Topic: 400 to 455 conversion

[SoonerTA]

Thanks Geno for all your help!  With everything we have talked about with the 455 crank, Crowler 60916 cam, 6X-8 heads with valve job, 1.77 exhaust valves and port work what kind of HP and torque numbers should I be expecting with this setup?

Or...If I am going to go ahead and get the TCI Saturday Night Special converter should I just go to the Crowler 60243?  If this cam can produce good vac. so I can run all my accessories and is streetable why not, right?  haha  Would there be that big of a difference between the two HP wise?

[72blackbird]

Chris,
If you get the heads ported to 240-260 cfm, you should see around 425-450 hp, 475-500 ft-lbs. The difference between the 60916 and 60243 might be less than 10-20 hp, but as you've noted the 60243 has a higher rpm range- with that cam I'd run a 2500 stall converter.

The 60243 is a little lopier by nature, due to the increased duration, but will still run your power accessories.

Geno

[SoonerTA]

Thanks again Geno for all your help! I have a lot to think about.

[72blackbird]

Chris,
Which block are you using to stroke a 400 to 455? I recently bought a 76 400 (I knew it was a 500557 motor, but the price was right- $75) which initially I thought I would stroke to 455- thinking about it I decided to just overhaul it, put some 5140 rods in it, rebalance it and designate it my smog motor (going into my 76 TA, which has to get smogged in CA). Since I have to get screwed by CA every two years w/ the smog deal, I'll go back to the 'shell game' I used play w/ CARB and build a 461 stroker w/ a spare 75 481988 block I have and swap that in after I pass w/ the smog engine.

I think the 500557 400 would be able to handle a 4.21/6.625/3.0 stroker kit and make a nice 425-450 hp, but if I'm gonna go through the effort of doing a stroker engine it may as well be with a better block, heads and cam to make 500+ hp. The 500557 400 will also make a decent spare engine w/ good forged rods, stainless valves, slightly better cam, etc.

Geno

[SoonerTA]

It is a 557 casting because it is the original engine in my '78.  I thought that block could handle the 4.21 stroke?

[72blackbird]

Yep- the 500557 400 block can still support a mild 425-450 hp 4.21" stoker build.

[RainMan]

Geno are the better blocks hard to come by ? I suppose you can't find them new.
I agree in that if your going to the trouble anyways that you may as well go with the thicker casting .
I wonder what the weight differance is between a 75 and 78 block?

[72blackbird]

The 70-75 481988 400 block is always a better foundation for a stroker build- when you compare a 500557 and a 481988 block side by side you know which one you want to use. The 481988 blocks are getting hard to find, but nowhere near as hard to find  as the 485428 455 blocks. I don't think the weight difference is significant, but the thicker main saddle area of the 481988 block is noticeable and does make a big difference.

Geno

[RainMan]

The 70-75 481988 400 block is always a better foundation for a stroker build- when you compare a 500557 and a 481988 block side by side you know which one you want to use. The 481988 blocks are getting hard to find, but nowhere near as hard to find  as the 485428 455 blocks. I don't think the weight difference is significant, but the thicker main saddle area of the 481988 block is noticeable and does make a big difference.

Geno

A stroker SBC or BBC  is looking better all the time lol

I guess for my purposes the 557 block is fine . In the 400 hp range is all I really want someday

[72blackbird]

A stroker SBC or BBC  is looking better all the time lol

I guess for my purposes the 557 block is fine . In the 400 hp range is all I really want someday

WTH?!!!

Go wash your mouth out w/ soap, Dirty mouth!!

Do a 4" stroker kit- will make 400+ hp easy and will make more torque than a 3.75" stroke 400.

My 500557 400 will be a smog engine, but I"m not building it bone stock- it will get a healthier cam, better ignition, some porting, and just enough work to bring it up to the 300+ hp range.

Geno

[RainMan]

A stroker SBC or BBC  is looking better all the time lol

I guess for my purposes the 557 block is fine . In the 400 hp range is all I really want someday

WTH?!!!

Go wash your mouth out w/ soap, Dirty mouth!!

Do a 4" stroker kit- will make 400+ hp easy and will make more torque than a 3.75" stroke 400.

My 500557 400 will be a smog engine, but I"m not building it bone stock- it will get a healthier cam, better ignition, some porting, and just enough work to bring it up to the 300+ hp range.

Geno

lmao I thought that may strike a nerve ,and yes I washed my mouth out but with beer though lol.
I was actually wondering about a 4 inch stroke also ,but some say get the most bang for the buck with a 4.25.
Myself I suspect a 4 inch stroke will be just fine ,maybe even keep my compression down to a safe 9-1,although I don't know for a fact where it will land ,and of course there are differant pistons available to . Does the 4 inch stroke crank require grinding out the block ,or is that only with the bigger strokes .

[72blackbird]

Most of the new 4" and 4.21", 4.25" stroke cranks don't require any block prep, but it's always a good idea to check the crank installed in the block before installing the rods/pistons. The 4" cranks come in two varieties- one w/ 3.00" mains that uses 6.625" Pontiac rods and stock 428 pistons, or one that uses the 6.8 BBC rods and custom pistons.

The 4" stroker crank will give you 8.7:1 SCR w/ a 98cc head (6x-8), or 9.1:1 SCR w/ a 91cc head (6x-4).

Geno

[RainMan]

Well as always thanks for the Info Geno.
I like those numbers compression  wise. Not that it really matters but I do like
the idea of a square engine bore and stroke wise.
I suspect the extra HP will be welcome

Sorry for seeming to steal the thread Chris,but this is an interesting subject you started

[SoonerTA]

No problem RainMan, I always like to see what everyone else is thinking.  I am learning alot about this topic and always welcome all the feedback.   And thanks for Geno helping out with ALL my questions. 

[72blackbird]

Guys,
The fun part about doing Pontiac engines now is the number of choices you have when building a 400 up- even w/ the 500557 block it's easy to make 400+ hp, and it doesn't have to be a fire- breathing stroker engine w/ a lumpy solid roller and expensive ported aluminum heads. Pontiac enthusiast recent covered a 500557 4" stroker rebuild w/ iron heads and it made 445 hp- not bad for a motor using cast-iron exhaust manifolds.

My 76 400 came w/ 6s-7 heads, identical to 6x heads but have smog tubes- these can also be made to make decent power like the 6x's. I wouldn't be surprised when I go through this engine if it ends up w/ a 4" stoker crank too.

Geno