Boost timing curve on sbc - Hot Rod Forum : Hotrodders Bulletin Board
Hotrodders.com -- Hot Rod Forum



Register FAQ Search Today's Posts Unanswered Posts Auto Escrow Insurance Auto Loans
Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Engine
User Name
Password
lost password?   |   register now

Reply
 
LinkBack Thread Tools
  #1 (permalink)  
Old 07-22-2012, 04:33 PM
spinn's Avatar
He got me, like he got you
 

Last journal entry: This makes a huge difference
Last photo:
Join Date: Oct 2004
Location: Midnight
Posts: 2,546
Wiki Edits: 0

Thanks: 14
Thanked 88 Times in 85 Posts
Boost timing curve on sbc

My 305 had a supercharger installed the begining of the month. There have been a few hurdles to deal with. My fuel pump went after changing the pump outlets 90's. The fuel pressure is now stable after replacement. I have been recurving my distributor every few days. There is power, but at higher rpms it seems like power is not ramping up.

build
305 rebulit short 8.9:1
peformer cam
Ls6 beehives little retainers
vortec 906 heads 60cc
E force 122 eaton supercharger
650 cfm AVS
E curve MSD no box
3000 stall
3.73 8.5 rear 28" tire

The manual explains that timing should be reduced 2 degrees for every one lbs of boost. It also recomends a MSD retard boost timing box which I really dont want for 5-6 psi . My curve has been 12 intial 20 more at 3000 rpm for 32 . 8 in the can at 10 " vacuum. After the supercharger locked out at 20 works surprisingly well. The faster the charger spins the more power it makes all the way up. At 10 intial plus 15 at 3000 works good too. Anymore than 25 total after 3000 doesnt work well. The gas is 89 octane.

I do not want to use the MSD box and boost retard. What is the normal acceptable timing curve for a supercharged mild engine? 20 and 25 sound a little short for totals. This also affects normal cruising. Has almost brutal throttle response cruising without the higher timing.

If I go down in plug heat range more will that allow higher total numbers?

Good news, mpg has not changed much.

    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 07-22-2012, 05:08 PM
F-BIRD'88's Avatar
Yada Yada Yada
 
Last photo:
Join Date: Oct 2005
Location: Ontario, Canada
Posts: 9,153
Wiki Edits: 0

Thanks: 5
Thanked 380 Times in 374 Posts
The cam is small. Limited top end power.

The timing curve needs work.

WHY 89 octane gas? you want to run the best fuel possible
if you want supercharged power. 92++++ octane gas allows more timing and more boost and more safe power.

The distributor needs to be torn down and reworked to get the right curve
without a boost retard box.
the carb is small. Should be a 750. It will need reworking.

Crap gas a 8.9:1 cr will really limit the timing @WOT under boost and blower boost (blower drive ratio)
and power.

Your 305 cam make huge safe supercharged power on good gas. Consider water methanol injection.
10-12+psi boost 32-34deg timing 750carb 214 224 cam A mild solid street cam (blower fiendly) would rock
EG LUNATI 401A3LUN

PERFORMER RPM INTAKE MANIFOLD.

Crap low octane gas is not your friend. You are not saving money.
Pistons and multiple rebuilds are expensive. If you want to lean on it get good gas in the tank and see what you are missing.
what is the blower pulley drive ratio?

Last edited by F-BIRD'88; 07-22-2012 at 05:22 PM.
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 07-22-2012, 05:51 PM
F-BIRD'88's Avatar
Yada Yada Yada
 
Last photo:
Join Date: Oct 2005
Location: Ontario, Canada
Posts: 9,153
Wiki Edits: 0

Thanks: 5
Thanked 380 Times in 374 Posts
Quote:
Originally Posted by F-BIRD'88 View Post
The cam is small. Limited top end power.

The timing curve needs work.

WHY 89 octane gas? you want to run the best fuel possible
if you want supercharged power. 92++++ octane gas allows more timing and more boost and more safe power.

The distributor needs to be torn down and reworked to get the right curve
without a boost retard box.
the carb is small. Should be a 750. It will need reworking.

Crap gas a 8.9:1 cr will really limit the timing @WOT under boost and blower boost (blower drive ratio)
and power.

Your 305 cam make huge safe supercharged power on good gas. Consider water methanol injection.
10-12+psi boost 32-34deg timing 750carb 214 224 cam A mild solid street cam (blower fiendly) would rock
EG LUNATI 401A3LUN

PERFORMER RPM INTAKE MANIFOLD.

Crap low octane gas is not your friend. You are not saving money.
Pistons and multiple rebuilds are expensive. If you want to lean on it get good gas in the tank and see what you are missing.
what is the blower pulley drive ratio?
delete the RPM manifold brain freeze

couple more hyd blower cams

Crane HMV272-2
Crane HMV278-2
Comp NX262H-13
Comp CS268AH-14
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 07-22-2012, 09:50 PM
spinn's Avatar
He got me, like he got you
 

Last journal entry: This makes a huge difference
Last photo:
Join Date: Oct 2004
Location: Midnight
Posts: 2,546
Wiki Edits: 0

Thanks: 14
Thanked 88 Times in 85 Posts
Yes, the cam is small , but for a mild 305 it is good unless you want to start trading off low end. It shifts at 5200 so the build is right in the power curve.

The supercharger is awesome and does what it is advertised to do. It pulls hard. Not to sure more cam would even make a difference in power. Unless you move the power band over 6000rpm.

The MSD E curve distributor cannot be reworked. It has 2 dials to change around the timing. Super easy.

The ratio is, well 7" crank pulley drive, and 3.75" blower snout driven. Bad news is the blower pulley is pressed on. No easy bolt on pulley to make boost. Should be over 5 psi at 5200.

I tried the 800 AVS and it was not any better at 5200 rpm . The 650AVS with .110 high flow needle and seat, set rods 4 % richer .065x.047, orange spring. It is a little under 13:1 a/f on the O2 at power using a tail pipe probe.

The 89 octane fuel works no better than the 93. That probably indicates I am at a limit of some sort. Could be the manual is right and you need to retard for the boost. What did people do before MSD had the boost retard box? Under conditions of light load the timing at 30 feels right over 3000rpm. Under hot, heavy load and up hill it rattles with 93 octane. It is backed off to 20-22 total now and in the summer heat it is safe.

The vortec heads didnt like timing much over 30-32 either before the blower.

Last edited by spinn; 07-22-2012 at 10:06 PM.
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 07-22-2012, 09:55 PM
F-BIRD'88's Avatar
Yada Yada Yada
 
Last photo:
Join Date: Oct 2005
Location: Ontario, Canada
Posts: 9,153
Wiki Edits: 0

Thanks: 5
Thanked 380 Times in 374 Posts
The carb jetting is probabily too lean. You should start tuning with plenty rich jetting.
+6 to 8 jet sizes. both pri and sec... You should be using a electric fuel pump EG carter P4070. Fuel starvation under boost will knock.

If 93 octane is knocking at only 5 psi and 30deg timing something is wrong.
What ever you are putting in the tank may not be 93 octane gas. Or the AFR is lean @WOT.
Or the supercharger is being feed very hot air. Cool air is better.

100F daytime temps will require the best fuel and or Water/methanol injection.

VOrtec head timing funny mine run just fine and make real good power at 36deg BTDC. 3 different sets on two different motors
3 different cams, different compression ratios.
, same timing requirement, 36deg BTDC @WOT.

If anything a vortec head should be more tolerant of timing under boost. with good tolerance to overtiming without being knock critical.

On my motors with vortec heads I can over advance the timing (beyond what produces best power) and it does not knock
ever.
But I use good fuel Sunoco Ultra 94 and the tuneup is right.

Where do you have the vacuum advance hose connected to? What is the blower pulley drive ratio ( pulley sizes)
carb jetting, max observed boost?

Use cool champion RS9YC or equal .035" gap.

Last edited by F-BIRD'88; 07-22-2012 at 10:13 PM.
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 07-22-2012, 10:37 PM
painted jester's Avatar
TAKE A KID TO A CAR SHOW
 

Last journal entry: mopar hump back
Last photo:
Join Date: Jan 2011
Location: Central Michigan
Age: 68
Posts: 1,841
Wiki Edits: 0

Thanks: 103
Thanked 292 Times in 240 Posts
Why did you choose a 3000 stall converter with a supercharged engine and small cam? Firbirds got you covered so Ill bow out but I was just curious

Jester
Reply With Quote Quick reply to this message
  #7 (permalink)  
Old 07-22-2012, 10:43 PM
spinn's Avatar
He got me, like he got you
 

Last journal entry: This makes a huge difference
Last photo:
Join Date: Oct 2004
Location: Midnight
Posts: 2,546
Wiki Edits: 0

Thanks: 14
Thanked 88 Times in 85 Posts
The plugs are autolite? 605's which should be 2 stages colder than stock plugs. Before they were 3923's by autolite. I will try those RS9YC champions.

I am 2 stages or 8% richer on the chart at cruise , and 1.5 stages or 6 % richer on power.

Pullies are 7" crank, 3.75" snout.

I have this crazy outlet hose that twists around to clear everything. Could that cause any problems? Temps stay within 180-190 on hot days in traffic.

With 5-6lbs of boost I should be able to run 32 degree total timing at load without detonation? Shifting at a limited 5200.

If so what have I done wrong? Is my compression way more than 9:1 ? The 305 has 9.2:1 pistons with the 58cc heads. Now the heads are 60 cc vortecs? Are my plugs the incorrect heat range?

What are you shifting at in your vortec builds?
Attached Thumbnails
Click image for larger version

Name:	sc305aa.jpg
Views:	60
Size:	63.2 KB
ID:	66954  

Last edited by spinn; 07-22-2012 at 10:52 PM.
Reply With Quote Quick reply to this message
  #8 (permalink)  
Old 07-22-2012, 11:06 PM
spinn's Avatar
He got me, like he got you
 

Last journal entry: This makes a huge difference
Last photo:
Join Date: Oct 2004
Location: Midnight
Posts: 2,546
Wiki Edits: 0

Thanks: 14
Thanked 88 Times in 85 Posts
Those autozone people gave me 605's and they are the same heat range according to a search on google. I need to get cooler plugs.

The stall happened that way because it was built in steps. First a cam, the heads, then a stall, recently a supercharger. It worked well together and figured that a supercharger would work well on an already good running engine package. This is my first time with superchargers. It has been a blast. The power is there.

That 3000 stall is welcome. No negative effect or downsides. Dymanic converters built it and regular driving I cannot even tell it is there. It is not as loose as 10" stalls and not as pointless as most 12".

What does it sound like when you hit the rev limiter? I could be doing that to. If the govenor is reprogrammed to shift at 5200 and the MSD E curve limiter is set below that, could that be confused with detonation?

Last edited by spinn; 07-22-2012 at 11:11 PM.
Reply With Quote Quick reply to this message
  #9 (permalink)  
Old 07-22-2012, 11:24 PM
painted jester's Avatar
TAKE A KID TO A CAR SHOW
 

Last journal entry: mopar hump back
Last photo:
Join Date: Jan 2011
Location: Central Michigan
Age: 68
Posts: 1,841
Wiki Edits: 0

Thanks: 103
Thanked 292 Times in 240 Posts
I was curious because a supercharged engine torque curve is right from Idle to upper rpm range! your not having to brake torque the engine to 3000 rpm to hit the engines torque curve like a naturally aspirated engine with a big cam and your small cam should work very well with the forced induction!! The 3000 stall will have slippage even if you don't notice it and youll lose bottom end power! And with the torque a supercharger produces at bottom end your 3000 stall converter could even be stalling at a higher RPM like 3500 or 4000! Stall converters are sold with average stall calculations and the higher the torque applied and the faster it comes in the higher the converter will stall ! I was just curious I ran superchargers for many years and you'll enjoy it it just takes a little tuning in and firbirds got you on track

Jester
Reply With Quote Quick reply to this message
  #10 (permalink)  
Old 07-22-2012, 11:27 PM
F-BIRD'88's Avatar
Yada Yada Yada
 
Last photo:
Join Date: Oct 2005
Location: Ontario, Canada
Posts: 9,153
Wiki Edits: 0

Thanks: 5
Thanked 380 Times in 374 Posts
I am 2 stages or 8% richer on the chart at cruise , and 1.5 stages or 6 % richer on power.

the cruise does not need fattening if at all. The power mode and sec ondarys needs the fat jetting. Thats when the blower is creating boost.

What carb model number / what was the stock jetting?

What are the pri and sec jets , now ? what pri metering rods, now?

what power step spring?

You need way richer sec jets + 6 jet sizes.

you cr may be higher than you claim.
Flat tops ? dished piston? what dish volume, deck height, gasket etc.
true Head cc.

Start by telling me the carb jetting.

NGK:
BP7EFS
NGK:
BPR6EFS
NGK:
BR7EFS
Autolite:
104
Champion RS9yc

The engine water temp is not he critical factor. The temp of the air that is going down the carb,,,, is..... Hot inlet air creates detonation.

I shift my 400 at 6000 rpm .

I bet you barely see 2500 real converter stall with that "3000" stall behind a 305

I have this crazy outlet hose that twists around to clear everything no idea what you are saying...

Last edited by F-BIRD'88; 07-22-2012 at 11:33 PM.
Reply With Quote Quick reply to this message
  #11 (permalink)  
Old 07-22-2012, 11:49 PM
F-BIRD'88's Avatar
Yada Yada Yada
 
Last photo:
Join Date: Oct 2005
Location: Ontario, Canada
Posts: 9,153
Wiki Edits: 0

Thanks: 5
Thanked 380 Times in 374 Posts
The 650AVS with .110 high flow needle and seat, set rods 4 % richer .065x.047, orange spring. It is a little under 13:1 a/f on the O2 at power using a tail pipe probe.

This is way too lean on the power with a supercharger . You are going to burn up this motor.


Start with this rich but safe base line

.101" primary jet .065x .037" primary rod .107" sec jet
Use a orange or pink power step up spring.
DO NOT ATTEMPT TO TUNE USING LOW OCTANE GAS.

The carb secondary air valve may need adjustment. (Looser faster opening)

I bet it did not knock with the 800 carb on.

Last edited by F-BIRD'88; 07-23-2012 at 12:19 AM.
Reply With Quote Quick reply to this message
  #12 (permalink)  
Old 07-23-2012, 02:44 PM
painted jester's Avatar
TAKE A KID TO A CAR SHOW
 

Last journal entry: mopar hump back
Last photo:
Join Date: Jan 2011
Location: Central Michigan
Age: 68
Posts: 1,841
Wiki Edits: 0

Thanks: 103
Thanked 292 Times in 240 Posts
When I mentioned stall characteristics of a torque converter! I wasn't meaning that your specific engine torque would stall the convertor at 3500 or 4000. It was just an example to get a point across.

Jester
Reply With Quote Quick reply to this message
  #13 (permalink)  
Old 07-23-2012, 02:54 PM
painted jester's Avatar
TAKE A KID TO A CAR SHOW
 

Last journal entry: mopar hump back
Last photo:
Join Date: Jan 2011
Location: Central Michigan
Age: 68
Posts: 1,841
Wiki Edits: 0

Thanks: 103
Thanked 292 Times in 240 Posts
Quote:
Originally Posted by F-BIRD'88 View Post
I have this crazy outlet hose that twists around to clear everything no idea what you are saying...
F-BIRD I'm interested in the thread but don't understand this sentence? I read it over and overLOL.

Can you still get blower cams from B.D.S.? ( Blower Drive Service) They had many grinds available from street to full race plus #1 through#4 stage

Chris

Last edited by painted jester; 07-23-2012 at 03:11 PM.
Reply With Quote Quick reply to this message
  #14 (permalink)  
Old 07-23-2012, 04:00 PM
spinn's Avatar
He got me, like he got you
 

Last journal entry: This makes a huge difference
Last photo:
Join Date: Oct 2004
Location: Midnight
Posts: 2,546
Wiki Edits: 0

Thanks: 14
Thanked 88 Times in 85 Posts
I got new plugs. Not sure if that is the problem.

Twisting the MSD limiter to 5k , I felt what that is like. It is not like detonation. Scratch that one off.

The carb is a 650 edelbrock AVS. Jets are primary .098 secondary .105 , The rod is .065x.047 , orange spring, the air door has been loosened, an has .110 high flow seats.

This morning I droppped in a .065x.037 rod to add more fuel , and returned to 30 total timing at 3000. The sound has been affected. Strange that i set the carb with a gas probe, and it is lean. So that was not a suspect. Your calibration suggested is off the map, but I get where you are coming from. With a plug change to the recommended plugs rs9yc , a richer power mixture it should work out. My belief is the combination of heat range and lean mixture is the cause.

The air is from the engine compartment. So it is hotter air.

It only makes the noise right before it shifts, when the blower is making the most boost.

That water outlet hose does not have anything to do with it. Pretty sure .

The fuel is 89 octane . Both side R n L are full. I will fill one side with 93 when it is time.
Reply With Quote Quick reply to this message
  #15 (permalink)  
Old 07-23-2012, 05:02 PM
F-BIRD'88's Avatar
Yada Yada Yada
 
Last photo:
Join Date: Oct 2005
Location: Ontario, Canada
Posts: 9,153
Wiki Edits: 0

Thanks: 5
Thanked 380 Times in 374 Posts
Quote:
Originally Posted by painted jester View Post
F-BIRD I'm interested in the thread but don't understand this sentence? I read it over and overLOL.

Can you still get blower cams from B.D.S.? ( Blower Drive Service) They had many grinds available from street to full race plus #1 through#4 stage

Chris
The blower cams sold by BDS are Isky Cams.
You can order the same cams from Isky.
You can get any LSA you want. Single pattern, dual pattern, reverse pattern. All you got to do is call and order.
The Isky cams are really really good.
ISKY Racing Cams - Do It Right. Race with the Legend. Camshafts, Connecting Rods, Valve Springs, Lifters

I believe you can custom order custom grind Isky Cams thru Summit racing too.

All it takes is a phone call and a credit card.
Reply With Quote Quick reply to this message

Recent Engine posts with photos

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Hot Rod Forum : Hotrodders Bulletin Board forums, you must first register.
Please enter your desired user name (usually not your first and last name), your email address and other required details in the form below.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
locked out timing or timing curve? z-adamson Engine 17 08-05-2012 03:57 PM
E curve distributor n timing curve for BBC topwrench Engine 10 02-12-2012 06:11 AM
SBC Suggested Timing Curve adantessr Engine 4 11-27-2011 06:17 PM
SBC Suggested Timing Curve hoops Engine 9 07-01-2010 04:25 PM
timing curve tomthecomic Engine 2 07-01-2007 02:01 AM


All times are GMT -6. The time now is 10:41 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright Hotrodders.com 1999 - 2012. All Rights Reserved.