The LT1 intake/miniram is supposed to sacrifice some torque for top end HP, right. Also, people on these boards have said that after driving an L98 car, an LT1 car felt like a 4 cylinder--no torque.

Why then, are LT1 F-bodies and vettes supposedly so good down low, but can't keep up on the top end, according to what I can gather from other sites like www.camaroz28.com and www.ls1.com?

I realize that individual cars are obviously different, but my above question reflects the general feelings toward LT1s. Isn't the incredibly short runner design specifically for top end? Can someone explain this to me? Vader? Madmax?

I have just been wondering for a while and finally decided to ask.

 

The guys on CZ28.com are comparing their LT1 motors to LS1 motors. LS1's have a very flat torque curve, with very good top end HP. LT1's have to add about 40 HP to come close to running what a stock LS1 runs, and most of the time, it's with a cam change. If you compare LT1's to L98s, the the L98 has gobs more torque down low, but no higher RPM power. The LT1 still has great torque down low, it just doesn't seem as great when comparing to a Tuned port setup. Try an LS1, then you really feel like there's no torque, but it has power all the way through 6500 RPM.

 

Oh, thanks. I really wasn't just directing this towards the moderators. I expected to get a technical response about short runner setups and we all know that the moderators are great at that. I have never driven an L98 and never got on it the one time I drove an LT1. Combine that with the fact that it's been too long since I drove an LS1, and you see I really have no appreciation of the relative torque argument. I just didn't realize that the LT1's-are-strong-down-low "position" exists because of the less peaky LS1 powerband.

 

I've driven all 3, own a modded tpi and an lt1. The lt1 feels plenty torquey, just not quite as punchy down low. It pulls hard 5500, then falls on it's face. The tpi pulls hard from idle, and falls flat by 5000. The ls1's I have driven feel like an electric motor. I never felt that huge sudden rush, but it was the same rush from 2k to redline. My actual impression was this doesn't feel fast, but if you watch the speedo it is. All three engines just feel completely different.

 

In compairing my low mileage 91 350 TPI Z28, stock, with a stock 30th Aniversary Z28 there is no comparison. The LT1 is a nutty engine. If people complain about the LT1's not having enough torque they obviously are used to a big block, heh. Later.

Adam

 

From what I've read, the torque vs. horsepower comes from the runners. The TPI has a total intake length (distance air travels to the head) of somethin' like 21 inches vs. LT1 with 3 in. and LS1 w/ 13 in. This long track (TPI) makes for gobs of torque, but won't feed the engine up high. On the other hand, the LT1 feeds the engine up high, but doesn't generate the same torque. And similarly, the LS1, being in the middle, has a good compromise of both.
A side note of similar meaning: larger tube headers give more hp but less torque than smaller tubes.

An interesting fact: Also from what I've read (same article) the name "tuned-port injection" comes from the fact that GM actually designed the TPI intake runners to get an extra "charge" of air at a certain rpm. I don't remember exactly how it happens, but it has to do with the intake velocity and runners working together to greatly increase the intake charge velocity, thus acually forcing air into the cylinders.

 

It's called harmonics, as in 2nd and 3rd harmonics that affect the TQ at certain rpm's. That's why it's called "tuned port" injection. It can be looked at as a pressure wave that bounces back and forth gaining strength as it returns and enters the cylinder chambers.

 

Basically understood as when the intake charge rushes into the cyilnder and the valve quickly and abruptly snaps shut it piles that charge up behind the valve harmonically, when it opens again its got more pressure than before.