Curious... How is it that 347's are getting in the same rwhp as 408's?

[Pokageek]

I am hearing a lot of internet talk about people with NA 347's in the 400-500rwhp range. I have a ton more tq but what are they giving up? What am I missing that they have? If I am in the same range with a much bigger engine? My guess would be I would say streetability? But then you here them say that their car is real streetable.

 

[Rookie71]

I'm guessing on similarly setup 347 vs. 408 you should see a ~60rwhp advantage and a flatter torque curve with the 408. To make up that gap a 347 should have either more compression or more rpm?

 

[BlackVert]

a 347 that makes 450 at the wheels is more "maxxed out" than is a 408 that puts 450 there. max the 408 to the same degree as the 347, and the 408 will be over 500 horses.

also, if you put 2 450hp dyno sheets next to each other, one from a 347 and the other from a 408, and i guarantee you'll see a difference in torque

with the proper combination, a 408 can outperform a 347 every time.

 

[Grn92LX]

The right parts. Its really not hard at all.

 

[5spd GT]

There is more to it than just parts.

It takes compression, goals, and budget, and knowing the right people to match.

The main issue, is that many do not put large enough heads and intake on the 408+ cubic inch engines.

There are WAY more 408 CI with 450 rwhp than 347 CI. More streetable at that.

 

[Pokageek]

Makes sense. Alsi Ithis is not a 347 bashing thread BTW. I was just curious though.

 

[5spd GT]

It typically is easier to try to squeeze out the most power out of smaller engines than larger.

 

[final5-0]

I would kinda break it down like this

We have seen many OEM block based NA h/c/i combos do the 1 rwhp per
1 cubic inch thing and drive just like a little stocker Stang.

It stands to reason the same can be said about ..........
350 cubic inches or 400 cubic inches

however

400 rwhp from only 350 cubic inches is a 1.14 to 1.00 kinda thing

Just a bit more aggressive as I see it
but
Not ... all that ... more aggressive

The C U B E S can make for some really awesome torque

You just get benefits from them you don't get with a smaller motor.

I don't see 400 rwhp from either method as being bad ... just different

Then again ..............

If you had a 400 ci motor with that same 1.14 ratio ...........

Well ....... We're now talkin 456 rwhp

Grady

 

[Black95GTS]

Guys putting 225s on a 347 would be like throwing CHI canted valve stuff on a 408, which not many people do because you're talking big dollars. There is also the mentality, which is true, that if you bump the cubes and the heads then the camshaft doesn't have to be as radical, (NOTE: Chevy's LSx stuff) so a lot of 408s are under cammed.

A typical 408 is similar to a high dollar 347... a big dollar 408 will blow the 347 out of the water.

I'll paraphrase baglock (does he exist anymore?) and say you could take a coffee table to 200mph with enough money.

Adam

 

[BlackVert]

It typically is easier to try to squeeze out the most power out of smaller engines than larger.

just curious ... why?

 

[5spd GT]

just curious ... why?

A couple reasons really that seem to be related...

It can come down to budget and the amount of flow the heads can provide.

There are not as many "big" heads for the 408-427, as compared to the same "big" heads for the 331-347.

For example, if I was to put together a 347, I would seriously look into using the AFR 205cc heads. So, let us stay on the same playing field. The next readily available head from the same company is the 225cc.

There is a 17.5% larger cubic inch volume to fill between a 347 and a 408.

There is 9.7% difference in intake runner volume between the AFR 205cc and AFR 225cc heads.

Or even better, just look at the average cross section numbers between both heads:

AFR 205 - 2.50" (squared)
AFR 225 - 2.74" (squared)

There is only a 9.6% difference between the two heads.

So we are trying to feed more cubes, with potentially, less head flow.

The goals is to fill the added voluve, but 17.5% (between cubes) does not equal 9.6-9.7% (between heads)for the same power potential.

The 408-427 guys really could use more cylinder head, that typically is not out there so readily.

Now, you can port and get speciality heads that the big boys use and have no issues.

But think, porting an AFR 225 head is going to be $3000+ easy.

How many guys are willing to put forth that type of dough?

Few, and far between, which is why you see more smaller cube/high hp, compared to larger cube/high hp. It is typically limited by budget, but relates to engine flow needs as well.

In some applications for higher revving 3.4" guys, I could see even the AFR 225 heads being utilized with the proper package. So what heads, with the same goals, are going to supply enough flow to the 408+ engines?

 

[Rick 91GT]

A couple reasons really that seem to be related...

It can come down to budget and the amount of flow the heads can provide.

There are not as many "big" heads for the 408-427, as compared to the same "big" heads for the 331-347.

For example, if I was to put together a 347, I would seriously look into using the AFR 205cc heads. So, let us stay on the same playing field. The next readily available head from the same company is the 225cc.

There is a 17.5% larger cubic inch volume to fill between a 347 and a 408.

There is 9.7% difference in intake runner volume between the AFR 205cc and AFR 225cc heads.

Or even better, just look at the average cross section numbers between both heads:

AFR 205 - 2.50" (squared)
AFR 225 - 2.74" (squared)

There is only a 9.6% difference between the two heads.

So we are trying to feed more cubes, with potentially, less head flow.

The goals is to fill the added voluve, but 17.5% (between cubes) does not equal 9.6-9.7% (between heads)for the same power potential.

The 408-427 guys really could use more cylinder head, that typically is not out there so readily.

Now, you can port and get speciality heads that the big boys use and have no issues.

But think, porting an AFR 225 head is going to be $3000+ easy.

How many guys are willing to put forth that type of dough?

Few, and far between, which is why you see more smaller cube/high hp, compared to larger cube/high hp. It is typically limited by budget, but relates to engine flow needs as well.

In some applications for higher revving 3.4" guys, I could see even the AFR 225 heads being utilized with the proper package. So what heads, with the same goals, are going to supply enough flow to the 408+ engines?

David, glad to see your learning...lots of good CORRECT info here

We make 680HP+ on 345ci, all NA.....how much do you think that cost?????? Way more then most will ever spend on a motor, but it fits a specific class and goal. low low 9's @ 145+ I can tell you the heads are much bigger then 225cc and the carb required flows more air then any big cube motor I have ever built.

It comes down to BUDGET and how radical and maintence friendly you want a motor. I can honestly say I have built customers big cube motors that vary 100hp+ just based on the induction and valve train, camshaft selection. I have smaller cube motors that make more power, but they are more aggessive and near all use more compression and RPM to acheive it.

My big cube high HP combo suggestion is
11:1 or more comp
225cc or more cc head
Ported intake, Super Victor is carbed, EFI spyder, Victor 5.8 or TFS R
Solid Roller or aggeresive hyd
1.875" header, 3.5" collector, 3" exhaust, un chambered muffler....

 

[PUNISHER RACING]

It all comes down to how much money you are willing to spend , and what you deem streetable in my mind. Hell the NMRA Pure Street engine makes 450 horse with only 310 inches of motor but I am broke now because of it. Its all in the parts and whether you want good, better, or best and how close are you willing to go towards divorced to acheive it. There are plenty of people that made 450 horse with 306 inchers but sacraficed reliability and longevity in the process. The beauty of the bigger inch motors(windsors) is you dont have to spin em to the moon to make the number therefore with routine maintenance they will live a long happy life. I drive my PS car on the street here at home but with 260/[email protected] duration going from stoplight to stoplight is no treat let me tell you.

 

[final5-0]

It seems to be all the same to me ... over and over and over

Everybody (yes...me too) loves to TALK about ... big power

and then

There is the REALITY of ... big power

Reality will tell you that 400rwhp or more is gonna cause you to deal with

Transmission Weakness
Suspension Weakness
Rear End Weakness
Unibody Weakness
Cost to operate it
and
More

after you get that high horse power motor built

You can really put a BIG strain on your little 94-95 Stang with a simple
NA h/c/i combo :Word:

I'm not trying to be critical and bring everybody down

It just seems like more and more peeps are running around with their
heads in the clouds and thinking big power is so easy to come by

It almost seems like the attitude is

"Lets build a nice little ... Street Car"

"400rwhp or more is just a bit more effort than a typical bolt on combo"

and

"You'll suffer no compromises at all if you go for that level of performance"

Grady

 

[5spd GT]

I am with you Grady

It is not easy to be pushing out big numbers like some would have you to believe. Usually when power numbers are not the "norm", there is typically a reason for that.

Budget, details, know-how, tricks, loss of driveability, longevity...

Well Rick, I am trying

That combination you listed made me drool...

 

[Pokageek]

It all comes down to how much money you are willing to spend , and what you deem streetable in my mind. Hell the NMRA Pure Street engine makes 450 horse with only 310 inches of motor but I am broke now because of it. Its all in the parts and whether you want good, better, or best and how close are you willing to go towards divorced to acheive it. There are plenty of people that made 450 horse with 306 inchers but sacraficed reliability and longevity in the process. The beauty of the bigger inch motors(windsors) is you dont have to spin em to the moon to make the number therefore with routine maintenance they will live a long happy life. I drive my PS car on the street here at home but with 260/[email protected] duration going from stoplight to stoplight is no treat let me tell you.

:Word:

"Its all in the parts and whether you want good, better, or best and how close are you willing to go towards divorced to acheive it. " Funny but TRUE!!!!!

 

[final5-0]

I am with you Grady

It is not easy to be pushing out big numbers like some would have you to believe. Usually when power numbers are not the "norm", there is typically a reason for that.

Budget, details, know-how, tricks, loss of driveability, longevity...

Thanks for the support David

Hey ... I'll be the first to admit it

I ALWAYS want ........... Something for Nothing

I know I'm not the only one who sees over optimistic expectations
when
It comes to putting together a nice ... Street Car

but

You see it at A L L levels of performance in our hobby

I can't tell you how many pm's I've gotten where peeps wanna duplicate
my combo results with a few hundred dollars spent on a handful of OEM
parts they might pick up at a junk yard or swap meet.

I mean ... I would have done that very thing :Word:
if
Research results had showed me it was possible

Grady

 

[Redsnk95]

The 347 is also going to have turn a lot more RPM for the extra hp as compared to a 408. The area under the curve will be better with a 408 as well. Plus it is less expensive to build a 6000rpm 408ci motor than it is to build a 7500+ rpm 347ci motor.

Also if you put 302 parts on a 347 it will make 302 power. Same goes if you put 347 parts on a 408 it is going to make 347 power.

 

[5spd GT]

If you have a 302 with the said 302 parts, you are going to make that 302 power.

If you add 45 more cubic inches, you are going to make more power, without a doubt.

So are you still making 302 power?

If you have a 370 rwhp 302, as we have seen this before, and add the same top-end parts off the 302 on a 347, will you still make the same 302 power?

I know my answer.

So does 302 parts actually make 302 power?

 

[igotyofire]

i think there is a gap between running a built 347......to spending so much money you might just skip the 351 block and go straight for a big block? which will do it easier...... im not really knowledgeable on this but the 460 is the only thing i can think of heh