BPE HEI Distributor

[Ricks70Duster340]

I have a 408 with a 750/3310 carb, HEI style distributor, 727 with 3500 stall converter, 28" tires with 3.23 gearing. Am using MVA as the engine seems to like it. Though I can feel slight vacuum at idle, there is such low vacuum at idle that the vacuum canister does not respond (vacuum gauge at idle jumps all around so useless to tune with). The off-idle transition does not bog, but I think it should be a bit crisper. I tried running without VA but had to advance the timing such that the starter dragged when the engine was hot. The idle screws are both out about 2.5 turns. The engine will not run with them any further in. I changed the PV to a 3.5 and that helped the low speed pep & the plugs no longer run pig rich. At idle/low speed the exhaust smells rich. I've never "tuned" an HEI distributor so wondering if anyone with a BPE setup has done so. Distributor cent. advance is below:

Initial timing=16 @ 650
16 @ 1000
26 @ 1500
31 @ 2000
34 @ 2500
36 @ 3000

 

[Dave999]

You killed me with the accronyms
BPE Blueprint engines or Bouchillon performance electronic?

etc

anyway if it has initial of 16 BTDC and starts ok when hot with the vacuum advance connected to manifold rather than ported vacuum
and the vacuum gauge jumps about at idle
i'd suggest you must be getting some advance off the vacuum can when cranking and just starting. i.e it will stomach a bit more initial and you can put the vacuum pipe back on ported

if you remove vacuum advance from the equation and it then needs more initail to run ok in the low rpm range, that follows on from above

but then kicks back when hot on starting !!!!

that seems to idicate that it needs more initial to start and run cleanly but not so much as to casue a starting issue at a time when its all warmed up

unless starting issue when hot are heat soak into the starter and not an initial timing induced kick-back

its quite a big motor i wonder if you just need the advance to come in quicker. to smooth the transition from idle to mid rpm

if there are facilities in that dizzy to restrict advance and change springs etc you can go with less spring to bring advance in quicker
and its worth seeing if you really need 34 total, wedge heads might, but open chambers on a high compression motor, might not
depends on cam carb and balanced distribution across cylinders

if it uses an HEI module for spark and dwell it will be a 4 pin version

if you switch to a A 5 pin module from an 1980 Oldsmobile 260
you get, as it says, a 5th pin which is handy
that 5th pin when grounded retards the igntion timing by 10 degrees

would allow you to connect pin 5 to a switch to gound it out when starting or when having a starting problem

i.e have 6,7 8,..... BTDC for start
flip switch off and go to whatever initial timeing gives you the clean tailpipe at idle and gives you the "on the peddle" kick in the pants thats missing

you can then tune the vacuum advance on the ported vacuum port. to do what it was inttended to do rather than usiing it as an assistant with starting...

i have only ever had a manual 4 speed car so the whole "use the vacuum can on manifold vacuum" situation that you can do with a highlt tuned v8 on an auto always feels wrong to me, but thats just my view. pleanty have great success really seems to depend on Cam

i may have mis interprested what you meant,
i'm in a different time zone and country which means i see stuff that is not answred before some of the USA does

I have motor with half the capacity of yours
mine runs 15 initial and 28 total i can't start it at 17 initial without risk of smahing my starter 16 is marginal for me.

Your question had no answer, what i have said may or may not be on the right track but those 5 pin modules are quite cool


Dave

 

[Ricks70Duster340]

You killed me with the accronyms
BPE Blueprint engines or Bouchillon performance electronic?

etc

anyway if it has initial of 16 BTDC and starts ok when hot with the vacuum advance connected to manifold rather than ported vacuum
and the vacuum gauge jumps about at idle
i'd suggest you must be getting some advance off the vacuum can when cranking and just starting. i.e it will stomach a bit more initial and you can put the vacuum pipe back on ported

if you remove vacuum advance from the equation and it then needs more initail to run ok in the low rpm range, that follows on from above

but then kicks back when hot on starting !!!!

that seems to idicate that it needs more initial to start and run cleanly but not so much as to casue a starting issue at a time when its all warmed up

unless starting issue when hot are heat soak into the starter and not an initial timing induced kick-back

its quite a big motor i wonder if you just need the advance to come in quicker. to smooth the transition from idle to mid rpm

if there are facilities in that dizzy to restrict advance and change springs etc you can go with less spring to bring advance in quicker
and its worth seeing if you really need 34 total, wedge heads might, but open chambers on a high compression motor, might not
depends on cam carb and balanced distribution across cylinders

if it uses an HEI module for spark and dwell it will be a 4 pin version

if you switch to a A 5 pin module from an 1980 Oldsmobile 260
you get, as it says, a 5th pin which is handy
that 5th pin when grounded retards the igntion timing by 10 degrees

would allow you to connect pin 5 to a switch to gound it out when starting or when having a starting problem

i.e have 6,7 8,..... BTDC for start
flip switch off and go to whatever initial timeing gives you the clean tailpipe at idle and gives you the "on the peddle" kick in the pants thats missing

you can then tune the vacuum advance on the ported vacuum port. to do what it was inttended to do rather than usiing it as an assistant with starting...

i have only ever had a manual 4 speed car so the whole "use the vacuum can on manifold vacuum" situation that you can do with a highlt tuned v8 on an auto always feels wrong to me, but thats just my view. pleanty have great success really seems to depend on Cam

i may have mis interprested what you meant,
i'm in a different time zone and country which means i see stuff that is not answred before some of the USA does

I have motor with half the capacity of yours
mine runs 15 initial and 28 total i can't start it at 17 initial without risk of smahing my starter 16 is marginal for me.

Your question had no answer, what i have said may or may not be on the right track but those 5 pin modules are quite cool


Dave

Hi Dave. The engine is from Blueprint Engines. It is a 10:1 magnum engine with aluminum Edelbrock heads. @Mattax has been very helpful in the past with fine tuning the advance curve. Perhaps bringing in the advance a bit earlier would help here.

 

[mbaird]

Without knowing the cam specs / intake or actual vacuum reading its hard to determine where to start .

 

[Ricks70Duster340]

Without knowing the cam specs / intake or actual vacuum reading its hard to determine where to start .

This is what they advertised for my build:

Cam Type: Roller
.580 Intake .577 Exhaust
235 Intake / 242 Exhaust duration
@ .050 - 110 degree lobe separation

 

[mbaird]

You should have around 12-17" of vacuum at 750 rpms .

 

[mbaird]

Try moving to a 9.5 or 10.5 power valve and dropping 5 jet sizes .
I run an 8.5 on a 246/250 @ .050 solid roller on 108.
Have you done a compression check ?
Should be 180+ psi

 

[Ricks70Duster340]

Try moving to a 9.5 or 10.5 power valve and dropping 5 jet sizes .
I run an 8.5 on a 246/250 @ .050 solid roller on 108.
Have you done a compression check ?
Should be 180+ psi

I'm trying to think through the logic of making those changes to the carb. No, have not done a compression check since it is a new (2000 miles) engine. The vacuum at low speed is so low & erratic that the PV would switch on and off if I went to a higher # valve. The carb was born with a 6.5, and the engine was drowning at low speeds. I put in a 3.5 and that helped a lot. Before changing the PV, I did drop the main jets from 73 to 68. Had a definite lean condition, so went up 2 sizes and that eliminated that (at 70 now).

 

[Mattax]

Rick timing through the entire range should be the same regardless of the format. With MSD because it might be a little different but still only a degree or two.
HEI can create a stronger flame kernal so you may see better burning under less than ideal conditions.
Set it (the new dist curve) to be as close as it can to what it was we worked out before.
If its a GM type advance mechanism, screen name Tuner has some tips for setting those up on the Racing Fuel Systems forum (tapatalk version). Ive probably p[osted links to it.
I've Gotta run - you can do it

 

[Ricks70Duster340]

Rick timing through the entire range should be the same regardless of the format. With MSD because it might be a little different but still only a degree or two.
HEI can create a stronger flame kernal so you may see better burning under less than ideal conditions.
Set it (the new dist curve) to be as close as it can to what it was we worked out before.
If its a GM type advance mechanism, screen name Tuner has some tips for setting those up on the Racing Fuel Systems forum (tapatalk version). Ive probably p[osted links to it.
I've Gotta run - you can do it

Thanks! The original posts you and I worked on was on a basically stock 360 with a Mopar style electronic ignition distributor. This engine is a different animal completely. Was wondering if the curve we worked on with the old engine was still appropriate for this new one. Guess you're saying it is!

 

[mbaird]

Could this low vacuum be due to an incorrectly installed cam ?

 

[Mattax]

Thanks! The original posts you and I worked on was on a basically stock 360 with a Mopar style electronic ignition distributor. This engine is a different animal completely. Was wondering if the curve we worked on with the old engine was still appropriate for this new one. Guess you're saying it is!

Ok Ok. Different engine then situation will change to some degree.
Just pretty linited on time but see what I can point you toward.

If the valve overlap has increased, compression is lower, or things like that which dilute the fuel mixture at idle or take heat (energy) from gasifying the fuel mix at idle, then more initial will be needed. In the 'how to' section of FABO Halifaxhops posted a chart of suggested initial timing for cam duration and engine displacment.
If the cam is now more performance oriented and say a 4 bbl carb instead of a 2 bbl and enaything else that builds efficiency and heat into the mixture with rpm, then less advance is needed in the curve. For examples look for some of the factory hi performance 440 timing curves I've posted vs say a 2 bbl 383 or 318.

Timing on engine.

If the engine wants more timing at 1000 rpm (you're using MVA to accomplish that) then 16 at 1000 is probably not enough.
You're smelling raw fuel indicates its not burning completely or misfiring. Classic.
I agree wiyth your gut instinct that more initial is needed on this engine.
I do think that to use with vac advance, the mechanical timing over 1800 rpm will need to be reduced.

Get the idle and off idle, then go look for the thread on afjust GM type advances at RFS.
Also note his warning about using unequal springs on certain types of advance mechanism. In that case just make a compromise.

I have a 408 with a 750/3310 carb, HEI style distributor, 727 with 3500 stall converter, 28" tires with 3.23 gearing

well I can help with the 3310

The off-idle transition does not bog, but I think it should be a bit crisper. I tried running without VA but had to advance the timing such that the starter dragged when the engine was hot.

Thats pretty extreme. Shouldn't need that much advance.
Seems like it will be worth checking out the transfer slots.

The idle screws are both out about 2.5 turns. The engine will not run with them any further in. I changed the PV to a 3.5 and that helped the low speed pep & the plugs no longer run pig rich. At idle/low speed the exhaust smells rich.

Well that's interesting.
The idle mix screws are needed to provide extra richness, but then the PV is somehow helping by making it a little leaner off idle.

I'd be interested in the t-slot position at idle, along with rpm and vacuum in N and in gear.

 

[Bewy]

This engine is going to want AT LEAST 30* at idle & probably more like 35*.
The best, simplest way is to use MVA [ man vac adv ]. There is NO WAY that this can be done with a non-adj stock VA unit. I expect this engine would have about 10-13" of vac at idle & this will work perfectly with an adj VA unit. They have about 30* range. Turn the Allen Key fully CW. Limit the amount of VA via plunger travel. If your dist is a GM based, then Crane make an adjustable plate that limits plunger travel. Or, just make a plate that goes under the mounting screw. Measure the total plunger travel, which is usually about 9mm. This represents about 30*. So you make the stop on a proportional basis to provide 20* [ for the example below ] to allow 6mm of travel.
Example: use 16* initial + 20* MVA for 36* at idle.
The centri curve is THE LAST thing you do & unless you have access to a dyno, it just becomes an educated guess with modified engines.

D. Vizard has written over 30 books. The statement below is about ign IDLE timing, but it is in a Holley carb book. Hmmm? Ign timing in a carb book? And ign IDLE timing is mentioned more than once in this carb book. Hmmmmmmmmmmm? And it is because idle timing is sooooo important for idle quality, vacuum, cooling & tip in response. It is the FIRST thing you do when dialling in a modified engine.
Page 30: ' The optimum idle advance is typically about 35-40* for a short cammed street engine & [ though not commonly realized [ as much as 50* for a street/strip engine'.
I would love a dollar for every engine I have added MVA over the last 30 yrs that fixed low vac, poor idle, off idle flat spot.

 

[Ricks70Duster340]

On a whim, I changed the dist springs to the lightest ones I had. Changing the HEI springs is a real joy compared to disassembling the Mopar unit! The result with VA disconnected:

16" @ 650
23 @ 1000
26 @ 1500
36 @ 2000 (tops out)

Reconnected MVA and took it for a test drive. The engine really "laided down" upon acceleration. Disconnected the VA unit entirely and that went away. Performance did not decrease with the VA disconnected. No doubt too much timing with the MVA connected. The process continues....

 

[oldkimmer]

Best place to start is with @Johnny Mac @Blue Print. Kim

 

[Johnny Mac]

I have a 408 with a 750/3310 carb, HEI style distributor, 727 with 3500 stall converter, 28" tires with 3.23 gearing. Am using MVA as the engine seems to like it. Though I can feel slight vacuum at idle, there is such low vacuum at idle that the vacuum canister does not respond (vacuum gauge at idle jumps all around so useless to tune with). The off-idle transition does not bog, but I think it should be a bit crisper. I tried running without VA but had to advance the timing such that the starter dragged when the engine was hot. The idle screws are both out about 2.5 turns. The engine will not run with them any further in. I changed the PV to a 3.5 and that helped the low speed pep & the plugs no longer run pig rich. At idle/low speed the exhaust smells rich. I've never "tuned" an HEI distributor so wondering if anyone with a BPE setup has done so. Distributor cent. advance is below:

Initial timing=16 @ 650
16 @ 1000
26 @ 1500
31 @ 2000
34 @ 2500
36 @ 3000

Hey Rick, happy to try and help. Looks like you have a bunch going on, and alot of chefs in the kitchen already. Lots to read above, but my biggest observation is you are searching for a sweet spot with ignition timing, but you have some things going on with the carb that tell me that needs addressed also.

Mixture screws at 2.5 seems like more than this engine should want, and the fact it won't run below that is telling me something else is going on. The idle bounching so much you can't get a vac reading is also off. These engines leave BPE with those mixture screws at 1 to 1.5 turns, and the stock equipped power valve. I think asking it to idle at 650 may be why it seems so choppy also. I would try 750-800 for starters. How do the plugs look? I would think it has to be rich at 2.5 turns.

You will have to remind me exactly what distributor this is, (big cap, small cap with external module, or msd clone?)

This is the roller cam 408 correct?

Engine should only want 32 to 34 total mechanical, which should get you a few degrees back for initial mechanical, and the sake of easier starting.

Feel free to email or pm me and we'll see what we can do!