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Always on the limiter
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7 Posts
Discussion Starter · #1 ·
I run a sr20de in a under 2lt sports sedan in Australia.
It's a turbo rwd block, crank and rods with arp rod bolts. Toyota 3sge pistons at 13:1 comp running racing fuel. A gtir head with 312 deg duration, 0.470 lift and 95 lb seat pressure dual valve springs. Tomei rocker stopers and adj cam gears. Gtir quad throttle bodys and gtir injectors. Tuned length 4 into 1 headers. Autronic sm2 ecu and cdi. 3 stage dry sump oil system.

We made 250 hp at the flywheel at 7300rpm. We have a problem when we rev it over 8000rpm we brake rockers. We would like to rev it to 9000rpm and make 280 - 290 hp.

Any suggestions
 

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Bitter Old Man
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2,637 Posts
Andreas Miko and Mike Kojima are about the only two guys on this board that have the resources or knowlege to experiment with alternate rockers. Nobody else has mentioned your problem other than in context of over-revving and subsequently spitting HLA adjuster shims. You're a pioneer, keep us posted.
 

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Infiniti Parts Guy
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979 Posts
VVL motors have a different head. Their rocker arms are fitted to a rod that goes the length of the head. I don't know how good this would be up around 9K rpms, but I know the stock SR16VE revs over 8000rpms. You may be able to lock, or modify the rocker arms to work with a standard (as in one lobe per cylinder) racing cam as well?

I took this pic for my Nissan Performance Magazine article. you can kinda see what I'm talking about, under the cams...
 

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SE-R GREEK
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2,581 Posts
NAGTIR said:
The gtir head has solid rocker posts.
Ooops. I missed the part about the GTiR head, only thought it was the quad from the GTiR. :(

Now, I doubt that someone here can help you, experience with GTiR heads and solid lifters is rather scarse in the States. The alternative rockers/lifters mentioned in a previous post has o do with hydraulic lifters so there is not much relevance here.

Simple comments:

I know it may be stupid question but I assume you have the Solid Lifter version of the Tomei rocker stoppers right? If not this might be the problem.

You say you got max power 250 crank hp at 7300rpm. This is rather low for a 312 degree cam, I think with 312 max power on an SR20DE should be close to 7500rpm or more. Maybe the fact that the lift is rather low (11.94mm, close to what JWT makes for stock valve train with hydraulic lifters) limits your power. What cams are they? Asking because I have I cannot recall a 312 deg cam sold for the GTiR.

Finally, in Greece we rev stock SR20DE engines at 8000rpm and they do not have a problem (contrary to what conventional wisdom says). Granted, it is not reved up there for extended time periods like you may do in road racing but I find it strange that you have problems with rockers braking a little above 8K.

Do you also have wheel HP measuremetns for the 250 crank hp run?


Chris
 

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Always on the limiter
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7 Posts
Discussion Starter · #7 ·
The rocker stoppers are solid lifter type.
We haven't played with valve timing much and throttle bodys are only 45mm. Looking at gonig to 48mm throttle bodys in the future.

The cam grind is call nissan 78 grind. There is one with a litte bit higher lift, but we thought it might make our problem worse.

We run a super close ratio 5speed gear box, so thr revs don't drop below 6800rpm. It also seems to happen 20mins into a race.

We only dyno it on an engine dyno. So we don't have to worry about the stress on the car.

Thanks for the info.
 

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SE-R GREEK
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2,581 Posts
Maybe your TBs are indeed the problem.

Depending on the actual distance from the TB buterfly to the intake valve in the head configuration you have and your "target" 9000 rpm, the 45mm should be good for 240-280 hp (again this is at 9K rpm). Maybe you need to look into the 48mm ones.

Do you have or can you measure the actual distance from the buterfly to the intake valve plane on the head?

Chris
 

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Always on the limiter
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7 Posts
Discussion Starter · #9 ·
From the intake valve to the butterfly is 225mm.

The only reason we would like to rev it to 9000rpm, is to get more hp. We are going to play with the cam timing, to see if we can get some more out of them.
 

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SE-R GREEK
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2,581 Posts
Well, I believe you probably need to "hit the books" at this one but now, I positively think the problem is on the TBs.

I had saved some calculations a long time ago but the original source of the formulas eludes me so I cannot really refer you to them.

The numbers I have in the hand-written sheets indicate that for 8000 rpm, a quad TB with 45mm bodies, 105mm long airhorns, 100mm from buttefly to mounting point of airhorn, 300mm from the end of the air horns to the intake valve (a.k.a. ~ 100-110mm from buttefly to intake valve) would be good for approximately 250 bhp.

However, these numbers imply that the distance from the baterfly to the intake valve is ONLY 100mm (I did not have head measurements back then). In your case (225mm), you probably need a larger butterfly diameter since it needs to "taper" down to the same final diameter in the intake port within a much larger distance. Since you do not have low-rev restrictions in your engine (312 deg cams can hardly work in low revs) I would guess that even 50mm would be a reasonable choice but I strongly believe you need at least 48mm!!!

Unless of course you go with a specially built intake and ITBs in which case you may be able to reduce the distance from the butterfly to the intake valves and the calculations indicate otherwise. Still, 48mm seems reasonable for your target hp in any case.

You should also account for the fact that your max 250bhp are made at 7300 rpm. Revving to 9000 rpm will not net any more hp, will it? Probalby cam timing in this case is your 1st choice.

If and when you get around to it, please let us know what happened!!! There is a great lack of info on the actual performance of ITBs on our N/A engines.

Chris
 

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Always on the limiter
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7 Posts
Discussion Starter · #11 ·
For the valve to the end of the air horn is 320mm. From the valve to the mounting face is 170mm.

Thanks for all your help.
Will keep you posted.
 

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sleeper
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5,445 Posts
my initial guess is the valve springs might be too stiff, putting too much of a bending moment on the rocker arm. good luck!
 

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Registered
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351 Posts
whoa that car is sweet looking i know it's off topic but what is that (sold in australia i assume) or is it some sort of kit?
 

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Still not my president
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5,173 Posts
this is some crazy infor im glad i took the time to read all this....thaks for all this info....that car looks sick i would love to have one on the roads over here
 
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