Turbo Cam selection

[240Z Turbo]

How about alot of fun trying to research the selection of a turbo cam for the L motor. I find the best place to start is to see who is running what and what kind of power are they making. I have seen people generate some good hp #'s using the stock cams, but it is usually peaky and then falls back off. I think one of the big kids on the block is ole TimZ with his 400+++hp@wheels monster. He is running the stage I Isky cam that is .475" lift with 222dur@.050. The cam peaks power at 5700-5800 rpm and holds good power until 6600 or so. I have been shopping for a new cam and had decided on the same cam for my car, until my Buddy Walker told me to call back and talk with Laurie @ Web Cams. Although Isky was very helpful, they did not have a cam that was a small step up from the Stage I jobber. Anyway, I called Web and Laurie was very helpful in explaining what I should look for based on her experience and the results TimZ was obtaining. For every 10 degrees duration you add you gain about 500-700rpm in the upper powerband. Web's 155 cam has .488" lift with 230dur@.050. This cam should outflow the Stage I cam and give about 400-500 rpm on the topend over the Stage I Isky. She actually suggested I run the 155a on the intake and the 155 grind on the exhaust. Both of these cams have .488" lift and 109deg lob seperation. I have not decided whether I will just do the straight up 155 or the hybrid 155a(intake)/155(exhaust). Giving a shorter exhaust duration. Here is the link if you are interested. http://www.webcaminc.com/datsun.html#2

Anyway, AEM suggested the cam to TimZ way back when(Tim is very old) and they had great success making power with it and for most applications it should be suitable. I will let you know how my cam turns out when it is installed next week. Any input is appreciated.

[Guest Tom Scala]

I notice most Datsun turbo cams have tight 109 degree lobe centers when most other blown/turboed engines use wide 112-114 LSA's. The wide LSA allows you to run more duration with less overlap and gives a broader less peaky powerband than a tighter design. A wide LSA will also breathe better at higher rpm. The tight angles usually make more peak power & torque but over a narrower rpm range and shut down earlier in the rpm range than a wide LSA. The wide angles make more average power throughout the powerband. Bore/stroke ratio has a big effect on optimum LSA with long stroke motors with quick piston speeds tending to prefer tight angles,sometimes as narrow as 104.

Again most of my experience has been with V8's,and there are alot of generalizations in the above paragraph and a whole lot I don't know or understand. But is there something different about the Datsun design that would require a 109 LSA and has anyone ever tried something a little bit different?

[Kevin Shasteen]

Well, I'm not edumacated on the turbo scene yet so I'm not sure exactly how they differ, but, I'll ask anyway: have you considered the cylinder head in your attempt at finding more power?

 

I forwarded some new found knowledge I discovered after reading Vizards book on modifying SBC cyl's heads. I know SBC cyl.heads are not the issue here; but the post had to do w/airflow w/in a port...any port of a cyl.head. Therefore, the principle is based on "Physics" & not the engine being a V8, Inline or anything else...just airflow!

 

It was rather lengthy but well worth reading. To make a long story short-it dealt w/determining what factors limited a cyl.head's ability to flow: "These factors" are what determine your engine's powerband. Once you've reached the limit of these factors-your engine's powerband falls.

 

In retrospect; if you know what the limiting factors are-then you can manipulate said factors in an attempt to minimize the "limiting" which should result in more power...or more rpm's/whatever your needs are.

 

If you are interested (I was excited when I finally understood what he was talking about) then you can find the thread in the Miscellaneous Forum under the title "Cyl.Head Airflow (another light bulb comes on). I just re-read it again; Vizard & his books always amaze me/the guy is a performance engine guru!

 

Kevin,

(Yea,Still an Inliner)

[Guest 75Turbo]

My two cents... I guess it depends on how Web Cams grinds their ramps, but it seems like 240 @.50i - 230 @.50e on 109 LC would be a pretty loopey cam from all the valve overlap that grind would probably have. My last N/A cam was 235@50 i/e (109 L/C) and it was VERY lopey. I think with that much overlap, the turbo would have a hard time spooling and you would get a lot of reversion into the intake... even under boost. I dont know this for a fact, but I have heard that outside of full blow race engines (ie CART) all turbo engines have more pressure in the exhaust (between exhaust valve and turbo) than they can create on the intake. At high RPM this may not be a problem though, due to the high "momentum" of the air through intake runner (the momentum may be stronger than the exhaust pressure).

 

My guess is that cam would be lopey, slow to spool turbo, but very strong above 5000RPM.

 

Interesting topic... hopefully you'll get some other opinions on this.

 

Happy boostin'

Nathan.

[Drax240z]

I'm thinking James isn't far off your full blown race engine... Aren't you running a 4100rpm stall James? Sounds like if it gives you more juice over 5000rpm it should work nicely for your application.

[Guest Tom Scala]

Speaking of cams,I've noticed the one in the P90 I'm going to use has some pitting on one of the lobes and if I decide to replace I was going to go with a custom grind. My setup is much closer to stock than the home run hitters on this site with a 3" exhaust,good IC,SDS,60mm throttle body,Buick GN hybrid turbo & 420cc injectors being the only mods. I was thinking of something along the lines of 215 degrees intake/210 exhaust at .050" lobe lift ground on a 114 LCA with the intake advanced to 110. Lift would be whatever the available lobes in that duration range have to offer. This should hopefully keep my shiftpoints at or below 6500 which is as high as I would want to take a(my) stock L28 shortblock,& be a worthwhile improvement over the stock cam. Whadya guys think?