Cambered Rear Vs. Weight Reduction Vs. Power Mods - Help Me Decide!

[Fabman]

Okay, I had to upload the clip to my youtube to make this work....whew.
He's stuck behind a slower car here but yes, 5th gear is a thing.

 

[SMGDHG]

Okay, I had to upload the clip to my youtube to make this work....whew.
He's stuck behind a slower car here but yes, 5th gear is a thing.

Thanks for sharing!!! Looks like 126mph down the front straight, very impressive. That car moves. He does that 4-5 upshift at about 6.5k. Funny enough his min speed for the turn before the front straight and mine are virtually identical, yet my car only got to 116mph. It’s such a turd. I think it was about 90° that day though. Not sure what the conditions were in that spec mustang video.

Wouldn’t it be faster to not bother with the 4-5 upshift and just rev the car higher for that stretch of track? Im not sure. My gut tells me the up/downshifts are a time waster. But these spec mustangs race for what, 30 mins at a time? So they may have a bigger concern for longevity vs. me who really only does 2 hero laps at a time and then lets things cool off. Very different styles of competition.

 

[Fabman]

Thanks for sharing!!! Looks like 126mph down the front straight, very impressive. That car moves. He does that 4-5 upshift at about 6.5k. Funny enough his min speed for the turn before the front straight and mine are virtually identical, yet my car only got to 116mph. It’s such a turd. I think it was about 90° that day though. Not sure what the conditions were in that spec mustang video.

Wouldn’t it be faster to not bother with the 4-5 upshift and just rev the car higher for that stretch of track? Im not sure. My gut tells me the up/downshifts are a time waster. But these spec mustangs race for what, 30 mins at a time? So they may have a bigger concern for longevity vs. me who really only does 2 hero laps at a time and then lets things cool off. Very different styles of competition.

View attachment 91972

Personally, I like to wind everything to the moon, but Roger says it's not making power up there and he goes faster by short shifting.
Again, he was stuck behind a slower car so he does make more MPH on a clear track.

 

[Bill Pemberton]

My guess would be at 126 mph with 3.73 gear and his rev limiter is set similar to yours ( 7200 ) he might be all over that limit for awhile. Short shifting to 5th while still pulling is likely a bit of a smooth move , so not hurrying the downshift and braking back to fourth in a super quick sequence. I just have to believe even at 7500 RPM he is getting close to jumping on the limiter at the end of the straight.

 

[67GTA]

Good question. I don't have the dyno sheet in front of me but I want to say peak tq was somewhere between 4.6-5.2k and peak hp was around 6k.

Would love to get cams to raise the rpm of my peak tq.

Do you recall what the measured value is for peak torque?

 

[SMGDHG]

Do you recall what the measured value is for peak torque?

oh. it was 318WTQ

 

[67GTA]

I couldn’t find a compliance database for the Spec Iron classes. I know they have very strict power to weight & torque to weight rules, but it doesn’t look like competitors are required to upload their compliance docs like ST & TT classes are. Was hoping to review random dyno sheets from across the country to get a feel of the “norm” of the 4.6.

 

[SMGDHG]

I couldn’t find a compliance database for the Spec Iron classes. I know they have very strict power to weight & torque to weight rules, but it doesn’t look like competitors are required to upload their compliance docs like ST & TT classes are. Was hoping to review random dyno sheets from across the country to get a feel of the “norm” of the 4.6.

Thanks for looking!! I've seen a couple, Sean actually overlaid one of the spec iron cars dyno sheets vs. my car.

I think the only limitations they have are on whp and weight, which I know for a fact it's 315whp but not sure on the weight. I think either 3100lbs or 3300lbs, I can't remember. They might have a wtq limitation too but not sure.

 

[EF1]

Straight from NASA's website:

Spec Iron has a strict 11.75:1 horsepower-to-weight ratio and 11.25:1 torque-to-weight ratio limit as measured at the rear wheels. All cars that compete in this class may have less than the specified amount, but may not exceed the 11.75:1 horsepower and 11.25:1 torque ratios.

All Spec Iron participants must have a dynamometer certification report prior to the start of the race or make arrangements to have a dyno test performed immediately after the race.

 

[EF1]

Minimum weight is 3,350 pounds, with driver

Look hear for additional info:

Spec Iron - National Auto Sport Association

Introduction Everything You Wanted to Know About Spec Iron Racing Series Spec Iron was devised to give late-model Ford Mustang enthusiasts an affordable series in which to race. It represents a step above Camaro-Mustang Challenge and a notch slightly below American Iron, making it a viable...

drivenasa.com

 

[SMGDHG]

Minimum weight is 3,350 pounds, with driver

Look hear for additional info:

Spec Iron - National Auto Sport Association

Introduction Everything You Wanted to Know About Spec Iron Racing Series Spec Iron was devised to give late-model Ford Mustang enthusiasts an affordable series in which to race. It represents a step above Camaro-Mustang Challenge and a notch slightly below American Iron, making it a viable...

drivenasa.com

Ok, so I'm confusing myself here. Spec mustang vs. spec iron appear to be different.

Beyond Spec Miata: Spec Mustang + Spec Iron - Winding Road Magazine

Beyond Spec Miata: Spec Mustang + Spec Iron - Winding Road Magazine

windingroad.com

 

[EF1]

Ok, so I'm confusing myself here. Spec mustang vs. spec iron appear to be different.

Beyond Spec Miata: Spec Mustang + Spec Iron - Winding Road Magazine

Beyond Spec Miata: Spec Mustang + Spec Iron - Winding Road Magazine

windingroad.com

View attachment 91974

I may have confused things. I thought the discussion was centered around NASA Spec Iron. SCCA has a Spec Mustang class that is similar, but not the same.

 

[Fabman]

I may have confused things. I thought the discussion was centered around NASA Spec Iron. SCCA has a Spec Mustang class that is similar, but not the same.

Probably my fault for using the spec mustang for gear comparison.

 

[Fabman]

This just in from Roger:

*********************

This is with the stock 5th gear, 3:90 rear end

Roger


I’m on Nankang CR-S tires (200 TW I believe) and Mikhail was on Goodyear slicks

 

[SMGDHG]

This just in from Roger:

*********************

This is with the stock 5th gear, 3:90 rear end

Roger
View attachment 92002

I’m on Nankang CR-S tires (200 TW I believe) and Mikhail was on Goodyear slicks

And he’s running 2:02’s at Thunderhill? Bypass or cyclone?
Seems like a good guy to know.

 

[Fabman]

And he’s running 2:02’s at Thunderhill? Bypass or cyclone?
Seems like a good guy to know.

Cyclone. He's a customer, I built two cars for him.

 

[Don Lariviere]

#SMGDHG- Notice where he is shifting, 6500rpm, that's about it for a 3V. You are not going to be shifting at 7200rpm like you used in the gear calculation sheet. Even my ported 3V with the Ford intake peaks at 6200 and is on it's way out at 65-6700rpm. Cams to raise that just kill the torque and end up being slower. If you want to get up to 7200 rpm and make more total power (area under the HP curve) your going to need more compression and as much bore diameter and ports as you can get. From what I see on the socal tracks the 3.90 is probably the hot ticket over the 3.73 as long as you have a 0.81 5th gear so you can use it in the fast bits. My car was power limited to about 155mph at cal speedway with the 3.73 and 0.81 5th at around 5krpm. I'd have to go look the exact numbers up its been a while since I was there with it...

 

[SMGDHG]

#SMGDHG- Notice where he is shifting, 6500rpm, that's about it for a 3V. You are not going to be shifting at 7200rpm like you used in the gear calculation sheet. Even my ported 3V with the Ford intake peaks at 6200 and is on it's way out at 65-6700rpm. Cams to raise that just kill the torque and end up being slower. If you want to get up to 7200 rpm and make more total power (area under the HP curve) your going to need more compression and as much bore diameter and ports as you can get. From what I see on the socal tracks the 3.90 is probably the hot ticket over the 3.73 as long as you have a 0.81 5th gear so you can use it in the fast bits. My car was power limited to about 155mph at cal speedway with the 3.73 and 0.81 5th at around 5krpm. I'd have to go look the exact numbers up its been a while since I was there with it...

Thanks for the info Don, I agree in that 7.2k RPM shifts are not optimal, but am struggling to understand your comment regarding "cams to raise that just kill the torque and end up being slower".

I've seen dynographs comparing a stock camshaft 3v and then a 3v with some typical NSR cams, the engine with the aftermarket camshafts seems to have a more favorable powerband for a road race application. I struggle to see how total power is a relevant figure for a road course engine, as total power takes into account the power and torque of the engine across it's ENTIRE RPM band. 800-7000rpm. Total power from 4,000RPM to 7,500RPM? Sure, totally relevant. My 3v never spends any significant amount of time below, say, 4,000 RPM. So why should I care about a total power figure that takes this sub 4,000RPM range into account? If you can find me a total power figure comparing a cammed vs stock 3v from 4,000 RPM to 7,000 RPM that shows the stock camshaft engine makes more total power, I will confidently say I am wrong


It is well known that a performance cam kills low end torque and horsepower, which can "artificially" lower your total power. But low end torque and horsepower is not a significant concern for me, as I just don't see it being relevant for what I do.

The same goes for camshafts. The power, and most especially torque gains at the upper half of the RPM range that the more mild 3v camshafts offer are very difficult to ignore. 3v's have a truck camshaft in them. No ifs ands or buts about it. Drag racers have been installing cams for years and it seems they often unlock additional time. A straight away on a road course is no different than a drag strip.

I did an exercise a couple weeks ago where I watched my Laguna Seca fast lap, and wrote down the time I spent at certain RPM ranges. Take a look:

Total lap time: 1:39.3s
69s spent on the throttle.
15s of the those 69s I was on the throttle at an RPM less than 4.5k.
69s/15s = 21% of the time I had my foot on the throttle, the car was at less than 4.5k RPM.

Given the above info then, why would I not choose to install a modification to my engine which makes it significantly better at RPM greater than 4.5k? Typical NSR off the shelf cams are all gains above 4.5k rpm. There are loads of dyno tests out there that show this. This is off that angelfire vlog who has some pretty cool info on the 3v:

The above info is what I have typically seen for cammed 3v engines. Less HP + tq at less than 4,500RPM, but then the aftermarket camshafts take over and produce a bigger and bigger delta of power as the RPM climbs. Gains of 40-60wtq beyond peak torque RPM are not at all uncommon to see in cammed 3v's. This has been the primary reason why I try and stay shifting at around 6.5k rpm. As you discuss, the torque curve pretty much falls off a cliff once you go 500PM beyond the peak torque RPM. Since the engine has truck cams in it, this peak torque figure it as a frustratingly low RPM, and gets in the way of road course work.

There is of course a lot that goes into camshaft design, and really this should be discussed with an engine builder, but I would imagine that a more prominent engine builder would give a road course car like ours a different camshaft than say an F-150 that needs to tow a boat.

 

[Fabman]

Thanks for the info Don, I agree in that 7.2k RPM shifts are not optimal, but am struggling to understand your comment regarding "cams to raise that just kill the torque and end up being slower".

I've seen dynographs comparing a stock camshaft 3v and then a 3v with some typical NSR cams, the engine with the aftermarket camshafts seems to have a more favorable powerband for a road race application. I struggle to see how total power is a relevant figure for a road course engine, as total power takes into account the power and torque of the engine across it's ENTIRE RPM band. 800-7000rpm. Total power from 4,000RPM to 7,500RPM? Sure, totally relevant. My 3v never spends any significant amount of time below, say, 4,000 RPM. So why should I care about a total power figure that takes this sub 4,000RPM range into account? If you can find me a total power figure comparing a cammed vs stock 3v from 4,000 RPM to 7,000 RPM that shows the stock camshaft engine makes more total power, I will confidently say I am wrong


It is well known that a performance cam kills low end torque and horsepower, which can "artificially" lower your total power. But low end torque and horsepower is not a significant concern for me, as I just don't see it being relevant for what I do.

The same goes for camshafts. The power, and most especially torque gains at the upper half of the RPM range that the more mild 3v camshafts offer are very difficult to ignore. 3v's have a truck camshaft in them. No ifs ands or buts about it. Drag racers have been installing cams for years and it seems they often unlock additional time. A straight away on a road course is no different than a drag strip.

I did an exercise a couple weeks ago where I watched my Laguna Seca fast lap, and wrote down the time I spent at certain RPM ranges. Take a look:

Total lap time: 1:39.3s
69s spent on the throttle.
15s of the those 69s I was on the throttle at an RPM less than 4.5k.
69s/15s = 21% of the time I had my foot on the throttle, the car was at less than 4.5k RPM.

Given the above info then, why would I not choose to install a modification to my engine which makes it significantly better at RPM greater than 4.5k? Typical NSR off the shelf cams are all gains above 4.5k rpm. There are loads of dyno tests out there that show this. This is off that angelfire vlog who has some pretty cool info on the 3v:View attachment 92089

The above info is what I have typically seen for cammed 3v engines. Less HP + tq at less than 4,500RPM, but then the aftermarket camshafts take over and produce a bigger and bigger delta of power as the RPM climbs. Gains of 40-60wtq beyond peak torque RPM are not at all uncommon to see in cammed 3v's. This has been the primary reason why I try and stay shifting at around 6.5k rpm. As you discuss, the torque curve pretty much falls off a cliff once you go 500PM beyond the peak torque RPM. Since the engine has truck cams in it, this peak torque figure it as a frustratingly low RPM, and gets in the way of road course work.

There is of course a lot that goes into camshaft design, and really this should be discussed with an engine builder, but I would imagine that a more prominent engine builder would give a road course car like ours a different camshaft than say an F-150 that needs to tow a boat.

Not being a pro engine builder myself, but very experienced in the art of race craft let me add some thought to this:
The broadest power band possible will likely give the best lap times. Any time spent under the curve will cost you. If you put in a cam that has less power at lower RPM and you have to use that rpm you will now spend even MORE time in that soggy spot than you have been, so don't disregard that fact. Drag racing all you have to worry about is RPM drop at the shift, and its all WOT in a car with momentum, so as long as you can stay in the sweet spot you are golden. Unfortunately with road racing you have to pull out of corners, sometimes well below the curve and the more you add to the top end the more that low end will suffer and that hurts lap times because you will now be spending even more time under the curve. That high rpm peak power is only as good as much as you can use it, and that depends a lot on the weight of the car, the gear and the track.

Example:
A 7 speed sequential can stay within a nice short power band so you are always in the sweet spot, you can get away with a peaky cam with a high HP number. That's why the closer ratio transmissions work so well.
I gave away a lot of peak HP with the super mild cams in my coyote, but I pull EVERYONE out of the corners and once I am ahead you are going to have your hands full catching me.
I've told this story before so if you've heard it already I apologize, but I think it applies here.
At nationals I met the guy with the Kenny Brown Boss 302 AIX car. He told me "I have been asking around about you, including other builders and all 6 of them told me the same thing:
"Sal is very good at beating cars with more HP than he has". I then yarded him coming out of turn 11 and by the time his car got on the pipe I was long gone. Unfortunately he lost his power steering pump later in the day and was done for the weekend so he didn't make the feature. I attribute that to the low end/mid strong cams that I have. Its kind of like turbo lag....I don't care how much HP you're making as long as I'm in front of you. I've had this experience for decades in circle track as well...I don't care if you catch me at the end of the straight because we are going to have to slow down and get on the gas again and I'm going to be gone while you're still waiting for V-Tech to kick in. LOL.
A side benefit is that smaller cams need less valve spring which saves heat and increases reliability. Broken cars rarely win.
Also, many bigger cams limit or lock out the variable cam timing which is a super great feature of these motors.

Moral of the story....be careful chasing big peak numbers, in the end its what's fastest over all that wins races.
That being said, my suggestion is ask Shaun at AED for a cam recommendation and believe whatever he tells you.

 

[Fabman]

Wow that was really wordy wasn’t it. I guess what I’m trying to say is a really good grind may be better than a really big grind. Choose wisely.