odds of my high rpm nitrous 306 surviving

DarkoStoj

Founding Member

Sep 4, 2002

929

13

39

Detroit

www.pacific-motors.com

Dec 26, 2005

#1

• Dec 26, 2005

• #1

I'm building a 306 for my 68 Mustang, and was curious if this was too much power for the bottom end to survive. I plan on shifting between 7,000 and 7,500RPM

Stock 68 Block .030 over
10:1 compression forged TRW pistons
Eagle I beam rods
Stock crank turned .10

Comp Cams XR280R Solid Roller
242/248 dur @.50
.608/.614 lift
110LCA

Box stock AFR185CC heads with the 58CC chamber
Vic Jr Intake
Speed Demon 750 Double pumper
NOS 150HP Cheater spray
MSD Digital 6+ Ignition
Mallory Unilite Distributor

Tremec 3550 with Billet Aluminum Flywheel and Centerforce D/F Clutch

4.56 Gear with Track lock (until I blow up my 8" and go with a 9" and probably 4.10's)

 

brianj5600

Active Member

Sep 19, 2003

1,964

2

39

Middle TN

www.cardomain.com

Dec 26, 2005

#2

• Dec 26, 2005

• #2

I would not worry about the bottom end. I would not trash the 8" though. Pull it out and sell it. My 8" with a similar combo last about 10' maybe at the track. Both caps blew off the back. The motor went to 9200 rpms according to the recall on the tach.

 

S

steel1212

Active Member

Jun 24, 2004

1,180

0

36

48

Frankfort, Ky

Dec 26, 2005

#3

• Dec 26, 2005

• #3

Yeah, why waste a good 8? Sell it to recoupe some of the money for the 9.

 

MustangMatt1966

New Member

Mar 11, 2004

1,004

1

0

41

Orlando Fl.

Dec 26, 2005

#4

• Dec 26, 2005

• #4

I agree with the two above posts, with the horsepower you will be making, the 8 is not going to last long at all...sell it while it is in good shape, get a 9 and you will be good to go

 

Dark Knight

Founding Member

Feb 1, 2000

2,578

0

0

Chandler, Az.

www.mysticspeed.com

Dec 26, 2005

#5

• Dec 26, 2005

• #5

Personally, I would have run a lighter piston.. TRW's are HEAVY!
Hope you spent the $$ for a good balance job too. I had my old 289 balanced with the crank pulley, clutch and pressure plate installed.. but I was spinning it over 8k rpm

 

thehueypilot

Active Member

Feb 25, 2004

1,084

0

37

62

Medina,Tennessee

Dec 26, 2005

#6

• Dec 26, 2005

• #6

I would put a main bearing girdle (steel) on the lower end to keep everything from moving around at that RPM.

 

DarkoStoj

Founding Member

Sep 4, 2002

929

13

39

Detroit

www.pacific-motors.com

Dec 26, 2005

#7

• Dec 26, 2005

• #7

thehueypilot said:

I would put a main bearing girdle (steel) on the lower end to keep everything from moving around at that RPM.

Click to expand...

I've read on higher horsepower motors main girdles stiffen up the block not allowing it to flex during high pressures which lead to cracking.

 

65ShelbyClone

Founding Member

Sep 9, 2000

4,675

38

119

Antelope Valley, SoCal

Dec 26, 2005

#8

• Dec 26, 2005

• #8

Girdles really only prevent main cap walk. They dont seem to strengthen or weaken the block at all. The general concensus is that a girdle might save the crank if you split the block.

 

1

10secgoal

Active Member

Dec 1, 2003

2,801

3

49

46

San Diego

Dec 26, 2005

#9

• Dec 26, 2005

• #9

Yes, a girdle will hold all your parts in a neat pile. But I would be carfeul spinning that high. I've seen N/A motors split blocks at that RPM, not even making much HP. The difference between 6k and 7k is exponentially different as far as stress goes. There are some guys that I envy like 1320stang. He's gone 10 flat in a stock 289 block N/A. Not much you can do about it with a stock block other than a little hard block. And with nitrous.....just wanna let ya know not to be surprised.