Hello all,

The carb conversion on my 2.8 (2.9) has been a long journey with lots of mistakes and miscalculations. It isn't quite finished yet, which I will explain as we go.

I took the car to Chandler Technologies here in London http://www.chandlertechnologies.com/ for a long overdue Dyno.

What we found is that the carb settings for the 3.4 carbed cars is wrong for the 2.8.....go fig eh?

Within a couple of hours in the dyno shop, the experts there were able to determine exactly what the car needed. Currently as you will see in the dyno graph, the car is still not quite there. The accellerator pump nozzle (shooter) is still too big causing a little bobble and dip in both the torque curve and the hp curve and especially the fuel air mixture. I am waiting on a .021 nozzle coming in, to install.

The reason, so far as I can tell, that the engine is still lazier than it should be, is that I very likely have the valves too tight. It can't make its revs quick enough with the valves too tight. That will be the next big item, to reset the valves with the engine running. For an engine it is a little like one size too small underwear when you are trying to high jump.

Here is the dyno result in simple form



Here is the running gear that was dyno'd.

2.9 liters
ported heads
re-cut valve seats
roller-tipped 1.6 rockers
Edelbrock Torker II intake
Holley 390 carb
Blazer distributor set to open vacuum
ported exhaust manifolds into 2.5" mandrell bent
Magnaflow muffler
MDS coil
Power Pulley
11* initial advance with 36* overall advance

The carb specs used successfully for the 3.4 were just not good for the 2.8. The car had a rich bog off idle and went richer as soon as the secondaries kicked in. This created poor performance.

Here is what was dyno'd and proved best on the dyno with the 2.8, before switching out the shooter (it will be changed to .021 shooter with 17 cc cam)

.025 shooter with 19 cc cam
4150 secondaries conversion kit with .052 jets on the secondaries (stock is a .056 metering plate)
.512 primary jets (standard .51's are actually .50)
purple secondary vacuum advance spring
check ball in vacuum removed to open secondaries quicker

Here is something really important.

The car did a rolling start at 1500 rpm and was measured in 3rd gear. The ACTUAL RPM was 1200 on the dyno.

The engine was revved to 6,000 rpm on the tach, but was ACTUALLY 5200 rpm on the dyno. Lesson learned, you can't trust your tach on a 20 year old car. It could be majorly out.

We got a 163 peak torque and 132.6 peak hp at the wheels. Not bad, but open to improvement

As I mentioned, the car is reving too slow and this is directly affecting the power curve. It just wasn't getting enough power either from launch, or down the line. So, I will be re-setting the valves and working to fix this problem.

For anybody contemplating a carb conversion for the 2.8, this carb is now very smooth,and very well behaved. It is very handy if you have a carb expert in town and a dyno, which I did not have for quite a while, but these setting will get you a nicely performing carb'd 2.8.

John and the guys at Chandler Technologies were absolutely great. I am hoping we can do a dyno day for SOFA this season in London.

He plans to be at our 12 August Great Lakes Fiero Show, and you can tap his brain that day.
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[This message has been edited by Arns85GT (edited 06-24-2006).]

Just curious, how much did this cost?

I would love to have someone dyno tune my Fiero.

Glad to see another piece of the puzzle coming together for you Arn.

David

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His Fiero: 1984 2M4 Coupe

Her Fiero: 1984 2M4 Convertible

The local dyno shop charges $60 cdn for 3 pulls or $100 per hour. I went hourly because that gave their techs some time to analyse my engine and give me advice.

Arn

Well more experimenting and more results measured at the wheel.

We found the car was bogging badly with #25 shooter and I changed the #25 to a #21 with the white cam on #1 (17cc's)

Here is the result using the #52 secondary jets and #512 primary jets

Notice the glitch on the chart which was due to some transient vibration. Edit - Turns out the glitch was likely a sticking brake caliper which unstuck mid run. That would account for the lower hp curve below 4000 from my first run.



The biggest change was the feeding in the gear ratio into the program. This gave us a much more accurate read.

You will see the hp curve is almost flat from 4500 rpm to 5800 rpm, and the torque curve while a little lower peak, remains relatively flat right out to 5000 rpm. Also, the hp gain is even with no bog.

There is still a problem with the shooter which I have to reduce a little. Also, the primary jetting needs to be leaned out. What seems to be happening is the shooter is too strong and the primaries are therefore also too strong. The car seems to like running a little lean. The rule of thumb is that 12.5 is a good air/fuel ratio, however, the car seems to be better at about 13. My secondaries are likely coming in a bit too early.

What the guys told me is that the car should be around 20% line loss which puts the engine at about 157 hp. If you look at the torque which shows max 152.3 ft/lbs and apply the 20% you get 182.76 ft/lbs.

Here is something worth thinking about. When the stock compression is compared to the hp with 10.5 compression, they calculated the car would be at about 177 hp. vs. the current 157 hp. Lesson learned for me is that if you are working on the 2.8 engine for power purposes, you want to install higher compression pistons.

My current project is to strategize about how to reduce my shooter a little more and get my primaries just a little leaner. I think I'll try the regular #51's which actually meter out at 50. I think I'll try hole #3 hole on the white cam which will lengthen out the shot and bring it on more gradually.

I hope this helps somebody.

Arn

Edit - I changed my tach filter for the Fiero Store tach filter and my tach is now within 200 rpm of the dyno

[This message has been edited by Arns85GT (edited 07-25-2006).]

Hi Arn,
I am thinking of a carb'd 3.4 for my '86 SE. I'm in Collector Car class now so I'm out of the inspection / emissions test routine. I see you mention settings for the 3.4 in your first thread. Can you point me towards a thread for the 3.4 that has this info? If my current 2.8 didn't have so many miles on it, I think I might replicate your 2.8 effort.
Thanks,
Mark

Oreif, Stratohacker, and Ditch are good resources with Oreif being the name to search.

As I recall, he was using #49 main jets, standard secondary plate (#56) and a yellow secondaries spring.

The 2.8 is lighter in application.

I am still working on my setup.

One thing that is a real problem is the accellerator pump circuit. It is just too fat for the size of the engine. I have found a supplier for smaller shooters. He supplies them for 4 cylinder racing cars. I have ordered a custom #18 and a #14. This will push out less initial volume but extend it over a longer shot. My main jets will likely have to downsize. I will post what works. (I may end up with #49 or #50 jets, with #52 secondary jets, plain secondary spring, white cam on #1 hole, and the #18 shooter.)

If you are interested in the contact info for the custom shooters you can PM me. I don't want to post his phone on the web without his permission.

Arn

Arn,
Holley info says you need to find the smallest shooter size till the crispest response is found.
However decreasing shooter size will only lengthen your shot and not affect total volume.
About cam positions:
One=longer shot
Two=more initial volume with lesser total volume
Other thing that affects total volume is the cam (assuming you remain under the max capacityof the diaphragm)
Can you tell me what color cam provides how much cc's (in either position 1 or 2)?
thanks!

In the case of the White 218 cam, #1 delivers at the rate of 17cc while #2 delivers at the rate of 19.5cc.

Orange 466 delivers 19cc @#1 but 24.5cc@#2.

Black 234 is the odd one. It delivers 19cc@#1 and 18cc@#2. (#2 is longer duration but less volume) Also Red 240 has shorter duration on #2 but more volume.

If you look at the cam mechanism, #2 normally gives both more lift and more duration. There are 8 cams to chose from.

You are right about using the smallest shooter. The problem with the 2.8 is that Holley doesn't produce a small enough shooter.

The smaller the shooter, the longer the shot because you are squeezing the same amount of fuel through a smaller hole.

My shooter presently lasts almost 800 rpm under full throttle. If I go to a smaller size it may stretch out to 1200 rpm duration. That will impact my jet action. I'll have to reduce primary jetting or end up too rich still.

What I really need is a smaller cam, but I haven't been able to find one. I have 2 custom shooters on order, a #18 and a #14. I may well need to use the #14 and really cut back my primary jet size. Only time will tell.

A good read is "Holley Carburetors" by Dave Emanuel.

Arn

[This message has been edited by Arns85GT (edited 07-25-2006).]

quote Originally posted by MarkS: Hi Arn, I am thinking of a carb'd 3.4 for my '86 SE. I'm in Collector Car class now so I'm out of the inspection / emissions test routine. I see you mention settings for the 3.4 in your first thread. Can you point me towards a thread for the 3.4 that has this info? If my current 2.8 didn't have so many miles on it, I think I might replicate your 2.8 effort. Thanks, Mark

Here are a few to check out:
https://www.fiero.nl/forum/Archives/Archive-000002/HTML/20040710-1-037964.html
https://www.fiero.nl/forum/Archives/Archive-000002/HTML/20031229-1-033988.html
https://www.fiero.nl/forum/Archives/Archive-000001/HTML/20060206-2-067287.html
https://www.fiero.nl/forum/Archives/Archive-000001/HTML/20050119-2-056484.html
https://www.fiero.nl/forum/Forum2/HTML/070870.html

If you have any other questions, there are a few of us who (mentioned above) who can help you out.

And it would look like this in the car:



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Happiness isn't around the corner...
Happiness IS the corner.
ZZ4 Powered !!

[This message has been edited by Oreif (edited 07-25-2006).]

I spoke to Larry at Holley. Very helpful.

He sent me these charts. They seem to show that the black cam is the way to go for the 2.8. So I'll be trying the black cam with #18 shooter to see what happens.





Arn

Isn;t carbing fun?
just looked over the dyno numbers, and your primaries look too big, as you said, I think you'll likely end up with 48's. if it's too small, you can wire it out a half size, that's what I used to do, as those things get expensive after a while.
what rpm are your secondaries coming in at? 3000? the chart almost looks like 2500, but I think that is me misreading it.
I should just shut now, as I didn;t follow the build, so I don;t know what you did for exhaust work, and heads/valves etc.
one comment on the compression, watch the over 10 numbers, with the crap quality of gas lately, you can run into problems.
the 9.5:1's are happy at 87 tho...

Oreif, pretty motor. I wish I didn;t have smog nazi's here, I'm so limited...

I think I have it sorted. So here is close to the final, subject to a little tweeking.

2.9 liters
ported heads
re-cut valve seats
roller-tipped 1.6 rockers
Edelbrock Torker II intake
Holley 390 carb
Blazer distributor set to open vacuum
ported exhaust manifolds into 2.5" mandrell bent
Magnaflow muffler
MDS coil
Power Pulley
11* initial advance with 36* overall advance
Black accellerator cam on #2 hole
#25 shooter
30cc Accellerator pump diaphram
#51 primaries (actually .50 thousanths)
#52 secondaries
Not sure about whether I'll end up on the purple or the plain secondaries spring.

When I deployed the black cam, my #21 shooter suddenly leaned out and the engine took its time catching on to the kick I gave the gas.

When I deployed the black cam with the #25 shooter, the car started laying rubber from standing start. Remarkable difference for a very small change.

I'm still experimenting with #2 and #1 holes on the cam, as I am with the secondaries spring. I'll take it out to the strip as soon as I can to see what it will do now.

Thanks for bearing with this rather long post. If you are building a carb'd 2.8 you'll want what this last post is telling you.

Arn

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I've been able to determine that the #21 shooter is too small, and the black cam on #2 is not quite enough to reduce the accellerator pump action to where the engine needs it. I am using the #25 shooter and #2 on the black cam and I have made it work.

Here is a trick that seems to work well. The adjuster screw on the accellerator pump lever needs to be loosened up. By tightening the nut down on the bolt, you can create slack in the lever action. This slack disappears as soon as you depress the accellerator even a little. Especially if you are launching from - say - 3500 rpm. By creating slack, you reduce the overall travel of the accellerator arm and therefore reduce the shot given. It is kind of a cheat, but, in the absence of a smaller cam, it does the job and you really don't see any delay once your foot is on the gas, and there is no delay or bog.

Here is the EDIT.

In consultation with Scotty McLendon, I found the final answer to the bog. It completely solves the problem and the car now has a whole lot of snap from any rpm. The answer is reducing the shot. I took the orange accellerator pump cam but the white cam will do about as well. With the carb off the car, you remove the screw holding the cam in place. You then pivot the cam on the armiture so the #1 hole on the bracket is between the two holes on the cam. You then mark the cam with a magic marker and remove it. You then drill a hole the same size as the other holes through the spot you've marked. You then install the cam using the new hole on the #1 screw hole.

You then have to adjust the accellerator pump arm. If it is the metal one, you bend the tab until the arm returns to zero setting. If you have the plastic arm, you tighten the adjuster screw until there is some slack (very little) between the accellerator pump arm and the pump lever.

You will then have immediate throttle response with an overall shot of about 1/3 to 1/2 of the original cam. In my case, the new hole was about 40% of the distance between the two original holes. My shot is therefore reduced from 19cc to around 12cc.

Believe me when I say that this fix changes the response of the engine very noticably.

The plain secondaries spring that came on the carb seems to work well.

I have put the primary jetting back up to #512 (a true 51 thousanths)

Arn

[This message has been edited by Arns85GT (edited 08-09-2006).]

I thought I wasn't going to get this engine out to the track to verify the numbers, however, as luck would have it, the engine will be at the St. Thomas Dragway Park this Saturday night with the SOFA Great Lakes Fiero Show crowd.

I understand there are some other fresh mods making their debues so it should be a great show and we can potentially embarrass some Rustangs and Ricers to the bargain. I'll post the bad news on this one when it's in.

Arn