Hey Hey, I don't know if this is a good sign or not but..... Tuning the Duke up after a long slumber and the porting job. Now, I have an inline fuel pressure gauge installed and a Holley Throttle Body with an adjustable fuel pressure regulator built into it. It appears that now I can dial it up to 15 PSI where as before turning up the pressure maxed 13 and not beyond. That suggests that maybe porting has allowed for more fuel to mix with the extra air coming in....! Again, I don't know if that's what it means for sure but it seems logical. It will be few weeks before I can take it for a spin to let you know.
------------------ 84 Duke, Holley TBI, Manual Trans 4.10, CompuCam, White
[This message has been edited by White 84 SE (edited 08-19-2014).]
Oh, sorry I did not get back in a timely manner. Results? Definite performance improvement. I would guess perhaps 15 Hp. Has it become a racer....no. Does it compare to new model 4 cylinder cars on the road? For the most part I would say yes but not to the performance geared cars. What are the differences? Well it does not resist bolting up to 4000 RPM. Before 0-60 was about 12 seconds and now more like 8 1/2. Clearer air passages and a stronger spark seem the main reasons. It also tends to run rich but not enough to cause drivability issues. Before, I was sort of embarrassed about the lacking performance and now I feel mostly satisfied. The concerns now seem to have shifted to appearance and rust elimination and also noise reduction. I say it was totally worth porting the Duke and getting a performance coil.
------------------ Good Thoughts, Good Words, Good Deeds
If you really went from 0-60 12 down to 8.5 seconds, you picked up a lot more than 15HP. 8.5 is getting in the ballpark of what a V6 will run, so you are near 140HP (if that 8.5 is accurate).
Hmm... well Ed, I have not tested it on a track and I doubt 130 HP. I estimate more like 110 HP. What do ya think maybe 10 secs at most? All I've done is implement the FS performance cam, the Holley Throttle body, ported the head and intake, performance coil. Since it's running rich I may try stacking TBI gaskets to make a spacer. That and add an aeration screen to improve air/fuel mix.
------------------ Good Thoughts, Good Words, Good Deeds
Hmm... well Ed, I have not tested it on a track and I doubt 130 HP. I estimate more like 110 HP. What do ya think maybe 10 secs at most? All I've done is implement the FS performance cam, the Holley Throttle body, ported the head and intake, performance coil. Since it's running rich I may try stacking TBI gaskets to make a spacer. That and add an aeration screen to improve air/fuel mix.
Interesting project and it appears that you got some good results. As for 1/4mile track testing, I would just be careful to keep the revs under 5K... Those rods (and the block) were not designed for higher RPM use.
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
Originally posted by Dennis LaGrua: Interesting project and it appears that you got some good results. As for 1/4mile track testing, I would just be careful to keep the revs under 5K... Those rods (and the block) were not designed for higher RPM use.
Point taken Dennis. It does seem the best performance is had at the 4000 RPM mark for the Duke and it might be easy to push 5000 without knowing it. Next I will likely open the valves to 1 5/8" and maybe even go 30* since the intake runner to chamber angle is so abrubt. This particular engine needs a larger bore and rings as it is getting a little blow by and the compression is low. I just want to say the Duke is not a total waste of time, theres lots of things to try on it.
------------------ Good Thoughts, Good Words, Good Deeds
Point taken Dennis. It does seem the best performance is had at the 4000 RPM mark for the Duke and it might be easy to push 5000 without knowing it. Next I will likely open the valves to 1 5/8" and maybe even go 30* since the intake runner to chamber angle is so abrupt. This particular engine needs a larger bore and rings as it is getting a little blow by and the compression is low. I just want to say the Duke is not a total waste of time, there's lots of things to try on it.
I am far from a Duke engine expert but from what I have read, the Duke block is a thin wall casting. I believe that those blocks can be bored a maximum of .020" oversize. They can use a performance cam and high compression small block pistons, but you can only go so far as the red line is low. . If you like working on the Duke engines for more power, and find it fun, that's great, but the point is that you reach a plateau rather quickly.
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
Let us know how it works, I hope it gives you a noticeable improvement. What year is your motor?
CsJag, yeah I have been running around town with a bit now and realize that this porting thing is the bomb for the Duke engine. Mine is an 84. There is no doubt that it has much more pick up and it sounds great too! The flow now lends itself to keeping the Duke in it's power band. It accelerates best from 3-4000 RPM and cruises at around 2.5.
Hey Kurt, you don't think that's ok? Honestly, I would have to enlarge the entire exhaust passage to open up any thing there. I could gasket match but why? I consider you to be a bit of an expert although Vizard suggested that really, the intake is where to concentrate your efforts.
KurtAXX, yeah I think now that gasket matching the exhaust and blending in will lend itself to better scavaging and likely a smoother sound so it will be worth doing.
Hmm... well Ed, I have not tested it on a track and I doubt 130 HP. I estimate more like 110 HP. What do ya think maybe 10 secs at most? All I've done is implement the FS performance cam, the Holley Throttle body, ported the head and intake, performance coil. Since it's running rich I may try stacking TBI gaskets to make a spacer. That and add an aeration screen to improve air/fuel mix.
What are you using to determine the air/fuel mixture? A wide-band O2 sensor will tell you what it is so you can adjust your fuel line pressure as needed to get things in the right range. Stacking TBI gaskets won't do what you want.
I port heads for a living and the typical GM swirl ports take a lot of porting to flow well. Much better to go to a non-swirl head and clean that up if you want power. The porting you've done probably improved air flow about 5-7% over stock.
What are you using to determine the air/fuel mixture? A wide-band O2 sensor will tell you what it is so you can adjust your fuel line pressure as needed to get things in the right range. Stacking TBI gaskets won't do what you want.
I port heads for a living and the typical GM swirl ports take a lot of porting to flow well. Much better to go to a non-swirl head and clean that up if you want power. The porting you've done probably improved air flow about 5-7% over stock.
Hey thanks Mender, how would one use a wide band O2 sensor? The ECM might not be able to utilize it. I would guess that a wide band could be used to diagnose only? The rich condition is intermittent at idle only. I am now sporting a 1/8" hole in the throttle plate to lean out mixture at idle and may try 3/16" next.
Oh, to answer your question about measuring air fuel mixture. Well, I am relying on the ECM. It tells me that I am running rich and I notice the light only goes on when at idle. So it seems that the ECM is already diagnosing. Would a wide band sensor enable the ECM to compensate for a wider range? That would be a cool mod.
The stock Fiero ECM isn't compatible with a wideband O2 sensor. However, there are a few aftermarket ECMs that are, if you have a few hundred bucks to spare.
The alternative would be to install a wideband O2 sensor as a second sensor, connected to a laptop computer, so you can log data and use that to tweak your ECMs programming.
Oh, to answer your question about measuring air fuel mixture. Well, I am relying on the ECM. It tells me that I am running rich and I notice the light only goes on when at idle. So it seems that the ECM is already diagnosing. Would a wide band sensor enable the ECM to compensate for a wider range? That would be a cool mod.
I use an LM-1 wide band sensor for tuning, measures air/fuel ratio and can supply the narrow band signal that the ECU uses. Your ECU and narrow band oxygen sensor only read the exhaust gases in closed loop mode, ie, fully warmed up and moderate throttle. At full throttle the ECU reverts to a fuel map for injector pulse width info, so changing the delivered fuel pressure changes the mixture independent of the ECU.
So the answer is no, the ECU can't use the wide band; you have to tune it manually via the adjustable fuel pressure regulator as Blacktree said. To keep your engine safe, set your fuel pressure to get about 12.5:1 at full throttle and let the ECU take care of the light throttle settings. You'll probably find that your fuel pressure needs to be pretty close to the stock settings, maybe even a little less as the factory is usually a little rich already.
[This message has been edited by mender (edited 05-20-2016).]
Originally posted by White84SE: The rich condition is intermittent at idle only. I am now sporting a 1/8" hole in the throttle plate to lean out mixture at idle and may try 3/16" next.
Drilling a hole in the throttle plate does the same thing as opening the plate slightly or having the Idle Air Control motor open a bit; introduces more air but doesn't change the mixture.
The wide band sensor is the best way to know exactly what is going on.
...you have to tune it manually via the adjustable fuel pressure regulator as Blacktree said.
Just to clarify, I didn't suggest "tuning" via an adjustable fuel pressure regulator. That's a really kludgy way to tune an engine. IMO, the only purpose for an adjustable fuel pressure regulator is to get the injector flow rate high enough to supply enough fuel at high load / high RPM. All the rest of the tuning should be done via the ECM.
Once you get enough fuel pressure to keep the engine happy at high RPM / high load, I think you'll find it runs too rich in the low load / light throttle areas, and will run too rich when cold. That will need to be adjusted in the ECM programming. Otherwise, the engine will run crappy when cold, will have poor fuel economy, and may reduce the life of the catalyst.
I am pretty sure the hole in the throttle plate allows more air in at idle while the throttle position sensor reports throttle position as maximum closed. I shall JB Weld the Throttle Hole to see if it solves the rich at idle issue although so far it seems to have reduced the number of occasions it has occured. I did remove the diverter plate that is in the mouth of the intake manifold. It may function to keep the floor dry and divert fuel from the center pistons. It seems likely this may cause a subtle rich issueI- will put that back as well.
Yeah, I found out I had a TPS issue. Opened the hole again and it helps with rich idle. I will try enlarging the hole a bit now. This Duke performs better than ever. Switched the EFI to the standard some time ago. I bet with the porting that the 2" Holley EFI will work better. Will get the rebuild kit and put it back on and report back.
