fuel pressure gauge with long enough hose to duct tape to windshield
  • vacuum gauge
  • vacuum hand pump (Mityvac)
  • tach/dwell meter
  • compression gauge
  • leakdown tester

Keep a log book on your engine. Record each and every change. For example I note and date jet, metering rod or timing curve changes. If you make a change or changes that make it worse you can back track by checking the log book. Only change one thing at a time. If you change two things one might help and the other hurts, but you won't know which.

You should also check and record the cranking compression at regular plug changes intervals. The plugs are out and it only takes 15-20 minutes to check all 8 holes. If you are changing the cap and rotor you might as well take 2 minutes to check the timing chain slop. With the plugs out and the cap off you grab the balancer and turn it back and forth with the timing mark at 0. If you get more than a degree or 2 of movement before the distributor rotor moves it's stretched and needs replacing.

I often see people spinning in circles, frustrated from tweaking and adjusting worn out engines. Then they get it so far gone that they decide "it's the carburator" or "engine computer's junk" and start willy nilly replacing parts hoping they'll stumble on the "bad" component. The smart tuner does what a good physician would do. Test and take data before attempting to diagnose the problem
 

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I agree with Paul, to document everything. I am in the process of trying to fine tune A/F after a cam change, and hogging out an RPM Air Gap, and adding a HVH Street Sweeper 1" spacer.
I was pretty much in tune before those changes, now I am starting from scratch.
To give you an idea as to how a small change can affect things, we were on a rear wheel dyno with my new combination, and changed rear jetting 4 sizes and gained 27lbs of TQ. Now 27lbs is something you can actually feel the difference in your pants.
Fine tuning is a lost art, and I can only do so much myself, so once I have the set-up at least where I think it might want to be, I go to a rear wheel dyno to have everything checked.
In the next few weeks I am going back to the rear wheel dyno to do more rear wheel pulls from 2,500 to 4,000 left and right bank A/F, record the data, analyze, change jetting / timming, and start pulling to the power peak in baby steps. At all times, recording what we did for timing etc etc.
I have seen 50HP, and 50TQ " FOUND " on a rear wheel dyno. I sure hope my own home done tuning does not gain me that much, I would be a bit embarrased to say the least.
I don't have the equipment, time, or the garage space to set up a decent shop, so I am spending some loot on the dyno.
 

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Answer to first post of this thread? (Paul or Mike)

I know the first question asked, "Can we have a guide to tuning", or whatever it was, has a long winded answer, but it would be really useful for all of us! If possible, can someone who has the knowledge(and the free time) answer this for us? The information regarding logging information was great, but it didn't get into the details of tuning... If fully answered and laid out in detail for the average gearhead to understand, we would all be in your debt forever!!
 

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Discussion Starter #7
Thanks xnovassx, That's just what I was looking for when I started this thread...
It would be great if some could write down experiences when it comes to tuning ignition/distributors, carbs, cams, using the vaccum method, etc etc...
I think lots of people would find it both interesting and helpful.
Matt
 

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Tuning tips

I think this is an excellent sticky with the potential for a lot of good tuning and diagnostic tips. Hope more contribute to this thread/sticky.
 

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Getting the most out of an engine has everything to do with air flow.
The more air the motor gets, the more power it will make.
 

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I can't believe more has not been contributed to this thread. I figured you tuning guru's would be all over this. I for one would love to have a resource from strictly chevy people on tuning. I realize it was started in 05 but there is basically no content and "how to" in this sticky!
 

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tuning

The previous was a bit of a short answer, and I expect a little hate-mail for it.
Fuel injection and computer-controlled timing are the best innovations in autos since HEI, but show no signs of being obsolete.
A few of my own recommendations would be:
1.Good timing light(that reads base timing as well as timing advance)
2. Vacuum pump (most can also be used as a guage)
3. Adjustable spark tester
4. Common Sense
I am in no way a "guru" or "professional", but I have had to learn lots of things the hard way. I won't ramble on about my own opinions, but these are simple things that I do that work for me:
Base timing is important, but TOTAL timing is more important. Total timing should be checked at around 3,000 rpm, not to exceed 36* for most engines. Some more, some less. Most engines will start and idle fine with up to ~18* or more base timing. I chased a part throttle to WOT stumble and "lean out" condition for a couple of days before figuring out my 'adjustable' vacuum advance would hit about 54* peak timing at 2800 rpm. An advance timing light would've been nice. All I could check was base timing(8*) wtih my basic timing light.
Anyone that runs Holley carbs needs a vacuum pump and/ or guage. They are crucial for Power Valve choice and idle adjustment. Holley says 1/2 of manifold vacuum will be the correct one, most others say manifold vacuum minus 2"(10"Hg-2=8) or 8.5 since they only have half sizes.
Engine idle speed should be set to idle as fast as possible with the throttle plates as closed as possible. I don't know how to explain any better.
As for the spark tester:
Blue spark-good
Yellow-maybe not so good
No spark-:(
Common sense should always be practiced. No explanation needed.

I rambled more than I should have, but maybe somebody will get some help, or entertainment, outta this.
 

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Like Paul said start with the basics, the most basic thing I have seen is not checking for wide open throttle, always verify this from pushing down the pedal & not just from outside of the car. I have seen this one a bunch of times & have also been guilty of it myself.:yes:
 

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I don't think there is a simple/easy way you can make a list for tuning a motor. The first thing you need to do in my opinion is know what the weather is and what it does and why it does it. So you need a weather station with humidity, air temp and barometric pressure at a minimum. You need a log book to write everything down in. If the goal is to tune for best ET or best fuel mileage you need a standard coarse or track and again you need conditions and track temps. Checking WOT is not tuning as I know tuning. Tuning is changing timing, carb stuff, plug gaps, headers, exhaust, gear ration, torque converters, and tuning with a specific goal. All that starts with logging and recording data so you measure to a standard. The average person doesn't have the tools, time or patience to tune today, they bracket race or index race. Even the basic class racer is dialing the car today. Some people still like to set world records and they are tuners to me. They use the above tools and decipher the info they get. just saying, my thoughts on this
 

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I like the idea of this post. Tuning engines with carbs is becoming a lost art. And "art" is the key word here. Modern FI engines basically tune themselves with a little help from a timing light. But alot of people these days don't even know what points are!
I think this discussion should start with the definition of "stoiciometric" (sp?). As for the rest, VOLUMES have been written in the past. Most car magazines do write ups about tuning different engines at least every other year. But basic tuning needs to be broken down into all its various parts. Every part is independent of the others, but also must work with the others as well.
For instance, lets take carbs... I don't mean sit around on the couch with a handful of Doritos! Every style of carb is different in their tuning procedures, but the end results are all the same; to mix fuel and air for combustion. Tuning a Holley is different from tuning a Carter or "Rottenchester". And don't even get me started on multi-carb set-ups.
The best place to start for carbs is to get online and look up the manufacturer of your carb. Every reputable carb manufacturer has methods for tuning their carbs on their site. These are usually in pdf format and easy to download and print (so you don't get your computer all greasy!). That's the easy part.
Then we need someone to do a "how-to" on the rest of the tuning procedures. I'm not talking about using a weather station to figure out how to get down the quarter mile faster than the guy in the lane next to you. I think the most helpful info would be tuning for driving the car on the road. The basic steps for those people who drive their cars to shows, on weekends, or even daily drivers like mine.
Some mention has already been made about the tools needed to tune a car. Lets talk about the best ways to get the most out of those tools. Then lets break down the procedures into their parts (ie; tuning points vs. electronic ignition). And lets keep it simple so even those in the cheap seats can get it.
Even the top fuel racers started out knowing zilch about how cars work (even if it was when they were 2!).
 

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Hello.

I started following this thread hoping for some good info, so far I have learned little to nothing. I have learned what tools I need, but how do I use them? What are some common tuning problems? How can I tell if my engine is too lean, too rich? What about timing how do I really find the sweet spot with out using a dyno? I think these are questions our original author and I want answered. Please help I am really interested in becoming an artist of the sbc.
 

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this is what I've learned.

I wanted to chime in on this, because I just finished re-vamping my 72 Nova myself about a month ago.

I have an in line 6 (250) with a Rochester single barrel carb.

I could be wrong but I didn't see any timing marks at all so I set my points and timing by compression. When your piston is all the way up, that is TDC from what I understand. Once I had the points set correctly I adjusted the timing a bit according to the sound of my engine. I actually think my timing is a bit more advanced than what is recommended for my 250, because that's how it sounded the best.

After I set the timing I was having some carb tuning issues, as usual- i can rarely get the float adjusted correctly on the first try. There was gas overflow spilling out of the idle tube assembly attached to the accelerator pump. A couple quickknocks of a hammer released the stuck float and I was good to go. TIP: DO NOT USE THE FLOAT TO NEEDLE VALVE CLIP YOUR CARB REBUILD KIT COMES WITH!!!! You will encounter severe flooding issues!!!!!!! Throw that piece of crap in the trash can before you even start rebuilding your carb!!!!

Rebuilding carburetors is my favorite part of turning wrenches because it reminds me of a puzzle. They are so complicated but once you get to know your individual carb and engine combo tuning your carb is like listening to a fine symphony. :) I do not use a check ball in the accelerator pump in my single barrel Rochester, it's working great that way. My metering rod looked a bit worn as well, also seems to be working just fine. On my particular Nova, I attached the spark advance to the bottom, front vacuum opening on the carb as I wasn't getting enough pull from either of the side vacuum holes. I plugged off the top vacuum hole with a screw in the end of a short piece of vqcuum line and attached the other line to the bottom hole.

My carb is about 2 1/2 turns OPEN right now, I'm in Tennessee and not at a high altitude. That is with an advanced timing and I'm still getting some occasional dieseling when I turn the key off and shut her down. Still need to correct that issue but i removed the automatic idle qdjustment and chiseled a bolt at the top tokeep my idle where it needed to be because the piece of crap it came with was running away on me, loosening or tightening itself with normal engine movekent and my idle was going crazy! I had to chisel the top of the bolt so it would keep my idle set where I wanted it. My engine was a bit shaky at first, but after I found out where the idle wanted to be and advanced the timing bit, the shake went away.

Well, that's what I have right now- hope it helped. Also, if anyone can tell me why I'm getting the occasional dieseling when I shut down my engine that would be awesome.
 

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Hello.

I started following this thread hoping for some good info, so far I have learned little to nothing. I have learned what tools I need, but how do I use them? What are some common tuning problems? How can I tell if my engine is too lean, too rich? What about timing how do I really find the sweet spot with out using a dyno? I think these are questions our original author and I want answered. Please help I am really interested in becoming an artist of the sbc.
You can tell if your engine is too lean because it will sputter and not have the acceleration you want. If it's too rich you will have blue smoke from your exhaust and you will smell raw gas in/around your engine. I've never had a dyno and I've always set timing based on sound. When your engine is purring like a kitten you've got it right. You will usually have to adjust your timing, carb air to gas ratio AND idle adjustment together. Move each a little bit until they are balancing each other out. There is a sweet spot in your timing you can hear. When it's too advanced you will hear a very fast idle, when it's too low you will hear it bog down and lose power. Place your timing between those 2 extremes. Adjust your idle accordingly and I usually do the air to gas last, once everything sounds good to the ear.
 
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