Adding a blower to a 13:1 engine

[Big Rhino]

I am getting ready to add a 10:71 and alcohol injection to my 412 sbc.  Dart block, iron eagle heads and currently running 13:1 compression.  Is this too much?  Do I really need to drop down to a lower static compression?  This will be my "trial by fire" as this is my first time dealing with a blown engine.  Are mls gaskets OK with this set-up?
Thanks for any input!

[Frontenginedragsters]

In my opinion:
 13 to 1 static compression is too high.
You will find with that much compression that it will be VERY timing / tuning sensitive.
Its like trying to walk on a fence. You can do it but you have to be on your game.
11 to 1 was always considered a safer place to start.
MLS gaskets have no place on a supercharged alcohol engine.
SCE copper is the best way to go.
My opinion: Matt

[ricardo1967]

Matt, I agree with you, but... can you please elaborate this part?

...MLS gaskets have no place on a supercharged alcohol engine.
SCE copper is the best way to go.

[Big Rhino]

Many thanks Matt,
This is the kind of info I'm looking for.  I want to do it right the FIRST time.  11:1 it is, and I guess I'd better go swap out my gaskets!!  Thanks again,
Tom

[GlennLever]

10/71 seems like a lot of blower, not sure you need that much or you will have to under-drive it a lot. Is it stripped?

Currently running a 8/71 on a 13.5 to 1 on my blown engine.

Not by choice, I took a normally aspirated engine and added a blower to get to the 8.5 index I was looking for on the normally aspirated engine.

I did not need all that much, best run as the normally aspirated engine was 8.59.

At Bowling Green this past weekend I ran it at 8.03+ (I really need to pull that time slip back out).

The input I have received is that initial compression ratio is not as important as the finial compression ratio. I have had tuning issues as stated by Matt above.

[wideopen231]

I ran 13:1 on blown alky hemi with 14-71 at 54%/42lbss.droped back to 12:1 ran faster and hurt less parts.
 Also think about bottom end designs. Hemi not really better at making power but its better at handling it. Alan Starr ran nitor chevy way into 70's.He said stupid pride made him do it he should have went to hemi way sooner.

 If your running mild OD.Why not drop compression. If need more power throw cpl percent more at it.Easy,quick and better tunablity.Your winner ,winner chicken dinner thing. Only draw back to OD changes is it does effect distribution, small but note worthy.

 As for gasket question. I agree 100% that only copper gasket belong in blown engine.Hey if it works for T/F guys it should hold up for you right. I will tell you that I had lot less gasket problem once I started torque from out to in instead of norm in to out. Was billet heads and was told it would stop blowing gaskets and pretty much did.

IMO milder compression and more OD with slightly rich starting line,then leaning thru mid track  with riching valve for last 300 to 500 feet of track is great setup.Used if for last cpl years we ran funny. Car was quick top qualifier always a contender and for style racing and rpm we ran at not bad on parts.Even with outdated heads we should have chnaged years before.This was before timer systems allowed in alky cars.

[Big Rhino]

Thanks a lot for all the great info, tips, and experience.  As I said earlier, this is kind of an experiment for me.  The reason for the big blower (10-71 W/ teflon strips) is 'cause I am in the beginning stages of building a 582, (Callies bottom end) and was going to use the same blower (hopefully using the 412 as a learning bench).  I had initially planned to go with 8-port injectors, but have always been intrigued by the blowers.  I'm just trying to learn as much as I can about them first.  Most tracks down here are only 1/8th mile, so my goal is to get into the high 4s.  Probably not too realistic with my little Pinto (92" w/b and 2200 lbs), but I am looking at a couple FED's, hoping to make a move by Christmas. Great Website here!  Thanks again for all y'alls input!

[wideopen231]

8 port w/8 hats is standard setup.Very easy to tune and work with.One thing to remember with teflon stripped blower is to keep check on condition. Even if your not trying for max power every run. If you want consistent runs its even more important.Remember that fuel thru top of blower will help teflon live longer,keeps it cool and lubed.

  Tip I got from Swearinger was to check vaccum at idle .All you need is one extra nozzle hole(1/8 pipe) thats pulgged,pull plug idle will go up then stick end of vaccum gauge into it let it idle back to norm.If this number stays the same and Idle rpm are the same you are good to go. Maybe hard to believe but 1" differance will make change in performance. YOU HAVE TO HAVE SAME RPM and not be messing with air gap in butterflys.

    Have cpl extra holes in bottom of hat that are normally plugged,If idle drops pull a plug about 250 rpm increase.If idles high plug one.Very quick very simple and you are not screwing with barrle valve all the time.

[Big Rhino]

Once again, great information.  Thanks!
 I am seeing a trend here of recomendations to go with the Hemi block for the extra strength in the bottom end?  Is it a significant difference from a Bowtie or Dart block?

[wideopen231]

All depends om how hard you are going to push it. On decent setup with medium OD BBC works fine.If you are going to go after max power.All I can say is there is reason Top Alcohol ,Pro mod and extreme blower class cars run hemi blocks for the most part. If you are going this route you can make BBC work but IMO you are way a head starting with Hemi style motor. Look at the two block.With BBC the crank is knd of hang out like dead weight.With hemi the mains have way more support and stength. Parts being readily available is huge benifit.With mild setup you can shop and buy used parts that are more than ready for you needs.I would stay away from stuff like used rod or cranks from fuel teams. Heads,cams, blocks ,alky car cranks( have checked) Intakes and few others can save you lots of money.

[Big Rhino]

Well, it looks like I have a new mission.  Searching for a hemi.......

[225digger]

if you want the BBC , but also want the bottom end of the hemi look into the new century aluminum blocks , they have mains like a hemi and are alittle more stout than other aluminum blocks .

but you cant argue the fact about a blown hemi and parts aval

[coupemerc]

Real good advice by the posts above. I've been a Chevy guy forever but when my buddy and I decided to run a TAD years ago we ended up going with a Hemi. We ran a "dragster" combination...438 CI (4.310 bore X 3.75 arm), 10.250" decks, 14-71@ 44%over, 11.8:1 CR, Crane R296 cam, 13 gallons/minute@4000 RPM pump speed. You will have 5 second horsepower. The blower will try to lift the heads off the block when you lean on it. Head clamping with 1/2" and sometimes 9/16" studs is the other other advantage of the Hemi. Also, parts are everywhere. Some of the Chevy guys were real fast (Dale Hall, Rick Santos) but I remember them being somewhat limited by the smaller wrist pins and weaker main webs. Having said all that, if you just want to go out and run a bunch of 7's then the Chevys are fine. My $.02

[Big Rhino]

Finally back in the good ole USA.  Thanks a lot for all the really great info.  Lots to think about, need to get a plan on paper.  I really appreciate all the great technical opinions and experience.  Thanks again!

[dreracecar]

Sorry to join the party so late

Things to consider
On a SBC unless you install the Magneto up front or run an offset drive the "10" will not fit--this adds to cost. I had to modify my rear bearing caps on my "6" to get the mag to clear.
Trying to run that big blower with a SBC that has a standard snout WILL rip the hub off the end of it. The snout barely sticks out of the front cover and by the time you get everything lined up pulley wise its going to be out there 4 1/2" past the front cover. Add another keyway to the hub and crank and look at the material left on the hub from the keyway to the seal surface--not very much. The 7/16 crank bolt is long and with a lot of threads , with even a good bolt, it will still stretch.
So heres what happens when you apply load/HP
The hub flexes at the point of where the crank ends, this flexing causes the crank bolt to flex and stretch along the threads(root dia of threads is smaller than shaft dia). As the bolt stretches the load is transfered to the end of the hub which splits the hub along the keyways for lack of material.
The only ways to combat these issues is to
With a stock crank snout--use a front crank support and hub (eliminates flex- but is $$$$$)
At minimum use a hub that has a BBC od but bored for SBC (ATI has them) After time might break the snout off but the hub wont split.
Get a SBC crank that has a BBC snout, BBC hub, Larger crank hub bolt (very$$$$$$$$$)

Personally I would rather run a SBC in 1/8 mile racing, too much weight to get moving running a BBC (thats why you need to build them BIG).

MY  Car
1650# w/ driver   375ci SBC 10.2comp  6-71 (20 over)  3.90 gear  leaves off idle   33"x 12" tire
1.06 - 60'   4.50 - 1/8  1/4= 7.00 @ 198mph (and more left) AND NOT HURTING PARTS!!!!!!