Smog affect on performance
Thread Starter
Burning Brakes
Joined: Aug 2006
Posts: 793
Likes: 10
From: Grafton MA
Smog affect on performance
Does the smog system affect a car's performance/horsepower? Bought a second '71 LT-1 (the new one has the original smog and the other doesn't), and notice a pretty significant difference in power between the two cars. The car with the smog has noticeably less pep.
Safety Car
Joined: Apr 2000
Posts: 3,802
Likes: 61
From: Wichita KS
cc
Tech Contributor
Joined: Aug 1999
Posts: 14,375
Likes: 6,375
From: At my Bar drinking and wrenching in Lafayette Colorado
The equipment typically regarded as "smog" equipment really doesn't affect power much. However, compression ratios dropped in 1971 in order to lower emissions, and this compression ratio drop will affect horsepower along with the more conservative cam profiles. The distributor advance curve is slower on the emissions engines, and total timing is limited. This is easily corrected by setting the total timing correctly and running some softer advance springs.
Other comments:
Overall, the emissions controls themselves have little effect on WOT performance, but engine design (lower compression, cam profile, and advance curve) does have an effect on power output.
Lars
Other comments:
- The A.I.R. pump pulls insignificant power (about 1 hp).
- The EGR is operated by ported vacuum, so it only functions at light throttle cruise - no effect on WOT performance or idle.
- The vacuum advance controls on the emissions engines limit vacuum advance under cold conditions, under some cruise conditions, and at idle - they have no effect on WOT performance.
Overall, the emissions controls themselves have little effect on WOT performance, but engine design (lower compression, cam profile, and advance curve) does have an effect on power output.
Lars
Team Owner
Joined: Jun 2000
Posts: 38,923
Likes: 1,481
From: Southbound
Cruise-In II Veteran
Be careful comparing the two; too many variables. #1 might feel strong if it's had a recent rebuild; #2 might be unmolested stock and showing her age.
Whatever you decide, LT-1 smog equipment is nearly priceless. If you pull it off, you certainly want to hang on to it.
Team Owner
Joined: Sep 2006
Posts: 31,214
Likes: 4,301
From: Westminster Maryland
Hi,
I'll second Mike's point about the value of complete systems. It was taken off so many cars that to put a complete system together for a particular engine and model year is very expensive. $$$$
Finding the proper hoses, fans, pulleys and brackets, etc, drives people crazy.
Regards,
Alan
I'll second Mike's point about the value of complete systems. It was taken off so many cars that to put a complete system together for a particular engine and model year is very expensive. $$$$
Finding the proper hoses, fans, pulleys and brackets, etc, drives people crazy.
Regards,
Alan
