classic auto 3.5EFI dyno test

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melliferaman

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Help required please to interpret the lack of power shown on the dyno test. Can this be attributed to low compression 135-145psi dry, +10-15psi wet. Run was carried out in second gear. Box has been serviced by a specialist and given the ok. Performance on lpg feels similar to petrol. Have inspected and clocked the cam, ok. Ignition set 6btdc with strobe.
Many thanks
 

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Look at your air to fuel ratio. Ideal is 14.7:1. You don't get that in reality but yours seem very low. Not clawing it's way back to 13 until 4k rpm by which time the motor is running out of puff by then. Now I haven't messed around with this sort of tuning in years but I'm sure the fact the ratio is low points to a rich mixture. Better than it being lean. I maybe reading it wrong but it's worth investigating or discussing some more.
 
bencorkill said:
On lpg expect atleast 10-15% power loss, has it been serviced well? has the timming been corrected for the lpg?
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not nessary true...i got 10degrees more timing dialed in when on gas..=more power..espically on boost..

but anyway..thats about right for a tired 3.5..what are you expecting??
 
doz said:
Look at your air to fuel ratio. Ideal is 14.7:1. You don't get that in reality but yours seem very low. Not clawing it's way back to 13 until 4k rpm by which time the motor is running out of puff by then. Now I haven't messed around with this sort of tuning in years but I'm sure the fact the ratio is low points to a rich mixture. Better than it being lean. I maybe reading it wrong but it's worth investigating or discussing some more.
Click to expand...

+1 My first thoughts were - Hmmmm seems a bit rich. Anyhow, power isn't that far off what you'd expect - probably about 15 brake down max - don't expect book figures!
 
Many thanks for your responses, to clarify :
Dyno results are for petrol not lpg, on gas the engine feels just as gutless at low rpm.
Ignition is via an RPI amp set at 12 deg on gas, switching looks ok with a strobe.
My understanding is; that max power is achieved at around 12:1 the ECU is doing ok as the mixture is feathering as revs rise, avoiding detonation. 14.7 the stoichiometric ratio and weaker is for light throttle and crusing, dyno tests are supposed to be done at full throttle. What baffles me is the lack of torque at low rpm. Maybe I should confirm the tester had his foot on the floor ? The torque curve confiirms road tests, no go at low rpm, my old series vehicles the 2.6 and 2.25 just pull and pull given a boot full, (I pull heavy trailers) the six used to break half shafts frequently, but thats another story. I am trying to confirm how low speed torque relates to compression pressure, my gauge is 40 years old so could be way out, but all cylinders are similar. Have no experience of auto boxes can there be slippage before lock up ?
 
Considerable slippage before lockup. Compression figures are low even wet, more in keeping with a low compression engine. Usual fitment in autos was HC engine. So maybe it's more tired than you think if it's an HC engine. Should be around the 170/180 psi mark. From memory.
 
melliferaman said:
Many thanks for your responses, to clarify :
Dyno results are for petrol not lpg, on gas the engine feels just as gutless at low rpm.
Ignition is via an RPI amp set at 12 deg on gas, switching looks ok with a strobe.
My understanding is; that max power is achieved at around 12:1 the ECU is doing ok as the mixture is feathering as revs rise, avoiding detonation. 14.7 the stoichiometric ratio and weaker is for light throttle and crusing, dyno tests are supposed to be done at full throttle. What baffles me is the lack of torque at low rpm. Maybe I should confirm the tester had his foot on the floor ? The torque curve confiirms road tests, no go at low rpm, my old series vehicles the 2.6 and 2.25 just pull and pull given a boot full, (I pull heavy trailers) the six used to break half shafts frequently, but thats another story. I am trying to confirm how low speed torque relates to compression pressure, my gauge is 40 years old so could be way out, but all cylinders are similar. Have no experience of auto boxes can there be slippage before lock up ?
Click to expand...

Maximum power is rarely around 12:1, I've built all sorts of race engines from Minis to Suzuki Hayabusas maximum power is nearly always achieved in the 13:1-13.5:1 range. Yes there could be (intended) torque converter slip up to about 2K revs. There should be a brief over enrichment as the operator floors the throttle, perhaps he'd not flooring it quickly enough? I'd advance ignition timing and take fuel out.
 
Thing is he got standard ecu
Gonna be difficult to alter fueling and timing..

To be honest i suggest as mentioned before
That as most old rover v8's..its tired
Dont waste time and money on her.rebuild new rings atleast,new cam and followers etc..

Oh on boost...i run supercharged toyota quad cam v8 in a 2 door rrc for your interest.megasquirt controlling everything including gas.
 
StuckAgainSteve said:
Maximum power is rarely around 12:1, I've built all sorts of race engines from Minis to Suzuki Hayabusas maximum power is nearly always achieved in the 13:1-13.5:1 range. Yes there could be (intended) torque converter slip up to about 2K revs. There should be a brief over enrichment as the operator floors the throttle, perhaps he'd not flooring it quickly enough? I'd advance ignition timing and take fuel out.
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11 to 1 is usually regarded as choke fuel with 14 to 1 as ideal for and average road car for maximum efficiency. :):)
 
wammers said:
11 to 1 is usually regarded as choke fuel with 14 to 1 as ideal for and average road car for maximum efficiency. :):)
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Sadly modern cars run richer than they need to (sod fuel efficiency) to keep the stupid box of toxic heavy metals bolted to the exhaust-system happy.
 
StuckAgainSteve said:
Sadly modern cars run richer than they need to (sod fuel efficiency) to keep the stupid box of toxic heavy metals bolted to the exhaust-system happy.
Click to expand...

Yeah progress is sometimes not as good as is made out to be. Unleaded petrol and cats took so much power out of engines everybody went to four valves per cylinder to give motors a bit of umph back. On leaded juice with the cat off they would be really good.
 
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