odds of my high rpm nitrous 306 surviving

[DarkoStoj]

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]

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.

 

[steel1212]

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

 

[MustangMatt1966]

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]

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]

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

 

[DarkoStoj]

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

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]

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.

 

[10secgoal]

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.