Designing Camshafts

frenchyd said:

Since the block is open decked, milling the block would be straight forward. But dealing with the timing chain  would be a serious problem.  Removing links  could only be done  at certain spots without messing up The distributor,  which his driven by that.  And removing  deck would require milling the top of cylinder liners. 

Christ on a cracker! What are you decking the block with, a D-9 Cat?

We're talking about hundredths or thousandths of an inch here. I would be surprised if more than .060" was feasible. 

Cam timing will be affected slightly, but surely someone with your extensive knowledge  of engineering and deep reserves of mechanical experience can compensate for that with adjustable camshaft sprockets. 

In reply to frenchyd :

The idea with getting the RPM down is to work well with shorter duration cams.  but if the cranks aren't available that's that.  What about the 78.5mm? 

For CR...its is hard working with junk.  Normally for something like what I see I would get a set of pistons made with a bathtub CC in them  and get on with the build.  And with a 70mm stroke I'd be designing so 10-12k....on a street car maybe 9k when I design the cam, but you have what?, was it 210 degree @0.050" lift and .375 lift total which is a lower rpm grind so i don't know

In reply to frenchyd :

A usable powerband is absolutely important on a race car. If you can or want to only rev a motor to 6K, and you put cams in it that want to peak at 7K, you have an unusable powerband. Add displacement and it could bring the peak down to under your rev limit.

Also a spring that doesnt valve float on a stock cam until 8300 will not make it that far on a more aggressive cam before valve float. Springs need to be matched to camshaft. A stock cam with a lazy ramp rate is a whole different cam to an aftermarket cam made for power.

DarkMonohue said:

frenchyd said:

Since the block is open decked, milling the block would be straight forward. But dealing with the timing chain  would be a serious problem.  Removing links  could only be done  at certain spots without messing up The distributor,  which his driven by that.  And removing  deck would require milling the top of cylinder liners. 

Christ on a cracker! What are you decking the block with, a D-9 Cat?

We're talking about hundredths or thousandths of an inch here. I would be surprised if more than .060" was feasible. 

Cam timing will be affected slightly, but surely someone with your extensive knowledge  of engineering and deep reserves of mechanical experience can compensate for that with adjustable camshaft sprockets. 
  

  Oops rereading what you wrote. The reason for the complexity is there is one chain that goes from the crank up to the camshafts. Then down to a jack shaft that drives the distributor.  Back up to the other camshaft and then back down to  the crankshaft. 
 Milling the block enough to effect the compression enough to achieve  the 13-1. Number or better  would probably drop both heads down,  oh around .200. Since the timing chain goes over and comes down twice  that means we'd need about .7-800 shorter chain.  Without knowing the link length I can't tell for sure. But it's not straight forward.  
     The chain is only one issue.  The 54 studs would need to be removed. That's a  major issue since some go through the coolant. 
  Then having those studs remade,  relocating the chain guides,  plus several other issues  make impossible. 
   mke was talking about increasing compression ratio from the existing 7.8-1  closer to13-1   Without doing the math. ( because milling the block would be more expensive then buying pistons ). 
I'd need a lot removed.  
     I'm budget limited and people are offering suggestions .   Let me back up a bit.  I'm going to the $2000 challenge with the engine pretty stock except for a pair of turbo chargers.  Then I'm taking the car Vintage racing where turbochargers aren't allowed.  There I'll be out spent by a lot.  So I need to figure cheap ways of gaining power. Cams, compression, port work  and E85  are really my only  ways.  Unless I can come up with the $20,000+ it would take to be competitive. 
 
  But Like mke says. Finishing last is better than not racing at all.  So with a small budget  I need to carefully weigh modifications for potential gain.  
      Luckily computers allow me to do that with decent accuracy.  

frenchyd said:

mke was talking about increasing compression ratio from the existing 7.8-1  closer to13-1   

No, I asked if you could get the longer stroke crank which would take you from 7.8 to 9.3 the mill a little to go from 9.3 to 9.5.  You said the cranks are hard to come by so that's a dead end on a budget.

In reply to mke :

One suggestion made was milling the block for more compression. 
  You're right.    If I could find a 6 liter crank I'd gain stroke and by using the 5.3 piston  milled slightly I'd gain compression. 
yes the 6 liter crank fits. Everything is the same, except the rear seal ( which is better)  and the oil pump (which is bigger)

https://buildingthelegend.co.uk/introducing-the-tera

Neville has re created the XK13 engine and will happily sell you one, bit pricey tho

I had to laugh when I saw the pic.  The Ferrari 400/400i have the intake ports in the middle like that....which is a big part of why I've spent all these years  parting on head not like that :)

Opti said:

In reply to frenchyd :

A usable powerband is absolutely important on a race car. If you can or want to only rev a motor to 6K, and you put cams in it that want to peak at 7K, you have an unusable powerband. Add displacement and it could bring the peak down to under your rev limit.

Also a spring that doesnt valve float on a stock cam until 8300 will not make it that far on a more aggressive cam before valve float. Springs need to be matched to camshaft. A stock cam with a lazy ramp rate is a whole different cam to an aftermarket cam made for power.

I'll simplify things. Piston speed, crank , rod strength  etc on the V12 is such that the engine could safely rev over 10,000 rpm.   The stock camshaft flattens out at about 5500 rpm.  With reground camshaft it pulls to about 7000 rpm.  But you lose power below 3000 rpm. Increased compression adds power.  

In reply to Rigante :

Beautiful though isn't it?   The original version made 502 horsepower back in 1966  

    Lyons knew that Ford could out spend him 100 to 1 whereas it would have been a fair fight between Jaguar, Ferrari, Maserati, and Porsche. 

frenchyd said:

 With reground camshaft it pulls to about 7000 rpm.  But you lose power below 3000 rpm. Increased compression adds power.  

Yes! As duration goes up so must CR....cams usually mean pistons, in for a penny, in for a pound

There is a reason boost is so  popular

In reply to mke :

Just gotta let those vintage racer guys let me achieve power with a turbo instead of my wallet. 

frenchyd said:

  Any idea how thin stock pistons can be milled to before they will fail?
 
     Since the block is open decked, milling the block would be straight forward. But dealing with the timing chain  would be a serious problem.  Removing links  could only be done  at certain spots without messing up The distributor,  which his driven by that.  And removing  deck would require milling the top of cylinder liners. 

You can probably get an idea on that by loooking at the top ring land height.

In reply to Paul_VR6 (Forum Supporter) :

I should be able to measure thickness with some accuracy. The piston top is completely flat and using a carefully measured rod  calculate with a vernier caliper. 
     If I put a bowl in the top  I wonder How thin I could risk getting it. 

Maybe I should go back to the 1990's when I built the engine for the V12 XKE. 
     I bought 2 sets of 6" inch  Chevy racing small block rods. Then offset ground the crank to 2.100 ( from 2.300) 

 That  added .400 to the stroke.  Bore the cylinders out to  3.750 and use those pistons. 
  I would need to narrow the rod bearings to the Jaguar size  but everything else should be off the shelf.   That gets me to 384 cu in.  For about $1000. Hopefully I can get the 13-1  compression I need using Chevy pistons. 

In reply to frenchyd :

Dude...if you had the solution why ask?  That's a fine plan. ...not sure I'd worry about trying to hit 13:1 CR.....I'll run the graphs but  generally its not much gain unless you have really long duration in the cams.

That's a 0.200" stroke increase not 400 but still.

In reply to mke :

I haven't priced those out yet.  It may be cheaper to just pay for pistons or something. Don't forget I need to pay for 2 sets of rods, 2 of pistons& bearings.   
  
I'll try it tonight. 
   
   If I offset reduce the rod size from 2.300 to 2.100 I pick up .200 at the top and at the bottom don't I?  

The actual compression I wind up with depends on the stroke  I net out at. ( there is always a little loss due to wear  and blending )  plus I'm not sure what Jaguar's rod length is, just drawing a blank right now.   Then what piston will I wind up with.  Last time I had mine made.

    ( if I could find the 6 liter crank I'd wind up at 417 cu in )   Stock bore it's 366 cu in or 6 liters.  96mm is pushing it.  
    

frenchyd said:

   If I offset reduce the rod size from 2.300 to 2.100 I pick up .200 at the top and at the bottom don't I?  

When you change a circle from 2.3 to 2.1 the diameter changes by 0.2, but the center only moves 1/2 that distance so  the total stroke change is equal to the diameter change, which is 2x the change in centerline

Paul_VR6 (Forum Supporter) said:

I have a marketplace notification setup for v12, I kinda want one now 

In todays Facebook Jaguar XJS club.  There are two  for $500 one relatively close to you  he's asking $500 complete with the transmission included. 91 w/ 61,000 miles.  But locked up.  Most of the time that happens is someone tries to turn the crank backwards and it breaks the timing chain tensioner. ( it's nylon)   
      I'd offer  him $200.  
  There is another one down in Alabama that turns over etc. for $500 no mention if that includes the tranny.   If I was looking $300 is all I'd pay. 

Opti said:

In reply to frenchyd :

A usable powerband is absolutely important on a race car. If you can or want to only rev a motor to 6K, and you put cams in it that want to peak at 7K, you have an unusable powerband. Add displacement and it could bring the peak down to under your rev limit.

Also a spring that doesnt valve float on a stock cam until 8300 will not make it that far on a more aggressive cam before valve float. Springs need to be matched to camshaft. A stock cam with a lazy ramp rate is a whole different cam to an aftermarket cam made for power.

Depends. For autocross you probably want something with  a 4000 rpm band.  Road race you want  as little as 1500?circle track at Daytona. 700 rpm?  Realize I'm talking about peak power  where you are actually racing at. Not what you need to cruise in the pits or start with.  
  Increasing the size of the engine just broadens the power band. 

frenchyd said:

  Increasing the size of the engine just broadens the power band. 

not really.  Take a ship engine for example, its huge with a power band of maybe 20rpm.  The more meaningful term is turndown ration, which is the usable range compared to the total range.  In practice its about port velocity, cam duration, intake and exhaust tuning.

I don't have the software key yeyt but we'll get you answwers soon

mke said:

In reply to frenchyd :

Dude...if you had the solution why ask?  That's a fine plan. ...not sure I'd worry about trying to hit 13:1 CR.....I'll run the graphs but  generally its not much gain unless you have really long duration in the cams.

 

That's a 0.200" stroke increase not 400 but still.

Finally got time to shop a bit.  Cheaper just to order the pistons. In fact the 12 Chevy rods are only slightly cheaper than ordering 12 pistons. 

In reply to Paul_VR6 (Forum Supporter) :

In the 1970's Offenhauser's had a  2&3/4" stroke just like JaguarV12's. Were turbo charged, and used Alcohol based fuel.  They  also made over 1000 horsepower out of just 158 cu in. 
    How far would I be off patterning my camshafts after the Offenhauser?  Maybe not the camshafts for the Indy races but road races?  

If you were shooting for double that hp it would be a good design. With your bigger displacement and likely much lower boost a different design would be better.

In reply to Paul_VR6 (Forum Supporter) :

I wasn't thinking that, what I was thinking is the profile of the lobe used would be optimal  for a short stroke alcohol fueled turbo charged engine.  Then based on actual flow rates I can work on my computer to optimize lift, duration, and LSA.