I'm buying new oversized pistons for the 1000cc Ironhead and I am seeing that I need to select either High or Low compression pistons. A mechanic at the local Harley shop told me to look on the cams and see if they are stamoed P, PB, PB+, these should tell you if they are High or Low Compression. Well, Mine has neither of these. On the four cams the only stamping it has is 1Q, 2Q, 3Q, 4Q. Does this mean High or Low compression, and where can I find this information myself? Thanks.

 

Your stock cams would be Q cams. They're milder (less overlap) than the P and PB cams, so I probably wouldn't run high compression pistons. As for what constitutes low and high compression pistons, it depends on the numbers, but I wouldn't run anything higher than 9 or 9.5 to 1 without double plugging the heads. Otherwise, you're asking for a lot of pinging on today's crappy gas.

 

I have never heard of cams being described as high or low compression. I am not an expert on this, but i think he gave you wrong information.

You can get reliable technical data on cams from the charts etc on the Andrews web site ... http://www.andrewsproducts.com/

P and Q cams are stock HD cams. P cams were used in 1979 and previous; Q cams from 1980 to 1985. I do not know about PB.

The PB+ cams from Andrews will give you a significant power boost, especially starting about 4000 RPM, regardless of what pistons you run.

I am running Wiseco 10:1 [high compression] pistons with an Ultima electronic ignition. I had to both install a VOES and retard the ignition timing from 38` to 35` to get rid of the pinging.

Why are you going to oversize? Was there piston or cylinder damage? Or excessive wear? Just be aware that you can only oversize in increments of 010 up to 070 [some say 060], and you should only do it if necessary; after that youy need new cylinders. Oversize does not provide more power.

 

Well, the cams themselves aren't designated for high or low compression.

Usually, the higher performance the cam, the longer the duration (when both valves are open at the same time). Because the exhaust valve is open a little longer on the compression stroke, the cylinder doesn't build as much compression as it would if the valve was closed. That overlap helps high speed power at the expense of low speed power, but you can run higher compression pistons to make some of that low speed loss back up.

On a bike with milder cams, the working compression is higher with the same pistons, so putting in high compression pistons alone will create a lot of preignition problems. So, in practice, mild cams need lower compression pistons than radical cams.

 

As IronMick wrote Q and P cams are stock cams, PB is set of 4 cams, PB+ is set of new exhaust cams used with stock P intake cams (as I remember can be otherway round). Check from http://www.andrewsproducts.com/motor...SC_Cams_IH.htm
Notice that cams are specific 1981- Early 84 = no gear for mechanical tach but has gear for generator. Late 84 has altenator and cams are same as evo ( timing need to be checked)
Easiest way to rise compression in 83 is use older (thinner) cylinderhead casket.

 

The Q cams are EPA mandated, low performance cams as others have said. I think I'd stay away from that mechanic at the local Harley dealer. Here's some information on cam selection:

http://www.hotbikeweb.com/tech/0711_...fts/index.html
http://www.nrhsperformance.com/tech_camshafts.shtml
http://www.nightrider.com/biketech/hdcamsspecs.htm
http://books.google.com/books?id=cM9...page&q&f=false
http://books.google.com/books?id=8UO...page&q&f=false

 

Hey all, I appreciate all the info you all have given me about the cams. It will definitely keep me busy! All I am doing to the engine itself is boring it .020 to get rid of some score marks; the wear is very minimal compared to other jugs I have seen in the past. Well, I don't know when the last time you guys have looked at DS’s "old book", or any other parts catalog for replacement pistons but most of them break their pistons into either High compression or Low compression (for stock pistons). Just take a look at Drag Specialties-Old Book page 423, and you will see what I am talking about. As for the guy at the Harley shop, he seems like he knows what he is talking about and he doesn’t even bill me for his time when it comes to getting little things done, just like he is going to pull the motor mount stud from the engine casing for me. I'm a kind of guy that is smart enough to tell when some is throwing me a bone and I would like to think he is genuine, same as for all of you all. But thanks for keeping my interests in mind.
I want to put a thread up that is for the complete overhaul of my 83 Sporty, do you all think I should put it here in the Ironhead section or the Sportster section. I just want as many eyes on it as possible so I can get plenty of feedback.

 

You'll probably get more people who care/know about Ironheads looking at it in this section. I'd go with the 9:1 pistons, which are called high compression in the DS catalog. I believe that's basically what came in your bike (and mine).

 

This is the only section of HDForums that i visit, so i hope you post your thread here.

 

Then this is where it will be then! I really look forward to getting all of your guys help and to learn from your knowledge. I will probably create the thread here later tonight.