Speed-Density FI question

[jbrookstone]

I've been reading - and a little knowledge is dangerous... so...

The Esprit V8 uses a speed-density fuel injection system that does not measure the amount of air entering the engine. Instead it measures manifold absolute pressure, intake air temperature and engine speed in order to infer the amount of air being inhaled, and so can calculate the amount of fuel needed to be injected for combustion. To do this, the computer uses a table of engine volumetic constants, based on the volumetic efficiency of the stock engine. An exhaust oxygen sensor provides feedback to compensate for (small) errors in this table, due to wear or manufacturing variables.

So.... if boost pressure is changed, or intake air temperature is lowered(chargecooler), the MAP sensor and intake air temp sensor can report this and the system still works fine (I think). So far, so good.

But... if the intake manifold is modified, the intake valve port widened/polished, the compression ratio changed or the cam profile or timing modified, volumetric efficiency changes, invalidating the table of constants. This would require remapping of the fuel injection table... I think.

Does anyone have any experience with modifying any of the latter items on a V8 Esprit? Have you had to remap the FI computer afterward?

Best Regards,

Jay

[hilly]

If you make any hareware changes to the engine on a speed density EFI system then you will need to re-map the VE table.

Andy Hills
1981 S3 (with SD EFI)

[Paula&Marcus]

Hi All,
You are both absolutely right. If you change the engines "internals" like:

- cams
- valve sizes
- compression ratio
- intake path
- ......

then you are changing the engines efficiency and therefore you should remap all the efficiency tables.

BUT ... usually the changes (we all are actually able to do) are quite minor and you may get along with the stock efficiency tables. The closed loop learning tables will compensate for quite a large amount.

BTW, changing the turbos, cats and exhaust does not affect the efficiency of the engine itself !

Cheers
Marcus
www.PUKesprit.de

>> Edited by Paula&Marcus on Thursday 2nd February 14:50

[jbrookstone]

Thanks, Marcus!

Now... if I were to fiddle with the pistons (compression ratio) and cam (lift, duration) - are there shops (Southern California or...?) that have the equipment and know-how to remap the ECU? Or is this a big problem? Or would any changes here likely to be too small to require ECU remapping.

Best Regards,

Jay

[Paula&Marcus]

jbrookstone said:

Thanks, Marcus! Now... if I were to fiddle with the pistons (compression ratio) and cam (lift, duration) - are there shops (Southern California or...?) that have the equipment and know-how to remap the ECU? Or is this a big problem? Or would any changes here likely to be too small to require ECU remapping. Best Regards, Jay

Hi Jay,
IMHO there actually is not really a need for fiddling too much with increased compression ratios, because you will run into problems with higher boost levels. JFYI, very high boosting engines actually get the compression ratio reduced !
Better pistons (= good forged ones !) are a very good idea, indeed !!!!

For the cams (valve timing, overlap, lift, ...) you should not really try to increase the overlap, because a blown engine does not need this much overlap. If its too much you will get the fresh intake A/F mix just blown through into the exhaust, literally spoken. A slightly higher lift does not hurt. Also a ported and polished head and intake manifold also does not hurt.

IMHO whatever you do with your V8-TT engine (up to 500+ HP) you will not have to remap the RED Race ECU, because the engine itself will not really get a much different efficiency. What actually gets better are the turbos (= higher and cooler boost longer lasting and not collapsing) and the exhaust path. What you do is very simple ... you just make sure that 14psi/0.9bar boost is delivered in a HEALTHY way and the exhaust is as less restricted as possible. The Red ECU will manage all parametres for you. Of course the moving parts have to get upgraded in a way that they hold up the new power (= pistons, head studs, crank balancing, rods balanced/wheighted ...)

Marcus
www.PUKesprit.de

[jbrookstone]

Marcus:

Interesting reply. Essentially, any remapping needed is small and the red race ECU contains anything I might need for minor upgrades to volumetric efficiency.

I understand your warnings regarding upgrading of engine components to handle the added stress. I imagine the transmission would be the next weakest link needing upgrading.

Thanks again for your advice - as usual, you are a resource to the Esprit community.

Best Regards,

Jay

[Paula&Marcus]

jbrookstone said:

Marcus: Interesting reply. Essentially, any remapping needed is small and the red race ECU contains anything I might need for minor upgrades to volumetric efficiency. I understand your warnings regarding upgrading of engine components to handle the added stress. I imagine the transmission would be the next weakest link needing upgrading. Thanks again for your advice - as usual, you are a resource to the Esprit community. Best Regards, Jay

Yes Jay,
you are right, the tranny is a weak point here along with some other engine parts ...

Marcus
www.PUKesprit.de