Geoff2 wrote: ↑Sat Oct 02, 2021 4:21 am
Manifold connected Vacuum Advance benefits. Written by Lars Grimsrud, a GM engineer. The last three lines are moooooooost important.
No JCR.
I had the real deal, credit, name, etc all correct. Seems to have been copied a few times.
The link I posted is a thread that goes for 4 pages. All 4 pages should be a 'must read'. It shows all the confusion & misunderstanding about VA. For those that 'got it' there are examples of smoother idle, 2" increase in idle vacuum etc.
Heinz1 wrote: ↑Mon Sep 27, 2021 4:47 pm
Walter,
thanks for the info, i use your Timing advance settings as a start.
You don´t use vacuum advance?
It is very important that the engine is not overheating at idle and slow Car Speed.
I try different combinations of mechanical & vacuum advance Timing Curves on the Chassis Dyno, see what the engine wants.
Depending upon how quickly an RPM the mechanical advance curve starts and ends will determine whether I use a vacuum advance unit or not.
Early"in" curve = no vacuum ... later RPM curve I use vacuum and try both ported and full-time then use whichever runs the best in that particular situation.
To explain; the only reason to use ported vacuum is ... if the full vacuum at idle is low and causes the extra timing to come in and out continuously in a dithering manner, (usually because there is only enough idle vacuum to pull the vacuum advance unit part way and this causes the engine idle to be erratic), ported vacuum is then used merely so that scenario doesn't happen.
Otherwise full manifold vacuum is best.
Restrict the mechanical advance travel limt to 10° (crank) so timing is 22-26 base idle and 32-36 at max mech advance..
Restrict vacuum advance to a max limit of 12-15 deg at high vacuum.
Use ported or man vac as you wish.
Get a 750 HP double pump carb. Old 60's era corvette camaro 14" air cleaner. Use as tall a dual plane "RPM" hi rise manifold as will fit. Comp XS 274s-10 236/242 cam in on 104. (104/116)
or equal Lunati Voodoo solid.
Lunati/UDHarold street strip lil solid is another good choice Lunati #30310514
Best with 4 speed.. Auto trans will need correct custom hi stall converter.
little update,
installed a MSD adjustable Distributor.
Now the Engine is running good, no overheating.
Thanks all for the Suggestions and Tips.
Now i have a leaking 2-piece rear main seal.
After some miles of driving the 2-piece rear main seal starts leaking very bad.
Installed is a Fel-Pro 2901 seal, installed following exactly the Instruction / Manual.
Removed the pin for the standard rope seal, put silicon in the little hole in the main bearing cap.
Seal halves protrude 3/8" beyond parting faces of main bearing cap and saddle.
Before i install a new 2- piece rear main seal i want to hear your suggestions which seal to use.
Is the Fel-Pro 2901 ok to use or is their a better solution?
The rubber rear main seal is the way to go but they need to be carefully sanded so they don't hold the main cap up. They need to stick out a little bit to preload the seal. Its a fine line but the cap must sit flat on the block when torqued.
Original rope seals were made of asbestos and would work if installed properly. These new ropes have not had great success.
Mummert Machine and Development 4 stroke hp
Mummert Y-blocks
Starting about 10 years ago i have mandated that we machine back of sb Ford block for 1 piece rear seal or we don't touch block. PERIOD! Since then we have not had a single leak. On other engines that you cannot use a 1 piece similar seal we re machine existing rear seal groove of blocks in CNC machine concentric with rear main bearing housing bore. It is common to see the oem seal groove .015+ off center of main line . Back when we were still trying to make the rubber 2 piece seals work we had the best results by sanding the seal halves so that there was about .010 seal protrusion on all 4 tips of seal after seal was seated fully into grooves.
Bill and Mummert, Thanks for the advice.
Bill, i should have known before that it is possible to convert the block to a 1 piece rear main seal.
Just to be sure and i understand your advice right:
1. install the Seal halves in the main bearing cap and saddle, seating the seal halves full into the grooves.
2. measure the protrusion on all 4 corners and sand (if necessary) the seal tips so that they protrude about .010 on each corner.
3. rotate the Seal halves to protrude 3/8" beyond parting faces of main bearing cap and saddle or...?
Heinz1 wrote: ↑Sun Feb 13, 2022 3:07 pm
Bill and Mummert, Thanks for the advice.
Bill, i should have known before that it is possible to convert the block to a 1 piece rear main seal.
Just to be sure and i understand your advice right:
1. install the Seal halves in the main bearing cap and saddle, seating the seal halves full into the grooves.
2. measure the protrusion on all 4 corners and sand (if necessary) the seal tips so that they protrude about .010 on each corner.
3. rotate the Seal halves to protrude 3/8" beyond parting faces of main bearing cap and saddle or...?
Thank you
Heinz
Correct. I also like to use hylomar or a little silicone between od of seal and block groove. Before modification the seals typically are too big on od for groove in block and get crushed out of round when installed and cap gets torqued. It's too late to check now because the engine is assembled, but next time torque up a new seal in bare block and measure yourself. This is how I came up with the .010 protrusion spec. This seems to be the sweet spot where the seal stays round and there is still enough preload.
Heinz1 wrote: ↑Sun Feb 13, 2022 3:07 pm
Bill and Mummert, Thanks for the advice.
Bill, i should have known before that it is possible to convert the block to a 1 piece rear main seal.
Just to be sure and i understand your advice right:
1. install the Seal halves in the main bearing cap and saddle, seating the seal halves full into the grooves.
2. measure the protrusion on all 4 corners and sand (if necessary) the seal tips so that they protrude about .010 on each corner.
3. rotate the Seal halves to protrude 3/8" beyond parting faces of main bearing cap and saddle or...?
Thank you
Heinz
The blocks which originally came with rope seals usually are not machined on the EXACT same centerline as the bearing saddles but, close; I have not had issues with blocks which originally came with two-piece neoprene rear seals. Fitting seal end protrusion is a must.
