AFM upgrade questions

[chaseincats]

Hi guys,

My '78 has the weber "big throat" throttlebody on it but with the (I believe) stock AFM.  Would upgrading to a larger AFM noticeably improve throttle response considering the larger throttlebody or is that just a lot of fiddling for marginal gain? (yes I saw the atlanticZ page)

If there really is noticeable gain to be had with going to a larger AFM with my larger throttlebody, do you folks recommend the 280zx turbo or cressida AFM?  I've been doing a lot of reading on them but couldn't find a stern verdict.

 

Any ideas?

-chase

[siteunseen]

Too much air is a bad thing. Do you need more?

[chaseincats]

5 minutes ago, siteunseen said:

Too much air is a bad thing. Do you need more?

TBH im not sure.  I thought that was the point of the big throat throttlebody, no?

[EuroDat]

If you want throttle response, you won't get much by doing that, if any at all. These old efi systems don't like alterations much at all. It unbalances the components and the ecu can not compensate. It doesn't "learn and adjust" like newer sysrems can.

Changing to a sport air filter or a larger exhaust system can help a bit because they are outside the components and could be restricting the flow, but extractors can change the scavenge of exhaust gases and that could have a negative effect.

The easiest why to improve throttle response on these ols efi systems (without changing ecu, cam, head etc) is a lightened flywheel.

The standard flywheel is 23lbs. If you get one that has been lightened to 16-18lbs or lighten the one you have, it will repond a lot more the the throttle.

Or an aluminiun, but they are around 11lbs and that will reduce drivability a lot. Some people don't have any problem with the touchy throttle. You could match that to a 240mm clutch out of a 280Z(X) 2+2 or a 280ZX turbo clutch. That would gain a little weight over the standard clutch and would give you a heavy duty clucth with a light peddle. 

https://www.summitracing.com/search/brand/fidanza/year/1978/make/nissan/model/280z/part-type/flywheels?SortBy=Default&SortOrder=Default

Not trying to be negative, but a lot of changes often make the engine sound better and we think that makes it faster, but it's often our mind playing tricks on us. That sounds fat cool, so it must be faster. 

If I change anything to my car, I go to a quiet road near home and do a simple test.

I drive at at a certain speed, say 20 mph and give full throttle till it reaches 70 mph. Don't change gears during the test..

Have a friend (or my wife, if she is in the mood to waste time helping me on this thing) video the speedo and tacho and compare that with the results after you do the mods.

If the time reduces, than you made an improvement. You can plot the speed versus time in excel and get a kind of power curve. Plot both before and after and you can see if it improved in certain areas of the rev curve.

[chaseincats]

6 hours ago, EuroDat said:

If you want throttle response, you won't get much by doing that, if any at all. These old efi systems don't like alterations much at all. It unbalances the components and the ecu can not compensate. It doesn't "learn and adjust" like newer sysrems can.

Changing to a sport air filter or a larger exhaust system can help a bit because they are outside the components and could be restricting the flow, but extractors can change the scavenge of exhaust gases and that could have a negative effect.

The easiest why to improve throttle response on these ols efi systems (without changing ecu, cam, head etc) is a lightened flywheel.

The standard flywheel is 23lbs. If you get one that has been lightened to 16-18lbs or lighten the one you have, it will repond a lot more the the throttle.

Or an aluminiun, but they are around 11lbs and that will reduce drivability a lot. Some people don't have any problem with the touchy throttle. You could match that to a 240mm clutch out of a 280Z(X) 2+2 or a 280ZX turbo clutch. That would gain a little weight over the standard clutch and would give you a heavy duty clucth with a light peddle. 

https://www.summitracing.com/search/brand/fidanza/year/1978/make/nissan/model/280z/part-type/flywheels?SortBy=Default&SortOrder=Default

Not trying to be negative, but a lot of changes often make the engine sound better and we think that makes it faster, but it's often our mind playing tricks on us. That sounds fat cool, so it must be faster. 

If I change anything to my car, I go to a quiet road near home and do a simple test.

I drive at at a certain speed, say 20 mph and give full throttle till it reaches 70 mph. Don't change gears during the test..

Have a friend (or my wife, if she is in the mood to waste time helping me on this thing) video the speedo and tacho and compare that with the results after you do the mods.

If the time reduces, than you made an improvement. You can plot the speed versus time in excel and get a kind of power curve. Plot both before and after and you can see if it improved in certain areas of the rev curve.

This is all some great information thank you so much.  AFM idea is now down the drain for sure but for my edification, what's the point of a larger throttlebody then?

Will definitely look into the beefier clutch when I take everything apart.  Are there 18lb flywheels to buy anywhere, I can't seem to find any?  (I'd prefer to buy one so that when I have the trans taken out, we can put it all back together in a day instead of waiting for my flywheel to be lightened then come back leaving the car on someone else's rack)

[EuroDat]

The aftermarket throttle bodies are made for after market ecu like megasquirt etc. Then you have the ability to tune for performance and the extra capacity the throttle body can give.

If you don't want to use your flywheel, you could buy one that is already lightened. There are still companies out there thaf lighten them. Zcardepot sell one variant.

https://www.ebay.com/itm/Datsun-1970-83-240Z-260Z-280Z-280ZX-Competition-Clutch-Lightweight-Flywheel-161/323799190475?fits=Model:280Z|Make:Datsun&epid=1545121518&hash=item4b63ef8bcb:g:UscAAOxy039TKLJl&redirect=mobile

They are all around thd $350 - $400 mark. I don'tknow if buying a new flywheel and having it lightened would be any cheaper. You would need to find someone with experience in these flywheels.

Plenty of suppliers with kits including the flywheel.

https://www.ebay.com/itm/TR1-STAGE2-CLUTCH-KIT-FLYWHEEL-For-1975-1983-DATSUN-280Z-280ZX-2-2-TURBO-L28ET/333165142490?fits=Model:280Z|Make:Datsun&hash=item4d9230a1da:g:qBIAAOSwXNdcXLKm&redirect=mobile

Be carefull when buying a flywheel. You don'twant the one for the nissan trucks (D21) etc. The flywheel is heavier at around 28lbs. Not what you want.

[chaseincats]

6 minutes ago, EuroDat said:

The aftermarket throttle bodies are made for after market ecu like megasquirt etc. Then you have the ability to tune for performance and the extra capacity the throttle body can give.

If you don't want to use your flywheel, you could buy one that is already lightened. There are still companies out there thaf lighten them. Zcardepot sell one variant.

https://www.ebay.com/itm/Datsun-1970-83-240Z-260Z-280Z-280ZX-Competition-Clutch-Lightweight-Flywheel-161/323799190475?fits=Model:280Z|Make:Datsun&epid=1545121518&hash=item4b63ef8bcb:g:UscAAOxy039TKLJl&redirect=mobile

They are all around thd $350 - $400 mark. I don'tknow if buying a new flywheel and having it lightened would be any cheaper. You would need to find someone with experience in these flywheels.

Plenty of suppliers with kits including the flywheel.

https://www.ebay.com/itm/TR1-STAGE2-CLUTCH-KIT-FLYWHEEL-For-1975-1983-DATSUN-280Z-280ZX-2-2-TURBO-L28ET/333165142490?fits=Model:280Z|Make:Datsun&hash=item4d9230a1da:g:qBIAAOSwXNdcXLKm&redirect=mobile

Be carefull when buying a flywheel. You don'twant the one for the nissan trucks (D21) etc. The flywheel is heavier at around 28lbs. Not what you want.

Awesome, I'll look into these now.  I've heard that having someone lighten the flywheel can make them fragile/shatterable if done improperly is that true or an exaggeration?