c4 tuning
Thread Starter
Instructor
Joined: Oct 2013
Posts: 121
Likes: 6
c4 tuning
As I become familiar with my 88 l98 auto...Ive concluded the following....at 1/8 tank it stumbles due to fuel slosh in the rank....it shifts gears around 2.4k rmps and has a long first gear.....running hot (180 to 200)is a normal phenomenon compared to other chevys.... the turn radius is very short makes for interesting maneuvers out of a parking lot....So heres my next question books seem to say tps says to be set at .54 to .56 I've read for performance .60 can be used any concensus? Timing wise books say 6 btdc pros and cons of increasing or lowering setting for fuel economy? Thanks
Melting Slicks
Joined: Jun 2013
Posts: 3,065
Likes: 39
As I become familiar with my 88 l98 auto...Ive concluded the following....at 1/8 tank it stumbles due to fuel slosh in the rank....it shifts gears around 2.4k rmps and has a long first gear.....running hot (180 to 200)is a normal phenomenon compared to other chevys.... the turn radius is very short makes for interesting maneuvers out of a parking lot....So heres my next question books seem to say tps says to be set at .54 to .56 I've read for performance .60 can be used any concensus? Timing wise books say 6 btdc pros and cons of increasing or lowering setting for fuel economy? Thanks
I would set it to 0.54 volts. I like that better than the others that I've tried because all they do is lead to other problems.
I would go as far as 10* base timing, but you may be able to sneak out to 12*. I'd watch your scan tool at 12* and watch for knock counts.
Advancing timing would probably increase your gas mileage, and it'll have a little more spunk and more throttle response. After you advance it you wont want to go back to 6*.
Le Mans Master
Joined: Mar 2004
Posts: 5,107
Likes: 171
From: Dublin CA
.54 volts for the TPS is standard. If your going to race the car, then push it up to .60. It will respond to the throttle a little faster.
I would stay with the 6 degrees for economy. It get the most performance out of the car then push it up toward the 10 degrees. My 85 liked 10 degrees for base timing.
Thread Starter
Instructor
Joined: Oct 2013
Posts: 121
Likes: 6
Okay so it seems for fuel economy I'm good at the stock settings of 6tdc initial timing. Increasing to .60 tps is good for response but how about mpg? Also my distributor is not square to the plenum sort of twisted to the right should it be straight in relation to the plenum at stock timing?
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
I ran my prior '88 frequently at the strip and got 30-31mph highway.
It had TPS advanced to ~.63Vdc at base idle (450rpm), base timing 8-10deg BTDC, 160 deg T-stat with TB coolant bypass.
Also, don't forget to toss that "frisbee" from the front of your WP pulley.
BTW, I usually arrived at the strip with 1/4-1/3 tank of fuel; on a "good night" I had to limp to the nearest service station as the fuel gauge was near the "2-bar" point...
It had TPS advanced to ~.63Vdc at base idle (450rpm), base timing 8-10deg BTDC, 160 deg T-stat with TB coolant bypass.
Also, don't forget to toss that "frisbee" from the front of your WP pulley.
BTW, I usually arrived at the strip with 1/4-1/3 tank of fuel; on a "good night" I had to limp to the nearest service station as the fuel gauge was near the "2-bar" point...
Drifting
Joined: May 2013
Posts: 1,736
Likes: 31
From: Reno Nevada
The TPS reacts similar to an accelerator pump on a carb. At .60 it will add just a little bit more fuel at tip in, so not really a mileage concern here. Timing should always be at 6 degrees, because in the timing tables it goes as high as 32 plus initial of 6 for 38. While 10 degrees initial you may think you're helping it, you are really going slower. Distributor orientation makes absolutely no difference if the vehicle can be timed other than presentation, or personal preference. It may key into the cam at any tooth as long as you're orientated the oil pump shaft appropriately. Feel free to move it anywhere you choose as long as initial timing is set correctly.
Thread Starter
Instructor
Joined: Oct 2013
Posts: 121
Likes: 6
The TPS reacts similar to an accelerator pump on a carb. At .60 it will add just a little bit more fuel at tip in, so not really a mileage concern here. Timing should always be at 6 degrees, because in the timing tables it goes as high as 32 plus initial of 6 for 38. While 10 degrees initial you may think you're helping it, you are really going slower. Distributor orientation makes absolutely no difference if the vehicle can be timed other than presentation, or personal preference. It may key into the cam at any tooth as long as you're orientated the oil pump shaft appropriately. Feel free to move it anywhere you choose as long as initial timing is set correctly.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
2027 Corvette vs The World: Every Model vs Closest Competitor
Joe Kucinski
10 Most Common Corvette Problems of the Last 20 Years!
Joe Kucinski
5 MOST and 5 LEAST Popular Corvette Model Years in History!
Joe Kucinski
2027 Corvette Buyer's Guide: Everything You Need to Know!
Joe Kucinski
10 Things C8 Corvette Owners Hate (But Won't Tell You)
Joe Kucinski
10 Best Corvettes Coming to Barrett-Jackson Palm Beach 2026!
Brett Foote
Every Corvette Grand Sport Explained! (C2, C4, C6, C7, & C8)
Joe Kucinski
Grand Sport & Grand Sport X Launch Alongside All-New 535hp LS6 V8!
Michael S. Palmer
5 Reasons Bad Drivers Crash & 5 Ways to Avoid a Costly Mistake!
Joe Kucinski
Melting Slicks
Joined: Nov 2013
Posts: 2,264
Likes: 3
From: Orchard Park NY
How do you up the TPS voltage??? Can a tuner shop do that when I get dyno tuned? It seems that my throttle can be a touch delayed or slow to react... a touch more than I'd expect on a tuned port fuel injected car.
Melting Slicks
Joined: Nov 2013
Posts: 2,264
Likes: 3
From: Orchard Park NY
Interesting. Would that cure the slightly delayed throttle response that I feel sometimes? Or do you think my throttle blades/intake are gummed up from sitting for a year w/ 1+yr old gas in it?
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
I think advancing the TPS base setting will help throttle response off idle.
Since our L98 uses port fuel injection the intake is "dry"; not likely old gas could effect the intake.
Since our L98 uses port fuel injection the intake is "dry"; not likely old gas could effect the intake.
Melting Slicks
Joined: Nov 2013
Posts: 2,264
Likes: 3
From: Orchard Park NY
Oh nice the off-idle response does seem crappy, but everywhere else it seems quite snappy. Especially high rpm.
You dont think that just sitting around could have gummed up the throttle blade or anything else?
You dont think that just sitting around could have gummed up the throttle blade or anything else?
Drifting
Joined: May 2013
Posts: 1,736
Likes: 31
From: Reno Nevada
Thread Starter
Instructor
Joined: Oct 2013
Posts: 121
Likes: 6
I purchased these during my rebuild. They did not come stock with the car but they were 22lbs advertised Bosch design II 4 hole multi spray yellow version. But if that is the case if it were 23 and running lean how would timing advance help and what would then be the appropriate setting?
Last edited by Supahone; Apr 27, 2014 at 09:04 PM.
Drifting
Joined: May 2013
Posts: 1,736
Likes: 31
From: Reno Nevada
If you have Bosch yellows 280-155-700 get a scanner and check your BLM counts. If you're running lean with counts well above 140 you're getting a lean bog at off idle, or tip in. I've helped a few lower the flowrate in their programming to 20 lbs and it eliminates this problem. if you have a tuner he can do it for you. Timing will not solve this, if in fact you're lean.
Thread Starter
Instructor
Joined: Oct 2013
Posts: 121
Likes: 6
If you have Bosch yellows 280-155-700 get a scanner and check your BLM counts. If you're running lean with counts well above 140 you're getting a lean bog at off idle, or tip in. I've helped a few lower the flowrate in their programming to 20 lbs and it eliminates this problem. if you have a tuner he can do it for you. Timing will not solve this, if in fact you're lean.
Last edited by Supahone; Apr 27, 2014 at 09:15 PM.
Drifting
Joined: May 2013
Posts: 1,736
Likes: 31
From: Reno Nevada
The ecm has the capability to add up to about 10% fuel in closed loop. If it runs good when warm, and you may only experience this when cold prior to closed loop. Without knowing what the blm counts are it is just a guess. Start with a scanner and check. With base timing set at 6 degrees the car should operate well.
Safety Car
Joined: Aug 2009
Posts: 3,745
Likes: 275
From: Melbourne, Victoria, Australia
Okay so it seems for fuel economy I'm good at the stock settings of 6tdc initial timing. Increasing to .60 tps is good for response but how about mpg? Also my distributor is not square to the plenum sort of twisted to the right should it be straight in relation to the plenum at stock timing?
I have never had any hesistation with 0.54 volts dc on the TPS, she is always ready to light the tires at the touch of the throttle even when she was stock standard.
Headers really wake the TPI engines up without sacrificing fuel economy, that is the way to go.
Last edited by gerardvg; Apr 28, 2014 at 07:32 PM.