Fuel consumption V8

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Originally Posted by HangOver

I thought it was so you dont get any air in the fuel line, apparently the EFI's dont like it and backfire, or can?

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Air in the line would be pumped to the fuel rail and returned to the tank I imagine and the engine would probably start to stall as the injectors fail to open properly.

I haven't got my Driver's Handbook here at the moment but I will post later if says anything significant.

Well I am wrong about the 1/4 of a tank full bit from my previous post; the book says re-fuel when the amber light comes on which means 9 litres is left. It does say to never run the tank dry as the catalytic converter will be damaged but it doesn't mention the pump, so I am probably wrong about that as well. My experience of submersible pumps is that they like to be submerged, however, so maybe the 9 litres can achieve that. Apologies for my error,

Cheers Charlie

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Originally Posted by disc94

take it to jason M.R AUTOMOTIVE they r the best redcliffe

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This sounds promising, the best I get is about 500km out of 100lt which is 25km per 100km. This is with both the 3.9 and the 4.6 that replaced it, but more power with the 4.6

very early on it got much better fuel economy then dropped to this. It's been like it for years so I will try Jason / MR automotive once the dollars are back in a healthy range.

Also I have LPG and on long trips run the petrol tank dry then swap to gas, I've never had any sort of problems at all? fuel up wait for it to pump up and start it

With regards to the pump requiring to be "submersed", the swirl pot that it lives in has important design features to keep the pump fully submersed until the tank is completely empty. The return line from the rail is so plumbed into the swirl pot to be a "jet pump" for the inlet valve at the lower surface of the swirl pot. The inlet valve prevents fuel running out of the swirl pot when the pump stops. So under normal operation the swirl pot is overflowing until the last litre of fuel has been vacuumed up. No need to panic about needing 1/4 tank unless you are going on very steep angles. Just don't run 100% out of petrol and try to procede on gas, a sure way to cook the pump.

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Originally Posted by blitz

This sounds promising, the best I get is about 500km out of 100lt which is 25km per 100km. This is with both the 3.9 and the 4.6 that replaced it, but more power with the 4.6

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is that not 20l/100km? from memory in other posts you say you get around 25l/100k on lpg (mixer type with O2) so 20l/100k on petrol sounds about right.

(what's happened, you moved from adelaide? it's a long drive to go back to bee utey!)

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Originally Posted by pibby

is that not 20l/100km? from memory in other posts you say you get around 25l/100k on lpg (mixer type with O2) so 20l/100k on petrol sounds about right.

(what's happened, you moved from adelaide? it's a long drive to go back to bee utey!)

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Umm just checking to make sure you were paying attention :angel:

yes 20lt per 100km not 25

Yeah moved for several reasons, family being the biggest one. and Yes not having Bee Utey on hand will be a hassle. He is the best I have seen with gas and a gentleman to boot as well so I would go to him first second and third to get the gas and tuning sorted out.

for the gas I worked it out on how much it cost me to drive 100km on 98 RON then how much to do the same with gas (done over several runs to make sure of accuracy) then from my dollar value it worked out to be about 10lt per 100km on gas.

$37-00 gas to drive 250km city and Adelaide hills no highway except the down hill run to the city of about 20km on the freeway, and I never drove it gently as I have a lead foot.

Just filled up, got 21ish/100km on 98.

Seems fuel makes no diff to town economy, does run better tho so will use norm unleaded in future

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Just filled up, got 21ish/100km on 98.

Seems fuel makes no diff to town economy, does run better tho so will use norm unleaded in future

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Just to clarify, the REASON that 98 gives better economy in modern efis is that they usually have a very high compression ratio and use knock sensors to control pinging by retarding the ignition timing if it detected. The timing is set by teh ECU having a map inbuilt.

So the higher the octane , the lesser pinging the greater advance =the better economy.
The 14CUX has none of this nonsense relying on good old weights and springs. This is the reason that piggyback chips that give much more part throttle advance electronically work so well with a 14CUX.
Regards Philip A

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Originally Posted by PhilipA

Just to clarify, the REASON that 98 gives better economy in modern efis is that they usually have a very high compression ratio and use knock sensors to control pinging by retarding the ignition timing if it detected. The timing is set by teh ECU having a map inbuilt.

So the higher the octane , the lesser pinging the greater advance =the better economy.
The 14CUX has none of this nonsense relying on good old weights and springs. This is the reason that piggyback chips that give much more part throttle advance electronically work so well with a 14CUX.
Regards Philip A

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So Philip do you think the piggy back chips are worth it? If so are any of them better than the others?

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So Philip do you think the piggy back chips are worth it? If so are any of them better than the others?

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There are several threads on this but really its the best "bang for buck" that you can get but also depends on the dyno operators knowledge of the motor .

The key issue IMHO is that piggy backs take control of the vacuum advance and could probably control the centrifugal advance also. The Chips have a timing map like a more recent ECU. 14CUX fuelling is not too bad but it is also improved.

I have a Unichip fitted by Graeme Cooper but they have now relinquished the franchise and use Haltech. There are several forum members who have fitted Haltech and have reported being happy. These are the only 2 brands I have any experience with.
You will never get as good a result as Thor or GEMS because they both rely on knock sensors to retard if pinging occurs so can run advance right up on the knock limit. The advance of chip is usually conservative as the dyno tuner doesn't want burnt pistion comebacks should someone have had 98 in for the tune then go back to 91 for example, and this does happen.
Cooper's tune had about 4 degrees static advance but I have now got it up to 8 with no pinging on 91 even though there is about an extra 10-15 degrees at light throttle and 3 at full from the chip program..

Regards Philip A

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Originally Posted by PhilipA

There are several threads on this but really its the best "bang for buck" that you can get but also depends on the dyno operators knowledge of the motor .

The key issue IMHO is that piggy backs take control of the vacuum advance and could probably control the centrifugal advance also. The Chips have a timing map like a more recent ECU. 14CUX fuelling is not too bad but it is also improved.

I have a Unichip fitted by Graeme Cooper but they have now relinquished the franchise and use Haltech. There are several forum members who have fitted Haltech and have reported being happy. These are the only 2 brands I have any experience with.
You will never get as good a result as Thor or GEMS because they both rely on knock sensors to retard if pinging occurs so can run advance right up on the knock limit. The advance of chip is usually conservative as the dyno tuner doesn't want burnt pistion comebacks should someone have had 98 in for the tune then go back to 91 for example, and this does happen.
Cooper's tune had about 4 degrees static advance but I have now got it up to 8 with no pinging on 91 even though there is about an extra 10-15 degrees at light throttle and 3 at full from the chip program..

Regards Philip A

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Is it possible to retro-fit a newer system to an old GEMS engine? A few people I've known over the years have removed the Buick V8 and put in Holden ones, with all their added weight and other issues. However, I would like to keep the original engine and have it rebuilt in the next 12-18 months. If I can only go with a piggy-back unit, so be it, but if better somputer and induction systems can be installed, I just wonder who would do it and how much it would cost? Any thoughts?