High Rev Sohc's

[XXL4G64]

I kinda was thinking this at work say i was going to make a high rev 4g64 with a turbo. How far do you think it can rev with a fully built head.

[Galant306m]

6500 rpms.

[XXL4G64]

Is that because are transmission will not shift pass 6000 rpms? Or it is Just to be safe.

[Galant306m]

its because its a 2.4L. The bottom end wont handle being revved up that high.

take it this way my 63 head is built and can handle over 8000 rpms but im not going to rev it past 6500 because that all the bottom end can handle.

[mko]

You dont have to rev 8000 with 4g64. It makes all the power it needs at lower RPMs, and thats why theres no point of going into the high RPM range cuz you wont be making any power. And you cant go past 6000 cuz you hit fuel cut.

[galantofva]

Glad you guys are talking about this. I was actually wondering the same thing. You all keep saying 6000 rpm but mine shifts at around 6300 maybe even 6500. Under WOT that is.

[mko]

yeah its somewhere there.

[evil-G-nius]

Doesnt mean you should sit in that range. How often are you going around WOT hitting 6-65k? Like 306 said, there is no real point. The car hits peak hp at 5500 so the rest of that range is wasted. And if you boost...the power comes on around 2-2500 (from what I have heard) so that is a 3000 rpm range to shoot through. Thats more than enough

[4-G-rim]

A 2.4 has a longer stroke...so at higher rpms its not very safe to rev to heaven, because you'll burn it in hell. The longer stroke rotational mass gets very unstable at higher revolutions.

A bigger displacement motor will make its power in the lower end of the power band and no need to rev it crazy.

Transmission gearing doesn't restrict how much you can rev...it only limits your vehicle speed at a particular gear its on.

Having a DOHC or SOHC head doesn't matter either...as long the cam and valvetrain can handle the higher revolutions, you will be fine. A DOHC head just flows better than a SOHC.

[Galanttuner10]

i wouldnt rev high at all as what they have all said is true

turbo spools at like 25-3k and then you go to around 6k not much issue with 3k rpms of boost.. with a built bottom end and head i still wouldnt go about 6500 as we have a torque motor built for low end, the dohc 64s can go to like 6800 tho so i gues thats as high as id ever go

[peanotation]

DOHCstunr would be proud of this thread. he loves the sohc

[DOHCstunr]

The reason you won't make power up high with a 4g64 isn't entirely because of the longer stroke.

stroke is a factor in the rod angle, but its actually the rod angles that cause it to be volumetrically inefficient at high rpms.

the steep rod angles on the 4g64 grant a high piston velocity.
so high that when the engine revs beyond a certain threshold of HP increase, it will actually yield diminishing returns.
The pistons move so quickly, that smaller and smaller volumes of air have the time to enter the combustion chamber.


lets say you are drawing 5 grams per cylinder per rev @ 4000RPMS.
on a 4g64 even with good cams the pistons move so quickly at 8,000 rpms that you are only moving 2 grams per rev(these numbers are completely erroneous, and are only mentioned to deliver the basic concept)
however on a 4g63, because of the lower lod angles and lower piston velocity, it may continue to move more air until a much higher rpm value, yet due to lower displacement move much less air at cruising speeds.

I'm a couple beers in at this point so don't take this as flawless info.

[mko]

John, does it mean that destroker with 88mm crank and same 86.5mm bore will rev higher?

Im really considering destroking my engine when it comes time to rebuild it. im still debating if i want to use 88mm stroke or 94mm stroke crank.

[Galant306m]

y destroke your engine?

Actually what would be the plus you reving it higher! The engine has a point where it is going to stop making power destroking the motor will let you rev it higher but the fact that the SOHC head can only flow a certain CFM will cause it to loose power at those higher RPM rather then make it.

Same reason you cant run tons of boost through the 64 SOHC head it doesn't flow much air. When Voodoo puts boost up to 15lbs the car actually lunges under boost cause the head is actually making it choke.

I say if you want to make a hi reving engine build a 4g63 and have the head ported and polished.

if thats not what you want to do get a honda.

[XXL4G64]

yeah but thanks i wanted to know if it was a way but hell i pull on a 2002 max the 1st to gears and than the middle of 3rd he got me. i guess you get on it right and i would have pull on him harder

[Galant306m]

[bronxbombr]

You dont have to rev 8000 with 4g64. It makes all the power it needs at lower RPMs, and thats why theres no point of going into the high RPM range cuz you wont be making any power. And you cant go past 6000 cuz you hit fuel cut.

Ya but remember that the 94's with the ODB1/II has no guv'ner or fuel cut. I know cuz i had 3 of em.

[evil-G-nius]

I have a 96 obdII and no governor...not sure about the fuel cut though...I dont think so but I have only gone like 120-125 mph in the car so...I am still not near what the cut off would be

[galantofva]

Just out of curiousity, you guys are saying that a FULLY built 4g64, im talking head and block, and boosted still wouldnt make power after 5500? I see what your saying about the head not flowing much but lets say fully built @ 15psi with a port and polish on the head and the head would still draw smaller amounts of air at the higher rpm? Does the Evo head swap fix this?

[Shadow19]

You dont have to rev 8000 with 4g64. It makes all the power it needs at lower RPMs, and thats why theres no point of going into the high RPM range cuz you wont be making any power. And you cant go past 6000 cuz you hit fuel cut.

Idk about that dude. Ive hit wayyy past 6k before. More like 6800 when the road was wet one time.