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Amazingly only one spring was found in the wastegate but it was a bloody stiff one. Not sure what the story behind the spring pressure is because it came with the turbo many years ago. Anyway it was swapped over for two smaller springs and now sits at 7.5 PSI. It got one quick run on the Dyno without much timing or revs and pulled 200hp at the rear wheels. Hopefully get the tune completed tomorrow

Another problem, during a dyno pull a lifter crapped itself, probably from age and the hard facing failing and it’s flattened the lobe on the cam. Should have replaced the cam when I replaced the timing chain. Oh well time to pull down the front of the motor but a good opportunity to install a proper turbo cam.

Does anyone have any ideas on suitable cam specs for a turbo application. I had a quick talk with the dyno tuner and he mentioned that you don’t want too much overlap as it doesn’t work well with the boost but a bit of extra lift wouldn’t hurt.

my understanding is generally mild NA type profile but with wider LSA ie. less overlap. But really depends on the engine and turbo setup, overlap can actually help sometimes in spooling but I am no expert on it as I have done no work with boosted engines, have simulated them in software just out of curiosity.

From what I read the overlap thing really was more of a rule for the old turbo days when turbos were very lazy and less efficient, now days they look more like NA cams. Still the same applies for supercharged engines with the wider LSA as they don't need extra exhaust gases to help spool and need more overlap to trap the positive intake charge in the cylinder to get the best efficiency out of the SC.

Thanks vlad, now I just need to work out how inefficient my turbo is. I know it’s not a new turbo but it’s not a dinosaur either.

This is were I get completely lost. All this AR number and what not completely goes over my head. Even will all the understanding of engine wave dynamics pretty much all goes out the window with turbos so I can't get get my head around even with the engine design. Seems the software agrees with me too, absurd numbers and gibberish comes out when I start adding turbos.

SC are fine though as the same wave dynamics apply as does in N/A. basically the same as running the engine bellow sea level with exhaust side above sea level. With turbos the exhaust and intake dynamics are linked and form a complex feedback loop which can't really be modeled on wave dynamics. That needs fluid dynamic modeling I think?

I'm sure Delcowiz can chime in an give his 2 bob. He has heaps of experience with turbos just from experimenting and what not.

Are you considering a roller cam? If I was going to the effort I would go that way. Would recommend Clive cams in Melbourne. Billet cams are less than $500 and more than likely have a perfect one for your sepcs. They have profiles to suit just about any combo you can imagine and know which ones to use in what application.

I designed my own cam and they had a profile near identical to the one I designed so it was easy to get it made.

N/a cams work ok if you have good exhaust flow through the turbine and wastegate. Avoid too much overlap .early opening exhaust can help with spool but you don't want it coming on too early the hardest time for the engine is big boost at low rpm the force is tremendous .we run a little 222@0.050 289 292 advertised on 112 or 113 lsa its a class cam for na v6 touring cars works darn good other v6 can that was in the altered was 231@0.050 worked good too was made for tuned length headers and drags. Where as the 202 turbo cam I got done was 238 or 240 @0.050 to suit long tube extractor style turbo manifold it was killer torque for days.i just let my cam people spec them

if its going to be primarily a streeter then you don't want to go too big on the cam as you want to have power available in the lower revs area - take a look at a log of a normal day driving, you usually don't go over 2500-3000 rpm very often at all.

so with that in mind, you want to get more lift and more duration without going too crazy on the working rpm range, you'll probably find a lot of the n/a cams designed for torque/towing will be a good compromise for boost, but more often than not they will still have a smaller LSA than a turbo specific cam.

using my 202 as an example looking at http://www.camtechcams.com.au even the smallest N/A cam has 108/109 LSA, yet all the boost cams in the same motor range have 112-113 LSA, so given the fact that you are going to the trouble of getting a new cam, then I would strongly recommend you talk to a cam shop and get one custom made for your needs, it will be a little bit dearer but probably well worth it.

heff your cam problem has been a long time coming. It's common for cars like yours of that era having cam failure. The cause is the cam starts to crack the outer metal because of a hydraulic action eventually ending up like yours so it wasn't the dyno run but time and mileage. I agree with the comments on maybe a higher lift and reduced overlap. Research some cam specs for cars that are both NA and turbo to help you make the decision but yes consult a good cam manufacturer for advice. I think a roller cam is out of the question for that engine. I have never seen a manufacturer offering one as an option. The important thing is the new cam break in procedure. A good molly lube on all the lobes and on startup keep the engine revs high. A new cam can be destroyed in a few minutes.

Thanks for the input guys, lots of great info and comments there. The tuner has found a cam for me and I will post the specs soon.

I found this article if anyones interested.

http://www.hotrod.com/articles/ctrp-110 ... aft-guide/

Cheers

that article is quite a nice read, last few motors ive been around when there getting built, we've picked a cam, and went the next size down ahah,

265's have awesome heads, and they love cam, mates vg coupe, we stuck a hydraulic 230@50, with an edelbrock 500, and did nothing else, and loved it, quite a quick car on a budget, next build will be abit crazier