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LS1 cam, LT4 cam, vortec 350?

This is a discussion on LS1 cam, LT4 cam, vortec 350? within the Performance forums, part of the General Discussion category; Disappointed doesn't even begin to cover it... Don't waste your time and money. Lower mpg than I had last year ...

  1. #21
    Registered User skylark's Avatar
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    Re: LS1 cam, LT4 cam, vortec 350?


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    Disappointed doesn't even begin to cover it... Don't waste your time and money. Lower mpg than I had last year when it was stock (16-17). The best tank was 15.9. Power is lame. F this GEN 1 crap!!!
    89 GMC Stepside 2WD 4/6 drop, working on the stroker again!!!
    Y2K Chevy K3500 CCLB Dually 6.5, the Black Pearl.

  2. #22
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    Re: LS1 cam, LT4 cam, vortec 350?

    Quote Originally Posted by skylark View Post
    Disappointed doesn't even begin to cover it... Don't waste your time and money. Lower mpg than I had last year when it was stock (16-17). The best tank was 15.9. Power is lame. F this GEN 1 crap!!!
    I would double check the simple stuff. Something is not right. I had the LT4 production cam, installed straight up in 3 different engines and LOVED it in all 3. Great fuel mileage and plenty of HP/TQ over stock. I am having a hard time believing you are only getting 16-17 MPG stock.

    Before giving up on it, I would pull the timing cover and install/degree the cam straight up. Many chain sets have built-in advance anyway to compensate for chain stretch.

    I know you are just relaying your experience, but the LT4 cam and 1.6:1 rockers should have given you a very solid, noticable 20-30 HP (depending on the rest of your setup).

    EDIT...Forgot to mention had a sharp mileage drop-off and a tip-in hesitation start about 6 months ago on the Express. The city mileage went to hell and the highway mileage was down too. When you cracked the throttle in-town it would fall on its face, felt very lean. On the highway at highway speeds when you opened the throttle it still felt sick. Cold startups we often very difficult with random stalling immediately after. After checking the fuel pressure, reading everything with a scanner, I noticed that the EGR commanded % and actual % where nowhere close to matching up. So I removed the valve and found that the pintle was binding. The system never set a trouble code, but I replaced the valve and it was back to its normal 14-15 in-town and 19+ mpg highway. So don't overlook the small things.
    Last edited by Fast305; 09-08-2011 at 12:49 PM.
    1997 G1500 Cobra Conversion, 5.7, 4L80E, 3.73 14-bolt 9.5", L31 Marine Intake, CFM TB, 02 MAF, 0411, Custom cam. Doug Thorley Tri-Ys, full exhaust soon.

  3. #23
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    Re: LS1 cam, LT4 cam, vortec 350?

    It's probably not tuned.
    Quote Originally Posted by Quyonmob View Post
    Straight pipes are for peckerheads. . .
    '98 K1500 ECSB 5.7, 4L80E, 14BSF, 4.10/G80, 7,200# GVW springs, 8600# GVW calipers/pads, EFI Live, TB mod, UDs, block, crank, 285s, and a lot of stuff on the shelf.

  4. #24
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    Re: LS1 cam, LT4 cam, vortec 350?

    Even un-tuned on two different setups the LT4 cam still ran nice for me. L31s are terrible about having a couple small issues that the PCM never detects. One being a leaking fuel pressure regulator, a second being a malfunctioning egr, and yet a 3rd being sticking/dirty poppets.
    1997 G1500 Cobra Conversion, 5.7, 4L80E, 3.73 14-bolt 9.5", L31 Marine Intake, CFM TB, 02 MAF, 0411, Custom cam. Doug Thorley Tri-Ys, full exhaust soon.

  5. #25
    Registered User Jameslleary's Avatar
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    Re: LS1 cam, LT4 cam, vortec 350?

    Hey Fast, The MAF system on a 411 pcm should be able to adjust for an LT4 cam right? How long should it take? Maybe he hasn`t driven it enough?
    Last edited by Jameslleary; 09-08-2011 at 01:30 PM.
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  6. #26
    just the tip.
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    Re: LS1 cam, LT4 cam, vortec 350?

    lt4 cam worked great for me also, have only ran it with carb and single plane. just swapped new heads and set it back up for tbi- ebl flash should be here tomorrow i think. gotta swap in the vortec fuel pump and get to tuning it
    truckless

  7. #27
    Registered User skylark's Avatar
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    Re: LS1 cam, LT4 cam, vortec 350?

    Quote Originally Posted by speedracer326 View Post
    It's probably not tuned.
    Blackbear...

    Fast, I will look at the EGR command vs. actual on my scanner tomorrow. The poppets are gone and the mpfi conversion that I installed 2500 miles ago had a new regulator and it holds fuel pressure great when the key is turned off.
    89 GMC Stepside 2WD 4/6 drop, working on the stroker again!!!
    Y2K Chevy K3500 CCLB Dually 6.5, the Black Pearl.

  8. #28
    Registered User skylark's Avatar
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    Re: LS1 cam, LT4 cam, vortec 350?

    Quote Originally Posted by speedracer326 View Post
    It's probably not tuned.
    Blackbear...

    Fast, I will look at the EGR command vs. actual on my scanner tomorrow. The poppets are gone and the mpfi conversion that I installed 2500 miles ago had a new regulator and it holds fuel pressure great when the key is turned off.
    89 GMC Stepside 2WD 4/6 drop, working on the stroker again!!!
    Y2K Chevy K3500 CCLB Dually 6.5, the Black Pearl.

  9. #29
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    Re: LS1 cam, LT4 cam, vortec 350?

    Quote Originally Posted by skylark View Post
    Blackbear...

    Fast, I will look at the EGR command vs. actual on my scanner tomorrow. The poppets are gone and the mpfi conversion that I installed 2500 miles ago had a new regulator and it holds fuel pressure great when the key is turned off.
    You might check the pressure of the MPFI conversion. Mine was set insanely high on the one I bought back in 2006 when I put the engine in the Express. I lowered it back to the 58 PSI that it should have been.
    1997 G1500 Cobra Conversion, 5.7, 4L80E, 3.73 14-bolt 9.5", L31 Marine Intake, CFM TB, 02 MAF, 0411, Custom cam. Doug Thorley Tri-Ys, full exhaust soon.

  10. #30
    Registered User skylark's Avatar
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    Re: LS1 cam, LT4 cam, vortec 350?

    EGR was within 1% under all circumstances and at 0% on decel and at idle. I checked the fuel pressure with an old truck tire pressure gauge (I'm in Darien, IL currently and it's all I have) and it was at 53psi at idle. I guess I'm stuck until I get back to Oregon... The mpg I'm comparing this trip to was the trip immediately after we bought it in July of 2010 when we went to the mexican border of CA.
    89 GMC Stepside 2WD 4/6 drop, working on the stroker again!!!
    Y2K Chevy K3500 CCLB Dually 6.5, the Black Pearl.

  11. #31
    Registered User skylark's Avatar
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    Re: LS1 cam, LT4 cam, vortec 350?

    Ok I'm finally back home. Fuel pressure is at 59 at idle, 60 koeo, increases with a drop in vacuum and is at 85 deadhead. No fuel pressure problems. I'm not a happy camper. There is more power in the 2500 and up range but under that I think it is lower. I wouldn't care if I was getting good MPG.
    89 GMC Stepside 2WD 4/6 drop, working on the stroker again!!!
    Y2K Chevy K3500 CCLB Dually 6.5, the Black Pearl.

  12. #32
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    Re: LS1 cam, LT4 cam, vortec 350?

    Quote Originally Posted by skylark View Post
    Ok I'm finally back home. Fuel pressure is at 59 at idle, 60 koeo, increases with a drop in vacuum and is at 85 deadhead. No fuel pressure problems. I'm not a happy camper. There is more power in the 2500 and up range but under that I think it is lower. I wouldn't care if I was getting good MPG.
    Houston, I think we have found some of your mpg problem.....Fuel pressure should drop as vacuum is applied to the regulator with the engine running. You should see 58-60 psi with the key on engine off and at idle you should see approximately 1 psi fuel pressure drop for every 2 in/hg of intake vacuum you have. My LT4 cam idled at about 20 in/hg vacuum, idle fuel pressure should register ~50 psi.

    I am also wondering how much you shot yourself in the foot by advancing the camshaft. The cam really doesn't have much overlap and already has an early intake closing, so advancing it is not really necessary and may actually have done more harm than helped. The LT4 cam is already ground advanced on a 115* LSA and if memory serves me correctly an ICL of about 116*. The lobe design however created a certain amount of internal self EGR within the engine, eliminating the EGR valve on the LT4. EGR helps highway fuel mileage by helping eliminate pumping loss within the engine.
    Last edited by Fast305; 09-20-2011 at 12:21 PM.
    1997 G1500 Cobra Conversion, 5.7, 4L80E, 3.73 14-bolt 9.5", L31 Marine Intake, CFM TB, 02 MAF, 0411, Custom cam. Doug Thorley Tri-Ys, full exhaust soon.

  13. #33
    Registered User skylark's Avatar
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    Re: LS1 cam, LT4 cam, vortec 350?

    Well, I tried the advanced with the results above and last night I pulled the pump and timing cover and put it straight up. I did notice a minor loss on the bottom but it is minor at best. What should the map sensor read (kpa) for hot idle in park? I searched and it said this "Sorry - no matches. Please try some different terms.". I thought that with a vacuum referenced fpr that the pressure increases as hg decreases.
    89 GMC Stepside 2WD 4/6 drop, working on the stroker again!!!
    Y2K Chevy K3500 CCLB Dually 6.5, the Black Pearl.

  14. #34
    Registered User 96ImpSS's Avatar
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    Re: LS1 cam, LT4 cam, vortec 350?

    skylark, I just read through this thread and spotted a fallacy in one of your earlier posts. going with the LT4 cam in hopes of better mileage because of its wider lobe separation is not going to pan out. If you look closer at the cam profiles of the LT4 and L31 cams, you'll find the overlap is almost identical. The added duration is on the exhaust opening and intake closing sides of the LT4 lobes, thus the resulting 115 lobe sep. Also, advancing it 4 degrees is giving up cylinder pressure toward the end of the power stroke where you need it most for mpg at low revs. I'm sure you'll tune it and get some good results, but there was more to be had in mpg by sticking with the L31 cam.
    '98 XCSB, ZZ4 cam, Tri-Y's, Yank SS3600 TC
    PCMFORLESS.COM 87 octane tune
    14.30 @ 92.2 on motor
    13.47 @ 99.2 w/ a 50 dry shot

    '96 ImpalaSS
    10.98 @ 122 NA, 10.35 @ 128 on a 100 shot
    stock bottom LT1

  15. #35
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    Re: LS1 cam, LT4 cam, vortec 350?

    If advancing it gives better low end torque, how is it giving up mpg at lower RPM?
    Quote Originally Posted by Quyonmob View Post
    Straight pipes are for peckerheads. . .
    '98 K1500 ECSB 5.7, 4L80E, 14BSF, 4.10/G80, 7,200# GVW springs, 8600# GVW calipers/pads, EFI Live, TB mod, UDs, block, crank, 285s, and a lot of stuff on the shelf.

  16. #36
    Registered User 96ImpSS's Avatar
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    Re: LS1 cam, LT4 cam, vortec 350?

    Quote Originally Posted by speedracer326 View Post
    If advancing it gives better low end torque, how is it giving up mpg at lower RPM?
    By advancing the LT4 cam, he's back to near the same IVC as the L31 cam. But he's dumping cylinder pressure earlier on the power stroke, BOTH from the ground-in EVO of the LT4 cam AND by the additional advance. This EVO event is a move in the wrong direction for low rpm torque.

  17. #37
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    Re: LS1 cam, LT4 cam, vortec 350?

    To change one you affect the other. . . doesn't the intake have the more substantial impact? Not trying to argue by any means, just seeking enlightenment.
    Quote Originally Posted by Quyonmob View Post
    Straight pipes are for peckerheads. . .
    '98 K1500 ECSB 5.7, 4L80E, 14BSF, 4.10/G80, 7,200# GVW springs, 8600# GVW calipers/pads, EFI Live, TB mod, UDs, block, crank, 285s, and a lot of stuff on the shelf.

  18. #38
    Registered User 96ImpSS's Avatar
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    Re: LS1 cam, LT4 cam, vortec 350?

    Quote Originally Posted by speedracer326 View Post
    To change one you affect the other. . . doesn't the intake have the more substantial impact? Not trying to argue by any means, just seeking enlightenment.
    Yes, one affects the other.
    And I missed some of the posts earlier when I was skimming through the thread. Fast305 is reinforcing what I expected: "I am also wondering how much you shot yourself in the foot by advancing the camshaft. The cam really doesn't have much overlap and already has an early intake closing, so advancing it is not really necessary and may actually have done more harm than helped."
    Fast 305 doesn't touch on the early EVO, which I think is where most of the mpg loss comes from. I agree that since the LT4 cam is in there, it would be better installed straight up.
    '98 XCSB, ZZ4 cam, Tri-Y's, Yank SS3600 TC
    PCMFORLESS.COM 87 octane tune
    14.30 @ 92.2 on motor
    13.47 @ 99.2 w/ a 50 dry shot

    '96 ImpalaSS
    10.98 @ 122 NA, 10.35 @ 128 on a 100 shot
    stock bottom LT1

  19. #39
    Large Marge sent me SUBURBIAN's Avatar
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    Re: LS1 cam, LT4 cam, vortec 350?

    I don't even remember if it was mentioned... was the cam degreed in? Unless the OP knows exactly where it is, the thing could be even more advanced than 4...choking it out even more.

  20. #40
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    Re: LS1 cam, LT4 cam, vortec 350?

    Quote Originally Posted by SUBURBIAN View Post
    I don't even remember if it was mentioned... was the cam degreed in? Unless the OP knows exactly where it is, the thing could be even more advanced than 4...choking it out even more.
    X2.

    I installed the hot cam straight up and when I degreed it,the cam was actually 6* advanced. I ended up having to install the cam retarded to bring it closer to being "straight up".
    You have no way of knowing without degreeing the cam.
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