New 6 cylinder Motor Idea For My SDRA Dragster

[old28]

During the off season I want to put together a new motor for my SDRA dragster that has a little Chevy Gen 3 194" motor currently.

I am looking at a Chevy 250 block pour filled to within 1" of the deck, Bored .125 to 4.00 for 327 forged FT pistons, O deck the block, CR about 11.50-11.75, Clay Smith cam about .550/.550, Small chamber 62cc head with sbc 1.87/1.60 valves, After market 4bl intake with a 600 cfm carb. Will run water in 1" of the block and all of the head. This setup will make 266" and I hope 270-280 HP.

Just a note that we can not run slicks in the SDRA dragsters, only 6" DOT street tires so it helps to keep the bottom end power under control and make lots of top end. Dragster runs a PG with 8.8 Mustang traction lock and 3.77 gears.

What say out there, comments and any past experience with this type motor build? This is a home build motor with cost to be reasonable.

[Dolmetsch]

I give it two thumbs up. I think your will have no trouble reaching you goal power wise. Have built a few 250s for folks using the old 307 piston trick and they were more then powerful enuf.
Up here a Sr Dragster is a bit different because I built mine and called it that before I knew of your group's but non the less I really can appreciate the FUN factor and appeal of your style cars and of course still believe that 8 cylinders are for people who cant make HP ;>)
Don

[masracingtd1167]

Old 28 Looks like a lot of fun ! Nice job building it .

[masracingtd1167]

I found this old picture today . This was taken around 1964 . It was our club car for the Dragmasters car club I was 14 at the time

[old28]

Dolmetsch -- Ya Don I was going to go the 307/250 way but because of the 11.5-11.75 CR and the 7500 RPM I would like to use forged pistons and I have not been able to find any off the shelf 307 forged pistons. Also I really like to go outside the box and run something that is a little different. I think this motor if it can make 270-280 HP will be able to run with the Chevy 292/ GMC 302/ Ford 300 and even if it can't it will be a heck of a fun ride. Hoping for 11.50-11.75 ET.

masracingtd1167 -- Thanks for the good word, it is like all drag cars (a never ending project).
We are just getting a small group of SDRA dragsters going out on the west coast, 3 in CA, 2 in AZ.

[tylercrawford]

I am looking at a Chevy 250 block pour filled to within 1" of the deck, Bored .125 to 4.00 for 327 forged FT pistons, O deck the block, CR about 11.50-11.75, Clay Smith cam about .550/.550, Small chamber 62cc head with sbc 1.87/1.60 valves, After market 4bl intake with a 600 cfm carb. Will run water in 1" of the block and all of the head. This setup will make 266" and I hope 270-280 HP.

The single 4bbl is the only part that doesn't sound that great to me.  I think it looks more the part with a multi-carb setup.

[old28]

tylercrawford -- I agree with you that it looks right with the multi carbs and I am able to run

two (2x4) adapters on the intake I am currently running (not in pictures) so I could run four Holley 94

carbs. They make about 155cfm each for a total of 620cfm and this motor will need all of that plus

some.

[Hoss]

We have a pretty good class of SDRA cars that run here at Tulsa.
They need to change to slicks. They run a index so tires really do not matter.
The street tires really screw the track so they always have to run last.

Hoss

[Dolmetsch]

Sometimes inadvertantly rules get in the way of fun. A good crew will suck it up and make the change . BTW OLD28 I have been now turfed from the hokey grp so email or PM me here. I cannot even retrieve my PMs there. I wonder what I did? Frankly Scarlet.....................
Don

[old28]

Dolmetsch -- Have you ever bored a Gen-3 250 L6 to 4" (with or without block file)?

The main reason, it easy to find 327" forged pistons with a solid .125 dome that milled down to .040" will provide 11.5 CR with my block -0- decked and head milled .060". I an unable to find 307 piston in cast or forged with a .125" dome and FT 307" piston yield only 10.6 CR.

You know me, I've got to be different. Most other would drop a chevy 292, GMC 302 or a Ford 300 in and go have some fun.

[Dolmetsch]

Nope I haven't. However might I be so bold as to suggest a set of custom made pistons. They are not particularly expensive. I use Ross for most of my special needs.
Having said that , what is wrong with 10.6 to 1? A bit of head and block planning will get close to 11 to1.
Once I get to 10 to 1 static ratio the only reason I look for more is so I can add camshaft duration.  Compression in and of itself is not the factor. When we increase duration the intake valve is held open longer into the beginning of the compression stroke. This effectively shortens the amount of stroke available to make cyl pressure so the only way to keep pressure up where we want it is to rise the static ratio of the engine so the end result  is where it was before. I work a lot with cranking compression. I can tell far more from that then anything else including forty pages of math. A good powerful bracket engine expected to be competitive and run  long time wants a cranking compression is about 175 PSI regardless of cam used. I do whatever I need to to get there. (My slant is there right now) This relationship between engine compression and camshaft duration is the biggest speed secret. Once one understands that everything changes and much of your competition becomes cannon fodder.  There is among us  North  Americans a real tendency to always think bigger louder longer is better when in fact right is better and often more is just more $ spent often paying back nothing but bragging rights. I spend a lot of time sorting this relationship out and have now my cams custom ground to my specs to match my motors needs. Duration is determined by needed RPM. Compression is determined from Duration required. Lift is determined from Cyl head flow testing (since I am on the subject.)
don

[old28]

Don -- I sent you a PM today 11/13/2014

[Serendipity]

We have a pretty good class of SDRA cars that run here at Tulsa.
They need to change to slicks. They run a index so tires really do not matter.
The street tires really screw the track so they always have to run last.

Hoss

What effect do street tires have on the track?

Lenny

[George]

We have a pretty good class of SDRA cars that run here at Tulsa.
They need to change to slicks. They run a index so tires really do not matter.
The street tires really screw the track so they always have to run last.

Hoss

What effect do street tires have on the track?

Lenny

Besides tracking junk onto the racing surface the treaded tires tend to tear up the good rubber. I try and make sure a slick tire class runs ahead of our group. I would prefer the street tires not run on the same day. George

[old28]

Treaded tires on a SDRA or HA/GR dragster like mine with 250 HP or less don't tare up the so called good rubber like a 4000# door car with street tires. We have been running with the ANRA group out of Bakersfield, CA for over 10 years and have had no real problems. 9.60 index open wheel & 9.60 index gas door cars with slicks run right after use and have no problem hitting their index numbers. We do not use the water box so as to not pull any water up into the stage area.