Technical Timing with Dual Quads - HELP!!!!

But now I look at his original deal and he says I'm having a timing problem with dual fours!! I think you have a carb problem!! Jeez.

 

How many engines do you work with that can idle with 25º of advance, that also have a mild cam, and about 8:1 compression?

 

We're not. We are saying that he might have a timing tab/damper mismatch, and if anything, his timing might be ATDC by a few degrees.

 

I reread thru the posts and I humbly apologize.

 

I’m just following along as I have considered running two fours again on something in the future. Last time I ran two was almost 40 years ago when I was a dumb kid and it was direct linkage on two brand new 450 Holleys on a pretty healthy sbc (10:1, 550ish lift solid cam, ported 461 heads, etc.) and that was all the cfm it needed. Not sure if I got lucky or what, but it ran pretty good. I have never tried running Edelbrocks so am just curious how this goes.

 

I'm going with the concept that you did indeed match the timing tab to the damper and everything was indeed lined up at actual tdc.
Telling on myself, I fought the exact battle that Gimpy posted in post 14. I had a 78 350 in my 71 GMC using the short 71 350 water pump and an aftermarket timing tab that was probably set for reading at 0 degrees. I later changed to a long pump for a different reason and then could read the timing by aiming the light down behind the long pump.

 

Carburetors are not the issue, do not be afraid to run dual quads no matter the name brand of the the carbs.
This is the motor I made reference to in my earlier post, pair of 600 cfm Carters, one to one linkage and chokes wired open.

 

It is the little things that will drive a man crazy!

It did not help that Chevrolet had 10º and 30º dampers on the market, in the same era, and that the variance could have been, in certain years, van, versus not van.

I believe that at 1986, the 5.0 and 5.7 (which were the modern names for the 305 and 350, respectively) were all 30º (and had a 1-piece rear main seal).

As for a crate engine, it would depend on exactly when it was made, and what block and crank were used.

Hard to say either way. That's why it is best to confirm TDC, and then mark, or tab accordingly.

As for the OP, I have extreme difficulty with the concept of idling at 25º BTDC. My blower motor has that, all-in. I have stared and warmed up new builds, and found them at 5º ATDC, and they idled fine. Well enough to set the timing, at least.

 

@Lloyd's paint & glass.I am here, but some pretty good ideas done been stated.
I would find true TDC first. Get intial timing and all in set first. My question is do you really need progressive linkage on this engine? To my way of thinking you want both carbs opening at same time. But I have never been able to get eddys to work like I could holleys. You can make a simple piston stop from a old spark plug. Get your intial and all in timing right first.Then go from there.

 

However, he also said that if backs the timing off it runs very poorly, but if he advances it enough to run well he has detonation problems as if it's advanced too far. Something's not right, I agree, and he needs to start with identifying true TDC, but I'm not sure that timing is the problem, or the only problem.

 

Just to be clear, I'm not saying the carbs screwed my timing up.

I've been trying to work off of the manual that came with this engine, since I'm working under the likely-correct assumption that the GM engineers and techs are better at this than I am. The manual is here. https://www.chevrolet.com/content/d...0-290-hp-long-block-crate-engine-19172591.pdf

The manual calls for timing at 12 degrees BTDC and 32 degrees all in at 3000 rpm. However, that is also considering the recommended dual plane intake with a single 650 cfm carb and an HEI. I'm deviating from that setup with dual quads and stock appearing electronic distributor. I also know that multiple carb applications tend to need more initial timing than in a single carb application, so that's where I thought my issue was arising.

However, as has been pointed out, my timing mark is potentially off and I've been basing my numbers off of faulty information. I would agree that the best move here would be to get some more correct information on timing, take another stab at it, and reassess.

I'd also add that there is no way I can swap the balancer. I documented in a prior thread about how I FUBAR'ed the threads on the crank snout putting the balancer on with an impact wrench. I've gotten away with that move dozens of times but this time I didn't. You live and you learn. I put this balancer on with an installation tool after having those threads repaired, and I'm not risking tearing the compromised threads out installing another balancer. In hindsight, I should have simply used the recommended balancer for that engine. But I thought I was doing something good by buying an aftermarket balancer that seemed better than a stock unit, and was also $100 less expensive. When you add in the machine work to fix the crank I could have bought 3 balancers. Oh well.

I ordered a piston stop, and some timing scale stickers for the 8" balancer. They should be here by Friday, but I'll be out of town for the weekend. Will give this a fresh shot next week.

 

I have not played with the advance springs or weights on the distributor yet, and honestly I'm glad I didn't. If the timing is off I'd just be back to square one there.

 

That's actually what I wound up doing, and the car would actually start fairly well, give me a smooth idle at start up, and hold a steady idle in gear. But then when I'd lean into it under load, it seems to detonate, especially with less RPM. Less of an issue when I get the RPMs higher.

I also know I should be running a lower (numerically higher) gear in the rear. This has a 3.08 in the Olds 9.3 with a 215/75R15 tire, and a 700R4. If I manually shift gears and get the RPMs up, the car will bark the tires into 2nd. But if I'm just driving in OD and stab it, it will kick down to 3rd but detonate. When I backed the timing off to alleviate the issue at the top end, the car would fall all over itself at idle.

 

What is your timing all in?

 

If the timing marks on my balancer are inaccurate to this application, at this point I honestly can't tell you.

 

The crazy thing to me is, at 8:1 you wouldn't think it would spark knock so easy, and if you did retard the timing enough to make it spark knock, it wouldn't crank up. I have had a few small blocks that obviously had the wrong balancer as far as the timing mark goes, but I found that spot where it would start without kicking back on the starter and left it there.

 

8.1:1? a supercharger or turbo could fix that... definitely needs a tad more squeezin, if you want more power. could be a nice runner as is.

 

8:1 probably doesn't have a very good quench and will be prone to have detonation problems unless it's running an EGR system.
I would shorten the mechanical advance.

 

I have all the parts collected to do a dual quad on my sedan project so I’m following along here too. I’ve done versions of 3x2 and 4x2 before, but never a 4x2 so I’m reading all I can at this point. Thanks to everyone contributing ideas/thoughts on this thread.

 

ive always heard of people deleting an EGR system, never adding one.

 

I'm gonna get flamed for this, but I can take it lol. Moriarity sent me a distributor for my 283, but I already had a billet electronic distributor in it, so after talking to him on the phone, I'm using the points setup in my big block. I fought with my car, switching carburetors, back and forth, modifying carburetors, crying, bitching, throwing tools, etc... and then I was watching engine masters and they revealed the truth about the single 4bbl tunnel rams, so I pulled the intake, and put a dual plane on it. In the meantime I dropped an HEI in the hole and got it back on the road. The little engine runs 10 times better than it did, and I'm running the same 600 Holley with 68 primary jets and the factory metering plate in the secondaries. The lightest spring in the vacuum canister, and a .035 squirter. The reason I didn't put the billet distributor back in is because I wondered all along if it was my problem, but I couldn't try the HEI because of the tunnel ram. The billet distributor was brand new. So my point is, new doesn't mean that it couldn't be in the distributor, right?

 

Power is a tertiary concern to me, maybe even lower, behind reliability and looks. This is a sled made for looking good, being comfortable to drive and crushing a shit-ton of highway miles. The 300 hp this engine came with from the GM catalog is a lateral move from what was in the car, but the low compression should let me do it on whatever junk fuel is handy wherever I find myself, as opposed to the high compression engine that was in there, that guzzled premium fuel only.

 

They're iron Vortec heads (not the ugly center bolt ones, the standard '59 and up pattern), 76cc chambers. I'd imagine they have better quench than some of the earlier offerings.

 

Looking good going slow is what it's all about brother! Sadly I'm convinced that you should try another distributor.

 

The head won't control that, it's the piston and how far down the hole and how thick the head gasket is.

 

i thought heads are a major part of finding the equation for compression ratio?

 

even 9.1:1 will run on about anything available nowadays if you have a responsible level of advance. knowing it has modern heads however, it'll be a nice runner as is. itll look good, be reliable, and have enough power for "get up and go" speed.

 

had this problem once and it ran well with both carbs running all the time, ran like shit with the progressive linkage

 

I am sure glad I am running what I am running!! 9.5to1 +. Pump gas . 3.36 gears behind a standard. Slight ping if I hit the throttle a little too much at low [ 600 or lower ] RPM in direct too quickly. Starts easily, all the time. BUT IT AIN'T NO SBC..

Ben

 

I believe he's referring to quench, not compression. The quench area is determined by the piston to deck height and the gasket thickness.