[Ocean-Angler]

Hey guys
I just bought my MSD pro billet mag pickup dizzy. There is no vacuum advance on this.
Im in the process of installation and wanted to know what the idle timing should be, that will give me a starting point as to which advance kit I want to use.
its a rebuilt 350
has stock heads with pocket porting, port matching, valve lapping, basically a full blown hand porting job, ( milled .35 thousandths too) minus valve seat grinding.

compression is porbably around 9- 9.5 :1

tuned and rebuilt Q-jet to match all the specs

headers

700r4 trans , 2000 stock stall
3.55 gears, small tires ( high rpm)
mild Melling MTC-1 Cam and lifters ( hydralic flat tappet)

WHat should my initial idle timing be at on this? 16 degrees?
And what should my total timing be?
With the MSd, I can tailor the curve to hit total advance in a wide range of RPMS, so thats what I want to figure next

[techinspector1]

Originally Posted by Ocean-Angler

There is no vacuum advance on this.

Is the motor going into a boat or aircraft or is strictly an off-road motor? If this is a street driver, then you have screwed the pooch.

Originally Posted by Ocean-Angler

Im in the process of installation and wanted to know what the idle timing should be

Stock to mild aftermarket cam, 12 degrees. Total 36-38 depending on chamber size and shape, all in by 2800-3000.

Originally Posted by Ocean-Angler

compression is porbably around 9- 9.5 :1

Bull Hockey. If you don't know the exact static compression ratio as determined by measuring all components, then you have no idea what cam the motor wants. You have screwed the pooch.

Originally Posted by Ocean-Angler

headers

Care to elaborate?

Originally Posted by Ocean-Angler

2000 stock stall

If this is a stock converter, it will not stall at 2000. You have screwed the pooch again.

[Ocean-Angler]

what in the HELL!!! LMAO crap
Well hopefully when i elaborate ona couple things, I wont have screwed the pooch too much haha

Originally Posted by techinspector1

Is the motor going into a boat or aircraft or is strictly an off-road motor? If this is a street driver, then you have screwed the pooch.

street driver.. is this because I got the MSD without the vac. advance?
And the reason I did that, is because I found a good deal on a CRANE HI6-N ignition box, which required a very specific MSD or other dizzy, but the MSD version didnt have the vac. advance...

Originally Posted by techinspector1

Stock to mild aftermarket cam, 12 degrees. Total 36-38 depending on chamber size and shape, all in by 2800-3000.

atleast 1 thing is done right.. I can put in the diff. springs, and the diff bushing and get the total timing in around there... really though? that low of RPM?

Originally Posted by techinspector1

Bull Hockey. If you don't know the exact static compression ratio as determined by measuring all components, then you have no idea what cam the motor wants. You have screwed the pooch.

Well the heads were stock with the 76 CC chambers. I had .35 thous. milled off them, so I factored that the main bearings are probably a little worn and instead of sayin 9.5 :1 I guess its .. 9.25 :1 ish...
For the cam, I went with an older engine balancer/machinist receomendation. Hes been doing balancing and machining for about 30 years. I explained to him the details of the motor, and had him mill the heads and give me tips on porting. He suggested in the cam, its a notch above stock, split duration.

Originally Posted by techinspector1

Care to elaborate?

Headers are 3/4 length. not full length, not block huggers.

Originally Posted by techinspector1

If this is a stock converter, it will not stall at 2000. You have screwed the pooch again.

Well the torque converter is a 2000 stall, but reason I call it stock is because it isnt a loose stall. Its stock size converter, just a higher stall. The trans is a severly built 700r4, almost looks like its about the only thing I did right LOL

will be changing the stall to a serious billet machined 2600 Loose stall when I get the ignition system dialed in

[454C10]

here is a nice timing link.

has some timing numbers towards the end of the article.

http://www.corvette-restoration.com/.../Timing101.pdf

[cobalt327]

Originally Posted by Ocean-Angler

street driver.. is this because I got the MSD without the vac. advance?
And the reason I did that, is because I found a good deal on a CRANE HI6-N ignition box, which required a very specific MSD or other dizzy, but the MSD version didnt have the vac. advance...

To start with, having no cam specs and not knowing what the real compression ratio is, along w/no idea (I'm guessing) what the quench distance is, there's gonna be a lot of guesstimating going on here...

Having a vacuum advance has far more advantages and basically no drawbacks on a street driven engine. It aids economy, it will allow a cooler running engine, at idle especially. It can help smooth the idle. Definitely a good thing to have.

I can put in the diff. springs, and the diff bushing and get the total timing in around there... really though? that low of RPM?

Basically, you want as much timing advance, as soon as possible- w/o the engine detonating at all. Detonation (pinging) will kill power the moment it begins and in severe cases will ruin an engine outright. To answer your question, no- 2800-3000 RPM is not to low of an RPM to bring the total in by. BUT, this will depend on a lot of things: vehicle weight, use, fuel octane rating, gear ratio, carb tuning, etc. There is no number that's correct for all engines. The numbers given are a starting point from where you will add and subtract timing as required to keep the engine out of detonation and making the best power.

Well the heads were stock with the 76 CC chambers. I had .35 thous. milled off them, so I factored that the main bearings are probably a little worn and instead of sayin 9.5 :1 I guess its .. 9.25 :1 ish...

First, there is no amount of main or rod bearing wear that will ever be great enough to cause a significant change in the compression ratio.

To compute the CR you need to know the head gasket and cylinder bore diameter, the stroke, the piston deck clearance (how far down the hole the piston is), the head gasket thickness, the piston volume and the chamber volume. If you don't know these figures, you're guessing and the difference could easily be more than a 12% variation.

The large chamber SBC heads are crappy flowing and the chambers are inefficient. Given that, the work you did may or may not have actually helped flow- w/o a flow bench, this is a crap shoot once you alter the stock port profile. Just cleaning up the ports and port matching the heads to the intake can help.

I seem to get that you didn't get a valve job done. And that means that likely the guides are also untouched. These two areas are wear points that have to be addressed on every used SBC OEM head I've ever seen. The guides always wear and are loose after being used for any real length of time. The seats being done correctly w/a multi-angle valve job and back cutting the valves will give you more flow increase at the lifts where it matters most, than most anything else a home porter could ever hope to accomplish unless the home porter has a lot of experience and/or has served under a pro.

He suggested in the cam, its a notch above stock, split duration.

What are the specs from the cam card?

Headers are 3/4 length. not full length, not block huggers.

Always use long tube headers any time they CAN be used. The shorter headers leave power on the table.

will be changing the stall to a serious billet machined 2600 Loose stall when I get the ignition system dialed in

I doubt seriously you need a billet torque converter! Use a good TC builder and get a TC that has a stall RPM that about matches the torque peak RPM of the engine, or slightly lower. That does not mean the TC will rev to the torque peak every time you pull away from a stop sign. It will mean that when there's traction and you mat the throttle, the TC will flash to where the engine is making the most torque for the best launch.

[Ocean-Angler]

Originally Posted by cobalt327

To start with, having no cam specs and not knowing what the real compression ratio is, along w/no idea (I'm guessing) what the quench distance is, there's gonna be a lot of guesstimating going on here...

Having a vacuum advance has far more advantages and basically no drawbacks on a street driven engine. It aids economy, it will allow a cooler running engine, at idle especially. It can help smooth the idle. Definitely a good thing to have.

Basically, you want as much timing advance, as soon as possible- w/o the engine detonating at all. Detonation (pinging) will kill power the moment it begins and in severe cases will ruin an engine outright. To answer your question, no- 2800-3000 RPM is not to low of an RPM to bring the total in by. BUT, this will depend on a lot of things: vehicle weight, use, fuel octane rating, gear ratio, carb tuning, etc. There is no number that's correct for all engines. The numbers given are a starting point from where you will add and subtract timing as required to keep the engine out of detonation and making the best power.

First, there is no amount of main or rod bearing wear that will ever be great enough to cause a significant change in the compression ratio.

To compute the CR you need to know the head gasket and cylinder bore diameter, the stroke, the piston deck clearance (how far down the hole the piston is), the head gasket thickness, the piston volume and the chamber volume. If you don't know these figures, you're guessing and the difference could easily be more than a 12% variation.

The large chamber SBC heads are crappy flowing and the chambers are inefficient. Given that, the work you did may or may not have actually helped flow- w/o a flow bench, this is a crap shoot once you alter the stock port profile. Just cleaning up the ports and port matching the heads to the intake can help.

I seem to get that you didn't get a valve job done. And that means that likely the guides are also untouched. These two areas are wear points that have to be addressed on every used SBC OEM head I've ever seen. The guides always wear and are loose after being used for any real length of time. The seats being done correctly w/a multi-angle valve job and back cutting the valves will give you more flow increase at the lifts where it matters most, than most anything else a home porter could ever hope to accomplish unless the home porter has a lot of experience and/or has served under a pro.

What are the specs from the cam card?

Always use long tube headers any time they CAN be used. The shorter headers leave power on the table.

I doubt seriously you need a billet torque converter! Use a good TC builder and get a TC that has a stall RPM that about matches the torque peak RPM of the engine, or slightly lower. That does not mean the TC will rev to the torque peak every time you pull away from a stop sign. It will mean that when there's traction and you mat the throttle, the TC will flash to where the engine is making the most torque for the best launch.

Hey thanks for all the help and answers -

Looks like the amount of money I spent on this motor, I shot myself in the foot.
THe origional idea was just to give it a little power, till IU bought my LS2 motor and built that a little. But after everything, Ive overspent on a motor that wasnt properly tuned it looks like

Cam specs -
.050 duration - 204 intake 214 exhaust
sae duration - 278 intake 288 exhaust
valve lift .422 intake .444 exhaust
Lobe separation - 107 int 117 exhaust

.050 timing BTC -5 ABC 29 BBC 44 ATC -10 (??)

engine is a goodwrench crate 350 with stock 8:1 compression ( if that helps for compression calculation)
I didnt get a valve job done, I spent quite a bit of time lapping the valves, also cleaned the valve bowl really well.

I couldnt fit long tube headers, theyd be about 1.5" off the ground if I put them on

car weighs 3600 lbs

I dont know if any of this helps..

With that non vacuum advance diz, do you think its really gonna kill me on gas? and rough idle?

[prostreet6t9]

[QUOTE=Ocean-Angler]Hey guys
I just bought my MSD pro billet mag pickup dizzy. There is no vacuum advance on this.


MSD explains it pretty good here... http://www.msdignition.com/instructi...df?terms=85551

[cobalt327]

Originally Posted by Ocean-Angler

Hey thanks for all the help and answers -

Looks like the amount of money I spent on this motor, I shot myself in the foot.
THe origional idea was just to give it a little power, till IU bought my LS2 motor and built that a little. But after everything, Ive overspent on a motor that wasnt properly tuned it looks like

Cam specs -
.050 duration - 204 intake 214 exhaust
sae duration - 278 intake 288 exhaust
valve lift .422 intake .444 exhaust
Lobe separation - 107 int 117 exhaust

.050 timing BTC -5 ABC 29 BBC 44 ATC -10 (??)

engine is a goodwrench crate 350 with stock 8:1 compression ( if that helps for compression calculation)
I didnt get a valve job done, I spent quite a bit of time lapping the valves, also cleaned the valve bowl really well.

I couldnt fit long tube headers, theyd be about 1.5" off the ground if I put them on

car weighs 3600 lbs

I dont know if any of this helps..

With that non vacuum advance diz, do you think its really gonna kill me on gas? and rough idle?

The only real issues I see are the chance that the valve guides might be a bit too loose and the vacuum advance missing.

The vacuum advance not being there is something that can be dealt with as easily as buying an eBay Skip White HEI distributor w/vac. adv. or just locate a good used GM Delco HEI distributor w/vac. adv. and the "4-pin" module. These were used in cars through '80 and some trucks through '86 and aren't hard to find at all. Sell yours to get your money back- or most of it, anyway.

The guides and the lapped in valves may or may not be a problem- you can check the valve seal, but that really doesn't tell you too much. The problem w/lapping valves to try to regain the valve seal is the guides- if not replaced- will allow radial runout of the valve and when you combine that w/lapping, you can end up w/the seat off center, etc. Just not an effective way to do it.

Choices as I see it, is to run them as-is and hope for the best, or bite the bullet and have the guides and seats done professionally.

I do not see the compression being a problem w/the cam you have. I would say to replace the stock valve springs if that's what you have on the heads now. Otherwise, you are fine (except for the vac. adv. and possibly the valve job issues) and the engine should be torquey and fun to drive.