Intake Valve Closing Most critical valve opening/closing point To early of an IVC and the cylinder may not have time to fill completely To late of an IVC and the cylinder pressure will overcome the inertia of the incoming airflow and revert flow back into the intake port This causes a serious disruption to flow and destroys any pressure waving tuning
Exhaust Valve Opening 2nd most critical valve opening/closing event Determines the balance between power event efficiency and exhaust pumping losses To early of an exhaust opening will reduce the amount of energy converted from cylinder pressure to mechanical force on the piston To late of an EVO will cause an increase in the amount of power needed to expel the burned exhaust gases from the cylinder
Exhaust Valve Closing Along with IVO it is the least critical valve timing event Along with IVO it determines the amount of valve overlap and exhaust scavenging Too early of an EVC will not allow the exhaust gas to be fully purged from the cylinder Too late of an EVC will allow fresh air/fuel mix to be purged into the exhaust system
Intake Valve Opening Along with EVC it is the least critical valve timing event Along with EVC it determines the amount of valve overlap and exhaust scavenging Too early of an IVO will allow exhaust gas reversion into the intake ports causing major flow disruption and intake charge dilution Too late of an IVO will limit the time available for the cylinder to completely fill
Just some more info, still working on the hard numbers.
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12:26 PM
Scoobysruvenge Member
Posts: 550 From: Richmond Virginia Registered: Apr 2009
So far this is what I have I have looked at some V6 turbo grind cam specs for mild street performance, this is what I have as some preliminary numbers represented as WIW below (What I Want) of course I have a lot more work to do before I settle on a hard set of numbers
I am also assuming that the – negative IVO / EVC numbers on the factory cams are referenced to TDC therefore they are at BTDC and the IVC / EVO are referenced to BDC as the specs given for the stock 3.4 DOHC cams do not include this information.
IVO difference between the two is - 14.5 Degrees TDC IVC difference between the two is + 25.5 Degrees BDC EVO difference between the two is - 31 Degrees TDC EVC difference between the two is - 19 Degrees TDC
What do you boys think???
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11:28 PM
Nov 20th, 2009
Scoobysruvenge Member
Posts: 550 From: Richmond Virginia Registered: Apr 2009
Here are some of the things that caught my eye while cruising the Turbo cam grinders websites.
1. “Turbo cams open late as, much as 40 degrees over NA engine in some cases, so getting the valve open faster makes large improvements.” I am unsure whether he is referring to the intake valve or the exhaust, I am guessing it is it is the exhaust from the information I previously posted in this thread.
2. “The exhaust valve closes very close to TDC (ATDC).” These numbers pan out with WIW numbers I posted for the EVC.
3. “Generally a shorter duration is favorable.” It looks like the cams could use a little more duration, according to the Grand National cam specs I referenced to get my WIW baseline numbers I posted.
4. “Cam lobe separation in the 112 – 114 degrees good for a well matched street turbo” No lobe separation numbers were posted with the stock camshaft numbers seen in this thread, if some one has that number I would like to have it.
5. “Lower lift is generally desirable, but can come with some draw backs.” No numbers are posted for lift at .050 for stock camshaft numbers seen in this thread. Will the lift be .369 either way? If someone can convert it or clear this up let me know.
I should be posting the 94/95 specs as a comparison soon.
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12:34 AM
Nov 23rd, 2009
Scoobysruvenge Member
Posts: 550 From: Richmond Virginia Registered: Apr 2009
Thanks for all the help guys, now that the stroke subject has had some research I will be moving back to my "Turbo 3.4 DOHC w/Aluminum Rods with all the conclusions found at
Stock piston height of the 3.4 DOHC is 1.464 (distance between pin center and piston top) if this number can be attained using a given stroke and rod combination the stock pistons could be used for example:
If I used a 5.7 SBC rod with a Honda Journal size 1.889 I could add .111 to the 5.7 rod measurements from earlier in this thread listed below it comes out like this.
5.7 Inch rod used Deck Height – 8.818 Stroke/2 – 1.771609095 Rod Length – 5.7 Piston Deck Clearance – .010 Compression Height = 7.481609095 Compression Height subtracted from Deck Height = 1.336390905 With .000 Piston Deck Clearance = 1.346390905 Minimum Deck Height – 1.200 Verdict – Usable with .000 PDC and .010 PDC
The numbers above are based on grinding the crank down from 2.25 to a 2” journal with 10 thousandths taken away for take up, so the available stroke for the grind is 2.15 If I add the extra .111 from using the Honda rod journal to the 1.346390905 you come up with 1.457390905 very close to the stock piston height of 1.464. This is less than 7 thousandths this small amount could be taken up surfacing the block deck and getting some of the 10 thousandths take up back used on the grind from 2.25 to 2.15.
So a set of 1.889 5.7 rods and I could use the stock pistons, I thought this was interesting, not that this is what I’m going to do but it is definitely on the table. This would also increase stroke by a little more than 3mm putting the engine displacement at roughly 3.8 as well as giving the engine a 93 x 93mm bore and stroke. This makes this a square engine which has some benefits of its own, with the addition of turbo super high RPMs are no longer necessary to make big power. My intentions are to have an engine that has a linear power curve all the way to redline. This should ensure maximum traction in the corners without any big spikes in power to unsettle the suspension.
