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Author Subject: Anyone running PT84's?
devere

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Post #1
Just wondering if anyone out there is running the Kent PT84 cams?

If so can anyone tell me how they are, and how the engine is.. as in powerband etc.

Been looking at the cam choices for my new engine, so some advice from someone with first hand experience would be good!

Cheers.
Posted 6th Nov 2010 at 18:08
anth

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Post #2
anything over 5k rpm probably :O
Posted 6th Nov 2010 at 21:43
devere

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Post #3
Well, the stated power band on the Kent webiste says 3000-8000. So hoping someone that is using them may be able to say if thats accurate! lol.
Posted 6th Nov 2010 at 22:39
smighall

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Post #4
Pretty sure they need different pistons, or at least the standard ones machined.

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Posted 6th Nov 2010 at 22:40
devere

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Post #5
With all due respect, thats not what im asking. I have new pistons, and rods, and a whole new valve train going in. Im weighing up my cam choice to go in the fresh head.

The description on Kents website of the PT84's seem like they are most suitable for what im after. But i dont want to commit myself to buying them without knowing a bit more about them.
Posted 6th Nov 2010 at 22:53
scoty18

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Post #6
What smighall means that even with a brand new engine fitting them cams will cause the valves to kiss the pistons resulting in engine damage. Theres a few topics about it. IIRC the pt81s are the most aggressive cams you can use without modifying the pistons.
Just thought id mention it as I wouldn't want to see you having any problems when the engines built.

As for the performance of the cams it would also depend on the engine set up i.e. Engine management, valve size, TBS etc. They will be aggressive cams tho...

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  • Posted 6th Nov 2010 at 22:59
    devere

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    Post #7
    Yeh i see what your saying. I have aftermarket pistons, and rods. So that is taken care of. Im assuming they will clear the aftermarket pistons! lol.

    It will be mapped with an OMEX, and running Jenveys, so the whole thing will be built with the bigger cams in mind.
    Posted 6th Nov 2010 at 23:07
    scoty18

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    Post #8
    After market pistons may not clear the valves, youll need to measure everything to be sure

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  • Posted 6th Nov 2010 at 23:14
    cwspellowe

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    Post #9
    scoty18 wrote:
    After market pistons may not clear the valves, youll need to measure everything to be sure


    +1, sort of. I'm assuming as you've taken the time to buy new pistons you'll be looking into max lift, valve angle and valve to piston clearance? That's your first port of call.

    Personally I would have specced the cams I want, THEN bought pistons with enough clearance. Now you need to find cams that definitely fit, and decide which is the best spec from there. If you're dead set on PT84's and clearance is marginal, a thicker metal gasket or machined cutouts in the pistons will help.

    As for performance of the cams though, at PT84 spec i'd imagine them to be choppy as hell low down with big gains 4k RPM +, although i've never used them myself.

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    Posted 6th Nov 2010 at 23:43
    devere

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    Post #10
    Well, saying i have the pistons, i am still to pick them up. So could change plans if necessary! lol.

    Im not dead set on the PT84's, more like im looking in to how suitable they would be.. I had also been looking at the Piper rally cams. Both those and the PT84's seem to be a step down from full race.

    WIth regards to piston to vlave clearance, does anyone know the max lift the Wossner high comp pistons will accomodate? The PT84's have a lift measurement of 11.73 and 11.02 respectively.

    I have done some looking into the wossners lately, but the main figure of valve cutout depths isnt one that seems to be easily findable on the net here.
    Posted 7th Nov 2010 at 01:47
    smighall

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    Post #11
    Apologies, most people who come on here who ask will these cams fit because they've mentioned "race" or similar in the description have no idea about valve clearance.

    As you're doing it properly, then there's no reason why they wouldn't work. I haven't looked into cam profiles in huge detail but i've heard a lot of good things about piper cams (on the basis some very good engine builders use them AFAIK). Also from memory duration would be better than ultimate lift.

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    Posted 7th Nov 2010 at 02:47
    Denis

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    Post #12
    devere wrote:

    I have done some looking into the wossners lately, but the main figure of valve cutout depths isnt one that seems to be easily findable on the net here.


    That is because it depends so much on the cam profile. The vale to piston clearance is a problem when the piston is around TDC, so the maximum lift figure is not relevant. The only way to make sure that everything is right is to dry-build the engine and measure clearance.

    If it helps, that is the graph of properly timed PT81s:


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    Posted 7th Nov 2010 at 02:48
    bigbadbowen

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    Post #13
    Who is building the engine ?

    Oil spray bars will be an issue on high lift cams as well and before you ask no don't take em out they are there for a reason

    Any engine builder worth there salts will be able to get these to fit the head properly ?

    Another question what size jenveys are you running ?
    Posted 7th Nov 2010 at 02:53
    devere

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    Post #14
    Im going to be doing most of the work myself. Although if it is going to take a bit of modifying here and there with regard to the spray bars, i may drop the head off to be built up somewhere. Luckily enough there are several engine builders around here.

    Ive seen somewhere that people made up small spacers to raise the oil spray bars, is that the done thing, or is it modified a different way?

    As for the clearance on the piston to valve, i would clay th engine anyway, to make sure it is all clearing properly.

    And i know what you mean, when you see a thread on big cams, it can quite often be someone just wanting race cams on a worn up standard engine! lol. This is my engine for next years rally season though, so needs to be something with a little bit of poke to it!
    Posted 7th Nov 2010 at 03:09
    bigbadbowen

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    Post #15
    And the size jenvey ??????

    Posted 7th Nov 2010 at 03:18
    Denis

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    Post #16
    devere wrote:

    Ive seen somewhere that people made up small spacers to raise the oil spray bars, is that the done thing, or is it modified a different way?


    Yes, you can put some small spacers under spray bars (from memory my spacers are about 1mm).

    With such high lift cams (PT84s) and solid lifters most people remove spray bars completely and limit the amount of oil going to the head.

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    Posted 7th Nov 2010 at 04:04
    daveyboy

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    Post #17
    I would have thought the 3000-8000 rpm power band a bit optimistic, In a little 16 valver like ours I can't see it producing anything meaningfull until around 5K+

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    Posted 7th Nov 2010 at 04:29
    scoty18

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    Post #18
    I reckon you will need to machine the pistons to suit the cams plus use solid lifters as mentioned before. I dont think they are going to be worth the problems they will cause. With the amount of money you will end up spending you could prob just fit the low boost super charger and get better results.....

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  • Posted 7th Nov 2010 at 07:21
    devere

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    Post #19
    Jenveys will be either 45's or 48's.

    Supercharging isnt an option. As i said, its going in my rally car, and im not moving classes to run with 3 litre+ M3's...

    It may cost a lot of money. But where supercharging isnt a possibilty some of us have to spend the money to get the results we want.

    Is there any disadvantage to removing the oil spray bars then?

    I would hope the power band will be something like the stated one. I know on my single cam, 1600 honda engine with the biggest cam you could possibly find the power band was starting at just under 5k. So with the added cc and extra cam, i would like to think its possible to tune to a reasonable mid range.
    Posted 7th Nov 2010 at 15:39
    welshpug!

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    Post #20
    I'd suggest speaking to an engine builder familiar with the XU10J4RS :thumbsbup

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    Posted 8th Nov 2010 at 03:47
    devere

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    Post #21
    welshpug! wrote:
    I'd suggest speaking to an engine builder familiar with the XU10J4RS :thumbsbup:


    Spoke to someone who knows his stuff. All i need to do now is hurry up and buy all the parts i need!! haha.
    Posted 11th Nov 2010 at 23:48
    welshpug!

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    Post #22
    LOL nice to hear, who was that out of interest?

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    Posted 11th Nov 2010 at 23:49

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