V8MiataMike

So on my mustang, I noticed oil pressure dropped... Did the usual stuff but because I had this happen a few years before (a 306 with a T5 and nitrous), I suspected another cracked block. If you look carefully you can see the crack.



The 302 stock block can only take so much before it literally splits right down the middle. Cracks form on the main webs and go up through the cam supports and right through the middle of the valley. Bummer.

The Mustang weighs 3300 lbs with me in it and will run mid 6's at a local track with 150 shot of nitrous. Engine is an internally balanced Eagle 347 with AFR 185 heads, solid roller cam, main girdle, C4 Trans, etc. It runs mid 7's on motor. I'm number 17 on the time sheet (yes, apparently not doing too well on the light!)











Last time out at the track I made the one run with nitrous (but because of the low oil pressure) then the rest of the day on motor only.

When the block starts cracking the cam bearings start to walk out. Number three is moved out about 1/4 inch so it has not been cracked for too long.

So now the smart thing to do is acquire a Dart block and move the internals over to it. Or...

Acquire a Dart short block assembly and move the internals over to the Miata 5.0 and run it on motor only. That may be cool...

.boB

That would be my choice. An aftermarket block is more money to begin with. But for racing it saves time and money in the long run.

V8MiataMike

By the way, i think I made a semi "negative" comment on another thread here about using a flex radiator hose. Guess what, there it is...

Maybe this is why I tend to not want to use them. It is a bit kinked at the radiator end. Never had a problem with overheating though.

Mike

MX-Brad

Well there's your problem right there...lol.
After taking in that righteous Mustang, it's the first thing I noticed.

tneyman

how much horsepower are you running without nitrous

V8MiataMike

It dyno'ed at 358 HP and torque at the wheels. Factor in the automatic trans (15%? 20% loss?) and I would suppose it is around 420 HP at the flywheel. Add the 150 shot of nitrous and "theoretically" its making about 570?

I shift it at 7000 RPM. On the dyno, it was still pulling well at that RPM. Rotating assembly is internally balanced and I was hoping that would help but block is still cracking...

Gator Bait

JBweld FTW!! ...sorry about the block..glad you caught it b4 more damage was done.

tneyman

you need ford racing 363 short block,wont crack,4500 dollars

V8MiataMike

You are correct!!!

The stock block just can't take beating. Even the Mexican block does not necessarily have the main webbing support to handle much more...

I'm leaning towards the Dart SHP block though. It has the taller cylinder bores...

Sumitt however has a machined and ready to go stock block for $750. So for about $1,000 I can move the rotating assembly over and be back in business. Maybe also back the nitrous off to a 100 shot and see how long it lasts. This one made it three years...

Cost of Ford Boss or Dart block puts me at around $2,500 alone just for purchase and machining. But a pay me now or pay me later situation for sure.

Mike

V8droptop

Sorry to hear. I've been wondering, ~500hp is about stock block limits, from second hand knowledge only. Seen only a few builds pushing that limit here. A friend is running a turbo 5.0 and I'm curious.

I would go the aftermarket block myself, as well. My ls7 block had been resleeved with Darton sleeves, as ls7 blocks do have cracking issues, which mine did, no valve or rocker isues, just thin cylinders. All good now.

engineer

Hi all,

i concur that the standard block is only good for up to 500hp long-term.

An after market block Dart or Ford racing will be so much better and can do double the horsepower. However the extra strength comes with a weight penalty. They are heavier than a standard block by a not insignificant margin. In a Miata this weight would be quickly felt.

if the budget stretches an aluminum alternative would be the best if both worlds...but at double the cost 😊

if I was a rich boy...i would go the aluminum block every day.

cheers

AnthonyS