twilsonx Posted April 15, 2008 Share Posted April 15, 2008 I've heard some of you guys talking about shaving .080 off the head of a P90 and putting 75-78 valves on it and shimming the cam tower and valve springs. I just bought a P90 to put on my '78 L28 and i'm keeping it N/A so I am looking to raise the compression rating. I need to know what all is involved before I get it done to mine. Here's the link to the site where I first heard about the P90 modification. http://datsunzgarage.com/p79/ A few particulars questions I had- Where do I buy cam tower shims? Has anyone used the Arizonezcar SS valves? are they worth it on a N/A car? Quote Link to comment Share on other sites More sharing options...
JMortensen Posted April 15, 2008 Share Posted April 15, 2008 Most machinists can get the cam tower shims for you. I think one of the major cam manufacturers still sells them (ISKY?). Check around for stainless valves. There was a guy in OR selling them on Ebay for cheap. I think Phil (username "preith") bought some. You might PM him to see how they turned out. My own impression is that they aren't necessary unless you're really going 10/10ths on the rest of the head. Quote Link to comment Share on other sites More sharing options...
twilsonx Posted April 15, 2008 Author Share Posted April 15, 2008 I want them to be able to handle Nitrous or a turbo if I do end up going that route in the future, so I figure I can buy them now. Quote Link to comment Share on other sites More sharing options...
Kevin.pk Posted April 15, 2008 Share Posted April 15, 2008 ive got a p90a with solid lifters that is already shaved and shimmed .080 ... its a clean head... fresh 3 angle valve job on it... i was gonna use it but ended up going turbo and then wound up going with a v8 swap... the head was bolted to a block but not run. lemme know if your interested i dont know if you would wanna pay for the shipping though Kevin Quote Link to comment Share on other sites More sharing options...
twilsonx Posted April 16, 2008 Author Share Posted April 16, 2008 I just bought a P90 off abes. Quote Link to comment Share on other sites More sharing options...
steveosupremeo Posted April 16, 2008 Share Posted April 16, 2008 pioneer makes 0.015 shims for L series, i have them on mine. Quote Link to comment Share on other sites More sharing options...
twilsonx Posted April 16, 2008 Author Share Posted April 16, 2008 pioneer makes 0.015 shims for L series, i have them on mine. How do I get .080" out of .015" shims? I'd have to use 5 1/3 shims. Quote Link to comment Share on other sites More sharing options...
steveosupremeo Posted April 16, 2008 Share Posted April 16, 2008 just use 5 shims. 0.075 is close enough. whatever material is ground off of the back of the valve or seat during the valve job is likely to be a 0.001 or so, which brings it even closer. i know bubbleguinnea used 5 of the 0.015 shims to do this setup. Quote Link to comment Share on other sites More sharing options...
twilsonx Posted April 17, 2008 Author Share Posted April 17, 2008 Will there be too much slack in the timing chain? Quote Link to comment Share on other sites More sharing options...
z-ya Posted April 17, 2008 Share Posted April 17, 2008 Will there be too much slack in the timing chain? 0.005" is not enough to make a difference in the timing chain slack. Your stock 78' L28 is around 8.3:1 CR. Putting the P90 on there with the stock dished pistons will drop the CR to around 7.4:1. So if plan on using the P90, you need to shave it or you will make less power than the N47 you have on there now. What are you HP goals? I realize you just got the P90, but the N47 will do what you need without shimming or shaving. The problem is that whether you shim and shave the P90, or just keep the N47, your CR will be too low to make enough power to make the work worthwhile. To make decent power on a street NA L28, your CR should be in the 9-10:1 range. The best way to do this is flat top pistons and an N-series or shaven P-series head. If you don't want to mess with the short block, do some work on the N47 and use a Felpro gasket to get a little more CR. Quote Link to comment Share on other sites More sharing options...
Careless Posted April 17, 2008 Share Posted April 17, 2008 How do I get .080" out of .015" shims? I'd have to use 5 1/3 shims. i think taking a shim to a machine shop and telling them to make another to your desired size is another option too. Quote Link to comment Share on other sites More sharing options...
twilsonx Posted April 18, 2008 Author Share Posted April 18, 2008 I'm swapping the rebuilt P90 in the same time I put Forged flat-top pistons on and bore 1mm over. And I plan on shaving/shimming the head so that it boosts the CR. Also putting on SS valves to be able to withstand the heat that about 75-100 hp shot of nitrous will produce. I already have a header and new exhaust, so that is taken care of. I'm either looking getting a lonewolf intake or make/buy one from the flange that Justin has been working on. Along with a new throttle body I should be making some decent horsepower. If anyone has any suggestions, just let me know. I'd like to keep it N/A but put nitrous on. Quote Link to comment Share on other sites More sharing options...
twilsonx Posted April 18, 2008 Author Share Posted April 18, 2008 Also, does anyone know of any good machine shops in the Illinois/Indiana area that is good with nissan heads? Quote Link to comment Share on other sites More sharing options...
thorfin Posted April 19, 2008 Share Posted April 19, 2008 I did this p90 modification in 2004. It is not easy to do right-- You will want to use or have flat top pistons and you will have a 10:1 compression, and will need to use premium gasoline thereafter. so my advice is make sure you really want to do it--takes time and study. Recommend to get the datsun hotrodding book and study up on method of adjusting the the lifter shims--these are different than the cam shims. You need to be very good, or have a shop that is expert with the z head. Here is a link to the shims, made by Goodson.com--you need the DHS-60 model shims---and do NOT use more than five(5) sets of .015 shims--more than 5 equals a problem! I don't know if Goodson makes them still------you will have to call them. 1-800-533-8010 about $80 for five sets. I have their catalog but don't see DHS-60 on their website now--Call! These are very precision with no burrs--you need to have consistent very flat shims to insure no problem with your cam alignment. http://www.goodson.com/technical_support/instructions/DHS-40.pdf OK!-- also the valves you want are made by "SI Valves" and they are the very SAME manufacturer that Datsun Competition catalog lists. I used the stainless steel swirl polished version and they were half price DIRECT from SI, compared to distributors like you listed--mine were $9 each in 2004. Here is a link to the valves I used-- http://www.sivalves.com/ocforeign_valvessp_nis.html To get a good cam wipe pattern on my performance cam I had to actually trim a few of the valves a few thousands in length to custom fit each one --again you need a very good auto machine shop to help do this correctly--it is not done by hand--need proper valve machine fixture to grind 100% flat and parallel. Have fun! it does work as described in article. ---Thorfin Quote Link to comment Share on other sites More sharing options...
jay28 Posted April 19, 2008 Share Posted April 19, 2008 Hi I dont mean to take away from this thread but im in a very similar position......building an l28 motor (f54 block) and also using a p90a head with solid lifters.......Im going to use 86.1mm flat tops, shave the head 0.080" and use tower shims, also have a msa stage 4 cam, not sure what CR im going to have tho, I was lucky enough to get shims off a guy on the forum, Thanks Quote Link to comment Share on other sites More sharing options...
jeffp Posted April 19, 2008 Share Posted April 19, 2008 I have read time and time again about doing this setup for the P90 head and the 280 engine. Head shims are not the correct method to compensate for the chain slop created when the head is milled this extensively. The correct way to fix the problem is to go with the chain adjuster from Kamalari (if I spelled that right) then all of your cam spacing is not an issue any longer. You will not have to bother with shimming the towers. Also, can you even shim the cam towers that much without hitting the top of the valve cover? I don't know because I would never do this to my engine. The L series cam is long, it needs a good foundation to secure to and that many shims just is not a good way to go. Remember, the head bolts go through the cam tower, so if you shim the towers with that many shims you are losing threads in the block for the head bolts. Spend the extra money and get the right part for the job. Also I would recommend the TOMEI adjustable cam sprocket. You can have that part in hand for about 150.00 shipped from Japan to your door. Worth every penny in my opinion. this is the very best way to go, and you can feel confident the cam timing is not going to change after you make the adjustment. Quote Link to comment Share on other sites More sharing options...
steveosupremeo Posted April 19, 2008 Share Posted April 19, 2008 its a Kameari adjustable tensioner and they also make an adjustable sprocket. as far as head bolt thread loss, 0.075 is less than 2 mm and would equal to about half a turn and probably wouldn't be issue at all with ARP studs. As far as goodson I did this work for you a few months ago, they do NOT make them or have them in stock any longer, they said they felt their product was inferior. This sounds like BS to me, I'm sure they just didn't see enough profit to continue making them. They recommended a company by the name of SilverSeal out of michigan or wisconsin or something and they can get them. OOOORRRR...look up the guy called Datsun Parts on Ebay and contact him about a set. He sells the Pioneer ones. they are also 0.015 each. I actually had to have two sets for my P90a. gives my turbo motor with 0.040 pistons a CR of about 7.9:1 with a nissan gasket. Quote Link to comment Share on other sites More sharing options...
naviathan Posted April 19, 2008 Share Posted April 19, 2008 Use an N42 with flat tops and you can net the same compression ratios as the P90 with all those mods. I dont' understand why the big fuss over the P90 when BRAAP and others have stated time and again that any L28 head can be made to perform just as easily as the P90. Do a quick port job on an N42, drop in flat top pistons and you've got a 10:1 compression motor ready to run hard. It's that simple...sort of... Quote Link to comment Share on other sites More sharing options...
jay28 Posted April 19, 2008 Share Posted April 19, 2008 Well I for one dont have a N42 head.......anbd as there are only about 5 z cars in Ireland I dont have much chance of getting one either........I do however have a p90a head which is why im using that.. Does anyone know what compression ratio a f54 block with 86.1 flat top, p90 shaved 0.080" will give? Thanks, Jay Quote Link to comment Share on other sites More sharing options...
twilsonx Posted April 20, 2008 Author Share Posted April 20, 2008 thorfin-thanks for the SI valves link. Jeff-you think that chain tensener(sp?) can take out all that slack? anyone on here use it before? Quote Link to comment Share on other sites More sharing options...
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