Contour Enthusiasts Group Archives Forums Modifications Duratec Performance David Z question...

David,
Has been some discussion about aftermarket cams for SVT and I wanted to pick your brain as the (former) owner of the trick heads.

It has been said that the hydrolic lash adjusters cannot support too radical of a cam grind (at least I think that was said). IIRC your cams were pretty hot - did you have stock hydrolic lash adjusters or something else? Stock 3L valves? Springs?
Also, what how big were those ports c/w stock 2.5L ports? What LIM and throttle body were you running?

Sorry for all the Qs & thanks..

Hydraulic lash isn't ideal for racing or really wild camshafts. About 8500 rpm the valves will start to float, which at that point there is a big chance of the valve hitting the piston tops then kaboom.

I used stock 3L lifters, relatively stock springs and stock 3L valves with steel seats. The ports were ported to 35/36mm spec which matched up to my PP 3L LIM. Stock 98.5 UIM and polished SVT TB.

While I wasn't really told the exact spec of the cams, they told me 20% more duration and less than 10MM of more lift.

** FYI **

I've come to the conclusion that the secondarys are actually a big restriction making this much N/A hp. This is due to them actually opening too slow and making that power dip in the power band much bigger than before.

In a stock SVT it?s just a small dip, but in a highly modified engine that revs much faster that dip is much bigger because they don't open faster to keep up with the fast reving engine.

If I manually keep them open or use a gutless LIM the power band is from 3-7K. Lotsa fun drag racing

If I let them open normally I have big torque at 2K rpm, 3K comes around and they start to open sapping out power. 4K comes around and they are finally open. Now my power band is from 4-7K. plain sux

If I manually keep them closed I get huge amounts of torque from 1-3K then it runs like an ol 2 valve GM motor. 2nd gear wheel spin is cool

I'm trying to develop a LIM that uses a HD electrical solenoid. This should yield a better mid range. Sorry for kinda getting off your topic

20% more duration DAMN!

The SVT intake cams have 3.2% (8 degrees) more duration then stock.

Do you mean 20 degrees more? (20% is ~50 degrees longer duration!)

Just under 10mm of lift would be stock lift. (9.8mm) That makes sense on a DOHC engine. Massive lift is not necessary.

I completely agree with you on the IMRC. I couldn't love them more pinned (removed) if I tried. Widens the powerband and makes better power right off shifting. Not to mention the instantaneous throttle response.

I believe he said it was 20%, maybe he meant 20º

The early engines didn't have piston valve recesses so they didn't want to take a chance when increasing lift. It looks like most newer engines built after 99 have recesses so you could give it a little more lift.

Very interesting & thanks. It sounds like the the hydrolic lifters were able to support your fairly radical cams though. So you were using the SVT single X-honed UIM and SVT optimized t.body and making near 100 HP/L or 80FWHP/L. This suggests that on the 2.5L SVT these parts may be good for up to 200 FWHP. So maybe that 65mm t.body and extra X-honing of uppper are not required??

I wonder what you could have pulled out of that motor with the 65-70mm t.body, extra X-honed UIM, and 2.5" exhaust with custom A-F tuning???

Yea, now all we need is for someone to swipe those cams and get them reproduced in a real quantity....

The hydraulic lifters on our cars will do just fine, only if your planning on running higher than 9k rpm or tons of lift will you have to worry about them. Chris Rienke ran his engine multiple seasons in the SCCA without any problems.

Without any tuning it ran 240hp at the wheels using stock 19# injectors. If I had tuned it, put larger injectors and stuck in a bigger exhaust 250hp would have been definately possible.

Had I used a dual honed upper and larger TB, probably could have picked up more torque across the whole power band.

I think the SVT upper and TB should do fine for 200fwhp, but I think the heads and LIM are going to need some work.

What compression ratio was/is your 3L running at?

Longer duration thrives on higher CR (and vice versa)

I'm sure that played a large part in how effective they were!

Also I bet with a real UIM your HP figures would have skyrocketed. Running large 35mm valves with those tiny SH UIM ports.
Why would a larger lower suddenly make a big difference when the upper is the piece already restricting the airflow? (I.E. If the lower is already larger then the upper. How does making the lower larger help if the upper stays the same? It's (LIM) not suddenly getting any more airflow.)

IMO the 5HP jump was mainly (3+) from the DH upper alone. The extra EH on the heads probably made up the last 1 or 2HP. The lower likely didn't account for much; if anything.

I had the chambers rewelded to increase quench area, it was calculated that my cr was 11.6ish. When I bought the heads he didn?t tell me if they worked on the chambers so that?s why I say its calculated.

I agree with you on that, if you have a high CR detonation isn't much of a problem if you run big cams either. Only once or twice did I ever hear pinging, but I think it was cheap gas. Plus we only get 91 octane here in CA.

Vadim told me that he made a ton of HP working on the lower, not necessarily making it bigger, just better. Originally he made 220hp on the engine, and then he said that just working on the LIM he picked up 10hp. I believe him.

Before I worked on my LIM I was pulling in a consistent 28-29lbs air/min. After I made the screws flush and decreased shaft area I was pulling in 30-1Lbs air/min. I think he did the same but he wouldn't tell me

I would have used a DH UIM but I couldn't justify the price since I also would have had to upgrade to 24# injectors. I actually had the injectors, it just finding someone who could acutally work on the ECU and retune it. Most of the shops that I called around said that they could do it for about $500-600 plus the cost of renting a dyno

Well I should be doubly set then... Both my UIM & LIM have been well worked & then port matched. Soon to be installed.

Looking at the head inlets. I can tell how nice a job the EH process did to them. However hand porting would fix the bad casting flash. (The non EH'd heads have to suffer from it badly )

That will be a pleasure if I ever go the 3L route... (At my time of choosing I hope! )