Hi guys,
Got my car rolling roaded on Friday.
Result was 187bhp (at 5300rpm) and 210lbft (at 3500rpm) at the wheels after a session adjusting the carb fuelling and a small amount of tweaking to the timing. I understand my LT77 transmission and associated running gear to have around 35bhp transmission losses, so around 220bhp at the flywheel as an estimate.
I’m pretty pleased with that, but as always, would be interested to know if I can get a bit more out of it.
Based on my spec below, do you think there is any obvious area for further potential? What I mean is, is there one area that is letting the side down, compared to the other specs of the engine? My expectation is that without knowing the exact CR and head specifications, perhaps it’s too difficult to say for certain.
The spec of the engine is below:
- 3.9l conversion from 3.5l
- Omega cast pistons (from JE 3.9 conversion)
- Weber 500 carb, JWR Dual Plane 360 manifold
- 4-branch tubular exhaust
- Viper Hurricane camshaft, hydraulic lifters
- Mallory dizzy with unilite electronic ignition
- Heads are a bit of an unknown, looks like some porting but unsure of quality and also what CR it is.
- Std cast Rover flywheel
I’m wondering if putting a lightened flywheel would give me real world benefits for acceleration? The engine is in a Dax Rush kitcar, so maybe a faster revving engine would liven things up further? Not sure what sort of driveability issues I might experience.
Be interested to hear your thoughts.
Thanks,
Gary.
3.9 RV8 tuning - Advice for next steps?
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mk1storm
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Yeah can't get away with a taller manifold unfortunately.
210lbft is at the wheels. So I am assuming that would equate to around 240lbft at the flywheel if I apply the same losses as there are for bhp? So if that's right then its 20lbft more than the 3.5 at 500rpm lower in the rpm range. Is that still resonable or summut still amiss?
210lbft is at the wheels. So I am assuming that would equate to around 240lbft at the flywheel if I apply the same losses as there are for bhp? So if that's right then its 20lbft more than the 3.5 at 500rpm lower in the rpm range. Is that still resonable or summut still amiss?
Hi
the first thing worth looking at are the heads, get all the ports to the same state, ballance up all the chambers to the same volume, get all the valves to the same depth in the heads, then you have a basis for improvment.
I would next invest in some proper stage 1 head porting, someone who has "done a bit of modification" is as likley to have made things worse as better, get the heads ported to match the lift profile of the cam, there is no point in getting better flow at .5" lift at the expence of lower lift if your valvas only open to .425". Match the inlet manifold to the heads , not the gasket.
How old is the carb? if it is maore than 2 years strip it and rebuild it with a rebuild kit replacing everything that is worn, if it is more then 5 years and has had fuel in it all that time then bin it and get a 4 barrel throttle body, some injectors and an ECU, actually I would do that as the next stage in tuning anyway as it will probably gain you more power at this stage than anything else.
How old is the dissy? again if it is anything but brand new convert to wasted spark ignition.
Find out what the CR is on each of the cylinders, if you have prepped the heads properly then they should be very close to each other, but with everything ballanced up and matched then you should be able to set the CR at 10.25:1 safely and if now you are running around 9:1 that should be worth 7-8 BHP. Get all this done and set up properly you should find another 20-25BHP without any other mods, but you will need the ECU controlling everything accuratly without the ECU you may squeeze another 12 as you will have to be conservative with the CR and ignition timing and mixture.
Best regards
Mike
the first thing worth looking at are the heads, get all the ports to the same state, ballance up all the chambers to the same volume, get all the valves to the same depth in the heads, then you have a basis for improvment.
I would next invest in some proper stage 1 head porting, someone who has "done a bit of modification" is as likley to have made things worse as better, get the heads ported to match the lift profile of the cam, there is no point in getting better flow at .5" lift at the expence of lower lift if your valvas only open to .425". Match the inlet manifold to the heads , not the gasket.
How old is the carb? if it is maore than 2 years strip it and rebuild it with a rebuild kit replacing everything that is worn, if it is more then 5 years and has had fuel in it all that time then bin it and get a 4 barrel throttle body, some injectors and an ECU, actually I would do that as the next stage in tuning anyway as it will probably gain you more power at this stage than anything else.
How old is the dissy? again if it is anything but brand new convert to wasted spark ignition.
Find out what the CR is on each of the cylinders, if you have prepped the heads properly then they should be very close to each other, but with everything ballanced up and matched then you should be able to set the CR at 10.25:1 safely and if now you are running around 9:1 that should be worth 7-8 BHP. Get all this done and set up properly you should find another 20-25BHP without any other mods, but you will need the ECU controlling everything accuratly without the ECU you may squeeze another 12 as you will have to be conservative with the CR and ignition timing and mixture.
Best regards
Mike
poppet valves rule!
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mk1storm
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- Location: St Neots, Cambridgeshire
Cheers for the info and advice.
Carb and dizzy are nearly new so no probs there.
Ok, so it sounds like no easy additional gains (not that there were ever likely to be any) without some reasonable expenditure and time/effort. With the engine running pretty well and me getting to grips with the car I don’t think I have the motivation at this stage to spend much time getting the other bits and pieces sorted for what seem like relatively modest power gains so I’ll stick with what I’ve got for now and spend a bit more time/effort getting the rest of the car sorted. Good to know where I stand though, thanks.
I could have gained a little bit more bhp with the timing according to the dyno guy, but started to get some pinking. Running on regular unleaded at the moment. Timing is set to 8deg static, with 32deg all in at 2800rpm. I guess this might indicate my CR is already relatively high? Wondering if using super-unleaded and adding a little more advance might provide a small worthwhile gain? Or adjust the advance curve on the dizzy to keep the 32deg all in, but advance the static so it has more advance earlier in the rev range? I'm running with the vac connected, set to a max of 5deg.
Cheers guys.
Gary.
Carb and dizzy are nearly new so no probs there.
Ok, so it sounds like no easy additional gains (not that there were ever likely to be any) without some reasonable expenditure and time/effort. With the engine running pretty well and me getting to grips with the car I don’t think I have the motivation at this stage to spend much time getting the other bits and pieces sorted for what seem like relatively modest power gains so I’ll stick with what I’ve got for now and spend a bit more time/effort getting the rest of the car sorted. Good to know where I stand though, thanks.
I could have gained a little bit more bhp with the timing according to the dyno guy, but started to get some pinking. Running on regular unleaded at the moment. Timing is set to 8deg static, with 32deg all in at 2800rpm. I guess this might indicate my CR is already relatively high? Wondering if using super-unleaded and adding a little more advance might provide a small worthwhile gain? Or adjust the advance curve on the dizzy to keep the 32deg all in, but advance the static so it has more advance earlier in the rev range? I'm running with the vac connected, set to a max of 5deg.
Cheers guys.
Gary.
Hi
If you are already on the edge of pinking and the dyno operator recons you could do with more timing then I think I may have slightly underestimated the gains you would get from ballancing up the chamber volumes, setting the valve seats the same and going to wasted spark ignition. it sounds like you have either one or more cylinder a smaller chamber volume, one or more inlet port out performing the other, or one slightly more restrictive exhaust port. This is giving the pinking on these cylinders whilst the majority are still needing more advance, combine this with the scatter inherent in any distributor set up and you have the situation you are seeing.
Get the cylinders ballanced and add crank triggered spark control and you can start adjusting the spark curve to make the most of the Volumetric efficiency curve of the engine. However if you are staying with a dissy I would be inclined to bring in the advance a little more slowly, use stiffer springs in the dissy to bring it all in by about 3500 (or just after peak torque) reduce machanical advance by 4 degrees with a spacer on the stop pin and add 2 degrees or so at idle
I am unsure what you are expecting form further engine mods. With 187 at the wheels of your current set up all the gains you can expect to make are small incriments, however make enough of them and they will add up.
Best regards
Mike
If you are already on the edge of pinking and the dyno operator recons you could do with more timing then I think I may have slightly underestimated the gains you would get from ballancing up the chamber volumes, setting the valve seats the same and going to wasted spark ignition. it sounds like you have either one or more cylinder a smaller chamber volume, one or more inlet port out performing the other, or one slightly more restrictive exhaust port. This is giving the pinking on these cylinders whilst the majority are still needing more advance, combine this with the scatter inherent in any distributor set up and you have the situation you are seeing.
Get the cylinders ballanced and add crank triggered spark control and you can start adjusting the spark curve to make the most of the Volumetric efficiency curve of the engine. However if you are staying with a dissy I would be inclined to bring in the advance a little more slowly, use stiffer springs in the dissy to bring it all in by about 3500 (or just after peak torque) reduce machanical advance by 4 degrees with a spacer on the stop pin and add 2 degrees or so at idle
I am unsure what you are expecting form further engine mods. With 187 at the wheels of your current set up all the gains you can expect to make are small incriments, however make enough of them and they will add up.
Best regards
Mike
poppet valves rule!
-
mk1storm
- Helpful or Confused
- Posts: 80
- Joined: Mon Jan 14, 2008 12:52 pm
- Location: St Neots, Cambridgeshire
Sorry, not really been making myself that clear. I think the dyno operator said 2-3bhp with a bit more advance, so I don't think there was all that much more to have from it. That's why he was happy to suggest setting it back a couple of degrees and making sure no pre-ignition.
I think you've basically answered what I was after, in that there is further potential of course, but not really in one place and from here on in it's multiple mods/tweaks together to gain significant increases. And because of that, I'm basically happy to leave things where they are (at least for the time being) and just enjoy the car.
Thanks for the info. I started off knowing very little about RV8's and engine's in general but have learnt a huge amount from you guys. Still know b*gger all in relative terms of course
I think you've basically answered what I was after, in that there is further potential of course, but not really in one place and from here on in it's multiple mods/tweaks together to gain significant increases. And because of that, I'm basically happy to leave things where they are (at least for the time being) and just enjoy the car.
Thanks for the info. I started off knowing very little about RV8's and engine's in general but have learnt a huge amount from you guys. Still know b*gger all in relative terms of course
