my big block is up and running!!!!!!! now i have a dilemma, it just isnt nearly as crisp as it used to be. what should i set my timing at? also i played very little with the carb and it cuts and misses at about 4500, but i have a good module, coil, and fuel pump so i dont know what to think. if you need to see my set-up i can post it im just kinda lazy this early in the morning.

*Eric*

 

Since you went pretty big on the cam, you likely have the power valve opening at idle due to a low idle vacuum. The power valve should be approx 1.5" lower than idle vacuum. You likely need a #45 power valve. This will help lean the idle.

As far as timing you will likely need a lot as well, likely in the neighborhood of 12-15deg. Give it what it wants to run cleanly. Just be careful that the large amount of initial does not overadvance the total timing amount. You may need distributor work to prevent over advance at high rpm. What is your total advance? This may be your high rpm problem as well.

Now the high RPM problem....
Does it do this in every gear? Please give some more details.

 

lets see... i have only taken it up to 4500 twice the first time it was fine the second time it just like missed i didnt stay in the throttle for very long becasue it scared me. i will try it again today, maybe it was just getting loaded up, i need new plugs the ones in it are getting pretty bad, this car likes to eat plugs bacause of the high compression and leaded fuel i assume. i am running 93 w/ an octane booster (the outlaw) lead substutute, and some marvel mysterry oil, the car has 12.5:1 L88/ZL1 pistions with closed chamber iron heads, i dont weant to put too much timing to it becasue i dont want it to ping so that is why im consertive with the timing, but i will try 12* and hopefully it doesnt ping. solid lifters i think would make it hard to hear detonation. i was thinking like 36* total advance, but i was questioning the procedure for total timing, dont you just keep increasing the rpm until the timing dosent move anymore, sorry for the long post... thanks lonnie!


*Eric*

edit: in every gear im not too sure of i have only tried it in 4th...
this thing is crazy, i got on it today coming out of mcdonalds at a 35 mph roll and it just annihlated the tires in 1st, 2nd, and 3rd... my friend here at school that was riding with me (huge honda guy) looked like a ghost, it was great!

 

Buy some race fuel before you junk it.......

12.5:1 with iron heads is a disaster waiting to happen. My car would not run on 94 w/ 11.7:1 & iron heads.

You may get by with 100 oct AV gas, but be careful.

If you want it to live, plan on some good fuel or it will break internal parts due to detonation.

Get rid of the Marvel Mystery oil....

 

I agree on the fuel. You're not going to get enough octane from any pump fuel even with "additives" to keep it from detonating. Some LL100 Avgas will help or try some VP C12. Even a C12/pump gas blend is better than the additives. Trying to back timing out to keep the engine from detonating will produce less power than having an engine that can run on pump gas with the proper timing. You build a high compression engine, you're going to have to pay the high price for the fuel to use in it.

36* total timing is fine. Where an engine likes the total timing depends a lot on the parts used. I've seen BBC enjoy 42* total timing while others won't go more than 28*.

Total timing is a combination of initial and mechanical advance. Initial is what you set the distributor to by using the timing marks. Mechanical is how much the mechanical parts will advance the timing inside the distributor. Since mechanical is preset when a distributor is built and can be changed by changing weights and cams inside the distributor, it won't change how much it will advance when you change the timing.

Lets say the mechanical advance of your distributor is 22*. If you set your initial to 12* then the total will be 34*. If you bump up the initial to 15*, the total will change to 37*. Although the engine may like the higher initial advance during low rpm operation, the engine may not like the higher total advance which should be in it at no more than 3000 rpm.

Don't worry about vacuum advance because that only comes into play during part throttle operation.

My distributor is locked out (race only option). That means there is no mechanical advance. The timing is set to the total timing. Currently it's around 36*. I have an adjustable timing retard that can retard the timing up to 20* to help start the engine but I've never needed it. My engine is 13:1 compression but I also run alcohol.

Was the piston to valve clearance checked? I don't see a lot of specs on what you have. What kind of dome is on those L88 pistons. Are they designed for the closed chamber heads? I know LS6 pistons need to be trimmed slightly when used with 781 open chamber heads.

 

i broke down and got some VP C16 i set the inital timing at around 15* but it acts like it wants more. my distributor is a Accel electronic and i cant see any way to change the mechanical advance, my total timing is reading 32* if im doing it right...
the PTV was very good, i checked it before i put it together so i dont remeber what it was, i have so many numbers going through my head im not exactly sure what it was, but it was well within the specs called for by comp.

you dont like the marvel mystery oil? a good friend always used it in all the motors he built that didnt have hardened seats becasue the beleived it reduced valve wear and helped out the lead substitute.

the heads are closed chamber and the dome looks like that chamber, they are pretty big i can email you a picture if you want... just let me know.

how do i know what my mechanical advance is? i havnt drove it much now becasue im not 100% on it. the inital timing is 15* timing goes to 30* after you rev it, that is all the further it goes. i didnt hear any detonation today when i drove it but i didnt beat on it either...

ok im tired of typing...


*Eric*

 

Marvel Mystery oil may be a good upper cylinder lube, but am unsure of the octane. The last thing you need is something to make it detonate.

15deg is not that much... my BBC likes 18 initial with a big cam.

Many Accel distributors have the advance mechanism under the pickup which requires disassembly. For now concentrate on initial & get it responsive. It sounds like your total should be within reason but keep an eye on it to be safe.


Before getting too much into timing.... check/ fix your power valve in the carb as I previously stated. This will have a drastic effect on drivability & timing requirements.

 

yeah i was going to do that today but its raining. i hooked up a vacuum gauge to it yesterday, it pulls like 12 in hg at idle, it think the PV is open at idle becasue when you screw the air screws all the way it dosent miss a beat, i have them one turn out on each side...


*Eric*

 

[QUOTE]Originally posted by Lonnie Pavtis
[B]Buy some race fuel before you junk it.......

12.5:1 with iron heads is a disaster waiting to happen. My car would not run on 94 w/ 11.7:1 & iron heads.

You may get by with 100 oct AV gas, but be careful.


Not really sure if this is true but I was told not to run AV gas. The reason is because it is made to run at high elavation. And so there is a lot of air in the fuel. And will make the car run lean because of all the air in the fuel. Not sure if this is true but maybe someone who knows will chime in.

I do know when I put AV gas in my car just recently with o2s I scaned the car it said it was runing lean and the computer keep adding fuel flooding the car.But would still run but like crap. Within an hour the car used 6 gallaons of AV. I thought I had other problems.
I bought new 02 sensors right away samething. computer said the car was lean. I Changed the fuel to VP118 car runs fine now and 02 are reading a little rich not lean anymore.

 

If your idle mixture screws are turned right in and it still runs, the throttle blades are open too much and the transfer slots are exposed. Turn the idle screw out to close the blades and drill some 1/8" holes in the throttle blades.

 

First AV gas is not oxygenated..... you have some bad info there. It is formulated for colder temperatures..... approximate 3deg loss per 1000ft evelvation, but I've never had a problem with it.

Cliff, How could your car run lean & also simultaneously flood the car?

Back to the original post,
Not sure how you have 12" vac at idle. I thought you had a big cam? I was expecting you to say it had 4-6" at idle. Even the regular L-88 cam had around 8". What are your specs & how high is the idle? As Stephen stated you likely have the primaries too far open. You can also open the secondaries slightly with a screw that is under the baseplate in many applications allowing the primaries to close slightly covering the transfer slots. This may take some trial & error but may allow you to keep from drilling.

 

i have a friend who is a mopar engine builder, he went over my car and tuned it for me last night, he spent about 2 hrs on it timing it and setting the carb. i have 21-22* initial 44* total and it runs good now, im taking it to the track tonight and if i can get some traction i might be able to turn an acceptable times.

the cam pulls 12" vac because the cam has 110* seperation angle compared the L-88 cam and the cam that wiped a lobe off that was 106* which made a hugh difference. i dont really like this cam as much as i thought i would, becasue if that seperation angle its very drivable but it had not real peak power which takes the fun out of it. i liked the other cam that was in it becasue it revved alot quicker and had a real peaky powerband which was much harder to drive but much more fun!

i got to go get some turbo blue and then im going to run it tonight ill post my times tomorrow, i am hoping for 13s, i know i have a serious traction problem so i think 13s will be a gift, and im not too sure of my tach either, i dont know how right it is so i guess im going to shift by feel basicall shift when it stops pulling... wish me luck! hopefully i dont break anything...


*Eric*

 

oh yeah and about the AV gas i will not run it due to bad experiences. i had a honda 250R that i raced MX on and i guy i raced with said it was the hot tip and he always ran it, so i thought i would try it, well to make a long story short... 255 lbs static compression + AV fuel = melted piston that runied head, crank, rod, main bearings, and cracked one case half... so i will never run it again. i even rejetted it and it looked good on the plugs, i didnt like the way it responded and then it exploded... fiirst of it just didnt make the same power and i just ran realy hot and i had it jetted a little on the fat side, i think it was detonating but with a 2 stroke its hard to tell bacasue they make so damn much noise anyways...

morale of story, rans spectular on Turbo Blue, and exploded on AV gas, whick means...
Turbo Blue = happy eric
AV gas = eric not like

that just my personal experience feel free to post your input


*Eric*

 

If you are running a big block with a solid cam, it may not quit revving before it scatters. Buy a good tach or a rev limiter otherwise it may only be saved by valve float & that isn't good either.

Since you never posted your cam specs, I cannot verify your potential, but my 402 with a 256/266 .708" pulls past 7600 so be careful. It also went in the 10's on AV gas.

 

its a comp magumn 292S... im not sure of duration but lift is .595


*Eric*