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Topic Review (Newest First)
01-09-2012 05:07 PM
b00tz
Quote:
Originally Posted by speedbump
And that's another reason to keep the total advance at 38 or so as, from my own experience, a couple of brews and some good dirt make the foot heavy and the ears deaf.

amen to that man... lol

when i get back home ill try playing with the vacuum advance a little more and see if i can get the can set to where it needs to be. or maybe ill just put a stop in the vacuum because it would probably be alot easier to get my inital to 24 with that than mess with my distrubutor.

its not just a question of max power, im all for that, but i dont want the engine to turn into a grenade either
01-09-2012 08:07 AM
speedbump Nothing wrong with your timing compromise, IMO. Another thing you could try is a 1" 4 hole spacer on top of that manifold. It could clean up the low end/idle a little for cheap. It did on my tunnel ram, anyway. There have been many apples to apples tests that don't support all the hype about single plane manifolds being so terrible on the bottom end/mid range. Besides, for having your fun, it's an easy give away for how hard it pulls from about 3,500 to 6,500. And that's another reason to keep the total advance at 38 or so as, from my own experience, a couple of brews and some good dirt make the foot heavy and the ears deaf.
01-09-2012 05:52 AM
454C10 http://www.chevyhiperformance.com/te...ild/index.html

Here is an example of a dome piston bbc with a set of stock heads requiring 42 degrees of timing for max power.
01-09-2012 01:00 AM
F-BIRD'88 http://www.hotrodders.com/gallery/da...limitlock2.jpg

Not that hard
01-08-2012 09:20 PM
b00tz lol looking at other posts looks like this aint the first time you two haven't agreed on total timing in bbc's. i googled it and this seems to be a common debate.

i do agree though that i would like to run a little more advance at idle, i'm going to mess around with it a little more when i get back home , heading up north to go to work for a couple weeks.

i just reallly dont like the idea of messing around with the distributor, is there a kit to buy to shorten the curve or do i actually have to braze the slots in?

when i get home i plan to take it out in the woods for a little test drive, maybe i can get some more tuning done while im out there actually running it instead of these lousy driveway tests. lol
01-08-2012 08:26 PM
F-BIRD'88 Take the distributor apart and shorten limit the advance curve.

The stock curve will not work.

40deg timing is too much. you want 24-26 base at idle and 38 total.

limit the mechanical curve to 10-12deg

Fix it. Its not that hard.
01-08-2012 07:15 PM
Custom10 Truck & driver sound right at home in Sask , regardless you need more than 20 deg advance at idle IMO.
01-08-2012 06:17 PM
b00tz
Quote:
Originally Posted by Custom10
So after all this where are we today then, how is the idle now?

Do you have a bogger you call a road truck or a road truck you call a bogger? You could lock the timing at 38 and do your WOT mud pulls and call it a day if its a competition truck.

If you have dual purpose truck then power time it to 38 Deg BTDC @ 4000RPM. Go to idle, adjust idle/carb mixture for max vacuum. Note the base timing, add vacuum advance to manifold vac, re adjust carb.
its an all around offroad truck thats road legal, we'll say.

if i want to get out for a romp on the trail and take er up the hills to my favourite fishing hole thats 40 miles back in the woods, i can.
if theres some trees in my way that need to be politely asked to clear the **** out, the pushbar takes care of that quite nicely
if i want to rip up some mud on the pipeline, she does a pretty good job of that too
and last but not least if i just feel like screwin around on the dirt road goin sideways around any corner i can find, well shes quite perfect for that too
i like to be able to do all this but still take it on the road for when we get those two foot snowfalls, or just feel like drivin my big *** truck through town. lol

i dont do mud drags or competition, the most competion it sees is our local mud runs through the woods once a year and thats just an excuse for us all to get together drink some beers and have some fun haha

ive tried setting it to 38 total and using my vacuum advance to make up the difference, yes i have to adjustable can, just couldnt quite get it working right. im currently not running any vacuum advance.

as 454c10 says i think ill try it with 20 base 40 total, it seems to be pretty good so far was just looking for a second opinion
01-08-2012 05:32 PM
Custom10 yep 2 deg either way is no different
01-08-2012 05:24 PM
454C10 20 initial and 40 total will work just fine.
01-08-2012 05:18 PM
Custom10
Quote:
Originally Posted by b00tz
almost forgot this too : i have the idle set to around 1200 , i have to fiddle with the screw alot sometimes it idles there and sometimes it decides to idle higher.

once in a while it backfires out the carb and it catches on fire :/

and when i shut it off she keeps rolling on a little bit dieseling. i dont think the butterflys are open too far but i may be wrong
So after all this where are we today then, how is the idle now?

Do you have a bogger you call a road truck or a road truck you call a bogger? You could lock the timing at 38 and do your WOT mud pulls and call it a day if its a competition truck.

If you have dual purpose truck then power time it to 38 Deg BTDC @ 4000RPM. Go to idle, adjust idle/carb mixture for max vacuum. Note the base timing, add vacuum advance to manifold vac, re adjust carb. How much vacuum advance?

If vacuum adv is adding more than 12 deg timing then limit it with the street fire vacuum adv limiter if you have that kit or get the crane limiter plate.

dont exceed 50 deg total timing advance

If you have 18 base timing and then add the 12 deg vacuum adv at idle you should be sitting pretty with 30 deg at a 900 idle as long as there is enough hg" vacuum to pull in the vacuum can. As the revs come up the mechanical adv will add advance as the vacuum adv drops out, I dont see many boggers idling at any less than 900 with a 4 spd so 1 stiff curve spring in there to avoid adding mech adv at idle, then change the other spring heavy/lite to get the curve right,,,all in by Xperimentation RPM
01-08-2012 02:21 PM
b00tz hey guys thanks for the advice , unfortunately changing intakes is out of the question right now. and i dont want to change my gears because its a road truck also. if i need more power i can always drop the transfer case to the low side which over cuts my ratios in half (1.00 high side , 2.61, low side)

in first gear on the trans ( not jumbo low , but first which is 16.32 : 1 ) i have absolutely zero trouble ripping the bark off the tires, so in theory i should be able to start off in 3rd or 4th gear in 4 lo , 3rd being a 20.2 : 1 ratio and 4th being 11.9 : 1 ) time will tell i guess. lol

i hit the engine with the vacuum guage and timing light today and it made the most vacuum at 24 degrees inital advance, only problem is my distrubutor ( MSD streetfire 8362 ) comes with 20 * mechanical advance, i tried to go for the happy medium and set it to 20 * initial which gives me 40 total, does anyone think this sounds a bit much? like i said i really cant tell if its detonating or not with the exhaust and all... it sounds alot more responsive though and seems to turn up alot better.

454c10 : it says on the receipt the exhaust valves are ferrea inconel 1.8 exhaust valves , and manley 2.19 intake valves

as always thanks for any advice in advance , my budgets pretty limited atm so just trying to tweak this as best i can with what ive got! lol
01-08-2012 08:01 AM
matts37chev
Quote:
Originally Posted by F-BIRD'88

Change to a RPM style dual plane manifold. The single plane has no low end grunt. it don;t get busy till 4500++rpm.
does anyone make a dual plane for the tall deck?
or will he need spacers?
01-08-2012 07:23 AM
454C10 Well, he built the engine and doesn't want to push it. When you dyno test an engine, you should keep advancing the timing until no more gains are measured.

The things that cause an engine to need more total ignition timing are the following:
1) big bore (long way for the flame to travel)
2) domes or dished pistons (makes the flame travel around uneven terrain)
3) inefficient combustion chambers (makes the flame travel slow)

A BBC with old style cylinder heads and domes will have all these issues. This is why BBC typically are less toleration to high compression as compared to SBC are most other engines.

I have seen dynos of old bbc requiring up to 42 degrees of total timing to make max power. My 454 runs best with 40.

I think your compression maybe lower than 10.5:1.
899cc/cylinder
-29cc domes
120cc heads
9cc head gasket (0.039" thick felpro)
4cc piston below deck

(899-29+120+9+4)/(-29+120+9+4)= (899+104)/104=9.64:1 cr

I'm assuming 120cc heads and some -deck height.

your exhaust valves should be 1.9's not 1.8's (I think, as 1.72 or 1.9 are the standard issues exhaust valves for bbc's)

Yes, not enough gear for 44's. You are running "an effective" 2.90 gear due the the extra tall tires. Like a 2.90 gear with 28 inch tire.
01-07-2012 08:57 PM
F-BIRD'88 recurve the distributor for 24 to 26deg initial advance at idle.

36-38deg total at max advance. ( shorten the mechanical advance curve to 12deg).

Change to a RPM style dual plane manifold. The single plane has no low end grunt. it don;t get busy till 4500++rpm.

holley 750 carb jetting should be 70 to 75 pri and 80 to 86 sec.
Needs a 4.5" power valve.

You need a lot more gear with 44" mudders.
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