horsepower gains through increasing total advance [Archive] - Nova Tech

: horsepower gains through increasing total advance


70ssBB
Feb 4th, 07, 10:53 PM
curoius what hp gains anyone has seen increasing total advance say from 25 to 35 degrees on a street/ strip big block. pump gas hyd. flat tappet

jays64II
Feb 5th, 07, 11:33 AM
that depends on your cam , comp. and cubes. what do ya have ?

DjD
Feb 5th, 07, 01:55 PM
curoius what hp gains anyone has seen increasing total advance say from 25 to 35 degrees on a street/ strip big block. pump gas hyd. flat tappet

Are you currently running 25degs total timing? What is your initial (idle with the vacuum advance disconnected and plugged)? How much mechanical timing is built into your dist (total - initial = mechanical)?

As Jay indicates every build is different but a ball park curve that would be performance oriented is to have about 20degs mechanical built into the dist. Then when you set your total to say 35degs your initial would be 15degs. From there you have to factor in vacuum advance which can work from idle to part throttle or just part throttle (manifold or ported vacuum respectively).

Anyway always test for pinging after making timing changes. Part throttle ping could be too much vacuum advance or advance coming on too early or too fast. WOT pinging is too much total advance. Pinging when lugging the engine could be timing related but don't rule out a mis-match in gearing and the engines torque curve... Guys install overdrives and often find this true at low rpm...

70ssBB
Feb 5th, 07, 03:36 PM
When I took possesion of the car the motor was set up with 7 dg. intial and 24 total with vacuum disconnected. Its a 454 with an unknown hyd cam. I would estimate a street/strip cam with moderate lope. dynoed at 290rwph/330rtq, shop did not compensate for convertor I believe. this was at 7 and 24 on the timing checked with no vacuum.

781 iron heads
runs on pump gas with a little booster.

I bought a sears dial back a little while back and re- set it to 20 and 36. It will show 51 with vacuum. all checked @3000rpm

So I backed it off to 17 to be a little safer. It runs like a scalded dog. It will smoke the street tires at 40mph locked in third (th350) 3000 stall/410 posi

Its run 8.3 at 85 in the 1/8th with the 7-24 setting. be interested this spring what happens.

As a side note Im running a msd ignition. the vacuum is hooked up on the top port of the holley 750 cfm double pumper right side.

vacuum hooked or unhooked at 950rpm has no impact on the light gun reading so it should be ported correct? Also under a load in actual driving conditions the high total advance # should disappear with the vacuum connected correct?

So I am at the 17-33 range vacuum unhooked. I did not feel or hear any pinging at the 20-36 range but had read you nver want to see more than 50 with the vacuum hooked up? Any way I have limited knowledge of the engine build as the guy who put it all together in 1994 could not recall all the details the engine shop did.

Hope this helps, thanks for your considerations.

jays64II
Feb 5th, 07, 03:54 PM
Well...it's kinda hard to determine what will work best since you do not have the data from the previous owner. If it is pump gas only then I would not go above 34 total if you are trying to keep it pump gas and out of the detonation zone. With the vaccuum hooked up how quickly does it advance when bringing the rpm's moderately from idle to 3000 rpm ? Does it take a big jump at any points in between and if so where ? Where is the timing at 3000 rpm ?

DjD
Feb 5th, 07, 05:28 PM
70ss - you are looking at 17 mechanical in the dist... Work the math from there, set the initial at 10 you'll have 27 total, set it at 20 and you'll have 37 total. Your vacuum advance looks like it's pulling in about 15 so now you have all the numbers...

Be sure the engine is at operating temp and pick a starting point, say 34 total (17 initial) and test drive the car. Go WOT, lug it and just drive normal and listen for pinging. If none, hook up the vacuum advance to a vacuum source (vacuum at idle) and test drive again. Pay attention to how the engine is at a stop light and when taking off (have your idle turned down fairly low and idle mixture adjusted for most vacuum each time you are testing.) as well as listening for ping. Now switch the vacuum to a ported source (no vacuum at idle) make your decision where you feel the car behaves best on the street... 51 with vacuum advance hooked up is not un-heard of, if it pings part throttle with the vacuum hooked up then you'll need to restrict some of the adv in the canister or get an adjustable vac can.

I kinda digressed into the vacuum advance because it's important for street drivability and even fuel economy if that is even something one can say in the same garage as a big block. Lets get back to your total... Make small, say 2 deg + and - changes from the 34 you started at and test drive, you never know what an engine really will like. Some small blocks really like 38-40 degs btdc total, typically big blocks like less, my 383 seems to run well around the 34 deg range.

Hearing pinging is one way to tell if you are detonating, reading your plugs is another. Don't rely on listening for pinging, if you are unsure take a plug reading. You don't want detonation to kill your rings or even rod bearings so play it safe. From a performance standpoint the track is your best test for what is right for your combo. It's always safer on the street to pull out a degree or two of advance. Tune for drivability until you get to the track... Hope that wasn't too long and it didn't put you to sleep... ;)

rhorne12
Feb 7th, 07, 07:13 PM
Man, DjD, you know a lot!!
I built boat engines for years and they are a true test of an engine. Most of the engines we did liked about 34 total degrees in at about 3000 to 3400 rpm.
The difference in performance from 29 to 34 degrees was usually remarkable and would increase power and fuel economy and lower temperatures.
Thirty four was almost always what we ended up with on the dyno and in the boat. Sometimes, a drag or street setup would like a little more timing, but you better not detonate it.

DjD
Feb 8th, 07, 11:57 AM
Thanks Robert... I started getting my hands dirty back in the early 70's as a teen. Amazes me some of it sunk in over teh years... ;)

rhorne12
Feb 11th, 07, 04:07 PM
I have been at this since 1960 as a teenager. I have raced almost every venue for cars and some boat drags and, of course, lake boats.
Interestingly, if you have too much compression for pump gas and have to reduce timing below 34 on a BBC, horsepower and mileage DECREASE as compared to proper compression and 34*.
Even with forced induction our properly set up engines liked 34. Any change of more than 2 degrees always hurt performance.
I had several engines in boats that could run at full throtle for miles at a time producing over 1,000 horsepower from 540 to 565 inches and all ended up at 34 degrees total timing-of course compression and boost had to be compatable with the gas to run.

Doug G
Feb 14th, 07, 09:22 AM
At the track I increase total till power falls off then back off 2* from best time. I've only seen a few tenths in the 1320.

rhorne12
Feb 17th, 07, 03:25 PM
I have found that if the timing is off more than 4* it can really affect performance.
Too high can explode the motor, too low will cause poor throtle response, poor economy, and excessive heat.
Doug's advise is very good, just start with a reasonable number and adjust up or down and test. I like to start with 34 total.

70ssBB
Feb 17th, 07, 09:11 PM
Thanks for the imput, When I hit a test n tune I will start at 34 and see how it goes. The seat of the pants factor so far has been a big improvement. I go to the track 5 times a year or less so not a huge focus but we all like to know what are machines can do and have them well tuned. This mystery motor that came with the car so far has been doing well for being a 1994 rebuild. Previous owner said he took it to the track once in the 10 years he had it. Sat in a garage mostly as he had other hot rod projects drawing his attention. Just wish he had written down the motor specs at one time.

LUMP
Feb 18th, 07, 02:34 AM
Some good advice above but i'll add my .02 anyways...

There is the CORRECT timing and the WRONG timing and the line between them is relatively thin. I would work from total timing first and then work on how quickly you go from initial to total and how to set up your vacuum advance.

For total timing the only way to truly tune it is a full throttle pass on a new set of plugs - long enough on WOT to mark them. I keep the heat line on the ground straps halfway across the flat before the 90 because i am conservative. Some people run it right to the threads.

But before you can set timing you need to have the fuel right and the correct heat range plugs.

If you set the timing first then take some fuel out of it you will then have too much timing etc etc it's a bit of trial and error.

The total timing will depend on a lot of things - from the efficiency of the chamber/piston (flat tops and efficient chambers need less total timing, domes and open chambers need more. Don't think more is better - think the RIGHT amount of advance to get peak cylinder pressure at the right time relative the piston...) to weight of the car, ambient temp, altitude, etc etc.

As said above i would start with 34 deg total. For a plug - you didn't say how much compression and cam you have but i would start with either an NGK B7ES or better NGK R5671A-7. You could make the 7's to 8's if you don't foul them driving around on the street (8 is colder than 7.)

Good advice above already re: vacuum advance - my first concern is total because you aren't going to kill it part throttle instantly - it would take a lot of noticeable rattling at part throttle to do damage...