Exidous

iTrader: (11)

I have been running the car with the setup in my sig for about the last 1.5 years and I have finally decided to try and do something about the squishy pedal feeling. I am still running a MAF so that is my first step. I am pretty sure the reason is the runner size of the PRC 5.3L's costing me velocity but I do not know for sure. The car is fine above 3.3-4K but in the 1.5-2.8K range the car just feels soggy. The AFR's are all dialed in and the timing is pretty good. Also, my highway MPG dropped about 6-7 mpg over a stock motor with LS6 intake and the exhaust below. Intake restriction does not exist. I get 99 kPa on the MAP at 6k RPM on the dyno and 101kPa on the freeway.

Static compression I believe is around 10.8-9 and dynamic is around 7.8. The head gasket is a .051" MLS and the heads are not milled.

I do have a fairly restrictive exhaust at the moment. 1 3/4 JRT LT's, 3" collectors immediately reduced to 2.5" into dual 2.5" high flow metallic cat's into a dual 2.5" to 3" merge. After that it is a 3" RX-7 catback from racing beat. The muffler is a straight through setup like a magna flow.

I have been considering going to a 383 to help increase the port velocity and redoing the exhaust. Just looking for some inputs.

Patrick

Sales4@Texas-Speed

iTrader: (4)

We try to keep the runner as small as possible on the 5.3l heads to keep port velocity up. It should have a 220cc runner. If you want more throttle response either smaller runner or more compression are the ways to go in my opinion. The 383 would also help with this because the extra stroke will help pick up more low end power.

Exidous

iTrader: (11)

Thats about what I figured. I wasn't trying to knock the heads at all nor did you imply I was. I would simply like to pick up the throttle response. I'd like to get the dynamic compression up as it seems quite a few folks say it helps a bit with the throttle response.

What do you think killed my MPG? The exhaust and bottom end are the same. The entire top end was replaced and you can see my narrow band O2's switching at cruise so I'm sitting dead on 14.7. Plus my wideband confirms this.

PREDATOR-Z

You answered you own question.
Also, you cam and put higher flowing heads on and you expect mpg to increase (or remain the same for that matter)? You wanted more power, that translates into more fuel consumption. It is really simple physics. You increased overlap which means unburned fuel and reduced engine efficiency (especially at lower speeds).
Logic please....

intenseblue

iTrader: (1)

I calculated a 8.4-8.6 DCR basing the intake centerline at a 108-112.

Exidous

iTrader: (11)

I suppose I thought that based on what other folks had been saying about their mods. I understand that the extra power means extra fuel consumption but in the cruising range the car feels like it has less power. :-) The LSA is 114 FYI.

Predator

Not sure what a "squishy" pedal feeling is but I do know that these engines have to be revved up before the power kicks in, even with a TR224/224 112 cam and 4.11s.

I ran an entire tank of gas around town and got 11 mpg.

Exidous

iTrader: (11)

Squishy refers to throttle response and engine power. I just miss the really low end torque the motor had when it was stock internally. As an example: in a tight turn in second gear at about 2k rpm I used to be able to break the rear out. Now that the motor is modded I can no longer do this. Keep in mind I am ONLY talking about low RPM's. Up top it runs like a champ.

Predator

Your experience doesn't match mine. When my car was stock it didn't have more low end torque than it has now, even before I installed the 12-bolt with 4.11s. Maybe you might want to look at your tune, log some scans, etc. Your cam isn't much "bigger" than mine, the results should be similar.

I'd take a good hard look at your VE table, especially at lower rpms. The MAF and VE tables are referenced during part throttle.

Exidous

iTrader: (11)

I know my OLFA table is the reason for my studdering when cold and at light throttle but that's another issue. My LTFT's and STFT's are usually off by 1% max warmed up during cruising so I don't think they are too far off but I'll take another look. My transients could definitely be off.

crazyelf

iTrader: (21)

Me and my friends have found some good entertainment in this thread.

Exidous

iTrader: (11)

At who's expense? :-)