LT1 vs LS1
 

I've been trying to read alot on this site. One thing i read shows LT1's having 265 and 275 hp depending on number of cats, another shows 275 and 285 hp. Can someone tell me which numbers are correct. I thought it is 275 and 285. Also I am wondering the differences in the LT and LS. What gives the LS more hp? I know the LS has a slightly smaller bore and slightly longer stroke, that shouldn't make a difference really, and they changed the firing order, not sure how that would make a big difference either. How much of that difference is just in the tuning?

the difference in power is all in the heads. the taller intake runners on the ls heads gives it a huge advantage

I did notice in pics that they were longer. Im kinda surprised that the intake runners on LT1's are so short considering how long they were on the tuned port setups. Does anyone know what advantage they gained by the shorter runners?

Also I read where some people had flowed LT1 heads and they flowed 195cfm stock and 240 cfm ported with 2.00 and 1.50 valves. Thats pretty good for factory heads! Does anyone know what kind of specs the LS heads have?

the lt1 heads had no advantage wit the smaller runners. and the problem is they dont flow enough the ls heads easily outflow the lt1 heads and thats the problem the lt1 has.

ported stock heads can flow in the 290 range if done right

Since the LS series was a complete redesign they have a lot more potential. Blk93Z28, it's not the longer intake runners on the intake manifold, it's the intake ports on the heads. The LS series has overall taller heads than a traditional SBC like the LT, not only does this allow for more port volume and a better angle into the combustion chamber, but the ports can also be shaped more efficiently. The LS series heads have a cathedral shaped intake port. This allows for a high volume for high RPM flow as well as a high flow velocity even at low RPM. High flow equates to high HP, the high flow velocity helps make torque. Since the entire motor was a ground up design, they also designed parts to be able to handle quite a bit more lift on the cam, which will obviously improve numbers.

Thanks 95slvrZ28, that makes sense. I'm new to the LT's and LS's so i'm trying to figure out things to do to my car. I've built 2 383's but they were carbed. One 400hp and one 450hp, all the difference was in the heads and a slightly bigger cam. Thats when I learned more about air flow. So just how much better do the LS heads flow?

The overall flow (cfm) that you can get out of the different heads are comparable. On good aftermarket heads you can see LS numbers around ~320/250 cfm and LT numbers are about the same (we're talking under 10 cfm difference). In practice is where it changes. The flow numbers are taken around .60 lift and above (for preak flow obvioulsly). 0.60 lift on an LT is pretty extreme, but the LS series is not nearly as stressed to run that lift or more. If your porting the stock heads the stock LT heads have a little less room to work with so you can't get quite that high of numbers out of them as the LS heads. Porting stock LT heads, as Whammer stated, you can push around 290/260, the LS heads have enough room that you can get them to flow around 320/270. Another thing to consider is these are preak flow numbers, what really matters more are the mid-lift flow numbers.

Thanks for the info. Im actually trying to decide if i want to put money into the car i have or wait a little while, sell it, and get one with an LS1. My fiance has an 05 Mustang GT so i neet to be able to outrun her lol. My car now has 2:73's (why did GM do that to us?) and just wont get the job done

what about cam lift and duration between the two? i kno obviously the ls1 has a taller head, will that allow for more lift on the stock motor? cuz there are some pretty sick cams out there designed for stock motor ls1/ls6's.


case in point: http://www.youtube.com/watch?v=1GpzCrzT7iQ