427 BBC tuning help
hey guys, im working on getting my 427 all tuned in and im having a little trouble so far , its kind of hard starting in the cold, and i cant manage to get it working quite right , seems to be sluggish in 3rd and 4th gears... and i know it shouldnt be because it has more than enough torque to roll it.
i know on the dyno we dropped the main jets from a 74 to a 71 and secondary from an 80 to a 78, dont know if this is the cause of my problems or not as i havent got the new jets yet.
this is all my info
427 BBC TD
punched .60 thou and balanced (439)
large oval GM heads with port work and manley 2.19 intake valves ,ferrea inconel 1.80 exhaust valves
SRP +29CC dome pistons with mahle perfect circle rings
im running comp hydraulic roller cam 11-443-8 ,
540 intake lift
560 exhuast lift
duration @ .50 is 242 int and 248 ex
scorpion 1.7 roller rockers
Dart high rise single plane intake
proform 750 double pumper with mechanical secondaries.
it made 530 horse @ 5650
550 torque @ 4400
the builder says compression should be around 10.5 : 1 , i dont have the head numbers ATM but its the standard TD truck heads.
im running 11 degrees base timing with no vacuum advance and 36 degrees total by i think 4000? i dont have a timing light ATM sorry :(
so far the only thing ive been able to set up properly on the carb is the idle circuit, had 10 vacuum with the idle circuit screws a half turn out, that was the best vaccum i could get.
i havent touched power valve , timing , or jets , and dont know whether or not to run vacuum advance.. im kinda lost lol never had a good engine like this before just old stock 350's... any help is appreciated.
oh btw its in my 87 chevy one ton 4wd , muncie sm465 with an np208 and 4.56 gears with 44 boggers, running a centerforce dual friction clutch.
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
It's lazy because the timing is way slow. You need about 18-22 degrees initial timing in that thing with the cam and single plane. Then limit your total mech adv to about 36-38. With the manual trans you can hook your vac advance up to mainfold vac limited to 12-14 degrees and turn your idle down to around 900-1,000 rpm or a little lower if it likes it. That will kill the run-on. You NEED a decent timing light with an advance capability and you can solve your problems.
thanks alot for the reply speedbump. im going to get a timing light and a vcauum gauge from my buddy tommorow and i will definitely try that, i thought it sounded a little low to me too but thats what he set it to on the dyno and i never touched it since
yes, low timing.
I would run 25 initial timing at 1000 rpms, 38-40 total mechanical in by 4000 rpms.
and use the vacuum advance if you drive it on the street. Use an adjustable vacuum advance canister set to 10 degrees.
The vacuum advance will not have much vacuum to work with due to the big cam. Will need at least 9 inhg which most likely will not happen that often. Maybe while driving down the highway or revving it up in neutral.
the only thing im worried about is if i put too much timing, would that hurt the engine any? i know not to let it detonate but he said he wouldnt run any more than 36 on it at the shop... maybe hes just a worry wart? lol
also, is there any easy way to tell if its detonating if you cant hear it? my exhuast is really loud and i do well to hear myself talk when its running lol
should i just hook my vacuum guage up and set the timing to where it has the most vacuum?
i did notice on the dyno that it picked up alot of power as we advanced the timing, i think something like 20 horse per every 2 degrees , we hit the 530 mark when we advanced it to 36 but he got worried about advancing it too far after that and didnt go any further, whats up with that? lol
its all forged internals with a good balance job and clevite main and rod bearings with durabond cam bearings , eagle h beam rods and the srp pistons are forged , as well as the gm forged crank that came in the TD...i thought it sounded pretty tough ? lol
i have the limiter set to 6500 RPM , does that sound a little high?
i really do apologize for all these questions im just totally new to all this aftermarket stuff and im looking for input, dont wanna blow a 10,000 dollar engine lol
thanks again for the replies everyone
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.
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.
or will he need spacers?
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
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 :D
20 initial and 40 total will work just fine.
yep 2 deg either way is no different
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 :)
Truck & driver sound right at home in Sask ;) , regardless you need more than 20 deg advance at idle IMO.
lol looking at other posts looks like this aint the first time you two haven't agreed on total timing in bbc's. :P 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
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