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Old 02-08-2009, 07:28 AM
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terrible driveability, tuning problem

Vehicle: 88' s-10 4x4 pick-up, 31 inch tires, 3.73 gears, 700r4 overdrive tranny.

Motor; Brand new HT383 GM Performance crate motor with Weiand "stealth air strike" intake, 1 inch spacer, GM distributer "vacuum disconnected" Holley 670 Street avenger with vacuum secondary's.

GM recommends a initial timing of 10 degrees at idle. I started with that and the motor seemed pretty strong. Acted like it could use a little more advance actually.

Huge problem: Shifting into overdrive with low RPMS or trying to cruise at 60 mph, 1700 rpms. It pings really bad.

In order to eliminate the pinging I had to back the timing all the way down to 4 degrees.

Now it has zero power, absolutely shudders and shakes and bucks when I accelerate, trys to stall when shifts happen.

On the highway temp is 180-185 and in town it will climb to 195. It's 30 degrees out here.

Engine vacuum is 18 inchs maybe a little higher depending on timing and carb adjustment.

Can a carb with to small of jets cause pinging? Just a guess.

GM recommends 87 octane, which is what I got in it. And yes it is fresh.

I really need help with this. I can't drive this money pit until it's fixed.

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Old 02-08-2009, 08:10 AM
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Do you have the TV cable on the tranny set up correctly. You may need a special throttle bracket to keep the correct geometry on the cable. If not set up right you can burn up your tranny in no time.
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Old 02-08-2009, 09:01 AM
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Yes, I have the adapter on the carb. And it shifts just like a dealership vehicle. Varys according to engine speed, load, and vehicle speed. I have no complaints there. The 700r4 guy at AAMCO transmission sold me a new auto adjusting cable and showed me how to do it and we clicked it one click tighter in order to increase the pump pressure so the clutches and band would grab a little stronger to hold the extra power I'm throwing at it.
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Old 02-14-2009, 06:51 AM
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Well, I've been doing alot of tuning and tweaking and I believe I got it almost perfect now.

GM claims this motor is built to run on 87 octane. This could be true, but GM can't control the quality of 87 octane throughout this country.

I put 89 octane in it and that cured alot of my issues instantly.

My out of the box 670 street avenger was jetted perfectly for my last motor set-up. Not the case for this motor and set-up.

Stock primarys were 65's and secondary's were 68's and the power valve is a 6.5 which is rather low.

I am now running 67 primary's and 70 secondary's and the same power valve. The motor is timed at 8 degrees and runs really nice now. In town driving is fun now and at 70mph on the interstate the motor is so smooth and efficient the flowmaster 44's are quietly humming instead of drowning out a polite conversation. It shifts solid and strong with no ignition ping and will lug all the way down 50mph in overdrive "approx 1400 rpm's" and take it with no problems.

My main focus right now has been to get this truck driveable so I can break this motor in properly and thats what been happening. Something about breaking in new motors makes my eyes roll back in my head so I 've been having my fiance do it for me. She's made two 150 mile round trips on the interstate varying her speed from 60mph to 80mph in 5mph increments every 5 minutes and throwing in a little two lane black tops at slower speeds with farming towns every ten miles for variety.

Understand that I have already put 200 miles on this new motor just trying to get it to run right and within the first 100 miles of her driving to seat those rings in properly, it now idles in gear 75 rpms higher than I had it set and in park it idles 150 rpms higher than before.

With her driving in this unusual manner, she has managed 15.2 MPG both times! Facter in that this truck has a suspension lift, bodylift, 31 inch tires, bug guard, lund moonvisor, 4 wheel drive, 383 stroker motor, 300 Ibs of sand bags in the back, and its freaking cold out, I'm very impressed. She would have gotten better mileage on the second run but the temps had dropped down to 26 degrees. Just imagine what 70mph wind chill is doing to my 80w-90 gear lube in my front and rear diff's and the fluid in my transfercase.

It does not matter how you tune it, jet it, anything, this motor DOES NOT RUN GOOD with the vacuum hooked up, ported or manifold pressure.

There's alot more hidden power in this motor. With 70 primary jets, it would make a NASTY Saturday night special. The power and acceleration is insane but it loads up bad at stoplights and at speed on the highway.

But for now, no more tuning until the motor is fully broke in and it's warmer out.
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Old 02-14-2009, 12:25 PM
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Quote:
Originally Posted by klr650
Vehicle: 88' s-10 4x4 pick-up, 31 inch tires, 3.73 gears, 700r4 overdrive tranny.

Motor; Brand new HT383 GM Performance crate motor with Weiand "stealth air strike" intake, 1 inch spacer, GM distributer "vacuum disconnected" Holley 670 Street avenger with vacuum secondary's.

GM recommends a initial timing of 10 degrees at idle. I started with that and the motor seemed pretty strong. Acted like it could use a little more advance actually.

Huge problem: Shifting into overdrive with low RPMS or trying to cruise at 60 mph, 1700 rpms. It pings really bad.

In order to eliminate the pinging I had to back the timing all the way down to 4 degrees.

Now it has zero power, absolutely shudders and shakes and bucks when I accelerate, trys to stall when shifts happen.

On the highway temp is 180-185 and in town it will climb to 195. It's 30 degrees out here.

Engine vacuum is 18 inchs maybe a little higher depending on timing and carb adjustment.

Can a carb with to small of jets cause pinging? Just a guess.

GM recommends 87 octane, which is what I got in it. And yes it is fresh.

I really need help with this. I can't drive this money pit until it's fixed.
This is a common problem with Vortec headed engines in vehicles using a carb and an overdrive transmission. The engine revs get pretty low and the mixture flow in the intake is insufficient to keep even cylinder to cylinder ratios. With the OEM L-31 port injection, this isn't a problem since there is no dependency on air flow in the manifold to keep the cylinder to cylinder mixture distribution consistent. But with a carb or Throttle Body Injection, this gets to be a big issue.

The least expensive solution is to up the octane. This will let you lean out the carb, push up the advance and still cruise in OD all of which will significantly improve fuel mileage without the engine trying to blow the heads off. You'll probably want to restore the vacuum advance as well.

Actually, the Swirl Port heads are a lot better in a set up like yours where the cruise revs are pretty low and induction is either a carb or TBI. Hot rodders tend to overlook them because they run out of breath over 4000 RPM. But if you're looking for good street manners and good mileage in the 2000-3000 RPM range in an OD gear, they make a lot of sense as they deliver better mixture ratios and higher swirl at low revs than the Vortecs do, which translates into more mid range torque which is right where you need it in this situation.

Bogie
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Old 02-14-2009, 05:45 PM
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I'm starting to think that I've fallen for more marketing schemes and outright lies. This motor has been raved about by several performance magazines as being the motor that is extremely easy to set up for 87 octane and used for any type of daily driver purpose. It's claimed to be perfect for any and all types of towing purposes in overdrive with having enough extra torque to rip up that next hill pulling a trailer without needing to downshift.

I won't dwell on that though. I do like this motor quite a bit now that it's starting to run really good.

Your comment about blowing the heads off has me concerned. This is absolutley the last thing I would want to happen.

Could you explain with more detail what I should be looking for, listening for, concentrating on, etc......

I'm still having bad memories of the last motor that was in this truck. It ran completely perfect and never had any tuning issues "after I started running 92 octane" or cooling problems and it ended up blowing oil out the tops of the valve covers the whole short time it lived and blew a head gasket at 6000 miles.

Blowing the heads off sounds far to familiar to me.
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Old 02-14-2009, 06:22 PM
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Quote:
Originally Posted by klr650
I'm starting to think that I've fallen for more marketing schemes and outright lies. This motor has been raved about by several performance magazines as being the motor that is extremely easy to set up for 87 octane and used for any type of daily driver purpose. It's claimed to be perfect for any and all types of towing purposes in overdrive with having enough extra torque to rip up that next hill pulling a trailer without needing to downshift.

I won't dwell on that though. I do like this motor quite a bit now that it's starting to run really good.

Your comment about blowing the heads off has me concerned. This is absolutley the last thing I would want to happen.

Could you explain with more detail what I should be looking for, listening for, concentrating on, etc......

I'm still having bad memories of the last motor that was in this truck. It ran completely perfect and never had any tuning issues "after I started running 92 octane" or cooling problems and it ended up blowing oil out the tops of the valve covers the whole short time it lived and blew a head gasket at 6000 miles.

Blowing the heads off sounds far to familiar to me.
I was referring somewhat tongue and cheek to detonation which in reality is more likely to take a piston.

When towing the transmission shouldn't be in OD nor the torque converter locked up. It puts too much load on the engine (an example of lugging) for the RPMs it's turning. In this situation, the burn time is too slow for the revolutions which results in a tendency to detonate and the moment on the crank journal becomes too high which blows the oil wedge out of the bearing.

Bogie
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Old 02-14-2009, 07:14 PM
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Quote:
Originally Posted by oldbogie
I was referring somewhat tongue and cheek to detonation which in reality is more likely to take a piston.

When towing the transmission shouldn't be in OD nor the torque converter locked up. It puts too much load on the engine (an example of lugging) for the RPMs it's turning. In this situation, the burn time is too slow for the revolutions which results in a tendency to detonate and the moment on the crank journal becomes too high which blows the oil wedge out of the bearing.

Bogie
Okay??!! Does 87, 89, or 91 octane have different or the same burn rates? Assuming the motor's state of tune is the constant. Lugging the motor with 87 octane creates pinging, "which is a form of detonation". Lugging with 91 octane could be detonating but I just can't hear it. Surely the crank journal would be subjected to similar high pressures.

Lugging creates higher cylinder temps than norm, I think or am I wrong. Diesel motors rely on high cylinder temps to ignite the fuel, which is a form of deliberate detonation and I have had the opportunity to run some very nice diesel powered trackhoes that at speed ran silky smooth and quiet. These motors truly hummed with no noise whatsoever.

Another thought thats bouncing in my head is that I can increase my jet size to eliminate pinging but if burn time is always the same then the extra fuel must be cooling the cylinders charge but detonation "ping" is still lurking. Possibly still having excessively high of cylinder pressures without the telltale "ping" talking to me.

NOT trying to argue. I find this a very interesting topic and just trying to understand it all. Technically setting my timing at 8 degrees before top dead center is a form of detonation. Yes I do understand that the flame front is relative and that is why timing must change to meet the rpm requirements.
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Old 02-14-2009, 07:57 PM
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This engine will not operate on 87 octane without computer controled air fuel ratio, functional EGR and a knock sensor.
Apparantly you think replacing busted engines is somehow cheaper than running the right gasoline for the job.

You need to get a pro that has a clue to set the motor up correctly, or get a money tree.
Never ever tow in OD. Never allow the engine to ping or lug.

Pinging is not a "form of detonation". it is detonation and quicky destroys piston ring lands.
Put some 91 octane gas in it ALL THE TIME and get a real timing light and learn how to set up a distributor advance curve (including vacuum advance).
Jet the carb with #68 or 69 pri and #76 sec.
If you have a intake manifold leak at least 1 cylinder wil run lean and knock.
If you have a leaky PB booster or other vacuum device leaking air it will ping.
Engines cost more than fuel.
The distributor has too much total timing. The advance curve is wrong.
What spark plugs are in it?
All modern unleaded pump gasoline has the same "burn speed"
Higher octane unleaded gasoline just resists knock,ping, detonation better than low octane.
Fuel octane is cheaper than pistons.

if you want gas mileage get a little little car with a little little engine and duct tape a egg to the gas pedal and leave the hood shut.

GM or any other engine builder is not responsible for engine damage caused by detonation. Operating an engine under detonation is owner/operator abuse and voids any warranty. They do not have to warranty it. It is 100% up to you to install it correctly. Tune it correctly and run the right fuel octane to avoid detonation. Even if that right fuel octane costs you more money at the pump.

You have the wrong intake manifold for efficient cruising at low rpm in OD.

Last edited by F-BIRD'88; 02-14-2009 at 08:38 PM.
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Old 02-14-2009, 08:38 PM
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what total timing/

whats your total and also what ignition system are you running?plugs wires and gap.that motor should have gobbs of torque.
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Old 02-15-2009, 09:24 AM
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Thank you F-BIRD'88. I've been waiting several days now for your input. Glad to hear from you. Obviously you remember me and my earlier situation.

I would like to clear this current situation up so we could make some headway.

When we talked last you firmly told me the L-31 heads would much better meet my needs than iron eagles and that If I couldn't find a reputable builder than I should consider a crate motor.

I took your advice to heart and did exactly that. I bought a GM Performance crate motor. It's the HT383. In case your not familiar with this motor, It is a L-31 headed stroker with 9.1 compression that you recommended. Smaller roller cam with almost the exact lift and duration that you suggested. In fact the whole motor set up seemed to have been tailer made with you in mind.

1. this is a GM built CARBURATOR crate motor that they built to run on 87 octane to be used for towing purposes and all daily driver uses.

2. I am using the GM required distributor for this motor that doesn't give full advance until 4000 rpms

3. GM's stated timing for this motor is 10 degrees at 650 rpms with full advance of 32 degrees at 4000 rpms. Repeated several times in the manual and instruction sheet that came with this motor, "DO NOT ATTACH OR USE THE VACUUM ADVANCE AT ANY TIME, THIS MOTOR IS TUNED AND TESTED TO USE THE ABOVE STATED DISTRIBUTOR WITH TIMING CURVE TAILERED FOR THIS MOTOR".

4. I have it at 7 and 29 respectively. I'm not trying to blow it up

5. I use two timing lights. different manufactures.One adjustable,one fixed,both are accurate with each other.

6. I am not allowing it to ping or driving it while pinging. My timing lights and wrench are on the seat next to me when I leave the driveway. Doesn't a person Have to test drive to find out if a tuning change has worked or not?

7. I'm not towing with it, just pointing out GM's huge claims of the torque monster this motor is. It should be able to haul my 4000Ib truck around with out struggling. On one dyno claim this motor is cranking 300ftIb at 1500rpm. If any small block chevy can knock out 300ftIb at 1500rpms, its not struggling.

8. As you well know, Holley factory jets their carbs with the secondary's being 5 to 8 sizes bigger than the primary's and popular opinion 7-8 sizes is perfect. Did you know that ALL the 670 and 770 series are ALL jetted and calibrated with a 3 size difference. WHY? WHY? WHY?

9. I can try 68's. It could run on them. I know it won't take 69's. 70's were drowning it bad.

10. My carb and spacer gaskets are not leaking and the intake is not leaking on the outside but, I Don't know how to check for a internal leak.

11. I am 100% positive that I don't have a vacuum device or line leak.

12. I am running the recommended AC plugs with recommended gap.

13. MSD 8.5 super conductor wires.

14. The recommended PCV by GM. It's chattering away like a machine gun.

15. currently tuned with idle 850rpms vacuum is 20 when the dual electric fans kick in, "THEY SUCK A TON OF JUICE" the vacuum drops to 19.

16. When I talk mileage "are we on the same page?"? Sure getting decent mileage is a concern and it is a goal to have a efficient vehicle. I plan on switching the whole drivetrain to synthetc. BUT, most importantly, when I talk mileage I am attempting to use mileage as another tool to use to tune the motor. If the motor is struggling, mileage will suffer. If the motor is strong and happy the mileage will be as good as it's gonna get. Follow me?

17. Maybe your right about my intake. I do know that several independant intake dyno comparo's have been done and that the results are the same. the Airstrike when tested on a L-31 headed motor has slightly better air distribution and stronger torque earlier in the rpm's in comparison to the RPM airgap. The RPM airgap out edges the Airstrike on any other motor configuration but for some reason the Airstrike likes L-31 heads. With or without spacer, results are the same. As you said before L-31's run out of breath quickly, and the Airstrike is supposed to be more tailered to the L-31's rpm range.

Your absolutely right. 100%. It is up to me to tune this motor properly and If I am driving around with my head up my *** allowing it to ping and rattle, then I deserve a busted motor. If I was ignoring all the recommendations on what fuel to use and what timing to use by the very people who developed this motor, than I deserve a busted motor. This motor was thrashed on by Hot Rod, Super Chevy and many others using a rpm intake and my distributor on 87 octane with excellent reviews. So what the heck is going on.

I don't care one bit about the price of fuel. What I do care about is that this motor is supposed to run excellent on 87 and it won't. When I first fired the motor up, I still had 91 in the tank for the last motor and it ran awesome until it got a taste of 87. 89 octane and a jet change helped some, not enough.

What would be your thoughts if you bought a 91 octane motor that wouldn't run unless you had 104 race gas in it?

YOU are the "pro with a clue"!! My advisers say screw GM's recommendations and hook up the advance, crank the timing to 36 degrees at 3000rpms and keep throwing bigger jets at it until it runs right. Can you imagine what my timing would be at idle? I"m guessing 16-18. yeah that'll work reeaall good.
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Old 02-15-2009, 12:31 PM
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Not to butt in here but I always thought higher octane burned slower and thats how it stopped or lessened detonation. But thinking about it now, it must just take a higher temperature to ignite? Is that right?
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Old 02-15-2009, 01:42 PM
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i know it's frustrating when an engine isn't running right, add to that a few very knowledgeable people that don't totally agree on everything, and all of a sudden, we let our emotions take control of what we really are seeking, good advice. i think we can all agree we are here to help, not hurt. my opinion, is that most of your problems, if not all, lie in your distributor timing. i would consider contacting performance distributors 901-396-5782, trying a different distributor. f-bird seems to know alot.
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Old 02-15-2009, 01:43 PM
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Quote:
Originally Posted by Torque454
Not to butt in here but I always thought higher octane burned slower and thats how it stopped or lessened detonation. But thinking about it now, it must just take a higher temperature to ignite? Is that right?
This is a common myth. Not all fuels with a high octane rating are slow burning. Some, Some high octane fuels do have a slower burn rate. The octane (resistance to autoignition) is achieved partialy by additives in the fuel blend that slow things down.
Typically these fuels are used in very high compression ratio engines.
The very high mechanical compression ratio speeds up the combustion.

Modern pump unleaded gas (and many modern racing fuels) are designed for relatively low rpm engines and quick combustion.
With relitivily low compression ratios. So it needs to have a higher burn rate ( speed).
The "octane" (higher resistance to auto ignition) is achieved by other means.
Additives and fuel blend that resists higher temps and pressure in the cylinder, but does not change the burn speed of the fuel.
The burn rate speed stays very near the same from regular to premimum, right up to 110 octane unleaded race gas.
The amount of spark timing that the engine wants to do the most work stays the same. It's just that if you don't give the engine enough octane ( resistance to knock) in the gas, you can't run the timing that it really wants.

Gasoline, as a fuel (in it's raw state) in a internal combustion engine is a crappy fuel. It wants to misbehave. You have to add all these additives and control the chemistry to keep it under control.
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Old 02-15-2009, 02:22 PM
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It seems that the actual quality of the "87 octane" gas sold in your area, is a bit lacking. You're going to have to live with putting something better in the tank than 87.
Like you said, GM can't control the fuel quality everywhere.
There may be a issue or fault with the carb, as you have used it on more than one motor that seemed to all be octane hungry.
Are any of the 8 spark plugs vastly different than the rest of the sparkplugs?
(porceline colour, ground strap colouring etc)
The cold plenum air gap manifold is going to want richer jetting especially in the winter, than a heated manifold will.

I don't easily accept that this engine cannot and won't benefit from some vacuum advance while cruising. But for now and until you are able to work out the problems, you are best to take GM at their word and leave the Vac advance disconnected.
This motor and many other carbed motors that are "supposed to run on 87 octane" are supposed to have functional EGR.
EGR at cruise acts a lot like water injection by regulating peak combustion temps to control/supress detonation which allows more spark timing under low load part throttle cruise. The inceased spark advance that the EGR allows, increases engine efficientcy and fuel consumption. while allowing reliable use of cheap 87 octane gas.
A side benefit is the reduction of NOX emissions.

The intake manifold GM sells for this motor has provision for EGR, but the EGR has to use a external source of exhaust gas. (add on external plumbing to t he exhaust manifolds like the L-31 motor has.
( something to think about)

I take back the harsh comments. You seem to have a lot more of a clue than I thought. I think you are right. The 87 octane gas sold there is junk.
10 initial and 29 to 32 deg basic centrifical should be about right for this motor on 87. The rate in and out may need fine tuning.
What happens when you run it on 94 octane? (or the highest, best gas available in your area) How much timing does it want for best acceleration?
How does it like vacuum advance when using high octane fuel?
My old 350 vortec motor (10.03:1) and my present 400 vortec motor (9.80:1) seem to both like 35 to 36deg. (Sunoco Ultra 94)
(I'm going to be testing less spark timing when get back up to the track)

What happens when you jet up the secondaries (#76) and add rear jet extensions? What happens when you try 68 or so primary jets? how does it run and what happens to the plug colour?
Please do all this tuning using 91+ octane for now.
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