Spinning up a 4.6 to 7500rpm

[ESP41]

Can a 4.6l be spun to 7500 (no more than 7800) "reliably" for short periods of time? Likely only be at those revs for no more than 10 seconds. Can the hydraulic power steering take it? A/C is deleted.

This is for a dedicated autocross only car (2900lb SCCA CP car). I have lots of decent power under the curve with tune, header, LW flywheel, LW damper, and Detroit Rocker cams (361T/337H). I have it spinning to to 6800. Bottom end is stock. Trans is stock with a LW clutch) I need rpms to get to 76-80mph more than I need power.

I get lots of good pedal control by having the 4.6 in the car. But I want reliability and hopefully no great loss in power to go higher in revs. I have no plans to do a power adder. Too much weight and complexity. I'm confident I can get there with cam, heads, rods, bore, and maybe an EPAS. But at that point things are getting expensive enough that a stock Gen2 drop in might be a better long term choice(especially if I sell my 4.6).

Can I get "safely"the rpms I want with just head work and cams (assume the power will still be under 400)?

Key points: Autocross only car. Weight is important. Good control of throttle important. Broad usable power under the curve more important than peaks. I'm lazy/old and don't want to fix stuff at the track

Thanks

 

[07 Boss]

I would think that if you can get the valve train to handle it, the bottom end should be no problem. Maybe I should ask, are you doing this to gain power or to keep from losing time shifting?

 

[Dallas281]

Well the heads need to be done with better springs and such for sure. I would upgrade oil pump and I don't think the rocker cams are 'good' to spin that high in terms of power vs something like the 127600 comp cams. Surely the rockers can spin that high but your rowing into uncharted lands as far as I know

 

[ESP41]

Already upgraded the oil pump. The rockers gave me 46 more hp above 4800 rpms, but taper off above 6300. I agree with you on the head and cam change.

Has anyone spun a stock bottom end(rods, crank, pistons) that high and how long did the engine last?

The more I think about it, the GEN2 seems to be the logical choice. In stock trim, it will give me the rpms I need, and I can always move from current 3.73s to 3.55s or 3.31 to get the mph without spinning it hard (and tame the gas pedal too). I have driven a GEN1 conversion with 3.55s and it had plenty of power everywhere. I had much less pedal range till frying the tires (315 Hoosier A7s on concrete)

I would think that if you can get the valve train to handle it, the bottom end should be no problem. Maybe I should ask, are you doing this to gain power or to keep from losing time shifting?

It a balancing act with "not shifting" taking priority. Shifting loses time in the shift, and having to shift at at the right place on the course as opposed to at the optimum rpm. That being said, having the power fall off loses time too.

 

[Midlife Crises]

My own experience says Detroit Rockers will not support your engine above 6,500 rpm. Head work is needed at that point also. If your not using a power adder more compression will be useful. There have been several threads posted here about valvetrain failures. Hi-pressure valve springs, 7,500 RPM, collapsed lash adjusters, failed or broken cam followers and broken chain tensioner dowels go hand in hand with valves kissing the pistons.

 

[Dino Dino Bambino]

Can a 4.6l be spun to 7500 (no more than 7800) "reliably" for short periods of time? Likely only be at those revs for no more than 10 seconds. Can the hydraulic power steering take it? A/C is deleted.

This is for a dedicated autocross only car (2900lb SCCA CP car). I have lots of decent power under the curve with tune, header, LW flywheel, LW damper, and Detroit Rocker cams (361T/337H). I have it spinning to to 6800. Bottom end is stock. Trans is stock with a LW clutch) I need rpms to get to 76-80mph more than I need power.

I get lots of good pedal control by having the 4.6 in the car. But I want reliability and hopefully no great loss in power to go higher in revs. I have no plans to do a power adder. Too much weight and complexity. I'm confident I can get there with cam, heads, rods, bore, and maybe an EPAS. But at that point things are getting expensive enough that a stock Gen2 drop in might be a better long term choice(especially if I sell my 4.6).

Can I get "safely"the rpms I want with just head work and cams (assume the power will still be under 400)?

Key points: Autocross only car. Weight is important. Good control of throttle important. Broad usable power under the curve more important than peaks. I'm lazy/old and don't want to fix stuff at the track

Thanks

The stock 4.6 3V bottom end has been known to survive up to 7600rpm in very short bursts, but you'd be courting disaster if you tried that for the following reasons:

1. The stock cam phasers can fail with prolonged bursts above 6500rpm. Your Detroit Rocker cams make peak HP at ~6300rpm so by 6800rpm they're done. You'd need a bigger cam e.g. 127500 or even 127600 with phaser lockouts.

2. The stock valve springs are rated to 6800rpm. If you add an SPR cam, you'd need to upgrade to valve springs rated up to 0.600" valve lift.

3. The stock intake manifold, even with a CMCV delete, will only make peak HP up to 6300rpm so by 6800rpm it's done. If you want the engine to breathe well past 7000rpm, you'd need to upgrade to the Ford Performance or Holley Sniper unit. The limiting factor for making more power then becomes the stock heads.

4. The stock powdered metal oil pump gears could break and it's bye bye engine. You'd need to upgrade to a higher volume oil pump with a steel backplate e.g. OEM '13 GT500 unit and add billet gears. You'd also need a higher capacity oil pan e.g. OEM '13 GT500 8.5 Qt unit to ensure adequate an oil supply and keep the oil temperature down. It's probably adviseable add an external oil cooler as well.

5. The alternator & PS pump could fail because they'd be overdriven. You can overcome that problem with a set of 25% underdrive pulleys.

6. I'd still be leery about repeatedly taking the stock powdered metal connecting rods to 7600rpm. A set of OEM Boss 302 forged rods are an inexpensive upgrade and a straightforward swap.

 

[ESP41]

Thanks Dino. Sounds like I am pushing my current setup to the limit and the next steps get spendy. I need to mull over putting the money into the 4.6 or swap it to a Gen2. I think the final costs will be close.

 

[Dino Dino Bambino]

Thanks Dino. Sounds like I am pushing my current setup to the limit and the next steps get spendy. I need to mull over putting the money into the 4.6 or swap it to a Gen2. I think the final costs will be close.

I don't know how much you think a Gen 2 Coyote swap will cost but don't expect any change out of 10 grand plus all the time you'll need to spend to complete the project i.e. weeks if not months.
If you merely need to get to 76-80mph in 2nd gear, you could swap in a 3.31 rear axle gearset and stick to 6800rpm.

 

[ESP41]

Heh. Yup months would be the timeline. 10k is way low, as I would want to ditch the whole stock wiring and go standalone megasuirt/ or Haltech. Maybe beef up the stock trans too. Luckily the car is stripped, so no accessories to worry about. Stand-alone Abs,EPAs, engine control and a dash. Going stand alone would save me weight and complexity. It’s all speedy up front, but I think in the long run it would give me a more stable platform, as I would not be pushing the Gen2 past its stock parameters.

3.55 or 3.31 with a stock-ish 4.6 won’t give me the needed power. I’ll stick to 3.73s and shifting till I can do it right. The car has trophied at Nationals already. So it’s pretty good. I’m just trying to get it to run with the top cars in the class. But unlike the top cars, I want it to be somewhat reliable. It’s no fun throwing wrenches at the car when you should be concentrating on driving. That reliability is something I’m not sure a built 4.6 could give me. (Even though I could get the power I need out of it)

Does all that make sense or am I missing something?

 

[Dino Dino Bambino]

That reliability is something I’m not sure a built 4.6 could give me.

A built 4.6 should be nearly bombproof.

 

[ESP41]

I’ve never driven a well built up NA 4.6, let alone know how reliable they can be. That is part of why I’m on here asking. Everyone either puts on a power adder or does the 5.0 swap. I’ll have to research the costs using your handy notes above. I appreciate the input

 

[Tman]

Seems like A roots Supercharger maybe a small Eaton m90 and numerically lower gear ratio would give you what you’re after with less money and less RPMs only downside I see is possibly a bit more weight. But then again I would imagine the coyote swap is a bit heavier anyway but don’t know that for sure.


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[Dino Dino Bambino]

But then again I would imagine the coyote swap is a bit heavier anyway but don’t know that for sure.

A 4.6 3V long block and a 5.0 Coyote long block practically weigh the same (~430lb) despite the Coyote being wider and having more moving parts.

 

[ESP41]

5.0 is a bit heavier. It does have two more cams. Turbo/supercharger with intercooler is a lot more weight. Plus it’s more things to go wrong and provides more HP than I can use. I’m really trying to keep things light and simple. If money were no object, I’d likely just built a 4.6 and go standalone to get rid of the wire weight/ complexity of the stock loom. But building an NA 4.6 the right way is not cheap. And if I’m going to eventually go standalone to save weight, I can call that cost even between the 5.0 and 4.6. So that makes the conversion pretty enticing.

 

[Midlife Crises]

It really sounds to me like your looking for a forged stroker kit to install in your block. Add a set of ported heads and chose cams that avoid the highest pressure valve springs and keep the VVT active. You can make good torque, stay under 7,000 rpm and have the power to pull a taller final gear if your trying to raise the mph. If you replace the stock rods and don’t rev the three valve cross eyed it is bulletproof.

 

[ESP41]

That’s an interesting thought. 3.55s @7k rpm get me to 75 mph. 3.31 go to 80mph.

How much extra torque would a stroke kit give me? Oh, and rulebook say anything over 5100cc is a 10% penalty; gotta avoid that.

 

[akylekoz]

What about the other gears in the equation? What is your second gear ratio, can you put in a TKX with a second ratio to get you a couple more MPH. Or change ratios in your 3650?

Maybe not at drastic as a rear end change.

With everyone swapping to a Coyote or LS there has to be a stroked 4.6 around somewhere to grab. That will get you the power to push a slightly taller gear.

 

[Dino Dino Bambino]

That’s an interesting thought. 3.55s @7k rpm get me to 75 mph. 3.31 go to 80mph.

How much extra torque would a stroke kit give me? Oh, and rulebook say anything over 5100cc is a 10% penalty; gotta avoid that.

If you scroll down towards the bottom of this page, you may find some inspiration:

https://www.angelfire.com/my/fan/Mustang2006GT/Dyno.html

 

[Rick Walford]

In the same boat as ESP41, Built a CP car late 90's and trophied first two years with it and could not return for several years. When I came back I was way behind by not continuing to progress. Great times though. Few years back I saved a 2007 from the crusher (no titile), but replaced the blown (rocker destroyed at 160K miles) engine. Car has all new Ford performance suspension, CAM C, but the stock (CAI, Tune, 3.73's) engine is not doing well competitively but only 48K miles). Observed a 2010 GT locally developed (Cams, supercharger, etc). We are at elevation and the boosted cars comparatively do better. I like torque but the rpm, bumping rev limiter at 6,250 for my car is disheartening. Have used taller 19" tires, now two sets of 18's, with the 285/30-18's better for accelerating, but bumping rev limiter sometimes 3x on a 60 second course in 2nd gear. Studys of cam changes does not improve much, if any over stock cams till higher rpms and the increase in a short area of the rpms. I had a 2017 GT and sold it (too many projects and space). The Coyote was very nice, missing the power band. Put lot of time and more $$ than I wanted to on this rescue but is fun, But hard to not be more competitive.

 

[ESP41]

Great info on the dyno runs Dino. Its obvious I can get what I want from the 4.6, but it comes at a pretty high cost. My build is at the heads, cam, bottom end stage. ($10-15K?)

I think Ill be patient for a bit and see if I can find a Gen1 5.0. I still have some improvement I can do to the rest of the car (Better ABS, Penskes, weight reduction).