383, drinking fuel badly and lots of knock

[atlantadan]

1995 LT1. Engine specs: 383 forged, -5cc flattop, 11.6:1 compression, TrickFlow 195's, new stock Caprice 3" MAF, 30# injectors, LT4 knock module, 1.6 rr's, RAISS cai, longtubes, new opti, new ICM, coil, wires, plugs, ECT, MAP. Running 93 gas, and tuned for 93.

Cam is 224/230 .560/.544 112 LSA

I've been working with a well respected tuner to get this new build sorted and I am still having loads of knock, and very poor fuel consumption. 10-11 in town. Now, I didn't expect this car to be a miser, but I was getting 16 around town with my clapped-out 350, so I expected something a little closer to that....

I'm attaching a TTS Datamaster log taken this morning. From a stone-cold start through town to warm-up, and then a long run on the interstate. At the end of the log, the knock is easy to see at part throttle.

I don't know if this is a 'no no' here, but could someone look at the log and see if there's anything blatantly obvious that myself and the tuner are missing? At this point, I've got hundreds and hundreds of dollars in tuning this car. Two tuners later (the first one was a comedy of errors), and here we are. I'll pay the right person if this can get sorted out.

[Fast355]

Engine specs: 383 forged, -5cc flattop, 11.6:1 compression, TrickFlow 195's, new stock Caprice 3" MAF, 40# injectors, LT4 knock module, 1.6 rr's, RAISS cai, longtubes, new opti, new ICM, coil, wires, plugs, ECT, MAP. Running 93 gas, and tuned for 93.

Cam is 224/230 .560/.544 112 LSA

I've been working with a well respected tuner to get this new build sorted and I am still having loads of knock, and very poor fuel consumption. 10-11 in town. Now, I didn't expect this car to be a miser, but I was getting 16 around town with my clapped-out 350, so I expected something a little closer to that....

I'm attaching a TTS Datamaster log taken this morning. From a stone-cold start through town to warm-up, and then a long run on the interstate. At the end of the log, the knock is easy to see at part throttle.

I don't know if this is a 'no no' here, but could someone look at the log and see if there's anything blatantly obvious that myself and the tuner are missing? At this point, I've got hundreds and hundreds of dollars in tuning this car. Two tuners later (the first one was a comedy of errors), and here we are. I'll pay the right person if this can get sorted out.

If your cam and converter are lugging that cam its not going to get good fuel mileage.

I have a 450 hp V8 sedan that is in the same 4,200 lbs range as your Caprice and I get about the same mileage in-town with my lead foot despite the fact the engine is direct injected and very techically advanced.

[lionelhutz]

You'll probably have to just disable the knock retard. The LT1 knock sensing seems to be easy to overwhelm and then it starts detecting knock a lot when there is no knock.

[atlantadan]

If your cam and converter are lugging that cam its not going to get good fuel mileage. I have a 450 hp V8 sedan that is in the same 4,200 lbs range as your Caprice and I get about the same mileage in-town with my lead foot despite the fact the engine is direct injected and very techically advanced.

The converter is a new Yank 3k, and this mileage is babying the snot out of the car around town. Trans temps are 145 on the interstate, and rarely get over 160 in-town with 95-105 ambient temps. 99% of the time, I drive like a granny. I understand that this engine/cam will drink down some fuel, but others with pretty much the exact same combo are getting mid 20's on the interstate @ 65. I'm getting 15, so something definitely is not right.


You'll probably have to just disable the knock retard. The LT1 knock sensing seems to be easy to overwhelm and then it starts detecting knock a lot when there is no knock.
Yeah, I've heard of others doing that, but in this case, the knock is audible.

[kur4o]

I think the cam is too small for that kind of compression and fuel with 93 octane is not enough.
You may try open loop with different afr. Runing richer not always mean poor fuel economy, because your making more power and use fuel more efficently.
Some engines don`t like 14.7 afr. Your cold start is really lean, you should fix that.
Get a wideband. If you want to dial the engine you definitely need one.

It will be great if you post your current bin.


Download and use much better program for logging like EEhack.
It also will give you some live tuning options.

[atlantadan]

I think the cam is too small for that kind of compression and fuel with 93 octane is not enough.
You may try open loop with different afr. Runing richer not always mean poor fuel economy, because your making more power and use fuel more efficently.
Some engines don`t like 14.7 afr. Your cold start is really lean, you should fix that.
Get a wideband. If you want to dial the engine you definitely need one.

It will be great if you post your current bin.

Download and use much better program for logging like EEhack.
It also will give you some live tuning options.
Here's the BIN. This cam was spec'd by Lloyd Elliot and Karl Ellwein, and it is a fairly common cam in 383's (CC503) that's been tweaked just a touch. I've got Moe working now on a re-tune, but I am curious what the community's thoughts are.

[Fast355]

I think the cam is too small for that kind of compression and fuel with 93 octane is not enough.
You may try open loop with different afr. Runing richer not always mean poor fuel economy, because your making more power and use fuel more efficently.
Some engines don`t like 14.7 afr. Your cold start is really lean, you should fix that.
Get a wideband. If you want to dial the engine you definitely need one.

It will be great if you post your current bin.


Download and use much better program for logging like EEhack.
It also will give you some live tuning options.

With an aluminum head reverse cooled LT1 that compression and cam will work just fine on 93. The iron head cars had 10.5:1 compression and a 191/196 @ .050 cam on a 111* LSA in stock form.