Mister T Posted October 4, 2010 Report Share Posted October 4, 2010 In the process of building my 421 cub and am needing some helpful info. Exactly what thickness cylinder base gasket is required on the 421 cubs? And where can I purchase them? Will be running a coolhead with 17 cc domes....and I am located at pretty much sea level.Good idea or no? Have read conflicting reports and some suggest 20-22cc domes at sea level. Carbs are 38mm PWK's....unsure what size jetting to use... Pipes are RDZ oof's The bike will be a asphalt drag bike now and then,primarily a show bike....but HAS to go !! lol Are my sights set tooo high in hoping for 100 hp? I have lots more questions and hope to get to know some of you over the next bit as I finish the build Thanks Quote Link to comment Share on other sites More sharing options...
Wildcardracing Posted October 4, 2010 Report Share Posted October 4, 2010 Will need to know a few things: What fuel do you plan to run? What crank and piston combination? Are you having it built or building it yourself? Are you planning to have it cleaned up, fully ported or running as cast? Most common base gaskets for a 421 are a .012 and a .020, selection is really builder preference. As for you question on the domes, 17cc is way too small. Dome size is really up to the builder as well. We typically use 21cc domes for 110 octane. The domes have to be sized for a 68mm bore or they will NOT work. Your absolute best bet is to contact a reputable builder and have them help you get the right parts. -Brandon Quote Link to comment Share on other sites More sharing options...
Mister T Posted October 4, 2010 Author Report Share Posted October 4, 2010 I can run a few different fuels 105 octane...c-12 which is around 110 octane....c-16....unsure of octane.Won't be running alky. Have a hotrods crank and rod combo with 68mm wiseco pro-lite pistons,which I believe are blaster pistons.The 17cc domes I have are 68mm big bore domes. I do have a set of 22cc domes,but didnt want to sacrifice horsepower with the lower compression.Some reading here on the forum has me wondering about that thought though The cylinders are currently out being full race port and polished Also...what is the typical safe rpm range for shifting these strokers Thanks for the info and getting this thing on the track running RIGHT Quote Link to comment Share on other sites More sharing options...
Wildcardracing Posted October 4, 2010 Report Share Posted October 4, 2010 If you have the cylinders being ported, you need to discuss the dome size and setup with your builder...If he can't make a suggestion for you then you really need to get your parts back NOW and send them to a builder who can help you set it up. -B Quote Link to comment Share on other sites More sharing options...
TNTS355 Posted October 5, 2010 Report Share Posted October 5, 2010 If you have the cylinders being ported, you need to discuss the dome size and setup with your builder...If he can't make a suggestion for you then you really need to get your parts back NOW and send them to a builder who can help you set it up. -B WORD and DITTO Quote Link to comment Share on other sites More sharing options...
J-Madd Posted October 5, 2010 Report Share Posted October 5, 2010 I can run a few different fuels 105 octane...c-12 which is around 110 octane....c-16....unsure of octane.Won't be running alky. Have a hotrods crank and rod combo with 68mm wiseco pro-lite pistons,which I believe are blaster pistons.The 17cc domes I have are 68mm big bore domes. I do have a set of 22cc domes,but didnt want to sacrifice horsepower with the lower compression.Some reading here on the forum has me wondering about that thought though The cylinders are currently out being full race port and polished Also...what is the typical safe rpm range for shifting these strokers Thanks for the info and getting this thing on the track running RIGHT Man there are so many 421s for sale cheap, there's no way I'd build one from the ground up right now. YOu'll shift it at or just past peak HP probably. With those pipes it should rev up to near 11,000 rpms depending on the porting. 100 hp on race gas is doable. On alky it's the default hp on any off the shelf 421 hp; imo.. If you can't get 100 on alky, something is bad wrong. Quote Link to comment Share on other sites More sharing options...
Mister T Posted October 10, 2010 Author Report Share Posted October 10, 2010 Man there are so many 421s for sale cheap, there's no way I'd build one from the ground up right now. YOu'll shift it at or just past peak HP probably. With those pipes it should rev up to near 11,000 rpms depending on the porting. 100 hp on race gas is doable. On alky it's the default hp on any off the shelf 421 hp; imo.. If you can't get 100 on alky, something is bad wrong. Actually I did buy this 421 cub instead of building one. Problem is the guy I bought it from ripped me BIG TIME !! Was supposedly buying a "SHOW QUALITY" engine....with 38 mm carbs...a neutral down 1-5 over ride trans... What I got is a well used and beaten 421....no carbs at all....a standard shee trans....no domes at all in the coolhead....was possibly a nice clean well polished engine at some point in its life...but not now!! And a$$hole also ripped me off a drag cut seat and polished front brake master cylinder So,I'm left trying to make something of this engine....and out a ton of $$$ because of idiot.Upon tearing apart the top end I find one cylinder is badly scored so I have sent it out to be re coated and might as well have it ported n polished at the same time. I have purchased a cometic 68mm top end gasket kit and have measured the base gaskets ....and I get either .024 or .025" part # B0066 base gaskets Prolly gonna need a o ring gasket kit for the head too as there wasnt even all the o rings there when i took it apart! So yes...I am gonna need some advise lol Quote Link to comment Share on other sites More sharing options...
sleeper06 Posted October 10, 2010 Report Share Posted October 10, 2010 If you running an asphault bike you dont really want that size dome,Im at sea level also.You want to be in the 165-170 psi range so you can play with the timing a lil without fighting itself on the big end.If you didnt get carbs go rite for 39mm pwks.Im running 21cc domes on a drag ported 421 at sea level ,reed stuffers,39s,shearer oofs,c-12.On asphault your stringing these things out for distance imo billet bowls are a must.Another good addition is a lockout it enables you to set it up for killer 60ft times,Tires tires tires,American racer sd23 compound 20-8-10. Quote Link to comment Share on other sites More sharing options...
Mister T Posted October 10, 2010 Author Report Share Posted October 10, 2010 If you running an asphault bike you dont really want that size dome,Im at sea level also.You want to be in the 165-170 psi range so you can play with the timing a lil without fighting itself on the big end.If you didnt get carbs go rite for 39mm pwks.Im running 21cc domes on a drag ported 421 at sea level ,reed stuffers,39s,shearer oofs,c-12.On asphault your stringing these things out for distance imo billet bowls are a must.Another good addition is a lockout it enables you to set it up for killer 60ft times,Tires tires tires,American racer sd23 compound 20-8-10. I did already purchase carbs ....38mm pwk's From what I am reading,sounds like 20-21cc domes are what I should run.Guess more comp isn't always better.How would this setup run with some nitrous added in?? Quote Link to comment Share on other sites More sharing options...
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