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Autobanmod
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Discussion Starter · #1 ·
I have seen exhaust gas temperatures in the region of 1100°C / 2000°F on my turbocharged 2002 V-Rod with abt 15 psi boost.
This is too high.
In my opinion this is mainly caused by the stock intake/exhaust camshaft characteristics, they are by far too "wild" for a turbo application. With a turbo fitted, the exhaust gas backpressure - owing to flow resistance caused by the turbine wheel and housing -is higher than the intake boost pressure (btw you don't have that problem with a mechanical driven blower). Of course the back pressure is not constant and fluctuates a lot, but let's try and keep things simple.
I have tried degreeing of cams (slotted sprockets), about 6-8° less overlap and 5° higher spark advance, but was not content with the results, the EGT was still far too high.

Some weeks ago, a member here approached me if I could give him advise on turbo cams, but until now I didn't really have the time to look into this subject more closely.
Meanwhile I have found an interesting comparision of Porsche Carrera cam characteristics, see attached table.
The source really is a "must read":
"Forced Induction Performance Tuning" by A. Graham Bell, ISBN 1 85960 691 1, first published 2002

Elsewhere in that book (page 238f) is a passage dealing with exhaust gas backpressure:
Exhaust gas could flow back into the inlet track. This gas then dilutes the inlet charge, taking up volume which should have been occupied by fresh air/fuel mixture. Also, the hot exhaust gas reduces charge density by adding heat to it, then in severe cases this extra charge can set off a chain of events leading to detonation.
Taking the specs of the attached table, the differences between the Porsche Turbo engine and the old 3,0 liter Porsche Carrera are:

Intake opens 2° later
Intake closes 14° earlier
lobe lift 17% less

Exhaust opens 16° later
Exhaust closes 6° earlier
lobe lift 14% less

The turbo cam profiles are much narrower and have consequently (?) less lift. The lobe separation angle of the naturally aspired engine is 113°, that of the turbo engine is 108°.
That means that the valve overlap is 2°+6°-5°=3° (minus 5° because of the smaller lobe separation angle)
Just three degrees reduced!

Bore and stroke and cam specs of the naturally aspired Porsche 911 are similar to those of the V-Rod "revo" engine.
Of course this should not be misread, I'm not saying that V-Rod turbocams should be exactly like those of a 1980 Porsche Turbo. But it's a good indication which way to take.
I will try and have my cams remachined accordingly and will report the results, that might take a good while though...
 

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Autobanmod
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9,896 Posts
Discussion Starter · #2 ·
By the way, I've meanwhile spent a couple of hours searching for real figures for stock V-Rod cam specs, alas without finding what I'm looking for.
I'd like to see the "real" specs:
intake opens/closes @... degrees
exhaust opens closes @...degrees
Not just the figures for 0,01" lift, or durations.
Maybe someone could post them here?
 

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I have seen exhaust gas temperatures in the region of 1100°C / 2000°F on my turbocharged 2002 V-Rod with abt 15 psi boost.
This is too high.
In my opinion this is mainly caused by the stock intake/exhaust camshaft characteristics, they are by far too "wild" for a turbo application. With a turbo fitted, the exhaust gas backpressure - owing to flow resistance caused by the turbine wheel and housing -is higher than the intake boost pressure (btw you don't have that problem with a mechanical driven blower). Of course the back pressure is not constant and fluctuates a lot, but let's try and keep things simple.
I have tried degreeing of cams (slotted sprockets), about 6-8° less overlap and 5° higher spark advance, but was not content with the results, the EGT was still far too high.

Some weeks ago, a member here approached me if I could give him advise on turbo cams, but until now I didn't really have the time to look into this subject more closely.
Meanwhile I have found an interesting comparision of Porsche Carrera cam characteristics, see attached table.
The source really is a "must read":
"Forced Induction Performance Tuning" by A. Graham Bell, ISBN 1 85960 691 1, first published 2002

Elsewhere in that book (page 238f) is a passage dealing with exhaust gas backpressure:


Taking the specs of the attached table, the differences between the Porsche Turbo engine and the old 3,0 liter Porsche Carrera are:

Intake opens 2° later
Intake closes 14° earlier
lobe lift 17% less

Exhaust opens 16° later
Exhaust closes 6° earlier
lobe lift 14% less

The turbo cam profiles are much narrower and have consequently (?) less lift. The lobe separation angle of the naturally aspired engine is 113°, that of the turbo engine is 108°.
That means that the valve overlap is 2°+6°-5°=3° (minus 5° because of the smaller lobe separation angle)
Just three degrees reduced!

Bore and stroke and cam specs of the naturally aspired Porsche 911 are similar to those of the V-Rod "revo" engine.
Of course this should not be misread, I'm not saying that V-Rod turbocams should be exactly like those of a 1980 Porsche Turbo. But it's a good indication which way to take.
I will try and have my cams remachined accordingly and will report the results, that might take a good while though...[/QUOTE

Jan, while your info pretty well sums it up, more simply put, yes overlap. However if your cylinder head temp is staying at reasonable range the EGT's will not harm anything physically, except lack of performance from the over rich condition and lack of poorer cylinder fill. We have run as high as 1980 on the rear due to the raw gases being introduced into the exhaust. PM sent
As long
 

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My understanding is less overlap & less LSA. Lift is dependent on amount of boost ( & when it comes in/ turbo efficiency) & where in rpm range you want the power band. Assuming a Trask turbo with fuel system upgrades, I would anticipate less overlap & LSA but more lift. If enough of us were interested maybe Jones or Comp Cams would step up again.
 

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Autobanmod
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9,896 Posts
Discussion Starter · #7 ·
Exactly my point - less overlap & less LSA cannot be achived by degreeing of cams alone, you really have to narrow the cam profiles.
If you just spread the I/E cams apart with slotted sprockets to reduce overlap, then you increase the LSA.
However I have a different opinion on valve lift:
I assume that Porsche also reduced the lift in order to keep the valve acceleration (bouncing) with the narrower cam profile under control. There might be other reasons and it will be different for a race engine.
My personal target for my bike has changed from top HP & max boost to finding a balance between fun and TBO. :)
 

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For what its worth, I was at the AETC in Orlando in 2006. One of the presentations was by HD jointly with Comp Cams. They stated that the destroyer valve train was stable to 15,000 rpm. Since the rest of the motor would never see that, they stopped there. I'd like to have more lift to run more boost ( & begin boost sooner ). I heard it suggested that the Trask configuration would support 250 rwhp , if everything else was in place.
 

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Autobanmod
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Discussion Starter · #9 ·
Tim, thanks for your PM
The highest temp I've seen was 2100° F, the turbo suffers, also the exhaust valves.
I want it down, so I can add more boost in return :D
 

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Killer Service Inc.
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Jan, was the temps higher in the rear or front cylinder.

Thinking post detonation on the front cylinder causing the burned up pistons.


This was e-mailed to me. http://www.pumaracing.co.uk/

Really good reading...
 

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lots of cams have been ground for turbo jap bikes that are medium lift and very short duration and are meant to be installed with little overlap...the porsche cams have very little overlap..please keep us posted on your testing, i am very interested in the results.. overlap is a problem with turbo`s lift isn`t .. i think the only reason for the porsche cams having less lift is the valve opening rate becomes really radical if the lift remains the same and the duration gets very short...the kawasaki turbo cams that i am familiar with had extremely small nose radius because of the short duration and medium lift and required a very carefull break in or it would wipe out the lobes..also the valve opening rate is limited by the follower(cam bucket )size...the stock 33mm bucket size of a v-rod probably can`t accept a very short duration at the stock lift...
 

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By the way, I've meanwhile spent a couple of hours searching for real figures for stock V-Rod cam specs, alas without finding what I'm looking for.
I'd like to see the "real" specs:
intake opens/closes @... degrees
exhaust opens closes @...degrees
Not just the figures for 0,01" lift, or durations.
Maybe someone could post them here?
Intake lobe lift .429" , Exhaust lobe lift .392"
Intake Duration @ 1mm lift 248°, Exhaust Duration @ 1mm lift 235°
Intake centerline 106° Exhaust centerline 105°
Intake Opens @18° BTDC / Intake Close @ 50° Abdc
Exhaust Opens @ 42.5 BBDC / Exhaust Close @ 12.5 Atdc
Opening and closing numbers are @ 1mm cam lift
 

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Intake lobe lift .429" , Exhaust lobe lift .392"
Intake Duration @ 1mm lift 248°, Exhaust Duration @ 1mm lift 235°
Intake centerline 106° Exhaust centerline 105°
Intake Opens @18° BTDC / Intake Close @ 50° Abdc
Exhaust Opens @ 42.5 BBDC / Exhaust Close @ 12.5 Atdc
Opening and closing numbers are @ 1mm cam lift
If I understand it correctly 270° = BDC so wouldn't that mean:
Exhaust Opens @ 47.5° BBDC
 

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I'm not sure what you mean. Where are you getting the 270° from ?
Apparently from a lack of sleep.

I thought about it a little more and see that what you posted makes sense:

TDC = -360 °, 0°, 360°, 720°
BDC = -180°, 180°, 540°

Exhaust opens 42.5° BBDC = -180°-42.5° = -222.5°
Exhaust closes 12.5° ATDC = 0.0° + 12.5° = 12.5°
Exhaust duration =12.5° - (-222.5°) = 235°

Intake opens 18° BTDC = 0.0°- 18° = -18°
Intake closes 50° ABDC = 180° + 50° = 230°
Intake duration = 230° - (-18°) = 248°
 

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Apparently from a lack of sleep.
That's o.k, I was scratching my head trying to figure out where my mistake was and couldn't for the life of me figure out what the 270 was. Opening# + Closing # + 180 = Duration.
 

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opening the lobe centers on the stock cams to somewhere around 114 would make a major difference in decreasing overlap... those numbers are not uncommon on jap turbo bikes.. if you are having custom turbo cams ground i would try to keep as much lift as possible at the shorter duration without getting too aggressive on the valve opening and closing rates..post the results and details.. very interesting subject to me...
 

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opening the lobe centers on the stock cams to somewhere around 114 would make a major difference in decreasing overlap... those numbers are not uncommon on jap turbo bikes.. if you are having custom turbo cams ground i would try to keep as much lift as possible at the shorter duration without getting too aggressive on the valve opening and closing rates..post the results and details.. very interesting subject to me...
Stock cams would look like this on 114° lobe centers:

Intake Opens @ 10° BTDC / Intake Closes @ 58° ABDC
Exhaust Opens @ 51.5° BBDC / Exhaust Closes @ 3.5° ATDC
13.5° of overlap ( Exhaust close# + Intake open #)

If you used an exhaust cam for an intake you could decrease the overlap further.
Exhaust Cams on 118° lobe center-line would look like this:

Intake Opens @ -.5° BTDC / Intake Closes @ 55.5° ABDC
Exhaust Opens @ 55.5° BBDC / Exhaust Closes @ -.5° ATDC
-1° of overlap
You now have negative overlap.
Somebody check my numbers, Its early and I haven't finished one cup of coffee.
 

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All the cam numbers I have posted are taken by reading the cam. This doesn't take into consideration the effect that valve clearance has on the duration or lift. If you measure at the valve using .013" clearance the stock intake duration of 248° @ 1mm lift is reduced to 237° and the valve lift is reduced by the .013" clearance. These were actual numbers checked at the valve in my engine.
 
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