my NA Project 800 hp 7000 rpm roadster

[Aevus]

Note to myself and thinking outloud



Image below are the flow numbers on my gen 3's ported heads.

0.596'' lift puts me around 307 CFM, with 2.6hp (V10) per CFM that translates to roughly 798 bhp potential, minus 15% loss on the drivetrain we're looking at 678 hp at the wheels.

Now, with different rockers ratio, I'd be able to hope for a maximum of about 312 CFM, which can potentially deliver 811 bhp / 689 whp.

That's potential only. Which means no bottleneck: injectors/fuel pump able to supply enough fuel, air intake able to supply enough air, exhaust system not restrictive.

Also, would have to bump up the rockers ratio on the exhaust even more, going from the actual 0.554'' to something close to 0.600'' (assuming the valve will clear the piston) and get exh. 243 CFM at max lift. and most certainly rework the exhaust system at the same time, to make sure it flows out good...
Since I have a dual profile cam (246/256 @ 0.050'') with a full 10 degrees more on the exhaust side, it sure helps making it up for the lack of flow, but I probably won't ever be able to get 100% intake/exhaust, no matter how good everything are around the heads...

So what's left?

Ethanol = to boost up that 2.6 hp per CFM ratio, chemically. At some point I won't be able to supply more air, but I can supply more fuel easily with my 69# injectors (and possible fuel pump upgrade). Will it work? I don't know, but sure will test it!

Scavenging = Getting the full benefits of the camshaft and spinning the motor as it was planned: hopefully with peak power between 6,500 and 6,800 rpm or so. Now that I know I have the valvetrain to support it, I just need to adress the air flow restrictions and see what happens.


The basic maths are very well explained here:

https://youtu.be/4SeKKXEGk3w?t=2128



--------

Of course, there is much more to it, that 0.26 hp per cylinder per CFM is not absolute. It's a rule of thumb.
Scavenging effect (big cam) and ethanol are two ways to cheat that rule on a N/A engine. I've heard of 1000 whp N/A monsters with ''only'' 400 CFM heads (V8!)

I'm now understanding why 24 degrees valve overlap cam was about the limit for a ''street'' Viper. It loses so much cylinder pressure at low RPM, it's just impossible to compensate with a tune. Idle is fine, but it's sluggish up to roughly 2,000 rpm... So either you have a high (or very high) compression ratio and 4.10 gears to, somehow, compensate... Or you forget the ''streetable'' altogether and just use it on the strip or on the track where low-RPM is not a problem anymore. Personnally I can't (won't) do it, because I'd like to daily drive the beast in summer... That being said, it's probably possible to bump to 25-26 deg overlap if you have 11.5 or 12:1 CR, but not sure at all it's worth it. Especially if the air flow is a bottleneck. Eh, look at me: I'm stucked with a camshaft and a valvetrain, at the moment, good for 6,700-ish... but the air flow limits me to 6,000 or so. Hopefully it won't be the heads or exhaust, but only the TB and manifold.

[Aevus]

Oh, and bytheway, if you have GEN 4 (ported) heads, you can come up with bigger numbers of course:

http://speedstore.ca/VP4_flow_sheet.html

360-370 CFM @ 0.625-650'' lift on the intake and about 260 CFM on the exhaust that is maxed out at 0.600'' lift.

These flow numbers are with 2.08'' valves (2.02 stock), so unless you have dual profile cam with tons of exhaust duration, the potential is not that good on these heads... I'm guessing it's very similar on the Gen 5 ?

Wish they'd make aftermarket heads for our cars, with better flowing numbers in/ex

[Aevus]

It's kinda crazy to think that I spent sooooooo much time on the valvetrain, the hydraulic lifters limitation, and then trying to figure out the perfect camshaft, then worrying about the oil system, and being anxious about the stock crankshaft...

to finally be stucked to 5,800-6,000 rpm BECAUSE OF THE AIR FLOW

Seriously, if the bottleneck is the heads and not the TB/manifold/exhaust, I think I'll cry.

[Aevus]

Nailed the problem tonight:

https://www.youtube.com/watch?app=desktop&v=h2L5TDR9fxk

By looking at it stock, it doesnt take a genius to understand there's a problem there... No wonder my engine hits a wall at high RPM

Will start with that. Then the single blade TB (already have the BBK)

[Aevus]

I love that guy

He explains very well the problem I'm facing:

https://youtu.be/Nbev14oIH6I?t=551

[13COBRA]

I don't think you'll reach 670-680 with just that.

[Aevus]

[heath1225]

I know the math theoretically supports around 800 hp, but that would assume everything is perfect. I don’t think 307 cfm will be near enough even with a better intake, TB, etc. to support 800 hp.

[heath1225]

With that said, if you had a stock gear (3.07) I think you’d put a lot more power down on the dyno, but the feel of the car and performance would suffer. But, with all the torque your engine produced maybe it wouldn’t be so bad.

[Aevus]

I know the math theoretically supports around 800 hp, but that would assume everything is perfect. I don’t think 307 cfm will be near enough even with a better intake, TB, etc. to support 800 hp.

Will try a single blade TB for sure if I can find one.

Then I'll get my intake manifold ported (or buy one already ported if any).

If I can't get any improvement there, it means I'm f**ked with maxed out heads. And that's gonna be the end of it because I'm not going to put Gen 4 stuff there.

[Aevus]

With that said, if you had a stock gear (3.07) I think you’d put a lot more power down on the dyno, but the feel of the car and performance would suffer. But, with all the torque your engine produced maybe it wouldn’t be so bad.

yeah it seems that my 592 whp run on 4.10 would translate to roughly 620whp with 3.07... (Dynojet)

But I'm not really chasing HP numbers, it's more about rpm. I had a target and I'm like 700 rpm OFF... It bugs me.

the more I think about it, the less I believe I've already maxed out the heads.

[Aevus]

One of the reasons I think I did not maxed out my heads yet, is because of that guy with his gen 3 who simply installed exhaust and a 18 deg cam (Roe racing's 710R)

IMG_1543.jpg


so he did a 583 whp run.... with a milder cam, stock headers.... and STOCK heads ( that flows 265 CFM at max possible lift )


it makes me believe the TB/intake is the limiting factor on the Gen 3.



...funny thing because the math goes like that: 265 CFM @ 2.6hp = 689 -15% drivetrain loss = 585 whp.

[T/A KID]

Ask the tuner what Map KpA is at 6000rpms and compare it to 3000… my guess is KPA is roughly 99-100 at 3000 and probably down to 95 at 6000 RPMs (if near sea level) this would tell me you have intake restriction

[Steve M]

One of the reasons I think I did not maxed out my heads yet, is because of that guy with his gen 3 who simply installed exhaust and a 18 deg cam (Roe racing's 710R)

so he did a 583 whp run.... with a milder cam, stock headers.... and STOCK heads ( that flows 265 CFM at max possible lift )

it makes me believe the TB/intake is the limiting factor on the Gen 3.

...funny thing because the math goes like that: 265 CFM @ 2.6hp = 689 -15% drivetrain loss = 585 whp.

That wasn't Twister, was it? As in, "bench racer extraordinaire" Twister?

[Aevus]

Ask the tuner what Map KpA is at 6000rpms and compare it to 3000… my guess is KPA is roughly 99-100 at 3000 and probably down to 95 at 6000 RPMs (if near sea level) this would tell me you have intake restriction

yes, I will ask

- - - Updated - - -

That wasn't Twister, was it? As in, "bench racer extraordinaire" Twister?

That guy:

https://www.youtube.com/watch?v=PGDCbY7N3lE

[Aevus]

That kind of spacer adapter for a 102mm LS throttle body exists, surprisingly..

https://sidewaysfab.com/products/3rd...adapter-flange

not sure if it would flow better than a single blade though

[Aevus]

Throttle body CFM info:


https://accufabracing.com/knowledge-base/cfm/

THE DATA HAS BEEN COLLECTED OVER SEVERAL YEARS OF TESTING. ALL CFM ROUNDED TO THE NEAREST WHOLE NUMBER.

PRODUCTS TESTED:
All CFM ratings shown @ 28”:


Dodge Viper
RT-10, Gen 1, 1992-1996 – 65mm – 611 cfm each
GTS Gen 2, 1996-2002 – 70mm – 697 cfm each



Ford Mustang 5.0L, 1986-1993
Stock – 495cfm
65mm – 664cfm
70mm – 787cfm
70mm (Race) – 896cfm
75mm – 924cfm
75mm (Race) – 1045cfm
80mm – 1142cfm
85mm – 1322cfm
90mm – 1369cfm
105mm – 1550cfm

Ford GT, 2005-2006
Stock – 1590cfm
Dual 75mm – 1807cfm
Oval Mono Blade – 2090cfm

Ford Mustang Cobra, 2003-2004
and Ford Lightning Pick-up, 1999-2004
Oval Mono Blade – 1696cfm

So my BBK dual 67mm flows probably around 1300 cfm and the Oval mono blade on the gen 3 Viper is probably around 1700-1800 cfm.

Highest flow TB I've seen on Summit racing is 2000cfm, so I think I should first try the oval mono blade and see. Next bottleneck will probably be elsewhere (manifold)

[Aevus]

again, thinking outloud....


I'm chasing the bottleneck with some math for the last two days. Feel free to correct me if I'm wrong.
They all say an engine is nothing but an air pump. So let's see:


8.3 liters = 505 cu.in. x 7,000 rpm = 3,535,000 divided by 2 (intake stroke only) = 1,767,500 divided by 1,728 (cubic ft.) = 1,023 cu.ft or air per minute.

So that N/A engine at 7,000 rpm needs 1,023 cfm with a Volumetric Efficiency (VE) of 100%. If the cam is good, I can hope for 105% = 1,074 cfm.

1,074 cfm would be the final number of air flow I'm looking for.


(thanks Facebook and Drag Radial Performance: https://m.facebook.com/DragRadialPer...549224/?type=3)


Now, I'm not sure anymore that my throttle body is really the bottleneck. Can't find the CFM on the BBK dual 67mm and the numbers on Accufab Racing are high for their comparable sizes...

Then, my ported heads. I have the flow numbers but it's tricky to calculate because the valves are opening and closing and in-between all the time, they actually spend very little time at the peak (max lift) and most of the time on the way up or down. Until I have the correct mathematical formula, I'll just average the worst (exhaust) from 0.200'' to 0.500'' (0.300'' travel in the middle of my 0.600 total) and it's:

0.200'' = 126.5 cfm
0.300'' = 183.7 cfm
0.400'' = 223.1 cfm
0.500'' = 237.3 cfm

average on the exhaust side = 192.65 cfm (per cylinder) for a total of 1,926 cfm on the heads.

and I have 10 degrees more duration on the exhaust side, so probably north of 2,000 cfm and close to match the 2,204 cfm on the intake side (using the same average formula)...

Bottomline, I'd say my heads are not maxed out and the bottleneck is elsewhere.

Whats left? Intake manifold and Exhaust.

Headers, downpipe, catalytic converters, muffler... Most probably that small magnaflow cat is the culprit on the exhaust side, can't imagine otherwise...

And the stock intake manifold's runners are probably restrictive.

[13COBRA]

SO...are you chasing a number or not chasing a number, I'm getting more confused by the day.

[Aevus]

SO...are you chasing a number or not chasing a number, I'm getting more confused by the day.

the goal is to spin the engine up to 7,000 rpm.

now, the valvetrain can do it right now. It's just useless to do so.

[13COBRA]

the goal is to spin the engine up to 7,000 rpm.

now, the valvetrain can do it right now. It's just useless to do so.

Ah. So you don't care about anything else, just to hit 7000 rpms?

[GTS Dean]

Conventional wisdom has spoken many times throughout his journey. Nobody said it couldn't be done, but I think most were politely trying to dissuade him - knowing there are diminishing returns with RPM on this platform. It's his car, his money, his dreams and I don't wish him ill will.

[13COBRA]

Conventional wisdom has spoken many times throughout his journey. Nobody said it couldn't be done, but I think most were politely trying to dissuade him - knowing there are diminishing returns with RPM on this platform. It's his car, his money, his dreams and I don't wish him ill will.

Agreed.

[Aevus]

Ah. So you don't care about anything else, just to hit 7000 rpms?

well, obviously there will be power gain.

How much exactly, I don't care that much. 630 or 670 at the wheels... who knows.

What I really don't like right now, is the power peakin' @ 5,900 rpm or so.

Was not the plan, at all.

[Aevus]

Conventional wisdom has spoken many times throughout his journey. Nobody said it couldn't be done, but I think most were politely trying to dissuade him - knowing there are diminishing returns with RPM on this platform. It's his car, his money, his dreams and I don't wish him ill will.

Oh but I have zero regret so far, Dean.

The very fact that I can drive the car, that is already the funniest I ever had, AND continuing the build project at the same time... I couldnt ask for more, really.

I have two Viper motors, so I can send the 2nd intake manifold to get it ported while I spend the summer driving the car with the stock one. And the exhaust/cat is an easy swap...

Bottomline, I see no reason to stop there.
I have spent lots of money, time and energy on few components that are not used to the fullest right now (ported heads, injectors, headers/exhaust, camshaft, valvetrain, forged internals, etc...) because it was built for 800bhp @ 7,000rpm.

So if it's only TB, manifold and cats that are needed, I'll sure do it.