Just pulled the vac advance and tried it at 11 initial+ the 20 for the mechanical. I got up to 45 (4th+TC locked), which is probably ~1300 RPM, then gave it a good bit of gas and it started pinging right around 1500.

Not sure where to go now. I tried richening the idle mixture by 1/2 a turn. I'm gonna go do the WD-40 thing now, and if that doesn't work I don't know what else to do besides manually shift from 4-3 when I need to accelerate.

 

qjets have a power piston that richens it depending on vacuum.
Is it too lean at 1500? very possible,
but, not having a gauge,
i'd press a little further on the gas-
do this several times(farther each time) to see if u can feel the power piston kick in AND hopefully stop the ping. if it works u can go to the sweet spot until u fix the carb.
it would be nice to know if the weights are adding anything at 1500; do u have a timing light?

 

Yeah I have a timing light, but nobody to watch the tach really. I don't think it's coming in at 1500 though, seems to rev a lot higher than that before getting much advance as far as I can tell.

As for the advice with the gas, you mean when it starts pinging I should just give it MORE gas?

 

I think you need to check the timing at various RPM settings to see what the advance curve looks like. You need a timing light...preferably a set-back type (dial that you can set to get the damper reading at zero; then you read timing off of the timing light scale). Check it at 1000, 1500, 2000, 2500, 3000. Hopefully, your total mechanical timing will all be in by then [but maybe not]. Once you determine those numbers, post them back here and let the engine 'gurus' give you some suggestions. You might well have some mechanical problem in the distributor. Without removing it and taking it to a shop, this is the only way to get a handle on that issue.

 

YES. a rich mixture will stop borderline ping.
Also it should downshift to 3rd and jump up to ~2000rpm at some point by itself.
.
just turn up the idle to check the advance curve.
i've gone to 4000 working alone

 

I see you have a 230/ 236 cam and 10.5 to 1. That is pretty high DCR. That combined with the lockup convertor is probably your problem. A proper timing curve might fix it, might not. My 383 with 10.4 compression and a 236 / 242 cam runs 8.25 DCR, you got to be higher. Jim is spot on regarding the KB hypers. They will not handle detonation. Fix it quick or you will be building another motor. I am running flat tops and milled the heads to 70 CC to get my compression where it is. If you have flat top pistons and 64 cc heads you are probably around 11 to 1 or more with decent quench. If so that cam is too small. If you have real big quench to reduce compression to 10.5 to 1 with 64 cc heads that will cause the detonation also.

 

Assuming that is the case, what kinda of cam would I be looking at to get me in an acceptable range?

 

If you have a true 10.5 to 1 and want to stay with a similar hydraulic flat tappet this cam will probably maintain streetability and solve the detonation issues if they are minor. It is a little bigger duration and has close to the same lift, ground on a 112 LSA. http://store.summitracing.com/partde...4&autoview=sku I would try to solve the problem with timing curve adjustment first though. See Barryk's sticky at the top of the tech and performance page for details on timing adjustments. If you are over 11 to 1 all bets are off. You start running into vacumn, torque convertor and streetability issues that are very difficult to balance well in a street car although some have done it and had acceptable results.

 

If this carburetor has the original calibration it will be lean in every system. I believe they came from Edelbrock with 73 main jets and the 50M main metering rods. These rods have the .036" power tips. This combo will never perform well on this engine. You need to richen it up. At the very least I would get those primary rods out of there and replace them with some '75 to '80 passenger car rods. NOTE: These rods are not available new from any source. (The only tuning kits that Edelbrock sells for this carburetor have the "M" rods). You must get them from old carburetors or parts recyclers.

Or, you could reduce the metering surfaces on the rods you have. This involves sanding the .036" power tips down to .026". This will help the mixture under heavy throttle. To help get rid of the low speed cruise rattle you can sand the .050" cruise metering surface down to about .045". This will richen the idle, off idle and cruise circuits.

THIS IS ONLY A TEMPORARY FIX!!!

The real fix is to do a complete jet/rod setup on the engine. What I have outlined is something you can do to keep from destroying your engine in the short term.

Depending on the air bleeds this carburetor has, your engine will want something around a 75 or 76 main jet and some .026" tip rods.

BigBlockk

Later.....

 

too many unknowns:
1. why does trans shift into od at 45?(55-75 more where i like it)
2. CR, quench, plug heat range,...
3. cranking psi
4. is damper mark correct?
5. is cam in correct?
6. A/F ratio
7. why doesn't trans downshift at <2000?
8. advance curve for weights & vac adv.
9. fuel- confirmed 93? or less than advertised?
10 did PO "fix" this by using an open spacer? try it again!
Good luck! (without above info, cure is a crap shoot)

 

I'm sorta leaning to a trans issue too until we know more detail. There's not much of anything like this that is going to take much load at 1500 rpm with a lockup converter. Usually at least converter unlocks when vacuum drops as you mash into it. Try driving a stick car at 1500 RPM in high gear and mashing into it hard...it won't be pretty unless you have an awful mild combo.


JIM

 

To Matt & 427, as I've said the transmission is a 700R4. It has a 2800 stall converter but the TC was set to lock up hydraulically. It has no electrical signal for locking/unlocking as far as I can tell. It will lock up in 3rd and 4th if over a certain speed as far as I can tell.

I don't recall seeing any vacuum lines going to the transmission. I think the TV cable is it, but I can get under there again and look.


Matt: I can't give you most of that info as I didn't build the engine. I have a build sheet for it which lists all parts, etc, but not how it was exactly set up. As I said above it shifts into OD so low because it's hydraulically controlled, and I assume that's where it was set to shift at. I am indeed getting 93 fuel. Since you mention the carb spacer, the previous owner DID have a 1/2" open hole spacer on it. I changed this to a 3/4" 4 hole spacer. Would that cause a lean condition or pinging somehow?

 

Regardless of comp ratio and the other issues being discussed here, 20 degrees of vacuum advance is way too much. Most performance engines won't take any more than 16 degrees of vacuum advance, and we're seeing with today's pump gas that the limit is dropping down to about 10 degrees of vacuum advance for most performance applications. You need to limit your vacuum advance to about 10-12 degrees (you can use a limit bushing on the vacuum advance shaft to accomplish this) in addition to whatever else you do to eliminate the detonation. Running ported vacuum to the vaccum advance isn't doing anything useful for you other than making your engine run hotter at idle and lowering your HC emissions - once you're off idle, ported vacuum is the same as manifold vacuum, so you may as well take advantage of manifold vacuum to your vacuum advance at idle.
Lars

 

Hi lars, I limited it to 8 yesterday already and plan on leaving it that way. Still trying to get the rest of this stuff sorted out though!

Thank again for everyones input so far, and hopefully this will get solved eventually. Right now I'm really wondering if the carb spacercould have effected it (Matt has me curious).

 

YES, the open spacer would give it EGR (exhaust gas recirculation), because at high cruise vacuum it would suck exhaust during overlap and dilute the intake charge. EGR is a well documented method to reduce pinging when it works properly. So i would try the open spacer since the PO had it on there and it may help.

 

I'll try the open spacer again this evening then, but for my knowledge, what's the difference as far is that is concerned between a 4 hole and open hole spacer?

 

As a side note it wouldn't take much work to make my own A/F ratio display with some LEDs and a circuit, so I might make one to see what I'm running. I just need to buy an oxygen sensor and have it welded into the exhaust pipe I guess.

 

1st u need to drive it like a sports car, not a pick-up truck with a RV cam and 8.5:1.
A. don't upshift until u hit at least 2800
B. anytime <2000, DOWNSHIFT
then
do cranking psi test, throttle open
and have a look at the plugs, post pics

 

Have you tried slowing your timing curve down, a little sluggish performance is better then replacing pistons. Builder may have the timing coming in at a fast rate.

 

I have the heaviest springs I can find on the dist right now. As for driving, it's an automatic 700R4 not a stick. While I wish I had a 5 speed in the car, I don't, and thus I don't want to screw up the transmission by trying to drive it manually (and on top of that it's a pain).