Fuelling + Compression

[Ice88]

The situation posed on facebook is around Fuel + Compression.

Compression ratio is simply an indication of how much smaller the compressed area is at TDC as opposed to BDC. I.e. the area for an 9:1 is 9 times smaller then BDC.

As you increase compression you either need to increase the octane rating of the fuel you are using or increase the amount of fuel (as a semi work around). This is due the increase in temperature. In a turbo engine this is a two fold problem as compressed air is hotter (hence intercoolers). Higher temperatures = more likely to ping.

The more air you cram in the higher your AFR will be. The higher the AFR the more likely you are to ping.

There's alot more to it and im simplifying a bit but am trying to answer the question without losing people. I can expand the above if peeps are interested...

EDIT: ok so didn't quite answer the question. A bpt ecu will inject alot more fuel then a BP ecu to compensate for boost. In theory a BPT compression + BPT ecu will make more power then a BP compression + BPT ecu. I'd argue that the latter is a better combination however.

[Mad Mat]

Originally Posted by Ice88

A bpt ecu will inject alot more fuel then a BP ecu to compensate for boost. In theory a BPT compression + BPT ecu will make more power then a BP compression + BPT ecu. I'd argue that the latter is a better combination however.

hmmmm not sure if i agree with that statement. but the question is, will the car runn lean with a high comp?? if i read your post correctly kris your saying that it will be over fueling causing it to ping if the right octane fuel isnt used...

so there for running rich?

[Ice88]

It will run leaner yes.

BPT wont be overfuelling for a boosted setup. Pinging will occur when insufficient fuel for that boost (aka compression) level causes temperatures to rise to the point it occurs alternatively it will occur when the octane rating isn't sufficient to resist detonation (which is pinging).

[Mad Mat]

Originally Posted by Ice88

It will run leaner yes.

BPT wont be overfuelling for a boosted setup. Pinging will occur when insufficient fuel for that boost (aka compression) level causes temperatures to rise to the point it occurs alternatively it will occur when the octane rating isn't sufficient to resist detonation (which is pinging).

Hmmm interesting.

Thanks for that knowlage Kris

NATHAN GET A WIDEBAND I WANT TO SEE WHAT UR CAR IS DOING DAM IT

[project.r.racing]

9.0:1 compression with bp26 ecu has been done before. It nets lower rpm spooling and bigger power. Few cars running around with this setup currently.

Cant argue with facts. The later is better.

[rodhog]

Well it sounds right

but the reality is different. But it also varys on other aspects.

With out getting too technical.

Yes Ideal would be a high comp with boost and BPT ECU. Perfect would be BPT and matching ECU.
But all have large or at least a wide spread of safety on them.

What kills them is not so much your Octane - it's where you take it out of a mild range.

I'd say a BP stock comp etc with BPT ECU and either a more efficient not larger more efficient like fitting a late model unit. But Running Similar to sock Boost levels. Would net the most. You could even run it on just 95ROn. not just 98ROn.

Many have done it in the past to even more safe tuned cars.

it's not the fuel so much it's the Timing, and temperature
I was on a Aus Rotary cruise with my mx-6 when a bit cleaner and going harder.
It was January and we went to blue mountains.
All the S4-5 's running stock ECU had no issues.
All the injection perfection etc well My tool kit helped restart two Rx-3's
The rest from heavy 20B's to old school 4cylidners in 1600's.
Well - lets just say. from the M4 motorway to Katoomba. My car never had a problem.
I think it pinged once a peck boost at 3000rpm but climbing up, it cleared never came back.
Others were babying it. A lot of them Especially the IDA and webber cars were struggling in the HEAT.
It was HOT and it's as they say thinner air.
Here is the kicker, I was running at the time on Unichip. so stock ECU but with unichip running the timming. It only removed so much fuel, and it stopped the ECU from seeing air intake temps. But being still restricted by the stock ECU meant its was not in danger of any damage.
Unichip can only mode the fuel so FAR. we even left the boost cut on just lifted to 15psi. Yes it beeped on cold nights.

but the amount of cars knocked by the heat was staggering. It's the one thing you can't account for unless you tune in summer winter and on long under bonnet build up - traffic hot days or car parked in sun.

The Stock ecu dont' know 60-80 degree under bonnet air intake temp it just knows above 40 or above 60 and compensates. more modern ECU's are better by a long shot. But still it's very broad.

Keep the base timing sane and it will run and run for long time. I know of a VL turbo still original with RB 30 bottom end that was built for N/A engine reco. car is driven it's stock NO intercooler fitted even. doesn't even drink oil. Driven by a dill. Considering I built the bottom end over 8 years ago.

[Ice88]

If they were using aftermarket ECUs then yes timing would have come into the equation but on a stock ECU you don't have control over that so your limited.

[Mad Mat]

hmmm this is an interesting read...

wonder how my 9.0:1 motor with vf8 is going to go with stock BPT managment

[project.r.racing]

Originally Posted by Ice88

If they were using aftermarket ECUs then yes timing would have come into the equation but on a stock ECU you don't have control over that so your limited.

you have control over the base timing. degree which is enough to deal with pre detination issue derrived from higher compression. dont confuse a bp engine with a fs engine.

[Ice88]

Forgot older BPs used distributor.

EDIT: Personally I don't see timing as a problem using a stock ecu.

[Clean_Cookie]

Originally Posted by Mad Mat

hmmm this is an interesting read...

wonder how my 9.0:1 motor with vf8 is going to go with stock BPT managment

no difference. MAF will know how much air is going in, how hot it is. it just will be at a lower boost pressure, which the ecu doesn't care too much.
, if you left stock na injectors in it could be a problem. what injectors are you using??

[Mad Mat]

The vf8 has a 4mm bigger compressor wheel than the vf10. Ill just run it at stock boost. That should be heaps

[TheMAN]

VAFs in BGs are not really that accurate, they're just cheaper to make... they got rid of them once the BAs came out

[Mad Mat]

Originally Posted by TheMAN

VAFs in BGs are not really that accurate, they're just cheaper to make... they got rid of them once the BAs came out

Im going to be running a holden hotwire maf with the bpt ecu. So i get rid of that horrable VAF. Its been done and proven to work well here in Australia.

[TheMAN]

nice... details?

[rodhog]

yes the VAFs are cheaper and crude but 100% more reliable and BEST IN THE WORLD IMO for the time. The great thing about the ECU's that use them is the crudeness.
It's why interceptors on these models worked so much better then anything else. Because you can make the engine ecu see and think so different. A simple example is on a intercepted ECU you can disconnect the AFM and it will idle and run maybe up too 3000rpm. A good job allows for it to use TPS and other signals to run the engine.

Mat - honest throw both into bin an run aftermarket.
I still have VAF in the mx-6. I've run the FE DOHC with 4 different intakes. the car that ran at a SAS on a 20 degree intake temp day made the most 86Kw's the least is 84KWs out at Penrith. Restriction, it's a bees dick difference and the 86kw was with a F2 VAF and intake pipe with resonance chamber.

[Mad Mat]

Originally Posted by TheMAN

nice... details?

i'll pm u the details

Originally Posted by rodhog

yes the VAFs are cheaper and crude but 100% more reliable and BEST IN THE WORLD IMO for the time. The great thing about the ECU's that use them is the crudeness.
It's why interceptors on these models worked so much better then anything else. Because you can make the engine ecu see and think so different. A simple example is on a intercepted ECU you can disconnect the AFM and it will idle and run maybe up too 3000rpm. A good job allows for it to use TPS and other signals to run the engine.

Mat - honest throw both into bin an run aftermarket.
I still have VAF in the mx-6. I've run the FE DOHC with 4 different intakes. the car that ran at a SAS on a 20 degree intake temp day made the most 86Kw's the least is 84KWs out at Penrith. Restriction, it's a bees dick difference and the 86kw was with a F2 VAF and intake pipe with resonance chamber.

i'll be going down the aftermarket (440D) path when i get the $$$ but for now i just want to be able to drive the car and injoy it.

[TheMAN]

Originally Posted by rodhog

yes the VAFs are cheaper and crude but 100% more reliable and BEST IN THE WORLD IMO for the time. The great thing about the ECU's that use them is the crudeness.
It's why interceptors on these models worked so much better then anything else. Because you can make the engine ecu see and think so different. A simple example is on a intercepted ECU you can disconnect the AFM and it will idle and run maybe up too 3000rpm. A good job allows for it to use TPS and other signals to run the engine.

Mat - honest throw both into bin an run aftermarket.
I still have VAF in the mx-6. I've run the FE DOHC with 4 different intakes. the car that ran at a SAS on a 20 degree intake temp day made the most 86Kw's the least is 84KWs out at Penrith. Restriction, it's a bees dick difference and the 86kw was with a F2 VAF and intake pipe with resonance chamber.

if they were really the best at the time, then explain why some cars such as the S13 came with real MAFs? They came out around the same time the BG came out

oh that's right... the S13 sold for more, was considered more premium... the BG was just an econobox

VAFs are just cheap to use in an era of lax emission regulations... it was solely to cut manufacturing costs... MAF technology was already reliable at the time as proven (by now) from the S13... my mate's S13 was still running the original MAF up until the car got wrecked a few years ago

[rodhog]

Yeah best of the time as in 1984 - I don't think just about BG I think of it as whole - reason it was on a 323. A 323 is cheap little **** box, a 626 is mid size **** box.
Everything comes on the big daddys first. These days it comes hand me down quicker because software and electronic updates or upgrades are so much quicker to implement.


What makes it the best was it's 1980 -1990 if not 1995 it's ****ING reliable - compared to it's other variant's/ Porsche used VAf's on Rally race engines till late 80's . Gibson motor sport still used one on the FJ20 powered Bluebird. EVEN TRD did on the MA powered Supras. It still gives reading and feed back. It's a more robust design in fact IMO COST is reversed. VAF are alloy construction mostly and require many stages to produce a simple MAF or even modern unit is smaller and mostly 1cent plastic casing.
In fact I'd say 0,05 cents per case of a modern unit. The wires inside are not longer as expensive and only the units with gold plating would be more so in terms of manufacture.


Hot wire MAF's were only becoming reliable late 80's early 90's. Early VL powered nissans had issues with them. over time the wire breaks down.
In some cases it's not even being feed into a more Precise ECU.
Yes Cost is a major reason in Mazda's case they were using Everything. FE DOHC had complete bosch J-tronic variants from mitsubishi. But they knew the market and didn't use it in the US market they used the more reliable early version with the VAF from Denso.

Yes come along to the BA some mildly tighter emissions but more to do with creating better power curves. but mostly better ECU's more processing in the K- series engines they were running up to two knock sensors, 3 02 sensors and variable ignition timing.
Compared to before regard less of AFM type. you were lucky to get a ECU with two major table for fuel and timing or even a knock sensors.
On reliability well, most cars with VAFs - the VAFs still work. All K-series engines I've touched I've done AFM - piece of crap always temp sensor failure in unit or it's totally gone. A 1 BF 1 BG 1 MA Cressida - 5 F2 engines - Never done AFM. I have extra units from by pass use.
Oh and ah all the ones from AE92 to AE111's and 4AGE 20 valve engines and stuff hmm VAF from memory oh that's right because HOT wire won't work or something ?


People claim restrictions but really - Really. NO - no such thing it's so minute.
The restriction goes back to the ECU every time. Plus it's not like you can unlock a hidden power and if and when it's restriction, You would be running a MAP sensor anyway.


You can't look at small cars of that time as read of technology. They always got the hand me downs. yes with some improvements.

End of the day I stand by VAF being more reliable more durable and best of all simpler stop boost cut.

I still stick to the fact you won't get nothing from the conversion.