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Topic Review (Newest First)
10-15-2008 08:12 PM
Icelander Thanks again.
Kristofer.
10-15-2008 08:05 PM
F-BIRD'88 The secondary jetting is a bit lean for a 750DP. Usually wants 79 to 85 sec jet.
Most times a 80 jet is fine.

Yes the vacuum advance gets reconnected after all adjustments are done. A generic fixed non adjsutable vacuum advance canister has a 90% chance of not being right for your motor. Get a adjustable one and mess with it to find the best setup for your car. Usually around 10-12deg of vacuum advance at higway PT cruise. The rate (diaphram spring tension) in and out needs to be dialed in too.
Vacuum advance moves the magnetic pick up in the distributor to advance the timing. Sometimes the vacuum advance move the mag pic up too much and adversly affects the distributor rotor phasing with the distributor cap causing cross fire and missing. If you cannot solve this by limiting the vac advance travel to 10-12 deg the the rotor/magnetic pick up orientation needs to be adjusted so that the spark fires when the rotor tip is aligned with the post in the distributor cap. (adjustable rotor) or move the mag pick up on its plate.
This vac adv/rotor phasing issue shows up on a few but not all distributors.
10-15-2008 07:52 PM
Icelander Thanks f bird.
im going to lay down the total set up.
lets start on top
14" k&n air-cleaner 4" thick, holley 750 double pumper, edelbrock performer rpm air gap intake, world cyl.heads 200cc int.runners, 2,02 and 1.60 valves, 64cc chamber, comp magnum 280 cam,230degr.@050, 480 lift and 110 lobe seperation, installed using degree wheel "to be accurate" 1,5 ratio roller rocker arms, Je srp flat top pistons, 6"eagle i beam rods, eagle 5140 crank with 3,75 stroke, and this hei ignition, maybe i should switch to msd ? or get me this curve kit you mentioned, and should i connect the vacuum advance again ? it felt like she ran smoother with out it ?!
This engine is just recently assembled so there is allot of tuning and testing left, i jetted the carb with #73 front and 75 rear and used 6,5 hg power valve. You did mention earlier i should use 4.5hg valve ? ok
Then comes a th 400 trans with 3000rpm stall converter, 3;73 gear ratio and 26" tires, all this is now sitting in my 72 ss nova.
Thanks for your time and effort. Kristofer.
10-15-2008 06:50 PM
F-BIRD'88
Quote:
Originally Posted by Icelander
Ok, many good advice, thank you all for your time, first i checked the play in the distributor and that was at minimum i believe, i guess it may not be to tight either, another thing i see you guys very often set your total timing at 34-36 degrees, in my experiments 38 has very often give me best results ? ! Maybe the cold here has something to do with it, at summer usually around 65 on Fahrenheit, and im going to try adding a switch on the ign.wire.
Thanks. Kristofer.
Either your balancer /timing tab is inacurate (very likely) , your carb jetting is too rich or too lean and or you're getting a better et from that timing cause your motor wants more inital for better initial acceleration.
When everything is accurate and jetted right with the proper spark timing curve, you'll probabily find 34 to 36deg works better than 38deg.
Every small block I;ve had has run best with less than 38deg.
BBC's seem to like 38deg. Different motor.
The more inital the better the trhottle response and low end torque.
24deg at idle is not too much at all. More base initial allows a smoother more consistant advance curve that does not need to be quite so agressive. Peaks at around 3000 3200rpm. 34-36deg.

The only other possibility is the pump gas in Iceland has additives that are slowing down the combustion speed as compared to the fuel here.
10-15-2008 05:55 PM
Icelander Ok, many good advice, thank you all for your time, first i checked the play in the distributor and that was at minimum i believe, i guess it may not be to tight either, another thing i see you guys very often set your total timing at 34-36 degrees, in my experiments 38 has very often give me best results ? ! Maybe the cold here has something to do with it, at summer usually around 65 on Fahrenheit, and im going to try adding a switch on the ign.wire.
Thanks. Kristofer.
10-15-2008 05:33 PM
Icelander Hi, to answer techinspector1. We did raise the hood and that for sure helped, out. The temp fell well down. Thanks for a good advice.
Kristofer.
P.s. forgive me not telling you before.
10-15-2008 04:40 PM
curtis73
Quote:
Originally Posted by ap72
Oh, its very simple, if you have 34* of timing at idle, and you're idle is set below 2,700 RPM or so, which I expect for that cam is probably around 900 RPM. Then it would be detonating a LOT from take off- that's kind of the whole idea behind having mechanical advance on a dizzy- so you have more timing when you need it, but not too much when you are carrying a high load at low engine speeds.

to simplify it 34* timing + that cam + that compression (at take-off)= BOOM!
Too many factors to say that is an absolute. I ran 9.5:1 with a 218/224 cam with 110 LSA and was able to lock out my mechanical and run 36* all the time PLUS ported vac.

Chamber design, altitude, thermostat temp, intake air temp, quench, piston design, carb tune, exhaust design/scavenging, stall speed, auto or manual, if the cam is installed straight up or advanced/retarded... the list goes on.

To say that its definite that he'll cause damage is pretty premature at this point.

Initial timing is a pointless number provided it doesn't cause problems elsewhere in the RPMS/load. You can get away with a lot more low RPM timing with an automatic since heavy loading (lots of right foot) will always mean elevated RPMs.
10-15-2008 03:51 PM
glen242
Quote:
Originally Posted by ap72
Oh, its very simple, if you have 34* of timing at idle, and you're idle is set below 2,700 RPM or so, which I expect for that cam is probably around 900 RPM. Then it would be detonating a LOT from take off- that's kind of the whole idea behind having mechanical advance on a dizzy- so you have more timing when you need it, but not too much when you are carrying a high load at low engine speeds.

to simplify it 34* timing + that cam + that compression (at take-off)= BOOM!
Sir:

I said the 34* centrifugal timing was in at 2600 rpm, as the post stated, that is where I set it with an adjustable timing light. I will bet you that I do not have 34* at idle.

I have looked at your other posts for the month of October, and I believe you are badly mistaken on a lot of them.

Things that jump out, aside from the bad advice:

10-02-08 quote

"stock 4.3L is 237 CI....." end quote
That = 55cc per L not the +/- 61cc per L that I learned in school.

10-10-08 + other posts: quote
"I am just an engineer, but..."
Your profile shows you as a mechanic, attending SEMo for construction management ...
Ocupation:mechanic, part time laborer

How can you call yourself an engineer, without a degree???

Your above post, concerning my timing, is stupid beyond belief! You either can't read or you have absolutely no idea what you are talking about!

You registered on this site on 6-13-2005. Your birthdate is July 24, 1985. You were almost 20 years old. You made no mention of studying to be an engineer, instead you said you were a mechanic, attending SEMo for construction Management.

So when and where did you receive your Engineering degree and in what discipline? Was it on the Chessie System (railroad line)?

How come there are no MORON Smilies?
10-15-2008 02:44 PM
ap72 Oh, its very simple, if you have 34* of timing at idle, and you're idle is set below 2,700 RPM or so, which I expect for that cam is probably around 900 RPM. Then it would be detonating a LOT from take off- that's kind of the whole idea behind having mechanical advance on a dizzy- so you have more timing when you need it, but not too much when you are carrying a high load at low engine speeds.

to simplify it 34* timing + that cam + that compression (at take-off)= BOOM!
10-15-2008 01:29 PM
glen242
Quote:
Originally Posted by ap72
Well it kind of matters IF and only IF you don't like holes through your pistons, but hey, some people go for that kind of thing.
How am I going to get holes in my pistons when my total centrifugal advance is limited to 34*????

PLEASE TELL ME!
10-15-2008 01:14 PM
ap72
Quote:
Originally Posted by glen242
BTW, I don't know what initial timing is, it does not matter.
Well it kind of matters IF and only IF you don't like holes through your pistons, but hey, some people go for that kind of thing.
10-15-2008 01:03 PM
glen242
Quote:
Originally Posted by Icelander
Hi, i have a chevy 383, 10,5 compression, iron heads with 200cc intake ports, and the cam is comp 280 magnum, 230@0,50 and 480 lift, and HEI ignition. when it idles best the timing is 18 degree and that is at 900-1000 rpm and the total is 38 degree, OK i was told that these are fair and normal figures but it punches the living hell out of the starter when im cranking her up, OK i can buy me self a high torque mini starter but wont he get the same punishment as this one ? And another thing it seems like the engine performs better with the vacuum advance blinded ?! this cam can barely be used with power brakes, OK can be fixed with a canister but will that somehow help the vacuum advance on the distributor ? Hmmm ? HELP please ?
Thanks in advance. Kristofer.
I have a 383 with a XE274 cam 230* intake, 236* exhaust, 10.36 static CR running on 89 octane pump gas.

I set my timing to 34* all in by 2600 rpm. I have 13" vacuum at idle and am using a vacuum can per Lars' specs.

Absolutly no problems cranking, either with stock starter or smaller high torque.

BTW, I don't know what initial timing is, it does not matter.
10-15-2008 11:37 AM
ap72 24* is way too much for 10.5:1 with iron heads, and that cam isn't that big. Kepp it at the 18 you have now and get the starter saver or wire a manual cut out switch to the ignition- a lot of people do it that way.
10-15-2008 10:52 AM
curtis73
Quote:
Originally Posted by F-BIRD'88
1. Install a MSD "Starter Saver" auto cranking ignition retard control box to retard the spark while the motor is cranking over and starting. Full timing is restored once the motor achives 500+rpm idle speed.

.
This is what I'd do.
10-15-2008 04:42 AM
techinspector1 Kristofer, what ever happened when you raised the hood on the 'Vette to experiment with a cooling problem. Just curious. Here is the thread....
http://www.hotrodders.com/forum/heat...ml#post1017543
This thread has more than 15 replies. Click here to review the whole thread.

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