[65nss4spdGTO]

What engine stroke would you build for your next race engine in a standard deck aftermarket Pontiac block if you had to choose from one of the following sizes?


3.750”
4.000”
4.250”
4.375”
4.500”
4.750”

Thanks.

Calvin Hill
Hill Performance
708-250-7420

[ho428]

4.25 bore x 4.0 stroke 454, since I have another 4" crank.
Already got two 4" stroke std deck 400/433's.

But would really like a 4.35 x 3.75, preferably in a short deck, aluminum even better.

That reminds me, I need to pick up a powerball ticket today...

[john marcella]

4.25 or 4.375 not sure yet but one will end up in my motor within a year or so. Maybe, i think. I need a bigger motor for Milan AM
Or maybe just do a little SB2?

[mike leech]

4.125 is nice size for most heads available. Port volume can be an issue with the bigger engines if you want them to rpm....

[bigchief468]

4.35 bore and 4.25 stroke for my new comb. and also to run heads up in Norwalk.

[mike leech]

Originally Posted by bigchief468

4.35 bore and 4.25 stroke for my new comb. and also to run heads up in Norwalk.

thats a nice combo.

[Hooter]

I wonder why more guys aren't running 4.75 strokes? If I remember correctly, aren't 632 BBC's a 4.75 stroke and a similar deck height? If it works for them, why wouldn't it work for us assuming you have a head that can feed it.

[badgto]

That's a good question Hooter. All Chevy guys I talk to that runs that combo, likes it has no issues. They have been running all year and putting on about 200 passes or more. I don't see why the Pontiacs couldn't run it too.

[BruceWilkie]

I like 482 CI 4.25x4.25 using stock deck height...seems right for a lot of reasons. Gasket sealing, intake runner length, piston speed, and available heads. I question crank durability not to mention ring life going much beyond 4.25 stroke. If you are going to keep rpm down I guess the 4.375 or 4.5 stroke is ok. (4.25 stroke 6.8 rod 7500 rpm = @8746 Feet per minute max piston speed, 4.375 stroke 6.7 rod 7500 rpm = @ 9040 Feet per minute max piston speed. By contrast the little 3.75 stroke 6.625 rod goes 8500rpm plus for same piston speed as 4.25/6.8 combo at 7500)

I like the 3.75" and 4" strokes with no more than 4.25 bore but think they are better suited for a shorter deck block. The piston/rod are kind of heavy at normal deck height. Shorter deck would favor intake with shorter runners for higher rpm power and lighter recip aids durability.

I'm doin a low budget 406 for time being till I can build my better motor the way I really want it. I'd prefer a forged crank in the 406 but confident factory cast will hold up just fine for the level of power it will make with the mostly old school parts I'm gathering.(550ish???)

[Steve Barcak]

My answer would depend on at leasr 3 otrher factors you did not list-

1. n/a? blown?
2. gas? alky? nitro?
3. application

Most of the strokes you listed can work nicely depending on other perimeters.

[badgto]

Ok Steve use mine for example. N/A on alky and a very heavy 3450 bracket car that needs the torque to get up on the back tires to make this car work. I have used a 4.50 stroke in the past and work good but, looking go to the next level.

[Ken -Ace- Brewer]

Just to put it out there. I have 4.375 assemblies IN STOCK. Flat Top Pistons.
http://www.pacificperformanceracing....ankshafts.html

Ace

[60man]

4.50 for obvious reasons.

[john marcella]

Originally Posted by Hooter

I wonder why more guys aren't running 4.75 strokes? If I remember correctly, aren't 632 BBC's a 4.75 stroke and a similar deck height? If it works for them, why wouldn't it work for us assuming you have a head that can feed it.

They also come with a 4.625 bore that lets them package adequate sized valves for the CID and RPM to make good power.
Cant get enough head

You cant ever look at 1 part by its self, it always is affected by another part ,as well as affecting other parts its self.

[DINO1]

Originally Posted by Hooter

I wonder why more guys aren't running 4.75 strokes? If I remember correctly, aren't 632 BBC's a 4.75 stroke and a similar deck height? If it works for them, why wouldn't it work for us assuming you have a head that can feed it.

Because they have heads that flow enough to support the cubic inches.

[65nss4spdGTO]

Bruces numbers are based on max piston speed, I like to look at the mean piston speed and the effects on the stroke / RPM. Shooting for a high mean piston speed, somewhere around 5400ft/min. Using that number, the target of 5400ft/min will require the following RPM's for each stroke listed:

3.750" 8640 RPM
4.000" 8100 RPM
4.250" 7623 RPM
4.375" 7405 RPM
4.500" 7200 RPM
4.750" 6821 RPM

Calvin Hill
Hill Performance
708-250-7420

[mysticmissle]

does rod length become a factor here or is it still just a byproduct of stroke and pin height

[Chupa]

Well my next combo will still be my 455 if it survives until I'm ready - after that 4.00 stroke in a IAII. I guess I could go larger stroke but then I could go larger heads then need to redo my chassis ... Oh man this is a viscous cycle$$$.

So just trying to keep it relatively cheap. I know myself the more cubes would be all the more reason to go larger head.

[65nss4spdGTO]

Originally Posted by mysticmissle

does rod length become a factor here or is it still just a byproduct of stroke and pin height

My position of rod length is more dependent on the application. N/A versus power adder and designing the piston with the pin, rings and weight for that application. I look at the airflow demand based on the average piston speed. Other factors do come into play such as side loading, ring depth and RPM range.

Calvin Hill
Hill Performance
708-250-7420

[65nss4spdGTO]

Originally Posted by DINO1

Because they have heads that flow enough to support the cubic inches.

The piston speed I used as my target would require cylinder heads to flow between 390 CFM and 440 CFM based on engine size in the 455ci to 510ci range to be efficient and make somewhere around 2/HP to ci.

Calvin Hill
Hill Performance
708-250-7420