Almost dyno day...another what’ll it make
 

I’ve refreshed my 400 and it is about ready for dyno time. I needed to replace the leaky rear main so I decided to swap out the 041 cam, get the heads ported, and upgrade to forged rods. Pistons are TRW flat tops from when I first built it 20 years ago.

Here are the new specs:
400 +.030
#13 heads ported to about 230cfm
9.75:1 compression
Factory 1970 intake with the ‘Ruggles mod’ done by me
Crower 60243 cam 228/235 @.050 .479/.494 lift
Rhoads V-Pro lifters
1.5:1 roller rockers
RARE long branch manifolds
Pro Systems 4150 785cfm carb

It will also be backed up by a Tremec TKX instead of the M20 when it goes back in the car.

Any guesses? I’m hoping for around 425HP.

They flow 230 at what lift, and if you have the flow chart, what do they flow at .200” lift?

I’m waiting for him to give me the final flow results. The most recent I saw as he was working on them were 159 @.200 and 220 @.500. They flowed around 230 at .600 but my cam is only .479 lift of course.

400-410
Similar to my build, but I have the slightly smaller 60242 cam

430/495...

462 HP max, more like 432 HP in reality.

Tom V.

430 hp.

415/475...based on my results from my similar build 2 years ago.

I will qualify this-depends on a generous or stingy dyno!! And to decide which you then need to run it at the track and weigh the vehicle. My RAIV pocket ported and more flow than those 400 zero deck 69cc chambers TRWs UD 231/239 @ 0.050 HFT cleaned up HO intake 73 SD Qjet AND headers-through mufflers only made 385 hp engine dyno not chassis-BUT "ran the numbers" in a 3900lb TA on mph.This is a stingy dyno!

the 455 in my TA now only dynoed 525 hp, based on mph depends on the calculator 550-575!

I'm going with 400hp/460tq.

It would make better numbers with a set of Hedman headers for a 67-69 Firebird, Harland Sharp 1.65 or Crane 1.71 ratio rockers and 10 to 10-2 compression instead of 9.75.......

I missed the exh manifold part so my guess is now 395 hp.

I'm going with 399hp/450tq.

trw slugs from 20 yr ago??
I'm going to guess your piston is .030 below deck?. and went with a shorter taller cam.... These things do not add up to greatness. Should be able to get some great torque, while your heads support 460 other things might not be as supportive.
380/450

with .065-.070 quench ...you will certainly be paying attention to detonation issues or really close eye on your total advance.

Block is zero decked.

didn't realize trw had dish pistons 20 yr ago. only -7cc 4 valve relief slugs. Arent #13's 72 cc.....at zero deck that would be more like 10.5 comp? My TRW's were .020 in the hole with 74 cc heads = 10.1 compression.
I'm sure you know more what you got than I do, but those numbers just seemed off.
ANYWAY...more compression will be better, zero deck is even better...now at 10.5:1 compression I would expect even better bottom end numbers as that is a fast action cam so you will not be bleeding off cylinder pressure as much as the 041 does. = even more torque :)

So update on my build.....
The builder got the engine and cam broken In without issue. He said the carb tuning seemed good out of the box. I stopped by to watch some dyno pulls and the engine wasn’t making power. HP was peaking at around 368 @ 5300. He was kinda scratching his head and thought maybe I had messed up the intake by modifying it. Well after doing some more digging he found that one of the cylinders was leaking down badly - over 40%. He took it apart and couldn’t find a smoking gun but thought the rings looked funny but piston and cylinder walls looked fine. He ordered a new set of rings and replaced them. Did another leak down test before putting everything back together and it was just as bad as with the first set of rings. So, all we can figure is something is wrong with the piston. Speed Pro won’t sell a single piston and he is hesitant to reuse the rest of the pistons now so ordered a new set of Icon flat tops. To be continued......

Was it bored and honed with a tq plate ? You can hone with tq plate only but you need to bore it .008 under.
Pontiac bores distort a lot if you do not do a proper bore and hone.

It was not done with a torque plate. He doesn't have one for a Pontiac. When he tested leakdown with the new rings he told me that he did it with just the head bolts for the bad cylinder snugged down, and then again with all the head bolts torqued, and got the same results. I am assuming that was to see if cylinder is distorted.

I know Barney Moravitz a Pontiac Stocker and SS race in San Antonio used to feel a torque plate did not really help a Pontiac block and he had his own machine shop,and did most of the heat treating on the 58-62 forged rods Butler sold before we have good forged rods.

That said my machine shop uses one.

The problem ended up being the piston. There was an area on the ring land that was rough feeling and I assume they is where the air was leaking thru. Put in the new pistons and he did a leak down yesterday and it was perfect.