Notices
928 Forum
Sponsored by:
Sponsored by: 928 Specialists

how many 7 liter strokers are out there????

 
Old 02-26-2018, 09:21 AM
  #166  
FredR
Addict
Rennlist Member
 
FredR's Avatar
 
Join Date: Jun 2005
Location: Oman
Posts: 5,802
Default

Is there anything in the GTS exhaust cam profile design to suggest that it is "less than optimal"?
FredR is offline  
Old 02-26-2018, 09:31 AM
  #167  
ptuomov
Super User
 
ptuomov's Avatar
 
Join Date: Jan 2009
Location: MA
Posts: 4,616
Default

Originally Posted by FredR View Post
Is there anything in the GTS exhaust cam profile design to suggest that it is "less than optimal"?
What's your objective function?

My opinion:

If you want to pass emissions with certainty even if the car is somewhat neglected and produce a flat torque curve in the factory decided power band, the factory GTS cams are probably pretty good for the GTS motor.

I think most of the views about GTS exhaust cam being "bad" come from people taking the factory manual misinformation at face value. This includes me a decade ago.

If you want to make more mid-range torque, I think you need more overlap than the factory GTS cams. So earlier IVO and later EVC. That will make the emissions tail pipe test a little more sensitive, but if everything else is set up well it's going to pass with much more overlap than what's ground into the stock GTS cams. If you want to make more power at high rpms, you probably want earlier EVO and later IVC. Those changes together should allow you to increase compression a little bit by shaving the heads and using the thin stock gasket. If you make all those changes, headers will start really helping. I think Roger Tyson's GTS has all those changes (including Elgin 65-6 cams) and he appears to be very happy with his motor. GT cams would also help, but less.

That's just my opinion. Don't confuse that with a fact.

Last edited by ptuomov; 02-26-2018 at 09:47 AM.
ptuomov is offline  
Old 02-26-2018, 10:44 AM
  #168  
FredR
Addict
Rennlist Member
 
FredR's Avatar
 
Join Date: Jun 2005
Location: Oman
Posts: 5,802
Default

Originally Posted by ptuomov View Post
What's your objective function?
That's just my opinion. Don't confuse that with a fact.
About 15 years ago there was a widely held opinion around that the GTS exhaust cam was constrained by design to stop the GTS from outclassing the 911 turbo's of the day on top end performance. When I was putting my current motor together [a 90 S4] I received a recommendation to use the GTS inlet cams with the S4 exhaust- no real clue whether it is an improvement or not but it seems to work ok. Given design tools available today it seems some of you chaps are better armed to evaluate prospective performance mods than folks were 15 years plus ago. What with the likes of Colin cams and other grinds around the possibilities presumably are more evident than at any other time previously.
FredR is offline  
Old 02-26-2018, 12:20 PM
  #169  
ptuomov
Super User
 
ptuomov's Avatar
 
Join Date: Jan 2009
Location: MA
Posts: 4,616
Default

Originally Posted by FredR View Post
About 15 years ago there was a widely held opinion around that the GTS exhaust cam was constrained by design to stop the GTS from outclassing the 911 turbo's of the day on top end performance. When I was putting my current motor together [a 90 S4] I received a recommendation to use the GTS inlet cams with the S4 exhaust- no real clue whether it is an improvement or not but it seems to work ok. Given design tools available today it seems some of you chaps are better armed to evaluate prospective performance mods than folks were 15 years plus ago. What with the likes of Colin cams and other grinds around the possibilities presumably are more evident than at any other time previously.
We learn new stuff every day. Often, the learning comes in the form of a conspiracy theory being discredited.

Will the S4 exhaust cam run better or worse in a GTS or S4 engine than the GTS exhaust cam? I don't have the info in my fingertips about the LCAs available for GTS and S4 intake and exhaust cams. One theory is that the S4 exhaust cam, although shorter in duration, increases the overlap. The increased overlap will boost the mid range torque, and the exhaust port of the 928 heads flows so stupidly well to start with that the shorter duration doesn't hurt too much. It's just a theory. If Rob posts the measured LCAs for these cams, then we can go on and theorize further on a firmer ground.
ptuomov is offline  
Old 02-26-2018, 01:51 PM
  #170  
Strosek Ultra
Addict
Rennlist Member
 
Strosek Ultra's Avatar
 
Join Date: Feb 2011
Location: Mostly in my workshop located in Sweden.
Posts: 1,338
Default

Some basics about cams. The exhaust cam usually has less influence on engine power than the intake cam. Very mild cams like the 928 stock cams, usually perform best having a retarded setting (intake valve closes late). Medium performance cams or some may call them sports cams usually perform best in a split overlap setting. Very hot racing cams usually peform best in an advance setting.
┼ke
Strosek Ultra is online now  
Old 02-27-2018, 05:14 PM
  #171  
Mark Anderson
The Parts Whisperer
Rennlist
Site Sponsor

 
Mark Anderson's Avatar
 
Join Date: Nov 2002
Location: Anaheim Ca
Posts: 6,216
Default cam experiment

Reminds me of something I tried years ago

Mark Anderson is offline  
Old 02-27-2018, 09:51 PM
  #172  
928sg
Resident 928 Modiholic
Rennlist Member
 
928sg's Avatar
 
Join Date: Mar 2013
Posts: 1,879
Default

Originally Posted by Mark Anderson View Post
Reminds me of something I tried years ago

Looks very similar to my original variocam experiment. I have several broken camshafts from experimenting.
928sg is offline  
Old 02-28-2018, 05:28 AM
  #173  
Strosek Ultra
Addict
Rennlist Member
 
Strosek Ultra's Avatar
 
Join Date: Feb 2011
Location: Mostly in my workshop located in Sweden.
Posts: 1,338
Default

Originally Posted by Mark Anderson View Post
Reminds me of something I tried years ago

Did it work well? Tell us more.
┼ke
Strosek Ultra is online now  
Old 02-28-2018, 05:31 AM
  #174  
Strosek Ultra
Addict
Rennlist Member
 
Strosek Ultra's Avatar
 
Join Date: Feb 2011
Location: Mostly in my workshop located in Sweden.
Posts: 1,338
Default

Originally Posted by 928sg View Post
Good luck with the cam mods. I tried to do that years ago and ended up with broken cams The factory cams are very brittle. but those don't look factory.... huge lobes~!
Tell us more about your broken cams. What happened? Any solutions/fix?
┼ke
Strosek Ultra is online now  
Old 02-28-2018, 01:20 PM
  #175  
SwayBar
Addict
Rennlist Member
 
SwayBar's Avatar
 
Join Date: Feb 2006
Location: Chicago Bears
Posts: 2,335
Default

Originally Posted by Strosek Ultra View Post
Tell us more about your broken cams. What happened? Any solutions/fix?
┼ke
There's a thread on that somewhere and it's a sad story.

One thing I remember was that the newly ground cams were broken during shipping.
SwayBar is offline  
Old 02-28-2018, 01:31 PM
  #176  
928sg
Resident 928 Modiholic
Rennlist Member
 
928sg's Avatar
 
Join Date: Mar 2013
Posts: 1,879
Default

One cam was broken in shipment. I broke another showing someone how brittle the factory cams are. Stand on one end of the cam with the toothed gear high center. Stomp on the other end of the cam & viola 2 pieces. The cam gear failures were catastrophic. just when you think something was strong enough, It decides to visit you by a sudden exit through the cam cover during idle & whiz by your head. I don't recommend that one. I don't know if I kept any of the broken bits. We are packing up for a move so it will be months before I find them again... if I even have them.
928sg is offline  
Old 02-28-2018, 06:26 PM
  #177  
Mark Anderson
The Parts Whisperer
Rennlist
Site Sponsor

 
Mark Anderson's Avatar
 
Join Date: Nov 2002
Location: Anaheim Ca
Posts: 6,216
Default

Originally Posted by Strosek Ultra View Post
Did it work well? Tell us more.
┼ke
The first set broke after just a few hours. This is the replacement part but we never tried them. If I remember correctly these had more teeth which required a longer chain
Mark Anderson is offline  
Old 02-28-2018, 09:32 PM
  #178  
928sg
Resident 928 Modiholic
Rennlist Member
 
928sg's Avatar
 
Join Date: Mar 2013
Posts: 1,879
Default

I broke 2 similar to Mark's picture, and went billet after that.
928sg is offline  
Old 03-01-2018, 07:48 AM
  #179  
Strosek Ultra
Addict
Rennlist Member
 
Strosek Ultra's Avatar
 
Join Date: Feb 2011
Location: Mostly in my workshop located in Sweden.
Posts: 1,338
Default

Originally Posted by 928sg View Post
One cam was broken in shipment. I broke another showing someone how brittle the factory cams are. Stand on one end of the cam with the toothed gear high center. Stomp on the other end of the cam & viola 2 pieces. The cam gear failures were catastrophic. just when you think something was strong enough, It decides to visit you by a sudden exit through the cam cover during idle & whiz by your head. I don't recommend that one. I don't know if I kept any of the broken bits. We are packing up for a move so it will be months before I find them again... if I even have them.
Sorry to hear about your camshaft problems. One guy over here in Sweden had one of his Lizard cams to break off during shipping. The 928 chilled cast iron camshafts are not more brittle than any other cams. One has to take care when torquing down the camshafts. I agree the chain gear being an integrated part of the camshaft is not suitable for the kind of drilling you guys have made in order to make it adjustable. Chilled cast iron is the far best camshaft material in respect of wear characteristics.
┼ke

There are various materials crankshafts are manufactured from-

Generally, the camshaft is made from Chilled iron castings, because this material has far superior wear characteristics than any other material.

Majorly two materials are used - IRON and STEEL

I) IRON
  1. Hardenable iron (developed in 1930)- low cost replacement for steel.
  2. Spheroidal graphite cast iron (used by FIAT in 1980s) - failed due to its low hardness value in cast form.
  3. Chilled chrome cast iron- Extremely good scuff resistance as mentioned above and most used material for camshafts.
II) STEEL
  1. Carbon Steel- EN8/EN9 (used during 1930ľ1945)- used nowadays for induction hardened camshafts due to its through-hardening characteristics.
  2. Alloyed steels-EN351 AISI 8620 and EN34 etc. - Best when run against a chilled cam follower.
  3. NITRIDING STEEL-EN40B- The best steel for camshafts. After nitriding it gives a surface hardness and finish similar to chilled iron.
Now when to use STEEL or IRON
  • IRON - High volume production
  • STEEL - Low volume production or high quality camshafts
Strosek Ultra is online now  
Old 03-01-2018, 11:06 PM
  #180  
V2Rocket
Rainman
Rennlist Member
 
V2Rocket's Avatar
 
Join Date: Jan 2007
Location: Rancho Cucamonga, CA
Posts: 42,574
Default

If you use 2x exhaust cams per head you can fit adjustable camshaft gears instead.
By enlarging the center bore you can fit Honda or the like gears that are sourced inexpensively from eBay. Just match the "donor cam gear" tooth count against your crank drive gear (y = 2x). Lots of options.
V2Rocket is offline  

Thread Tools
Search this Thread
Quick Reply: how many 7 liter strokers are out there????


Contact Us - About Us - Advertising - Cookie Policy - Privacy Statement - Terms of Service

© 2019 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
 
  • Ask a Question
    Get answers from community experts
Question Title:
Description:
Your question will be posted in: