4.165x3.25 engine combination?

[Dirtracer50]

My local track just went to a new rules package allowing the Brodix spec heads this season. Currently I have a couple of engines with iron heads but am thinking of putting something else together to take advantage ot the weight break with the spec heads.

I have a nice 4.165 bore block and a 3.250 crank I was thinking about using. Probably 6.250 rods so I could use an off the shelf 6 inch rod 400 piston. Would probably use a roller cam. Have to use an 8000 rpm chip.

Wondering if anyone would have some input on cam selection and if anyone has used a combination like this with the Brodix spec heads? I've talked to a couple engine builders about this but none of them have any experience with these heads. It would be a modified on 8 inch tires running a 3/8 track.

[perfconn]

Built many of the S.A.S. Spec engines.Best one on the dyno was 605hp.It was a 4.185 bore with 3.280 stroke.The Brodix spec heads don't flow real good.Brodix advertises them at 270cfm @ .700 but they actuall flow less than that.I said that because if you can run a good ported steel head,it will make a ton more hp.My best steel head 360ci made 685hp on the same dyno.

[powerslide]

So in all reality most nights the spec head will be faster in a mod come money time. Unless you qualify you should be ok with the spec head. mods have almost half the tire of the late models and rarely use 600+hp.

Question. What tire rule are you on? what size track are you running and is it slick or heavy majority of the time?

[TBRE]

Is the head a no touch??? The larger bore will not benefit the heads, if they can't be matched to the bore. The piston shape and bore, are an extension of the combustion process.TB

[stockcar5]

is 8000 rpm enough for that short of a stroke?

[perfconn]

Never used a 3.25 stroke but plenty of 3.27 & 3.28 stroke & never turn over 8100.Always used 6 inch rods though never 6.250.

[andy16]

i have a 4.165x3.28 with different heads but had it dynoed and learned engine was done at 8,000 started backing up there.dont necesarily have to scream it. i used to turn it 9,000 all the time but started limiting it at 82 after learning that. like the previous gentleman stated it may not matter much if you cant lay the chamber back. maybe 15 hp up top w the big bore, the head will flow slightly better w big bore doesn necesarily mean big hp gains. plus this combo is relatively expensive. if you want to lose weight w those heads i recommend using a stock 3970010 block w light assembly i know ima get blasted for saying use that block but i have used them sucsessfully in limited motors and they are much lighter than a dart/world block. maybe 20lb lighter than bowtie 184 30 or 40 lighter than dart world. w 23 degree heads and a 8000 limit should give you no problems and ive gone as far to mill the oil filter boss off and scallop the bell mounting flange for a steel block steel head engine. people didn like it tho?

[Dirtracer50]

Thanks for the replies. You guys have mentioned some of the same things I was wondering. The track is a 3/8 with pretty good banking and can be so tacky that you could lay down as much power as you want one night and the next week so slick that you could win with 450hp. The rules say that you can not touch the heads. I was also wondering if the 8000 chip would be enough to take full advantage of this combination? The 6.25 rods were just a thought to save some cash on pistons. This combination was just an idea to use up the block and crank I have laying in the shop taking up space but maybe I would be better off to build a 377 or 406 with these heads.

[stock car driver]

I would think the longer rod would be good. the pistons are 40 grams lighter for that rod.

[connor]

I have a engine with 4.175 -3.25 stroke with 6.2 rods and track 1 heads pulls good to 8200 good cheap engine to build for the money.