school me on the performer RPM

[dstang01]

I have the chance of getting a performer RPM upper and lower, but my car is going to be strictly street (track a few times a year) and a semi-daily driver. Im looking for torque, seat of the pants pull, average power, low end.. yea.. torque is the word so Im curious.. would a performer RPM on a set of aluminum gt40s be better than say... the aluminum gt40s with a cobra upper/lower? The performer RPM will no doubt yield more power, but Im really after "feel" with my combo

 

[BlownFiveLiter]

The Performer RPM probably isn't what you're looking for, if you're looking for low end power. It's a shorter runner than the stock intake to help breathing up top, so it'll shift your powerband up. An example, I run the Typhoon (Eddy RPM knockoff). With my cam and that intake, it doesn't really come alive until after 3k. If I side-step the clutch lower than that, it'll burn the tires, but easing off the line and putting my foot to the floor, it pulls, but not nearly as hard as after I hit around 3k.

 

[5spd GT]

With the combination you are looking at, I would stick with a Cobra.

Have the lower ported by Tom Moss (tmoss) for low bucks.

It will give you a more useable powerband and a better "feel."

The Performer RPM is no longer being made, and it shares the same lower as a Performer intake, but has a different upper plenum.

 

[dstang01]

Exactly my thinking, thanks for the confirmation guys

 

[tmoss]

I like the RPM intake - but it's not up to what you described - stick with a longer runner intake.

 

[90_Red_LX]

I personally ran my rpm intake on a otherwise stock engine other than full exhaust, t/b, maf, and cai, and there was no significant torque loss at all. It lost a little pep in the lower rpms, but it would still set you back. The only significant difference I seen was the car ran better shifting with a few hundred more rpm between shifts.

Would it still be the best option? Probably not on stock heads, but I planned to grow, and while gt40 heads aren't the best flowers I don't see why it wouldn't work pretty good. I think it would be close enough to justify getting it over a cobra intake and porting it.

If I'm dead wrong, correct me, I'm going based on how it worked for me.

 

[BlownFiveLiter]

I personally ran my rpm intake on a otherwise stock engine other than full exhaust, t/b, maf, and cai, and there was no significant torque loss at all. It lost a little pep in the lower rpms, but it would still set you back. The only significant difference I seen was the car ran better shifting with a few hundred more rpm between shifts.

Would it still be the best option? Probably not on stock heads, but I planned to grow, and while gt40 heads aren't the best flowers I don't see why it wouldn't work pretty good. I think it would be close enough to justify getting it over a cobra intake and porting it.

If I'm dead wrong, correct me, I'm going based on how it worked for me.

You actually confirmed what we were trying to say. No significant torque loss, but did lose some in the lower RPM range. That would be exacerbated by a matching cam which would take advantage of the higher RPM capability of the intake. In your case, you probably did gain a little across the board, and particularly higher up, but you were also coming from a restrictive factory intake. Not quite apples to apples, but it does make a good point for those who may be considering the RPM or Typhoon when trying to match parts.

 

[dstang01]

I heard somewhere that the performer and performer rpm lowers are identical, is this right? So could a performer plenum and performer rpm plenum be mixed and matched?

The reason I am asking about the performer rpm is because I've found a set of gt40x's that I want to purchase, and the seller also has a performer rpm that he would like to sell with it. I was planning on doing a heads/intake swap, so this would save me from looking elsewhere for an intake. The seller also offered to include an intake elbow (for sn95s) for free.

Anyways, my combo would be the performer rpm, stock cam (maybe with 1.7s), and the gt40x heads. I have no doubt that the gt40x/performer rpm combo makes power (the previous owner had good results) but Im not neccessarily looking for all out power, but I am looking for a great street curve. It also seems like the performer rpm would be out of place in a lower revving combo with the stock HO cam. Im thinking a standard performer intake might be better, so if I bought the rpm could I transform it into a standard performer by swapping uppers? Sorry for the questions guys, I dont have alot of money to throw around so I want to make my purchase once and be happy with it

 

[PJC Racing]

If you don't have alot of cash to throw around, I would go this route: Keep the Cobra intake, get a custom cam, a good set of rockers, and go with Thumper of Orange Park heads. This would save you cash and out perform the combo you described, IMO.

 

[tmoss]

yes, you can swap the Performer and RPM I uppers on the same lower.

 

[dstang01]

If you don't have alot of cash to throw around, I would go this route: Keep the Cobra intake, get a custom cam, a good set of rockers, and go with Thumper of Orange Park heads. This would save you cash and out perform the combo you described, IMO.

That would be a good combo too, but although it might seem less expensive it will actually cost me more... let me explain

Thumpers E7 heads cost 550 plus shipping both ways (must ship him back the core, aka your old E7 heads). Shipping will make this not feasible, as I live in Vancouver Canada. The used gt40x's in question (complete, not bare) are actually less expensive than thumpers retail price, PLUS I will only have to have them shipped one way (and @ appx 50 lbs lighter than the irons)

As for the intake, I dont have a cobra intake in my possesion (or any aftermarket intake for that matter), I have to buy one. The performer rpm in question is probably going to cost me the same as a cobra one would, so theres really no cost difference here. Im thinking I might as well go with the edelbrock, because I will have to port a cobra (more money) to get equal performance.

I plan to retain the stock cam because I cannot afford a tune/tweecer at the moment, and I NEED the driveability. The stock HO isnt a terrible performer (unlike those E7s) so I will leave it in and it should compliment the low revving combo Im looking for. Later down the road when I have saved up more, I want to go with a custom cam (tailored to well mannered street power), get a good tune (or invest in a tweecer), and perhaps have the gt40x's worked a little bit.

Basically, Im trying to set this up in two phases so that I can afford my dream combo. Phase one will be the heads and intake on the stock cam, should be good for 250-270 rwhp and well mannered. Phase two will be the custom cam, tune, and maybe some head work. This will keep the combo well mannered, but broaden the powerband and also step up the power to around 300 rwhp.

How does this sound?


PS: Thanks for the confirmation on the plenums tmoss

 

[stykthyn]

so longer runners on the upper plenum is better for low end?
what is the optimum runner length for a healthy low end intake?

 

[SuperStang83]

I agree the RPM is going to give a better top end, but you will lose some power down low. If you want to stay cheap you can pick up an explorer intake pretty cheap and give yourself good low end.

 

[5spd GT]

There really is no optimum intake length as you know But a good question, because there are formulas to get the theorized optimum runner length, based off the number of pressure waves one is acheiving.

A longer runner length promotes more low-end power.

Shape is quite important though, and keeping the runner lengths close to equal. I believe the Ford intakes have some air starvation problems with the first and fifth intake runners.

Larger plenums usually hurt the lower end. The plenum causes the incoming gasses after the throttle body to slow down, which ends up building pressure. In other words, it is able to make the air more compressed on it's way to the cylinders.

After all, the engine really does not care how long the intake runner is alone, but the total runner length of the head and intake combined.

Not all heads have the same runner length from the entrance to the valve opening.

Typically, with the EFI intakes you will see the longer runner lengths for the lower rpm powerbands, and the high rpm intakes will have shorter runner lengths.

 

[tmoss]

the "tuned" induction system length for a second harmonic wave is 23 inches for a 302 with stock or GT40 heads, the tuned length for a third harmonic is 16.1 inches. This includes both intake and cylinder port lengths. You can run other lengths and still make power but it won't be tuned to the harmonic wave.