rev limits

3362 Views 17 Replies 7 Participants Last post by 90crxhf_w/ZC, Mar 12, 2007

luober

Discussion Starter · Mar 9, 2007

what is it in the d16a6 engine that puts the rev limit at 6500 rpm? is it the limit on connecting rod strength at that rpm or does it have to do with the begining of valve float? i am asking because my si seems to be still pulling hard at 6500 rpm and i hate to cut back to shift. i feel that it could go possibly another 1000 rpm with power before shifting but i dont want to hurt anything. just thinking.

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dohcrxl

· #2 · Mar 9, 2007

I don't think there's one single answer. When Honda engineers sat down and drew up the a6 they had to consider power, fuel economy, tensil strength of the materials, and I'm sure much much more and program fuel and timing tables into the ecu. 6500 was decided on because it was the best compramise of everything they had to evaluate.

I know this is just a general answer but I think it serves our purpose and the limits of the stock a6. As for making power passed 6500, of course you'd have to be modified. In stock configuration, there's not much sense in raising the rev limit. I've always netted best times on a 67-6800 rpm shift.

And yes, you're on the right track with valve float. The stock springs are just spongy when revs reach those levels.

ludesrv

· #3 · Mar 9, 2007

dohcrxl said:
I don't think there's one single answer. When Honda engineers sat down and drew up the a6 they had to consider power, fuel economy, tensil strength of the materials, and I'm sure much much more and program fuel and timing tables into the ecu. 6500 was decided on because it was the best compramise of everything they had to evaluate.

I know this is just a general answer but I think it serves our purpose and the limits of the stock a6. As for making power passed 6500, of course you'd have to be modified. In stock configuration, there's not much sense in raising the rev limit. I've always netted best times on a 67-6800 rpm shift.

And yes, you're on the right track with valve float. The stock springs are just spongy when revs reach those levels.

Especially in engine only design to max rev at 7000rpm, pushing them near, or beyond that, is stupid and dangerous to the motor.

If you want a little bit more spunk out of your Si, put in a SOHC ZC cam, or a Delta cam. They offer great cam upgrade and it's very easy to do. If you have a clean motor you barely get dirty haha. I had a SOHC ZC and I swear by them as far as D series goes now.

90crxhf_w/ZC

· #4 · Mar 10, 2007

your generally runing out of can your valve train can not open and close fast enough to keep up with the rpm's that is what makes a valve float and your piston smacks a valve.

right right or am i wrong????? :umno:

ollie

· #5 · Mar 12, 2007

90crxhf_w/ZC said:
your generally runing out of can your valve train can not open and close fast enough to keep up with the rpm's that is what makes a valve float and your piston smacks a valve.

right right or am i wrong????? :umno:

No offence,but let me rewrite that so I understand you better.

"Your valve train can't open and close fast enough to keep up with the rpm's,and that is what makes a valve float and your piston smacks a valve."

You have it correct until you stated the smacking a piston part.(Although that can occur you would have to have a damaged spring or revving the engine way past its max RPM)

Valve float happens when the valves lose contact with with the cam lobes and
sort of "bounce" on the lobes at high RPM.This can happen when the springs are weak or are too soft of a tensile strength.
Does this help explain?

_______________________________
Back to the original posters question:
If you are looking to make power past the 6500 redline,pick up a aftermarket cam and cam gear.This will help you extract that higher RPM out of that A6.

I picked this cam up for my built A6 project.
Gude Bullfrog cam:
PART NO: HCCS07
POWER BAND 4000 RPM. to 8200 RPM.
IDLE: Good
SPECIFICATIONS: Intake LIFT - .415 DURATION - 241
Exhaust LIFT - .421 DURATION - 228

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jfrolang

· #6 · Mar 12, 2007

If you're replacing the cam and plan to rev the engine higher than its stock redline, I highly recommend replacing the valve springs as well.

90crxhf_w/ZC

· #7 · Mar 12, 2007

ok but did i have it right for the most???

ollie

· #8 · Mar 12, 2007

90crxhf_w/ZC said:
ok but did i have it right for the most???

I stated Yes up until the "smacking a piston" part.
So yes.

SETI20

· #9 · Mar 12, 2007

Actually, a piston smacking a valve is not as uncommon as you'd think.

This is what happened when I pushed my D16Z5 (dohc zc) well past it's limits.
Granted, it's not the -only- thing that happened. But there was most definately piston to valve contact.

Albeit, this is more frequent on cars that have really high cam lobes, which makes valve clearance an issue.

One of the biggest problems that can occur with valve floating, is that the valve is literally smacked apart. Breaking off, and falling into the cylinder altogether.

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ollie

· #10 · Mar 12, 2007

^^^ Thats why I stated..."You have it correct until you stated the smacking a piston part.(Although that can occur you would have to have a damaged spring or revving the engine way past its max RPM) "

So yeah I hear ya brotha..
BTW nice kill.. :wink:

SETI20

· #11 · Mar 12, 2007

Bad things all around. It wasn't the only piston with a problem.
#3 was gone completely. And last time I checked, 3 pistons in the "up" position was a -bad thing-.

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90crxhf_w/ZC

· #12 · Mar 12, 2007

haha ok.

and dang that bottom end is a goner

i think that is how you spell it gone-er i dont know i cant spell haha

SETI20

· #13 · Mar 12, 2007

Just like boner, only different.

90crxhf_w/ZC

· #14 · Mar 12, 2007

haha ok haha :lol: what happened to that bottom end by the way??

SETI20

· #15 · Mar 12, 2007

I over revved it with all the oil sloshed to one side, starving the oil pickup.
A whole bunch of stuff happened then. Rod bearings gave out on 2 of them, valve hit a piston on another, and finally a piston shattered, fracturing the girdle, and sending chunks through the rest of the block, breaking another rod.

Didn't even take a second.

90crxhf_w/ZC

· #16 · Mar 12, 2007

dang that sucks sorry to here that!! what motor do you have now?

SETI20

· #17 · Mar 12, 2007

B18C4. Check out the features. Im in there. We're getting offtopic.

90crxhf_w/ZC

· #18 · Mar 12, 2007

cool cool. yeah true.

what ecu are you running louber?

because if you are runing the ecu that came with the swap. upgrade to a Zc ecu they rev to 7500 stock

i have a ecu ill sell you if i get this zdyne ecu

its a pm7 jdm DOHC Zc ecu

1 - 18 of 18 Posts

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