| Author |
Message |
    
Andreas Kaupert
| | Posted on Friday, February 15, 2002 - 11:48 pm: |       |
I have a new HT383 motor installed in Sept. 2001. It has been modified to use the Pro Magnum Roller Rockers, an MSD Ready to Run Pro Billet distributor setup for 34 degrees total timing. Initial timing is 14 degrees and I am running a 7042208 Quadrajet carb. The jets have been upgraded from .071 stock to .074 to eliminate a lean running condition. The engine breathes through 1 5/8" Hedmen headers and 2 1/2" dual exhaust. The engine has lots of power at WOT and idles great, but running down the highway at 60 mph it takes alot of throttle just to maintain momentum. It cruises at 9-10" Hg and 2200 rpm (using a 700r4 tranny in OD) with 4.10 gearing. This does not make sense and I don't know why it needs so much throttle just to go down a flat, level road. With the original 350 using the same headers and carb. I had plenty of cruising power. What gives? This engine has tons more torque and the driveline, tranny all check out fine. I would appreciate any help in getting this "high-torque" motor to get me down the road without being passed by Ford Escorts! Every part on the engine is either brand new or rebuilt. The motor has only 1200 miles on it and is a total dog going down the highway. |
Scott
| | Posted on Saturday, February 16, 2002 - 2:05 am: | |
Are you using the vacuum advance? The best setup for the MSD distributors in a Vortec head application is the blue bushing with one light silver, and one light blue spring. Set your total timing at 32º and don't use the vacuum advance. It pulls in way too much advance. The re-jetting work may be part of the problem. The Q-jet carb is tuneable with needles as well as jets. Take plug readings and tune from there. |
Andreas Kaupert
| | Posted on Saturday, February 16, 2002 - 11:19 pm: | |
Scott, I am using the vacuum advance and it is working properly. I am using the black bushing with the light silver spring. As to not using the vacuum advance, MSD recommends it for best economy around town. This is in a 3/4 ton GMC 4X4. Do you still think I should run with the vacuum advance disconnected? I have just picked up some different size primary metering rods and will adjust the mixture with my Colortune, which allows me to see the actual flame inside the combustion chamber. Thanks for the help! Any other ideas? |
Scott
| | Posted on Sunday, February 17, 2002 - 1:22 am: | |
Use the blue bushing, with one light silver, and one light blue spring. Forget about the vacuum advance, unless you install an adjustable unit. The MSD vacuum pod gives you another 26º of advance, on top of what you already have. This is way too much. The Vortec head likes no more than 32º of advance. It's as simple as that. If you are setting your timing with the vacuum hooked up, this would cause the condition you are describing since the timing would be severely retarded. If you simply must run a vacuum advance, find an adjustable vacuum pod, and adjust it so you get only 6-8º of added advance. Even this small amount of advance will probably cause pinging. Simply put, the Vortec heads need 32º total. Make sure your vacuum advance is hooked up to ported vacuum, not full manifold vacuum. |
Andreas Kaupert
| | Posted on Sunday, February 17, 2002 - 11:29 pm: | |
Scott, thank you for the help! I will make the spring and bushing changes. The timing though was set with the vacuum disconnected and only reconnected after adjusting the timing. The vacuum advance is coming from the ported vacuum off the front of the Quadrajet. Once again ,thank you for all the help! |
Andreas Kaupert
| | Posted on Monday, February 18, 2002 - 11:12 pm: | |
Hello Scott!
I did the timing changes this morning as suggested. I already had the light silver and light blue spring installed. All I had to do was replace the black bushing with the blue one. I reset the timing (with vacuum advance disconnected) for 14 degrees initial on the crank. I then hooked the vacuum advance backup and had 32 degrees crank advance at 2500 rpm. Took the truck out for a 30 mile trip and noticed a slight improvement , but nothing that one would consider normal operation. The engine is still needing enough throttle to give only 9" Hg. vacuum at 2200 rpm at 65mph. The engine acts as if its all it can do to stay at this speed. Any faster and I would probably be at 5-6" Hg. just to maintain forward progress. This is on the flats without any wind. The slightest incline and I'm down to 1-2" Hg. just to make it up the hill. When I got to the end of the first 15 mile section, I disconnected the vacuum advance and returned home. Performance on cruise was about the same to a little bit worse, with take off from a start slightly worse also. Vacuum at idle is a fairly steady 19" hg. with a temporary drop to 18" hg. 20% of the time. I think the slight drop might still be a tight valve, as the motor only has about 1280 miles on it. The vacuum advance is connected to ported vacuum and I did not notice any change in timing at idle, whether it was connected or not. So where do I go from here? In addition, the engine seems to run roughly and have a vibration when running at 55-65mph, almost as if the engine inside has something holding it back. I want to get this thing running right so I can finally put my camper on it. As it is right now, I can't even try to put a load in the truck other than it's own weight. Any ideas or suggestion would be greatly appreciated. |
Cardiac
| | Posted on Tuesday, February 19, 2002 - 6:10 am: | |
Where do you have the pcv hooked up? If it's hooked to the intake manifold you'll lean out the #8 cylinder, on a dual plane manifold, which in turn will rob you of vacuum and HP. |
Howard Burkhart
| | Posted on Tuesday, February 19, 2002 - 12:20 pm: | |
Sounds to me like your power valve is not working in your Q-jet. You said before that you had to rejet because of a lean condition and this could be the cause. Check to see if your power valve is not stuck and that the passages are open. You should be pulling more vac. then this at cruise but this is caused by throttle position.I am no expert on this but maybe this will help. Good luck. |
69Z28302
| | Posted on Tuesday, February 19, 2002 - 3:47 pm: | |
What type of truck is this in? How heavy is it? It does sound like a carburetor tuning problem. If it runs good at WOT and idles good, it must be your cruise circuit in the carburetor. That carburetor must be off of an early vehicle. My AC-Delco book lists it as fitting a '72 truck. How did you make the choke work with the Vortec heads? I would definitely do something about this before you melt down the engine. |
Andreas Kaupert
| | Posted on Tuesday, February 19, 2002 - 11:53 pm: | |
The truck is a 1972 GMC Sierra Grande 3/4 ton 4X4, that just went through a 2 year restoration. The PCV valve is connected to the front of the Q-Jet. The carb. was a new rebuild last year when it was still on the old 350 and was running great. The last time I changed the jets to .074, I checked the power valve and it was not stuck or sticky. As to the passages, they could be blocked, but when I opened the carb. up, it was spotless inside. I just picked up 4 sets of primary metering rods and will try the "44"'s first to go along with the .074 jets. The electric choke is available from Ecklin, but you will have to make your own bracket to make it fit correctly. I adjusted the fuel mixture with a Colortune, so it should not be running lean. This is basically a clear sparkplug that lets you see the flame inside the running combustion chamber. Adjust the mixture for a light blue coming off of yellow and you have a perfect burn. Very easy to use and extremely accurate. |
Howardburkhartmsn.com
| | Posted on Wednesday, February 20, 2002 - 12:21 am: | |
what size tires are you running? |
Scott
| | Posted on Wednesday, February 20, 2002 - 2:14 am: | |
Going from a 71 to a 74 is way too big of a jump. That 3 jet size increase is comparable to 6 full jet sizes in a Holley carburetor. This whole deal sounds a lot like a 383 that we had rebalanced and dyno tested last October at Sallee Chevrolet. The engine made excellent power as long as you had a full load on it. Getting it to accept the load was kind of a handful, which is unusual in Quadrajet applications. The carburetor had a problem with the primary power circuit. I told the owner that the carburetor needed attention, and if it were me, I would swap it for a new Edelbrock 1904 with an electric choke. The $400 dollar price for the new carburetor sure beats the cost of rebuilding your new engine when the pistons melt from the excessively lean air fuel mixture. By the way, that engine made over 400 ft./lbs. of torque at 2200RPM, which is where you are running yours. To make a long story short, ditch the old '72 carburetor, set up the MSD as mentioned above, forget running the vacuum advance, unless you can locate a adjustable unit. The 26º vacuum unit on the MSD distributor is excessive. A more realistic number would be about 6º. It is a proven fact that the Vortec heads don't like more than 32º total, whether it be centrifugal or vacuum. These are just observations from tuning many Vortec engines and hours of dyno experience. P.S. if this is Andy at Integrity, call me on the tech line. |
Steve S.
| | Posted on Saturday, February 23, 2002 - 12:48 pm: | |
not really related, but where would you get this??
Colortune |
Andreas Kaupert
| | Posted on Saturday, February 23, 2002 - 11:07 pm: | |
The Colortune is available from Eastwood Automotive. They sell all kinds of things for working on your car, mostly auto body. Do a web search and you can find their website or search "Colortune". Good luck! |
Bogie
| | Posted on Wednesday, February 27, 2002 - 9:11 pm: | |
Andreas, welcome to the down side of a Crate Motor, you don't really know if it's put together correctly. Could be your carb's gone south, I've had several Q-Jets and a Holly act like this over the years and never found a soluton other than replacement, and I'm a pretty decent carb guy.
But, and this is a big but, it appears that you really don't know if the guts of this engine are correct. And on top of that you made some critical "improvements" i.e. roller rockers, and an after market distributor. And what mix of old engine parts i.e. intake manifold?
You need to get back to basics and determine some things.
1) Are you leaking air into the intake someplace? Disconnect all vacuum connections including the PCV and plug all the source tubes except where your vacumn gage is connected. Squirt a light oil around the base gaskets of the carb and the manifold gaskets with the engine running, your looking for a gasket leak. Search carefully for any opening to atmosphere, God help you if it's on the bottom of the intake. If you have a mix of part form variuos years, for example, you might have an EGR port hiding somewhere; were the heads milled? vis-a-vis the intake manifold, again are they from different engines or years?
2) Do a compression test. Write the values down.
3) While the plugs are out, check cam coordination to crankshaft. Remove rocker cover, on no. 1 side and watch valve movement, feel for TDC (on the compression stroke both valves will be closed) using a small screw driver in the spark plug hole, if you don't have a TDC tool. Be gentle and slow when you rotate the engine by hand (plugs out, ignition off).
4)Once TDC (on compression stroke) is found, you want to see that both valves are closed, as you come up on the compression stroke the intake will close shortly after Bottom Dead Center (BDC); check to see the timing pointer and the timing marks on the damper align to 0 degrees or "TDC" which ever is marked. Don't shoot for this alignment, rather this is what you want to see develop from the process your performing. Keep in mind that if your using a screw driver rather than a TDC finder, your measurement will always have some error, but work hard to minimize it. A slight error, especially if the cam is retarded a few degrees to the crank will give you a condition such as you described. Chevy timing marks and the damper's key are offset to each other, plus some dampers have more than one long mark so make sure you know what your looking at is the TDC mark. Again different years creat an issue. If your in doubt after all this, pull the front timing cover off and make very, very sure the cam and crank are in concert. What kind of cam? A roller against the incorrect distributor drive gear will eat that gear in no time at all, you'll find yourself putting more and more advance to less and less effect if this is the case.
5) Now with the engine resting at TDC on number 1, mark the number 1 position with crayon or chalk on the distributor's base. Then remove the distributor cap. Where is the rotor pointed? If your timed corectly it should be about 5 distributor degrees beyond the mark you made. If it's way off rotate the distributor to bring the rotor's terminal to the TDC position on number 1, we'll dynamic tune this later.
6)You changed rockers, question you need to ask is; are the valves closing completely or opening adaquatly? Don't know if your cam followers are solid or hydraulic. Assuming you've completed the efforts of the preceeding paragraphs, and have removed the screw driver or TDC tool from number 1, you can now proceed to measure the cam event at the valve. You need to check for complete closure and spec opening. If this is a solid cam rotate the engine bringing each cylinder in turn to TDC and check/set the lash. If this has a hydraulic cam, do the same engine rotation and back off the adjuster till the pushrod can just be rotated with you fingers. Now tighten the adjusters to the lifter manufacturer's specified number of turns, usually a quarter turn. Being an old fashion guy I like to rotate the engine and do each cylinder at a time rather than the method of rotating the engine a couple, three times and doing sets of cylinders. Now were ready for some measurements.
7) Measuring valve action on the rocker arm is easier with a dial indicator. Barring that, you can put a straight edge along the valve side of the rockers. There's usually enough valves closed at any one time to support the straight edge pretty well. Now take a machinist's six inch ruler or a caliper or some measuring device and check the open dimension against the spec. This doesn't need to be too precise for our purpose here, you wnat to know the valve opens .3 or .4 inch not .1, getting to know it opens .320 or .467
is not important at this point.
If all of this checks out, your now getting close to spending money instead of time. If it's the carb, I'd trash the Q-Jet and put a Holly on it. Not that a properly running Q-Jet is bad, the Holly is simpler and tuner parts are available everywhere.
Now button it up and light it off. Bring the hot idle to 600-700 RPM, with the vacuum advance disconnected and the port plugged. Advance the distributor to 8 to 10 degrees. With a timing light attached bring the revs up to 2500 3000 RPM, does the centrifugal advance come in? Now drop the throttle. Does the timing mark bounce more than a couple degrees, if it does your timing chain/gears and/or the distributor drive gear are/is shot. Everything OK? reconnect the vacuum advance and take a test drive, no more thirty milers, if it's bad it's bad and there's no sense in risking the engine. If after all this, it runs like it did then you need to check for 1) fuel flow; 2) carb setup, tuning and function. Like a said a long time ago, I've seen more than a few Q-Jets do this and 1 Holley 3 barrel. They all eventually went into the trash.
Parting thoughts;
1) Vacuum advance is good on the street, but you don't run soft centrifugal advance springs with it. You want vacuum advance in high vacuum low RPM cruise. When plugged in the proper distributor port this vacuum diminishes with RPM (more open throttle) and the centrifugal takes over. If you use soft springs so the advance comes in early (at low RPM), then remove the vacuum advance, 'cause you don't want both maxed at the same time. You need to take that distributor to a shop that can tune it, way cheaper than piston replacement from the effects of detination. If your running 4.10 gears and a 700R4, you only have low RPM cruise in 4th.
2) Don't know what "year" of parts are in your engine. You must be careful not to mix rocker arms from self aligning and non-self aligning engines. So if you have a later model set of heads that require self aligning rockers and either didn't use them or used them with a pushrod guide kit you can get problems similar to your vacuum pulsing. If you used older heads with cast in pushrod guides or an after market guide kit combined with self aligning rockers you have the same problem of binding the rocker. If you used newer heads designed for self aligning rockers and used non-self aligning rockers combined with not installing an after market pushrod guide kit, then you've got a problem resulting from the rocker sliding sideways and perhaps falling off the valve stem. At the least this will "jam" the valve sideways in the guide and at worst unlock the retainer. You'll definatly know if the latter happens.
Good luck. |
Denny
| | Posted on Sunday, June 9, 2002 - 10:17 pm: | |
I have the same problem with my new 383 vortex with about the same set up you have in a 1969 C10 Chevy truck. |
|
Message Archives