TBI and cam overlap
08-12-2006, 11:07 AM
#1
Member
Thread Starter
Join Date: Jun 2006
Location: Troy, MI
Posts: 307
Likes: 0
Received 2 Likes
on
2 Posts
Car: 1988 IROC-Z TBI
Engine: L04.3 = 305-310-336
Transmission: TH-700R4
Axle/Gears: 10-bolt, 3.42 posi
TBI and cam overlap
I'm looking at having a cam made with 43* overlap for a 334 TBI motor. The duration at 0.050" will be around 210/220 int/exh on a 112 LCA. Compression ratio should be ~10.0-10.1:1, which should give me about 16-17 inHg. I've used 37* overlap in the past and this required only minimal "tuning" of the EPROM, so I'm wondering about 43* overlap? Of course, I intend to re-tune, but I'm wondering how the car will fire-up and idle with the old chip. Any insights?
Last edited by Casey Butt; 08-13-2006 at 09:35 AM.
08-14-2006, 12:09 AM
#2
Supreme Member
iTrader: (2)
Join Date: Jan 2002
Location: Moorestown, NJ
Posts: 9,962
Likes: 0
Received 3 Likes
on
3 Posts
Car: 88 Camaro SC
Engine: SFI'd 350
Transmission: TKO 500
Axle/Gears: 9-bolt w/ 3.23's
With speed density and TBI its a complete crap shoot. The only way to find out is to turn the key and see what it does. Thats not a real big cam, so my guess would be that it should start up and idle in some fashion.
08-14-2006, 09:45 PM
#3
Supreme Member
I'm looking at having a cam made with 43* overlap for a 334 TBI motor. The duration at 0.050" will be around 210/220 int/exh on a 112 LCA. Compression ratio should be ~10.0-10.1:1, which should give me about 16-17 inHg. I've used 37* overlap in the past and this required only minimal "tuning" of the EPROM, so I'm wondering about 43* overlap? Of course, I intend to re-tune, but I'm wondering how the car will fire-up and idle with the old chip. Any insights?
My 350 Xfire uses 54d of overlap on a 108LSA. When warm, motor fires at "key on". Needs a couple of cranks when cold. Idles a 47kPa.
08-14-2006, 10:01 PM
#4
Supreme Member
iTrader: (2)
Join Date: Jan 2005
Location: Hurst, Texas
Posts: 10,002
Received 389 Likes
on
332 Posts
Car: 1983 G20 Chevy
Engine: 305 TPI
Transmission: 4L60
Axle/Gears: 14 bolt with 3.07 gears
My 312 with the L82 cam ran 61.5* overlap on a 114* LSA. After a little work on the VE tables and timing table, fired right up and idled at 60 KPA/ 750 RPM in Park/Neutral and 75 KPA/800 RPM in Drive. With the A/C on that number dropped to 80-85 KPA/900 RPM in Drive.
Fired on the first hit of the key, everytime. Idle timing was about 30* BTDC and the initial timing at the distributer was 18* BTDC.
Fired on the first hit of the key, everytime. Idle timing was about 30* BTDC and the initial timing at the distributer was 18* BTDC.
Last edited by Fast355; 08-14-2006 at 10:05 PM.
08-14-2006, 10:50 PM
#5
Member
Thread Starter
Join Date: Jun 2006
Location: Troy, MI
Posts: 307
Likes: 0
Received 2 Likes
on
2 Posts
Car: 1988 IROC-Z TBI
Engine: L04.3 = 305-310-336
Transmission: TH-700R4
Axle/Gears: 10-bolt, 3.42 posi
Well, I'm having the cam custom ground, so I can tighten up the LCA to 110* - which should be better for the stroked motor anyway - but that would give me 47* overlap on a 110 LCA. 210* should put the power in the range that I want it and I want the extra 10 degrees on the exhaust (220*) to account for any valve shrouding on the exhaust side with the square engine.
I'd prefer to go with 110* LCA but I don't want to make the idle MAP signal jumpy and cause tuning issues. Anyone see a "problem" with 210*/220* @ 0.05" and a 110* LCA (47* overlap)? I'd much prefer to go with that.
Dominic and Fast, how did you find tuning those cams?
I'd prefer to go with 110* LCA but I don't want to make the idle MAP signal jumpy and cause tuning issues. Anyone see a "problem" with 210*/220* @ 0.05" and a 110* LCA (47* overlap)? I'd much prefer to go with that.
Dominic and Fast, how did you find tuning those cams?
Last edited by Casey Butt; 08-14-2006 at 11:02 PM.
08-14-2006, 10:57 PM
#6
Supreme Member
iTrader: (2)
Join Date: Jan 2005
Location: Hurst, Texas
Posts: 10,002
Received 389 Likes
on
332 Posts
Car: 1983 G20 Chevy
Engine: 305 TPI
Transmission: 4L60
Axle/Gears: 14 bolt with 3.07 gears
Its definately workeable with the right tuning and a good match-up on the rest of the components.
If you end up with the EBL you shouldn't have any problems getting it dialed in after some work.
FWIW, my L82 cam was 291/287 @ .008", 224/224 @ .050, 114 LSA, .450/.461",
If you end up with the EBL you shouldn't have any problems getting it dialed in after some work.
FWIW, my L82 cam was 291/287 @ .008", 224/224 @ .050, 114 LSA, .450/.461",
Trending Topics
08-15-2006, 09:02 AM
#9
Supreme Member
Casey,
Both cams I have had in the car are CompCams HR. So you could add about 10d of duration for a comparable flat tappet cam. The first one is similar to what you are thinking about. It was a 264/270 adv.(212/218 .050) with .488/.495 lift at 112LSA. It idled very smoothly at 800rpm using just a 7747. Lots of torque. EBL makes tuning these cams much more feasible due to the granularity of the VE and SA tables along with several ancillary controls.
Both cams I have had in the car are CompCams HR. So you could add about 10d of duration for a comparable flat tappet cam. The first one is similar to what you are thinking about. It was a 264/270 adv.(212/218 .050) with .488/.495 lift at 112LSA. It idled very smoothly at 800rpm using just a 7747. Lots of torque. EBL makes tuning these cams much more feasible due to the granularity of the VE and SA tables along with several ancillary controls.
Thread
Thread Starter
Forum
Replies
Last Post
junkcltr
Tech / General Engine
6
08-02-2019 11:12 PM
509 camaro fan
Tech / General Engine
13
09-06-2015 10:43 AM
