1972 BBC dyno tune
Thread Starter
Heel & Toe
Joined: Dec 2006
Posts: 23
Likes: 0
From: Minneapolis MN
1972 BBC dyno tune
**** for the dyno folk:
I recently upgraded my 1972 LS5 ignition system to the MSD E-Curve, recounted in the article below (family thinks I should become a hand model
)...
http://www.vetteweb.com/tech/vemp_08...ion/index.html
however I was still having idle, and starting problems. So, I brought the car over to the local dyno tuner - and handed over the keys.
The post tune pull (blue) shows: upgraded flow through air filter, replaced secondary jets (116), A/F reduced, and the electronic choke disconnected...
I was fairly happy with the Max HP, but a bit dissapointed with the Max torque. I wonder if the carb is undersized, and the headers oversized (2.125")...
Anyway - this shows what 90 minutes of dyno tuning can do for your car - as I drove home with a big smile on my face, and a much happier car!
The engine is set up as follows: 454 LS5, Torker II intake, Performer cam, 750 cfm Performer carb, Hooker Super Comp headers with STS inserts.
I recently upgraded my 1972 LS5 ignition system to the MSD E-Curve, recounted in the article below (family thinks I should become a hand model
)...http://www.vetteweb.com/tech/vemp_08...ion/index.html
however I was still having idle, and starting problems. So, I brought the car over to the local dyno tuner - and handed over the keys.
The post tune pull (blue) shows: upgraded flow through air filter, replaced secondary jets (116), A/F reduced, and the electronic choke disconnected...
I was fairly happy with the Max HP, but a bit dissapointed with the Max torque. I wonder if the carb is undersized, and the headers oversized (2.125")...
Anyway - this shows what 90 minutes of dyno tuning can do for your car - as I drove home with a big smile on my face, and a much happier car!
The engine is set up as follows: 454 LS5, Torker II intake, Performer cam, 750 cfm Performer carb, Hooker Super Comp headers with STS inserts.
Race Director
Joined: Sep 1999
Posts: 11,360
Likes: 382
From: Plano TX
Yeah, you're right. The torque is low. For comparison, here's my '71 454 LS5. At the time it had a Torker II intake, Holley 750, Comp 270H cam (mild), Hooker Super Comps 1 7/8" headers and undercar exhaust.
The red curve is the same config except stock exhaust manifolds. It looks very close to yours so I'm wondering if your exhaust is the problem?
The red curve is the same config except stock exhaust manifolds. It looks very close to yours so I'm wondering if your exhaust is the problem?
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,116
From: Crossville TN
From your print-out, your HP & torque drop off sharply at about 4500 rpm. That would indicate either fuel starvation or a weak cam. Fuel starvation could be due to fuel pump, filter, or carb. However, your A/F mixture doesn't appear to be different at that speed, so I'd say it would be a cam problem. (What rpm was the rev limiter set to?)
Instructor
Joined: Mar 2005
Posts: 104
Likes: 0
The air/fuel is a bit lean. Most of the engines I have tuned with Performer carbs have liked the secondaries opened sooner than the out of box setting.(reduce spring tension on the air door) The last one I did underlines the fact that it is tricky and best done on a dyno or at the track. Mildly built small block picked up 18 hp/ 22 ft lbs with 1/2 turn less tension and lost 5 hp/ 8 ft lbs with another 1/4 turn less.
Last edited by Unforgiven1; May 14, 2008 at 01:19 AM.
Team Owner
Joined: Apr 1999
Posts: 21,953
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From: Reno Nevada
2024 C3 of the Year Finalist- Modified
The 2162 is 218/228 duration and .500 lift.
If you are using old valve springs it could account for the drop off at 4500 rpm.
The TQII is old junk also. It is 30+ year old design.
Race Director
Joined: Sep 1999
Posts: 11,360
Likes: 382
From: Plano TX
If you have the Performer 2162 cam and stock small port heads with low compression it would explain the lack of performance.
The 2162 is 218/228 duration and .500 lift.
If you are using old valve springs it could account for the drop off at 4500 rpm.
The TQII is old junk also. It is 30+ year old design.
The 2162 is 218/228 duration and .500 lift.
If you are using old valve springs it could account for the drop off at 4500 rpm.
The TQII is old junk also. It is 30+ year old design.
13.5:1 is way too lean though. Fatten it up to about 12.5-12.8 and make sure the secondaries open all the way.
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
That's all true but mine had the same crappy stock heads, TQII and low compression in the dyno graph I posted and I had almost 100 ft-lbs more torque. The cam I had back then was almost the same also, 219/229, hydraulic flat tappet.
13.5:1 is way too lean though. Fatten it up to about 12.5-12.8 and make sure the secondaries open all the way.
13.5:1 is way too lean though. Fatten it up to about 12.5-12.8 and make sure the secondaries open all the way.
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Drifting
Joined: Aug 2005
Posts: 1,682
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From: League City TX
I was fairly happy with the Max HP, but a bit dissapointed with the Max torque. I wonder if the carb is undersized, and the headers oversized (2.125")...
The engine is set up as follows: 454 LS5, Torker II intake, Performer cam, 750 cfm Performer carb, Hooker Super Comp headers with STS inserts.
some jetting changes, but the CFM is fine. The Torker II is also a pretty rotten intake.
As for the headers- If you were designing an ideal set of headers, a 2.125" primary is too large
for anything making less than about 700 hp. But the Hooker sidepipe headers have such a long
primary tube length that it helps to crutch it some. They are still better for show than go.
Team Owner
Joined: Apr 1999
Posts: 21,953
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From: Reno Nevada
2024 C3 of the Year Finalist- Modified
The shop I work at rarely does chevy motors. So I don't get to see them on the dyno to often. But it has been my experience to see power drastically drop off from valve float no matter what type of engine.
I also did some back to back testing years ago on the Edelbrock "Performer" intake manifold on a hot rodded SBC. 355 ci with 600 cfm Edl carb. more aggressive H-flat cam than the poster is using on his 454.
The motor just shut down in the lower 5000 rpms. So somebody suggested a bigger carb so we installed a 750. After some jetting runs we went for it and the same thing happened. The junky Edelbrock intake ports were limiting the amount of air the motor could get. We changed intake manifolds to a Chevy LT1 clone and it made power out above 6500 rpm even with the 600 carb back on it. After that I only ran quality single plane intakes (not Edelbrock)
Team Owner
Joined: Jan 2006
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From: Crossville TN
gkull...
I appreciate the info, but low 5000's is not 4650 rpm. I've never known of a decent, newly built Chevy engine that would totally "drop like a rock" at those revs unless it was 30 years old, tired and the valve springs/lifters were shot. I can see the HP & torque starting to taper-off...but that's NOT what his dyno chart shows. I'm still wondering what his real problem is.
I appreciate the info, but low 5000's is not 4650 rpm. I've never known of a decent, newly built Chevy engine that would totally "drop like a rock" at those revs unless it was 30 years old, tired and the valve springs/lifters were shot. I can see the HP & torque starting to taper-off...but that's NOT what his dyno chart shows. I'm still wondering what his real problem is.
Thread Starter
Heel & Toe
Joined: Dec 2006
Posts: 23
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From: Minneapolis MN
The rev limiter is set at 5500
Cam is a 2162
HP seems to be still climbing at the end - valve float seems likely
I agree with the 2.125 header size - way to big - I wish there were better options out there (stainless, side mount, BBC)...
Cam is a 2162
HP seems to be still climbing at the end - valve float seems likely
I agree with the 2.125 header size - way to big - I wish there were better options out there (stainless, side mount, BBC)...
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Just for reference. Cosworth 2000 cc 4 bangers use 2 inch.
