P90 With Dished Pistons (Yes, N/a)

[siteunseen]

Yeah I've heard of swapping the cam by loosening the motor mounts and raising the front to clear the radiator.  I guess if you loosened up all the rockers it would work?

[rcb280z]

IIRC the last time I removed a cam (1995) I just dropped the rad down a couple inches. Of course after loosening the rockers.

 

Sorry Colten, didn't mean to jack your thread man.

[HuD 91gt]

No problem.  Already heard what I need to hear I think

[EuroDat]

Hi Bob,

Common mod to get the CR up on the P90 in a N/A engine is to shave the head 2mm, shim the cam towers 2mm and use the valves out of the N47 head. You could do this to your P79 head if the bottom end is in good shape, this could be an alternative with the P79 head. Its not a perfect design with dished pistons, but the P79 is considered the better of the two heads.

Chas

PS: Might want to start a new thread if you are considering changing heads. It would be an interesting discussion.

[rcb280z]

You are right Chas, it would be a good thread. Haven't made up my mind yet but when I do I will post everything. Wish I knew what effect it would have on emissions before diving into it. 

[HuD 91gt]

It's good this thread got sidetracked. I ended up avoiding the L28et and put money down on a F54/N47 combo recently refreshed but never run. Now I need to figure out what cam I should run. Researching it sounds like I want something in the 280-290 range in duration to reduce some of the detonation which may be caused from the 10:5-1 compression. But at the same time from what I see, all the cams with this spec have a high power curve, probably not too well paired with SU's and a stock exhaust manifold (maybe the exhaust liners too?).

I'm still not very knowledgeable on cam specs, but what can the stock valve springs handle? I've read that 460 lift is about the max you should go?

A local company (colt cams) here in Canada will do a regrind and I'd love to support them. I would have to get my hands on new lash pads correct?

[HuD 91gt]

I emailed Colt Cams, and they replied in suggesting I should be pretty happy with this cam.   Anyone have any thoughts?  The thing that makes this stand out from other companies is the large lift of .510.   What effect will this have?

 

 

C.542.S.

INT.

224°

280°

.340

.510

108

PERFORMANCE

$185.00 CAN / US

 

EXH.

224°

280°

.340

.510

 

Best all around Cam 3000-6500+

 

[Zed Head]

According to Honsowetz (How to Modify...) the max valve lift for the stock valve springs is .460".  The valve seals also have a limit, which requires either an "A" type seal (not 100% sure what that means, vague memory) or Ford valve seals.  Can't remember the details on the seals.  Anyway, it doesn't look like a drop-in, it will take a little extra research.  

 

You've changed the topic of the thread, but it looks like you're now planning a high lift cam with flat-top pistons.  It would pay to verify valve clearance with the piston tops.  There might be a problem there too.

[siteunseen]

I'm going through this now too.  .460" is the max lift without different springs and shorter retainers as well as shorter valve seals.  My machinist says going to a .490" lift, which I wanted 1st, was more work and money for him.  Madkaw also warned me of that big a cam, a better ignition and triple carbs to start with so I changed my mind pretty quick. 

 

Get your rockers resurfaced whichever way you go.  I sent mine to Delta Cams, the guy on the phone said $3 each but everybody else said they paid $4 a piece.  Still way cheaper than new ones.

 

Read some over at hybridz.com.

[HuD 91gt]

Thanks for the replies.   The Colt cams specs seem very tantalizing, but as you guys have mentioned there could be a lot of expense to go along with it.   Thanks for the mention of clearance issues, i'll have to look into it.  Colt cams also offered me a T shirt because of my name (Colten), I think that is hilarious.  I've emailed them back and inquired about valve springs etc on what they think may also be required.

 

I've read many old threads that Delta cams offers that service.  Glad to see they are still doing it as it seems it is the most cost effective solution.

 

My other option is the Z specialties cam, either stage 2, or 3.  Both have a lift of .480, but they say stock valve springs can be used as long as the engine is not revved past 6500.  Any comments on this?  I should give them a call and see what they suggest for me.  These options look like they would be much more cost effective.

[madkaw]

You know you won't be able to just throw that cam in that head without lot's of other work.

Need to upgrade springs and valve seals. Valve lash pads will not be correct so your valve geometry will need to adjusted. I would strongly recommend degreeing that cam and than check piston/valve clearance.

Exhaust liners will be the least of your concern.

Tuning and proper valve geometry will give you best gains.

Why not try a smaller cam? That 90/47 combo should be stout and with good octane fuel and good tune should run great.

[HuD 91gt]

Which cam are you referring to Madkow?

Edit:  Looking at the post time, I think you must be referring to the Colt cam.  So yes, i'm beginning to realize that.   The Z specialities cams may be a better option.  The .480 lift with stock springs still goes against what i've been reading though.

 

The reason I am looking at such aggressive grinds, is the history of people having detonation issues with the N42/N47 head and flat top pistons. I may be reading all the horror stories, and missing the positive ones. I'd rather error on the side of caution then  go too mild and still get pinging.  I think a more mild cam would be more suitable (Stage 2) for the vehicle, as it is mostly a street driven weekend car, but it will see some auto-x and track days.  Although nothing competitive, merely fun.