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Mclaren924
Joined: 13 Oct 2021
Posts: 262
Location: Oceanside CA
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 Posted: Thu Nov 30, 2023 11:19 am Post subject: 1979 Sebring has poor acceleration |
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Just got car on road and registered and it has a hell of a time just getting out of its own way. I know it should be much faster than this, if there’s a small hill I’m capped at 60 if it can even keep a constant 60. On the highway it’s maxing out at 85 in 5th on flat. I reckon maybe fuel pressure isn’t adequate but I don’t see afr leaning out at all while nearing max speeds and it doesn’t break up at all. Just has no guts at all in 4th or 5th, 3rd is pretty bad too. First revs to red line pretty quick and second is seemingly also a little slow. I’m presuming either my timing isn’t right or I don’t have sufficient fuel, maybe I’m stupid and my throttle isn’t adjusted right. Just looking for ideas and possibilities while I brainstorm possible issues. Cheers all and happy holidays everyone
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1980 931 "Salt" Bucket wannabe racer (Dreaming)
1979 924 Sebring "Pepper" -Sold
1977 924 Slicktop "Pennie"-Most likely parts
1979 3/5 gt clone 924- Shop Test Car |
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safe
Joined: 18 Mar 2017
Posts: 698
Location: Sweden
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| Posted: Thu Nov 30, 2023 6:12 pm Post subject: |
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You have an wideband lambda? What does it say?
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/Magnus, Stockholm Sweden
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Porsche 924 -79 NA, EFI and Turbo.
Porsche 931 -79
Porsche 911 -77, 3.2 Targa
Porsche 911 -69, 3.6, Coupe |
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Mclaren924
Joined: 13 Oct 2021
Posts: 262
Location: Oceanside CA
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| Posted: Fri Dec 01, 2023 1:35 am Post subject: |
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| safe wrote: | | You have an wideband lambda? What does it say? |
It will ride around 12-12.4 constantly, under heavy load it will leave up to around 14 , I tried running it around 13 and 14 afr and none of which really seem to have made a difference. In 5th gear at 80 mph afr stays relatively unaffected even when it seems like it’s out of go, I would expect it to be breaking up or stuttering if lack of fuel but it just feels like thing has half the HP it’s supposed to. Compression numbers are good so it’s not that.
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1980 931 "Salt" Bucket wannabe racer (Dreaming)
1979 924 Sebring "Pepper" -Sold
1977 924 Slicktop "Pennie"-Most likely parts
1979 3/5 gt clone 924- Shop Test Car |
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safe
Joined: 18 Mar 2017
Posts: 698
Location: Sweden
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| Posted: Fri Dec 01, 2023 1:48 am Post subject: |
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| Mclaren924 wrote: | | safe wrote: | | You have an wideband lambda? What does it say? |
It will ride around 12-12.4 constantly, under heavy load it will leave up to around 14 , I tried running it around 13 and 14 afr and none of which really seem to have made a difference. In 5th gear at 80 mph afr stays relatively unaffected even when it seems like it’s out of go, I would expect it to be breaking up or stuttering if lack of fuel but it just feels like thing has half the HP it’s supposed to. Compression numbers are good so it’s not that. |
12-12.4 is quite rich on light load, while 14 is lean under heavy load. The reverse would be a lot better, I can understand that it feels gutless.
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/Magnus, Stockholm Sweden
=======================
Porsche 924 -79 NA, EFI and Turbo.
Porsche 931 -79
Porsche 911 -77, 3.2 Targa
Porsche 911 -69, 3.6, Coupe |
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Mclaren924
Joined: 13 Oct 2021
Posts: 262
Location: Oceanside CA
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| Posted: Fri Dec 01, 2023 3:22 am Post subject: |
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| safe wrote: | | Mclaren924 wrote: | | safe wrote: | | You have an wideband lambda? What does it say? |
It will ride around 12-12.4 constantly, under heavy load it will leave up to around 14 , I tried running it around 13 and 14 afr and none of which really seem to have made a difference. In 5th gear at 80 mph afr stays relatively unaffected even when it seems like it’s out of go, I would expect it to be breaking up or stuttering if lack of fuel but it just feels like thing has half the HP it’s supposed to. Compression numbers are good so it’s not that. |
12-12.4 is quite rich on light load, while 14 is lean under heavy load. The reverse would be a lot better, I can understand that it feels gutless. |
Hmmm, maybe I just need to tune my afr a little more. I had it idling around 14.5 first on my way out here (70 mile maiden voyage) and it would richen up to around 13.5 on full load. What would my ideals numbers be looking like at idle vs at 2500 rpm and at 5k rpm? She’s drivable in town but as soon as I get to 60 mph it’s like a damn brick wall. I will lean her out to around 14.7 afr at idle and see how she behaves.
_________________
1980 931 "Salt" Bucket wannabe racer (Dreaming)
1979 924 Sebring "Pepper" -Sold
1977 924 Slicktop "Pennie"-Most likely parts
1979 3/5 gt clone 924- Shop Test Car |
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Fifty50Plus
Joined: 28 Feb 2008
Posts: 1422
Location: Washington DC area
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| Posted: Fri Dec 01, 2023 5:06 am Post subject: |
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Check your timing. It may not be advancing enough. On my race car I start at 20 degrees with full advance to 41 at 6500 rpm. Street advance should be a bit lower.
_________________
1979 924 NA race car H-Prod SCCA
1982 924 NA race car - Sold
1981 924 Turbo sold
1982 924 Turbo sold
1972 911 E race car - traded for Cayenne Diesel
1975 914 1.8 Building for H-Prod SCCA |
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safe
Joined: 18 Mar 2017
Posts: 698
Location: Sweden
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| Posted: Fri Dec 01, 2023 5:22 am Post subject: |
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| Mclaren924 wrote: | | safe wrote: | | Mclaren924 wrote: | | safe wrote: | | You have an wideband lambda? What does it say? |
It will ride around 12-12.4 constantly, under heavy load it will leave up to around 14 , I tried running it around 13 and 14 afr and none of which really seem to have made a difference. In 5th gear at 80 mph afr stays relatively unaffected even when it seems like it’s out of go, I would expect it to be breaking up or stuttering if lack of fuel but it just feels like thing has half the HP it’s supposed to. Compression numbers are good so it’s not that. |
12-12.4 is quite rich on light load, while 14 is lean under heavy load. The reverse would be a lot better, I can understand that it feels gutless. |
Hmmm, maybe I just need to tune my afr a little more. I had it idling around 14.5 first on my way out here (70 mile maiden voyage) and it would richen up to around 13.5 on full load. What would my ideals numbers be looking like at idle vs at 2500 rpm and at 5k rpm? She’s drivable in town but as soon as I get to 60 mph it’s like a damn brick wall. I will lean her out to around 14.7 afr at idle and see how she behaves. |
Ideally 12.5 on full throttle (all rpms) is a good baseline, idle and very light throttle you would like to be near 14 - 14.7. Throttle positions in between, nearer 13 than 14.
If this is possible on k-jet, I don't know.
_________________
/Magnus, Stockholm Sweden
=======================
Porsche 924 -79 NA, EFI and Turbo.
Porsche 931 -79
Porsche 911 -77, 3.2 Targa
Porsche 911 -69, 3.6, Coupe |
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Cedric
Joined: 27 Aug 2004
Posts: 2805
Location: Sweden
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| Posted: Fri Dec 01, 2023 6:48 am Post subject: |
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| safe wrote: | | Mclaren924 wrote: | | safe wrote: | | Mclaren924 wrote: | | safe wrote: | | You have an wideband lambda? What does it say? |
It will ride around 12-12.4 constantly, under heavy load it will leave up to around 14 , I tried running it around 13 and 14 afr and none of which really seem to have made a difference. In 5th gear at 80 mph afr stays relatively unaffected even when it seems like it’s out of go, I would expect it to be breaking up or stuttering if lack of fuel but it just feels like thing has half the HP it’s supposed to. Compression numbers are good so it’s not that. |
12-12.4 is quite rich on light load, while 14 is lean under heavy load. The reverse would be a lot better, I can understand that it feels gutless. |
Hmmm, maybe I just need to tune my afr a little more. I had it idling around 14.5 first on my way out here (70 mile maiden voyage) and it would richen up to around 13.5 on full load. What would my ideals numbers be looking like at idle vs at 2500 rpm and at 5k rpm? She’s drivable in town but as soon as I get to 60 mph it’s like a damn brick wall. I will lean her out to around 14.7 afr at idle and see how she behaves. |
Ideally 12.5 on full throttle (all rpms) is a good baseline, idle and very light throttle you would like to be near 14 - 14.7. Throttle positions in between, nearer 13 than 14.
If this is possible on k-jet, I don't know. |
That's pretty much how a std kjet works, at least the euro ones ive mesured 
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1980 924 Turbo
www.instagram.com/garagecedric/ |
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Mclaren924
Joined: 13 Oct 2021
Posts: 262
Location: Oceanside CA
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| Posted: Fri Dec 01, 2023 9:57 am Post subject: |
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| Cedric wrote: | | safe wrote: | | Mclaren924 wrote: | | safe wrote: | | Mclaren924 wrote: | | safe wrote: | | You have an wideband lambda? What does it say? |
It will ride around 12-12.4 constantly, under heavy load it will leave up to around 14 , I tried running it around 13 and 14 afr and none of which really seem to have made a difference. In 5th gear at 80 mph afr stays relatively unaffected even when it seems like it’s out of go, I would expect it to be breaking up or stuttering if lack of fuel but it just feels like thing has half the HP it’s supposed to. Compression numbers are good so it’s not that. |
12-12.4 is quite rich on light load, while 14 is lean under heavy load. The reverse would be a lot better, I can understand that it feels gutless. |
Hmmm, maybe I just need to tune my afr a little more. I had it idling around 14.5 first on my way out here (70 mile maiden voyage) and it would richen up to around 13.5 on full load. What would my ideals numbers be looking like at idle vs at 2500 rpm and at 5k rpm? She’s drivable in town but as soon as I get to 60 mph it’s like a damn brick wall. I will lean her out to around 14.7 afr at idle and see how she behaves. |
Ideally 12.5 on full throttle (all rpms) is a good baseline, idle and very light throttle you would like to be near 14 - 14.7. Throttle positions in between, nearer 13 than 14.
If this is possible on k-jet, I don't know. |
That's pretty much how a std kjet works, at least the euro ones ive mesured |
Thanks for the info lads, she seems to be almost inconsistent at times. Sometimes Shes at 11.5 at wot or lower and other times 12.4 at wot. Going with that it noticeably has times or spots in power band where it is much happier going than in others. For instance, it is pretty slow in bottom of third but after 2500 or 3k rpm it really starts to take off. Same thing with 4th, it really likes to get going around 3k rpm in those gears. First and second seem pretty quick, fifth barely does 85 foot to the floor even with 12.3 afr. Giving her a break for now while I eat and then I think I'm going to recheck electrical timing and make sure it's set right. Am i correct in believing +3 is the timing for 79 US cars? Cheers guys
_________________
1980 931 "Salt" Bucket wannabe racer (Dreaming)
1979 924 Sebring "Pepper" -Sold
1977 924 Slicktop "Pennie"-Most likely parts
1979 3/5 gt clone 924- Shop Test Car |
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924RACR
Joined: 29 Jul 2001
Posts: 9064
Location: Royal Oak, MI, USA
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| Posted: Fri Dec 01, 2023 9:31 pm Post subject: |
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Per the manual, yes it says 3 degrees ATDC.
Yeah, my thought would be ignition timing being off... could definitely run more advance than that, I should think, as long as you're feeding it at least 87 octane...
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype |
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Mclaren924
Joined: 13 Oct 2021
Posts: 262
Location: Oceanside CA
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| Posted: Sat Dec 02, 2023 2:52 am Post subject: |
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I always give it 89 as the 87 out here in Cali tends to be more like 86 even if you're lucky. I played with distributor and only got it to be more responsive by moving off of the designated mark on the flywheel... I can feel it's happier and it seems to have most of whatever little nuts it had, but my brain is not happy about being off the timing mark. It doesn't make sense to me that the further I got away from the mark the better it ran and the closer I got the choppier and more mad it got. My guess is im currently around -5. Yes rpm was always +- 950 and the flywheel was indexed correctly. When set to the mark the car just feels like a dead fish no matter how I tune afr. I'm leaving it set here for now as it runs very smoothly and feels noticeably faster. MY top speed is probably 90 mph but im wondering if my tires being 225/60/15 could be messing with the speedo reading? Final thought is it seems like my cold start injector is either not working or if it is its god awful at cold starting my car lol. Have to floor the gas on cold start for it get going and then it starts up real cold and low rpm, eventually will work itself up to 950 in 5 min or so but car seems to do same thing with cold start plugged in or unplugged. It has fuel to the line but I will make sure the injector isn't stuck by putting in a bottle today. Cheers all
_________________
1980 931 "Salt" Bucket wannabe racer (Dreaming)
1979 924 Sebring "Pepper" -Sold
1977 924 Slicktop "Pennie"-Most likely parts
1979 3/5 gt clone 924- Shop Test Car |
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924RACR
Joined: 29 Jul 2001
Posts: 9064
Location: Royal Oak, MI, USA
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| Posted: Sat Dec 02, 2023 9:31 pm Post subject: |
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Welcome to the People's Republic of California, circa 1979, and the US in the depths of the gas crisis.
It wasn't tuned for performance, it was tuned for emissions.
Running with 93 octane (pump gas out here) and 9.5:1 compression we used to run 12 degrees advance at idle on the #77 racecar. Note that we ran mechanical advance only, no vacuum hookups.
Stock tunes suck, from that era. I drove a Martini a few weeks back, refreshed back to stock by my sponsor... and it was a slap back in the face just how slow it was. I've gotten used to at least the power of the ITB now Prod racecar for an NA... not to mention my Turbo...
Oh, as for the cold start - sounds more to me like maybe you want to be checking out the aux air valve? Dunno what level of cold you're getting in the morning, but it should be able to bump up the idle and help with the cold start... if you're having to hold your foot on the floor, makes me wonder if it isn't open at all...
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype |
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Cedric
Joined: 27 Aug 2004
Posts: 2805
Location: Sweden
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| Posted: Sun Dec 03, 2023 12:20 am Post subject: |
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There should be an acceleration curve in the owners manual, could be a good reference to see if the car is performing as it should.
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1980 924 Turbo
www.instagram.com/garagecedric/ |
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Mclaren924
Joined: 13 Oct 2021
Posts: 262
Location: Oceanside CA
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| Posted: Sun Dec 03, 2023 3:32 pm Post subject: |
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| 924RACR wrote: | Welcome to the People's Republic of California, circa 1979, and the US in the depths of the gas crisis.
It wasn't tuned for performance, it was tuned for emissions.
Running with 93 octane (pump gas out here) and 9.5:1 compression we used to run 12 degrees advance at idle on the #77 racecar. Note that we ran mechanical advance only, no vacuum hookups.
Stock tunes suck, from that era. I drove a Martini a few weeks back, refreshed back to stock by my sponsor... and it was a slap back in the face just how slow it was. I've gotten used to at least the power of the ITB now Prod racecar for an NA... not to mention my Turbo...
Oh, as for the cold start - sounds more to me like maybe you want to be checking out the aux air valve? Dunno what level of cold you're getting in the morning, but it should be able to bump up the idle and help with the cold start... if you're having to hold your foot on the floor, makes me wonder if it isn't open at all... |
Well today was good until it wasn't. Seems I have a habit of destroying distributor components. Rotor wasn't keyed in all the way and got off the spline and spun free. Car just quit on me in 3rd at 3000 rpm and then wouldn't idle at all and was leaning out to 24 at some points. Triple a got me home and I got it back up and running with an old dizzy cap and rotor I had laying around. I had a feeling the car was a gas crisis baby and it is ladled with smog components. Pulled off the one that helps clean up shifting related emissions which made it more responsive with rpm after shifting . Have got what I believe to be a squealing Ac belt to deal with tomorrow as well as a rattling exhaust, I think the cat is hitting the heat shield. Yeah I played with my aux air valve for a bit and even repinned it onto a new oem style connector because last one was only half way there. I belive it passed a bench test (If i performed it correctly) and it seemed plenty free to open and close with a small pick when I was messing with it. Even replaced it with another one and same result, it was getting 12v to connector as well. Side note is overall system volts when running, I top out at 13.4 v with a brand new alt and good battery when only car is running with no fans or lights. Feel it should be higher but would like to hear some averages.
[img]https://imgur.com/a/OvxcXfU[/img]
_________________
1980 931 "Salt" Bucket wannabe racer (Dreaming)
1979 924 Sebring "Pepper" -Sold
1977 924 Slicktop "Pennie"-Most likely parts
1979 3/5 gt clone 924- Shop Test Car |
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Mclaren924
Joined: 13 Oct 2021
Posts: 262
Location: Oceanside CA
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| Posted: Sun Dec 03, 2023 3:33 pm Post subject: |
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| Cedric wrote: | | There should be an acceleration curve in the owners manual, could be a good reference to see if the car is performing as it should. |
That'll be the first thing I do in the morning, thanks for a great idea Cedric
_________________
1980 931 "Salt" Bucket wannabe racer (Dreaming)
1979 924 Sebring "Pepper" -Sold
1977 924 Slicktop "Pennie"-Most likely parts
1979 3/5 gt clone 924- Shop Test Car |
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