mike c.

iTrader: (1)

i'm looking into a 402 or 427ci motor. ok..lets say i build a 402ci and it makes 500hp 470tq(just guessing #'s) if i put all the same stuff(heads,cam,ect)from the 402ci on a 427ci motor,how much difference in hp & tq would the 427 make over the 402ci with the same mods?
thanks, mike c.

LSxChevelle

iTrader: (4)

I'm very interested too...

David Gordon

iTrader: (1)

Me three.

Hennytime

iTrader: (33)

+4 ftw

Haans249

iTrader: (24)

Well, there is a formula somewhere that adds horsepower/trq with cubic inches. I would say probably 40-50 hp/trq depending on the setup. But, you wouldn't be putting the same cam in a 427 as you would with a 402 now would you?... I didn't think so

Once you start getting into the upper cubes starting with 427 ect... dynamics begin to change quite drastically.

Adrian

Blue Hawk

Assuming same intake, heads, cam, headers, etc... probably only 10-15 more hp at peak, and it would also peak at a lower rpm. But you can expect a bunch more tq in the low and midrange rpms.

Simply put, you're heads will max out sooner because with a 427, you have bigger cylinders to fill in the same amount of time than a 402, but the resulting higher gas velocity will help you having a higher/flatter torque curve in the lower rpms. However, that torque curve will drop rapidly after the peak because your intake, heads, headers and exhaust (that were designed for the 402) can no longer flow enough for the needs of the bigger engine.

If the 402 made 500hp/470tq, then my guess would be 510hp/520tq for the 427.

That's the way I see it.

mike c.

iTrader: (1)

well either motor i choose will have AFR 225 heads,FAST 90mm intake w/ NK 90mm th-body,42lbs injectors,85mm massair,kook 1 3/4 headers(for lower-mid tq) ud pulleys. the cam i put in a 402 may not be the same as a 427ci i would need to research that more. this would be the set up,what do you think?????

slow trap

iTrader: (22)

you're researching the same thing i am.i want to go 427 but don't know if it will be worth the extra money over a 402/408.i am gonna use katech stage 3 heads and reuse my qtp 1 3/4 headers also.cam is still undecided along with the motor.i was thinking the comp 244/248 with around 11:5 scr or tsp giant with around 12:0-12:2 scr.if you get any clear cut answers anytime soom let me know.

Blue Hawk

Wow! I think it would be a badass setup either with the 402 or 427.

With a different cam for the 427, you'll have way more than the 10-15 hp difference that I mention earlier (I was assuming same cam for the two engines). With the right cam to match the rest, you will probably have a 25-30 hp advantage for the 427 over the 402, and still much more torque down low.

I suppose that your car is a daily driver (low-end torque concern). With a duration in the 24x range, you will probably see around 530rwhp while keeping good street manners.

P.S.: This is just a guess... I'm no expert by any means

Good luck with your project broh. Have fun!!!

Bill00Formula

iTrader: (4)

It's kind of interesting that there seems to be such a big difference going from a 346 to a 402/408, even a 383 but then going from a 402/408 to a 427/43X the difference seems to be much less.

I'm still interested in seeing what the normal rwhp from an ls7 head/ls7 intake combo will be.

Like others I'm trying to decide if it's worth it, especially with the L92.

Haans249

iTrader: (24)

Well, tell you what guys, I should have my car together this weekend, and I'll hit the dyno in the next week or so. I have a 24X/25X cam with lifter .65X/.66X and I'm expecting close to 580 to the wheels. Katech has a smaller 22X/24X in their Street attack which made 640hp at the fly...of course they were using lightweight rods ect which would free up hp.

SLED28

iTrader: (7)

Uhh YEAH!! Either would fly...

I have a 402 AFR 225/s on the rollers as we speak we'll see what it makes with a 24x 25x .600 cam.... I also have another 402 with AFR 225's with a 23x 24x .650 higher lift cam heading to the dyno soon.

I am thinking that these AFR 225 402's will make 500-520 rwhp and the 427's in the 525-540 rw range.

Phoenix 5.7

iTrader: (7)

all of those parts sound good except for the 1 3/4 headers. u really should look at 1 7/8 with those cubes.

mike c.

iTrader: (1)

SLOTRAP-when i get the answer i'll let you know. so far it seems the 427ci will make around 25-40hp more and tq maybe the same,is it worth the extra $2,000? for me,yeah i think so.
RHOENIX 5.7- I was told by LG motorsports to use the 1 3/4 headers for the better lo-tq for street driving. the 1 7/8 headers may make 8-12 hp more up stairs,but i would loose some lo-end that may make my car drive nicer on the streert . evenknow i have a low 10 sec street car,(i hope 9's this october) i don't drive the **** out of it,i putt around in it alot.
anyoneelse with some more advice and even some cam choices let me know.
thanks, mike c.

383ss

iTrader: (14)

where do you guys get this stuff from? I keep hearing that, but never see any proof of it.


as for the post. all things the same, you'll get about 1 rwhp for each cube added.

Nemisis

I'll have a good example coming up for you guys. My 6.0 went bye bye in the goat and am having the heads/cam/intake and headers swapped over to a 402, same mods just more cubic inches, I'll let you know the dyno results.

mike c.

iTrader: (1)

NEMISIS-please send me a pm when you get the dyno #'s from that swap. thanks, mike c.

Nemisis

Will do!

chevynation

iTrader: (8)

wow, that kinda surprises me. i figured since the big block chevy guys are runnin 2 1/8 - 2 1/4 or something like that, 1 7/8 would be perfect for 402-427 cubes (even a street car).

i dunno. just seems like 1 3/4 works perfect for 346s and would block up bigger cubes. it does depend on your exhaust port, collector style, rpm range, etc too though... my .02

erik

black_knight

iTrader: (1)

The whole point of going to 427 is to take advantage of the better heads you can get when you run 4.125 bore. If you throw the same stuff as your 402 on it, then yeah it will only make a few more ponies. If you optimize your heads/cam/intake for a 427, then you have the potential to get a LOT more out of it.