401" or 428" SBC

[Fatman]

Hi,

Been viewing for a while and now hope to get some opinions on a SBC buildup. The two choices are either a 401" (4.125x3.75) or 428" (4.125x4).
Car is street/strip(1/4 ml), powerglide, about 2800 lbs inc driver.

Components that we have are 23 deg high port cylinder heads, 2.12x1.6, 2.6 min cross section. Midrange numbers are not great at about 245cfm@.400 but peak is respectable at 320@.700". Ported cast single 4 barrel. Don't know what the intake is but passes 305cfm @ .700.
Solid IR roller. 270/274@.050/106. .700 net intake lift with 1.6 intake rockers. Headers are 2" into 3.5".

Got to build a new short. Will run between 13 and 14:1 with alcohol and like to keep rpm at around 7000 maximum. Would like to make about 700 hp/580 so so ft/lbs which should be good for about 145 mph.

Will use a Dart tall deck block at 428" or standard block at 401". Is there any reason not to build a 428" motor? Would it be possible for the bigger motor to make less HP/torque.

No lb/ci rules or anything like that. Just want to be as fast and reliable as possible

Any advice appreciated
Fatman

[speedtalk]

Hi Fatman, Thanks for joining the forum. I'd build the 428". The only thing I see is the header maybe a fuzz big. Oh, when you say cast intake, I assume you mean aluminum?

[358T]

Hey fatman, I'm no expert but if it were mine and had to choose between those two shortblocks, I would build the 428. If you built a 428 I think it would act a lot like my combination which is being discussed in the "Cylinder Head Question" post. My combination has a smaller cross section but better flow and it starts flattening out around 7K.

Is a 414 ( 4.125x3.875) shortblock not an option? Based on the advise I'm receiving in the other post and personal experience, I think the 414 would be best given your current parts and criteria.

Heck, I'm also in here asking questions. So.... My opinions probably do not mean squat. But, I couldn't resit giving my opinion. Speedtalk and the others here far out-qualify me.

Scott

[Fatman]

Thanks Guys

Intake is cast Alum. Not sure what it is as all has been ground off.

Any engine size is an option. Just thought 428" as a 4" crank cost the same as a 3.75" crank. Would like to keep standard bore, just in case.

According to what i have been reading, the pipes are too big but built a 407" a few years ago with the same size pipes and that made 580 ft lbs at 5000 rpm with 665 hp at 6800 so still seemed quite strong. Went 144 mph in 2700 lbs.

Spoke to a few builders and got different opinions. Got the following:

-Wont make as much power at 428 as it would at 401 as the head will choke it.
-Even if the head chokes it it should still make at least the same power, maybe at a lower rpm, with fuller HP and torque curves.
-Even if the head is a restriction, might make less HP per ci but will still make more with more torque as well.

Agree with the last two but the first has me wondering.

Will the extra cost for those extra 27 inches produce a couple tenths and couple mph?

Thanks again

[EngineTech1]

Of your three quotes the first one is completely wrong and the second two are more right than wrong. No matter what the heads are the bigger engine will make at least the same if not more power, probably a little more, and will peak at a lower rpm with higher average numbers and a proportionally fatter power and torque curve. If you aren't restricted to engine size or if you don't get a good weight break then buy the 4 inch crank and make more power lower and make the engine a bit more reliable. Unless a weight break makes the smaller engine the advantage I would always build to bigger inches. I have seen engines dyno'd with nothing but a stroke and piston change to pick up displacement, same induction, cam, heads, everything else, and it peaked lower, made more peak power at a lower rpm, more power and torque throughout the entire range and went faster at the track. Go for it.

[Fatman]

Dano

That's what i was thinking. At least the same or more HP/torque with a higher average. The only extra weight that we will have to carry will be the few pounds more that the bigger motor will weigh if we go that way.

One shop actually said to destroke it into the 370" range and rev it harder.

Any other opinions out there?

thanks
Fatty

[EngineTech1]

My question to people that say things like that would be simply "WHY?" Why would you destroke it and rev it harder? what are you accomplishing with that? You're making less total torque probably a little less power, narrowing your rpm range and moving it higher while losing low range and requiring deeper less efficient rear gears. At the same time you can't necessarily run as agressive of a camshaft because of the rpm you are trying to turn starts pushing the envelope of valvetrain stability and also requiring more frequent valve spring replacement as well as more frequent freshens and higher stress loads on the rod bolts, wrist pin, piston and rod usually.

[Guest]

Dano

One shop actually said to destroke it into the 370" range and rev it harder.

Any other opinions out there?

thanks
Fatty

Well in the rain it will be easier to drive or if you put armor all on the tires!