I need some professional help... as far as the engine goes :flipoff2:

I just installed a 4.3 Vortec V6 and I'm cursed with a helluva spark knock going into 4th & 5th.

Here's the scenario-
'97 block (CPI originally, converted to 4bbl Carb)
'85 head
Edelbrock Performer intake
Holley 600cfm 4bbl (I tried for the Avenger but 670cfm is too much)
Flat-top pistons (compression within 10:1) & 93 octane
Stock camshaft :confused:
No computers... no ECM to drive the cam.
The valves have been checked.
I'm running a Holley fuel-pump, psi checked
Timing CANNOT be established, advance or retard doesn't fix it !

There are (3) possible timing-gear sets and (2) have been ruled out. The other one will be shipped tomorrow.

We replaced the module in the dizzy prior to all of this shite.

What the hell have I missed ?
Help a Newbie would ya :rolleyes:

If the truck isa knockin', don't bother rockin' :mad:
BLP

ya prolly wanna git rid of the computer cam. no ways the carb is gonna meter fuel that accurately.

What distributor are you running? The stock computer-controlled won't do what you want. You need a big-cap HEI off a '85 or '86 w/ carb. If you can't find that, get a mallory or msd. The stock computer distributor has no advance built into it.

Originally posted by lizard
ya prolly wanna git rid of the computer cam. no ways the carb is gonna meter fuel that accurately.

We couldn't find a difference between the 2 cams other than the fact that the 1 is controlled by the ECM. I'll have to get the specifics from the shop today.

Any other advice concerning the cam(s) is appreciated.

Originally posted by kbud
What distributor are you running? The stock computer-controlled won't do what you want. You need a big-cap HEI off a '85 or '86 w/ carb. If you can't find that, get a mallory or msd. The stock computer distributor has no advance built into it.

Yup. It's a big-cap HEI off an '85 and we STILL can't set the timing.
Everything mechanical is tell us we should be able to get the timing right.

This *does* seem to lean towards a cam/gear set problem but I've exhausted my limited knowledge:rolleyes:

Thanks for the ideas... any more ?

maybe the cam timing is off 1 tooth...

Ok, on the big cap, make sure you're using a 4-pin hei module. The 5-pins were computer controlled. You can take an earlier v-8 module and wiring out and use it in the v-6. Did you degree your cam? Does the balancer use two timing marks? If so, make sure you're using the correct one. What heat range spark plugs you using? Try a colder one if you're not already.

Originally posted by lizard
maybe the cam timing is off 1 tooth...

Initially that's what was hoped for... even a half-tooth, but we've checked (3) gear sets and none of 'em help get base-timing. Everything lines up :confused:

I'm still looking for an answer to whether or not a '97 (ECM controlled) cam, functions any differently than a '85-86 (pre-computer) cam... in a non-ECM environment ?

The plugs are ACDelco copper core for a 4.3 HEI.
I'd considered that as a problem before, but I wouldn't think the engine would spark-knock *that* bad. I'll double check tomorrow.

I appreciate the follow-ups :D
I need all the HELP I can get !

kbud- I'm not sure about the balancer but the dizzy will be removed tomorrow. I'll check the # of pins. Thanks for the tech info !!!

Damn I gotta lotta work to do tomorrow :beer:

I'll let you know what I find out...

As far as the cam, most fuel injection cams are not real aggressive. The cam might just seem weak. Other than that, everthing else should be the same for both applications. Did you remove the balance-shaft? I know you have to have a timing chain specific to a balance motor if you are using the shaft, don't know about it if you remove it.

Originally posted by kbud
Ok, on the big cap, make sure you're using a 4-pin hei module. The 5-pins were computer controlled. You can take an earlier v-8 module and wiring out and use it in the v-6. Did you degree your cam? Does the balancer use two timing marks? If so, make sure you're using the correct one. What heat range spark plugs you using? Try a colder one if you're not already.

Yes it is a 4-pin module.
Cam was degreed.
Balance shaft is still there.
Balancer only uses one timing mark.
The plugs are actually AutoLite (which I've heard bad shite about)

Got any recommendations for the plug-of-choice for my application ?

I read the post from Whitebrowithafro (http://www.pirate4x4.com/forum/showthread.php?s=&threadid=58269) concerning a ballast resistor in some of the HEI dizzys. Is this something I should check ?

Sorry for my ignorance but I'm use to EFI engines & coil packs.
The last carb'd vehicles I owned were a '67 Buick & a '77 Cutlass.

GonZu <-- showing my age again :rasta:

Damn OEM CAM...:smokin:
That's the problem.

Even though a computer-controlled cam WILL work on a carb'd V6 Vortec ('86 head, '98 block, flat tops, Holley 4bbl).
Said CAM will run weak (read: LEAN) = spark knock

Pictures for posterity sake :question:
http://www.mindspring.com/~mjblp/engineswap/nicefrontshot2.jpg

Funny, what a *difference* 2/1000ths makes:rasta:

GonZu

So, you swapped the cam and fixed the problem? What cam you go with?

Hmmmmm, me thinks me recognizes dat dar motor! Cool deal "GonZu". That's pretty damn funny/ironic...you figure your shit out and I break mine. Whole bunch of dammit! :flipoff2: No go on that piece of shit Waggy last weekend. Anybody got a spare D44 and springs laying around? :D

Long time no see guys.

I thought we had figured this out after problem cams, ignition timing, cooling system gremlins...

We got a custom grind from CompCams. Installed it and the thing absolutely KICKS ASS !!!


BUT (and that's a big fat butt), there's still a spark knock happening under load in 4th & 5th gear (albeit better than before). The consensus is the problem lies in the matching of the '97 block & the (pre) '85 head.

Here's the pisser. If the head/compression is indeed the problem, this will require tearing down the engine again b/c of the flat top pistons :mad: & replacing them with dish pistons.

I think I remember compression being around 160 on all 6 cyl (give or take 3psi). The last guy to do a compression check said it read 160. Today, the owner said it should be around 125.

Does this sound like a job for the .380ACP ? ;)
Any ideas ???
Could running 89 octane cause such a big difference ?

Oh yeh, Muddin is FUBAR'd :flipoff2:

Gracias,
GonZu

I think your Distributor may be the problem.. It seems like the early 4.3 V6's were odd fire ( I think they varied from 108 and 132 degrees between cylinders)while the later ones were evenfire (120 degrees between cylinders)..
The cam,crank, and rods are different between the two types.. If this is your problem you could probably get the pickup coil from an inline 6 and put it in your V6 distributor along with the inline 6 cylinder's cap..

That's some good info to start with hy_desert :D

Would ya care to share what year/model inline V6 (cap & pickup) I should be looking for ?

YES, I'm a newbie. Can you tell ? :rolleyes:

79 or 80 should work.. or you could try to find 87 or 88 V6 parts not sure what year they quit using the big cap on the HEI distributors but the best would probably be the inline stuff since you do not have the computer stuff.. another possibility would be Buick even fire dist parts from the late 70's or early 80's..

You want an '85 to '86 out of a fullsize truck, van, or astro van with a carb. No computer stuff involved besides ESC, which can be eliminated by changing out the condenser w/ an earlier v-8 unit. The v-6 cap doesn't line up correctly if you swap it onto a v-8 distributor. You'll have to recut the alignment notch. If space is a premium, get a pyramid cap off a '76 fullsize inline. The coil is remotely mounted.

Make sure you are not running a distributor out of a 200 or 229 chevy v-6. They are semi-even fire, and will run an even-fire, just not very well. I found that out the hard way. Anyway, pull the distributor out, and look at the pickup. There will be six points that should be evenly spaced around the bottom. If you have a couple close together and a couple farther apart, you've got a semi-even fire distributor. Swap out even-fire internals, you can buy them a autozone,etc. You'll have to remove the advance system and shaft, but no big deal. If the six points are evenly spaced, then you have a 4.3 even fire distributor. Lube the advance, make sure everything is working smoothly, and swap out the module while you're there. Are you sure the advance isn't coming in too quickly? If you think it is, get a spring kit at the parts store and try that.

Did you get it fixed yet??

Nope :mad:

Turns out the compression was up around 175 !
I'm seriously looking in to taking a mechanics class at the local tech college and doing this stuff myself next time. Hell, I just changed the t-belt on a 3.2 DOHC this past weekend for the first time. Learned a lot and saved a lotta moola too.

I've trusted this guy (who has extensive engine-building knowledge) to build the motor and fix the problems... but it turns into bigger problems.

I spoke to him last Friday. He said either the heads would have to be swapped for a late 90s model OR the flat top pistons would have to be pulled and replaced with dish-type.

The problem is the older heads and the flat pistons. If we simply change out the heads, we run the risk of the pistons making contact IIRC (not to mention the intake would have to be changed out to match the newer heads).

Hopefully I'll check back in a week with some better news.

If you put in a cam with a little more duration on the intake side it will let some of the charge back out and lower the compression pressure(not the ratio)and should fix your problem (If thet is actually the problem)

GonZu

I have a carb/HEI distributer from my 4.3 liter that was on my engine and was built-up for a high performace 4.3. Worked excellent until I switched to TBI injection with the TBI Distributer. I would imagine it would work for you. Email me at weigel.lee@marshfieldclinic.org if you are interested in it

I personally think the knock is in the ignition. Compression should not matter. More compression=More Power

Originally posted by weigellj


Compression should not matter. More compression=More Power

Too much compression = DETONATION= busted pistons +hammered rod bearings

Gonzu you didnt say what fuel you are running but you might try premium to see if it will help..

Originally posted by hy_desert_4wheeler


Too much compression = DETONATION= busted pistons +hammered rod bearings

Gonzu you didnt say what fuel you are running but you might try premium to see if it will help..

We did another compression test before the flat-top pistons were pulled today... 220 !!! :eek:
I can't get the mathematical ratio (nor do I have the patience), but you get the point.

Once the engine was tore-down again, I saw the piston tops, spark plugs & cylinders. Pistons REALLY need to be replaced with OEM, spark plugs are trashed, cylinders are OK.

The new CompCam grind seems to fit. I don't know the duration... but it runs like a scalded dog (so to speak) !

Keep in mind- this is a bastard-ized version of the Chevy 4.3.
We're going back to the OEM dish pistons... it seems like a match. The alternative is to run HIGH (really high octane).

Right now it's running 89-93 with an octane boost. I plan to drain the tank and make it pure 92-93 before it's cranked again.

BTW- Does anyone have any good experiences with McLEOD starters :flipoff2:

Sorry for the delayed update;)