318 build with XE268 AND 302 heads
IMO
the cam should fit the application.
One should not put a stick in an engine and then try and make that engine fit an application. Why are we building engines with power peaks at 5500, and shift rpms at 6500 to 6800, for a streeter that spends 98% of its life at sub-4000? And to make it work, we put 3500 TCs in 'em and 3.55 gears. That seems just so wrong to me.
If we spent all that engine money on decent torque multiplication, we would have so much better a street combo.
First gear in a 904/3.55s goes to 65 mph.Sure it's quick.But this is how we do it; we launch with a 3000 plus TC and force that engine to pull thru hundreds of low-power rpms to finally arrive at peak horsepower, and then past, and way down the other side of the curve. So the average hp during the run, ends up dismal. But we are so excited.
Imagine a snowmobile system with a CVT where the engine pops up to peak hp and stays there all the way from zero mph to 65 mph. That engine, in order to make the same average hp could be a waaay tamer item.
Below is a typical hp graph. I have no idea where it comes from, but it says 318 on it,lol, and it peaks around 5700, kindof typical for some street engines.
Notice the big torque hole below 4200.
Below 4200 is where this engine in a streeter would spend most of it's life.
Notice the torque doesn't even start until 3800 ish.
Notice the power peak. With an automatic transmission, this engine might want to be shifted up near 7500,to come in at 4450ish. This would average the power out at about 325.
>But say this was for a 1-gear run.
You would want a 4200 TC to cash in on where the torque really starts.And you would want to gear the car to run up just past the power peak, say to 6200. 3.23s it would be, with a 2.45 low.
This would give you a light-speed zero to 65 mph.
Now, imagine driving this beast, 95%: a) not WOT, and b) not over 4000 rpm, and c)most of the time at PT,part throttle,and d) occasionally cruising 65 mph, and e) try to imagine how much fuel this beast is gonna drink.
>Now imagine If you had a CVT that set at about 5700, the power delivery would be stuck at 365ish for the entire run. It would be way quicker.
So try to imagine detuning the engine to 325 hp to put out the same average power as that HO unit. It would still be just as quick. But go look at the hp line. Check out what rpm it takes in this engine, to make 325 hp. It looks to be 4800. So in other words if the CVT was kept to 4800, it would be just as quick as the 2.45low/3.23 combo.Now, the CVT idea is an idealism
>Imagine your teener pulling two gears to 65 mph, this is about the best we can do with the trannys available to us. And lets make it a manual trans cuz that is the only way to keep the little teener on the pipe.
And because we can see already that this is gonna take a deep rear gear, lets choose the 2.66 tranny for it's reasonable splits.
We are gonna need a bit more than 4800 to stay on par with the CVT so lets choose arbitrarily a 5200 shift rpm.
Look on the graph to 5200. This is about 350 hp.
The tranny ratios are 2.66-1.91-1.39-1.00
A little math kicks out 3.37 gears, which I will round up to 3.55s and increase the rpm in compensation.
I get 65= 5475 rpm. So since the hp peak at this power level will be pretty flat, I suggest that this 5475 can be 475 over the peak number and call the peak at 5000. Back to the graph and 5000 looks like 335 hp.
Now lets see how this works
Your left leg is quivering on the start line, as you get ready to blast off. You bring up the revs to 3900 where the torque peaks. The light turns green and it's go time. You dump the clutch and the car launches and its hammer down time. You get some wheel spin and you hold it at 4500 to 5000 until the tires stop spinning. The revs climb to 5500 and you have just crested 46 mph. You slam it into second and about 2 seconds later you are cresting 65mph at about 5500. Shazzam that was quick!
Your engine was at or over 3900 right out of the gate, with a momentary dip on the 1-2 shift to 3900ish. Looking on the graph this average hp comes in a 300@4700.
Now about this engine;.
With a 5000 hp peak,the torque peak will come in at around 3750.
This combo will get pretty good fuel economy, The starter gear is 9.44, not too bad. And with 3.55s will cruise at 65=2867
32mph will be 3670 in first, just below peak torque. So when you downshift at 32, you will be blasting off.
The torque production at lower than 3750 will be prodigious with this small cam; gone will be the soft spot.
Imo, This is how to match the engine to to the street-application, with plenty of torque production, and torque multiplication.
And you don't need a big engine.
Obviously a bigger engine will be a little quicker in the zero to 65 zone, but we are talking what? One half second? And the bigger engine,to be effective, will need to spend way more money on trying to put the power to the pavement.
I like the analogy of shooting a rabbit with a .22 or a .303. How dead do you need the rabbit to be?
If you can only fit 275s back there........ What's the sense in a streeter having much over 300/350 hp, the tires spin all the way to the speed limit anyway...
IMO
the cam should fit the application.
One should not put a stick in an engine and then try and make that engine fit an application. Why are we building engines with power peaks at 5500, and shift rpms at 6500 to 6800, for a streeter that spends 98% of its life at sub-4000? And to make it work, we put 3500 TCs in 'em and 3.55 gears. That seems just so wrong to me.
If we spent all that engine money on decent torque multiplication, we would have so much better a street combo.
First gear in a 904/3.55s goes to 65 mph.Sure it's quick.But this is how we do it; we launch with a 3000 plus TC and force that engine to pull thru hundreds of low-power rpms to finally arrive at peak horsepower, and then past, and way down the other side of the curve. So the average hp during the run, ends up dismal. But we are so excited.
Imagine a snowmobile system with a CVT where the engine pops up to peak hp and stays there all the way from zero mph to 65 mph. That engine, in order to make the same average hp could be a waaay tamer item.
Below is a typical hp graph. I have no idea where it comes from, but it says 318 on it,lol, and it peaks around 5700, kindof typical for some street engines.
Notice the big torque hole below 4200.
Below 4200 is where this engine in a streeter would spend most of it's life.
Notice the torque doesn't even start until 3800 ish.
Notice the power peak. With an automatic transmission, this engine might want to be shifted up near 7500,to come in at 4450ish. This would average the power out at about 325.
>But say this was for a 1-gear run.
You would want a 4200 TC to cash in on where the torque really starts.And you would want to gear the car to run up just past the power peak, say to 6200. 3.23s it would be, with a 2.45 low.
This would give you a light-speed zero to 65 mph.
Now, imagine driving this beast, 95%: a) not WOT, and b) not over 4000 rpm, and c)most of the time at PT,part throttle,and d) occasionally cruising 65 mph, and e) try to imagine how much fuel this beast is gonna drink.
>Now imagine If you had a CVT that set at about 5700, the power delivery would be stuck at 365ish for the entire run. It would be way quicker.
So try to imagine detuning the engine to 325 hp to put out the same average power as that HO unit. It would still be just as quick. But go look at the hp line. Check out what rpm it takes in this engine, to make 325 hp. It looks to be 4800. So in other words if the CVT was kept to 4800, it would be just as quick as the 2.45low/3.23 combo.Now, the CVT idea is an idealism
>Imagine your teener pulling two gears to 65 mph, this is about the best we can do with the trannys available to us. And lets make it a manual trans cuz that is the only way to keep the little teener on the pipe.
And because we can see already that this is gonna take a deep rear gear, lets choose the 2.66 tranny for it's reasonable splits.
We are gonna need a bit more than 4800 to stay on par with the CVT so lets choose arbitrarily a 5200 shift rpm.
Look on the graph to 5200. This is about 350 hp.
The tranny ratios are 2.66-1.91-1.39-1.00
A little math kicks out 3.37 gears, which I will round up to 3.55s and increase the rpm in compensation.
I get 65= 5475 rpm. So since the hp peak at this power level will be pretty flat, I suggest that this 5475 can be 475 over the peak number and call the peak at 5000. Back to the graph and 5000 looks like 335 hp.
Now lets see how this works
Your left leg is quivering on the start line, as you get ready to blast off. You bring up the revs to 3900 where the torque peaks. The light turns green and it's go time. You dump the clutch and the car launches and its hammer down time. You get some wheel spin and you hold it at 4500 to 5000 until the tires stop spinning. The revs climb to 5500 and you have just crested 46 mph. You slam it into second and about 2 seconds later you are cresting 65mph at about 5500. Shazzam that was quick!
Your engine was at or over 3900 right out of the gate, with a momentary dip on the 1-2 shift to 3900ish. Looking on the graph this average hp comes in a 300@4700.
Now about this engine;.
With a 5000 hp peak,the torque peak will come in at around 3750.
This combo will get pretty good fuel economy, The starter gear is 9.44, not too bad. And with 3.55s will cruise at 65=2867
32mph will be 3670 in first, just below peak torque. So when you downshift at 32, you will be blasting off.
The torque production at lower than 3750 will be prodigious with this small cam; gone will be the soft spot.
Imo, This is how to match the engine to to the street-application, with plenty of torque production, and torque multiplication.
And you don't need a big engine.
Obviously a bigger engine will be a little quicker in the zero to 65 zone, but we are talking what? One half second? And the bigger engine,to be effective, will need to spend way more money on trying to put the power to the pavement.
I like the analogy of shooting a rabbit with a .22 or a .303. How dead do you need the rabbit to be?
If you can only fit 275s back there........ What's the sense in a streeter having much over 300/350 hp, the tires spin all the way to the speed limit anyway...