Running a weiand 177 with a comp hyd/flat tappet cam (230/244, .553/.568 @ .050, 113lsa) and was wondering if the NGK UR5 is the correct plug for this application. I think I read in a thread somewhere that it is the equivalent to the ACMR41T.

That is what I ran in my Merc 525SC. It is the equivalent of an AC R41TS. Same heat range as the MR41T with a very slight extended tip.

Hawk motors are 8.8:1 mercs are 7.5:1 so I'd go a step colder

Hawks run less timing and less boost. I ran almost 8# of boost on my 525SC and no issues.
If you go colder than an AC 41 or UR5, they will most likely foul out at idle without an MSD box.

Good point, I forgot about that, yes hawks were only 26* and 5lbs

Wayne -- remember that you do not have a full Hawk engine you are only transplanting the blowers onto your merc engines...unless you have changed plans and are fully rebuilding the top end and changing pistons.

BTW--- i was on vaca when you called -- the port at the back of the intake manifold was for boost gauge on the dash...

Dave

Hey Dave, I figured that was what that port was for. Still kept the stock mag pistons with the cam swap and also did valve job on my 990 gm heads, also installed comp cams ultra pro magnum stainless roller rockers. Talked to engine shop today to try and get dynoed next week.

Wayne, Sorry I missed your call this weekend. Things got a little busy.

I would not run a UR5 in my supercharged engines. For 1, they are a projected tip plug. Also, In my opinion, "5" on the NGK heat range scale is hot.

http://www.summitracing.com/parts/ngk-2771



Ive been running these R5673-8. Non Projected, non resistor racing plugs. Ive had good luck with these, and Autolite AR134 Racing plugs in my boosted engines.

http://www.summitracing.com/parts/ngk-3249/overview/

The 5 in the UR5 is not the heat range designation. They are the same heat range as the NGK 8's.
I never had a problem with the extended tip and them gapped at .040 and they helped the engine idle better on very hot and humid days.

I was just going off what I have found online for the UR5 specs. Every site seems to show them to be a "5" on the NGK heat range. NGK's heat range numbers get colder as the number goes up. "6'' is colder than "5", and so on.

Wayne's gonna be running almost 9:1 Compression, iron heads,, and the small 177. I'd be careful with plug choice, as that's a lot of heat. I'd double check with NGK's techline before running the projected tip UR5 resistor style plug in that application.