mundo

Its head design.

The LT1 has higher compression than the LS1 and ZO6 LS6. LT1 has 10.4:1 compression, LT4 has 10.8:1 compression. LS1 (most C5s) with 853 heads has 10.1:1 compression and ZO6 243 heads have 10.5:1 compression.

The intake runners on LT1 heads are about 2" x 1". This is puny. The Intake runners are on 853 LS1 heads are abou 4" x 2 inches - huge! The combustion chambers on LT1 heads are smaller. I believe 52cc to LS1 54cc.

The exhaust ports look about the same size on both heads.

What about that 'heavy' metal intake manifold on the LT1? Looks to be about 20 - 35 lbs. It's a dry manifold - isn't it. If dry it could be plastic?

I believe its the intake runner size. LS1 853 heads with less compression make more power than the LS4. The LT1 / LT4 can't breath.

Does anybody make a set of heads with similar size intake runners as the LS1 for LT1. Why doesn't anyone make a plastic intake manifold? When I put an LS6 manifold on my LS1 it probably weighted < 10lbs. Why doesn't FAST make a plastic manifold for LT1 / LT4?

cv67

Probably not enough willing to spend the money on them. Looked into it a few yrs ago and to make them 50 state legal for LTx and L98 the cost was stupid high pretty risky.

LSx heads flow a bunch of air at all lifts totally different design than gen 1 sbc also have a different valve angle. Gen 1 23 deg LSx was 15, 12 something like that? Compression plays a small part but its more the head and tuning capabilities than anything imo. Lotsa LSx experts that may chime in with better info though.

Orr89rocz

Its the valve angle on the heads and the fact they flow so much more air than a LT1/LT4.
They also got bigger cams than LT motors. Duration wise maybe a little less but much more lift which on higher flowing heads it makes more power.

LT4 vettes can run with LS1 vettes tho. Bolt ons to bolt ons I think the LS1 wins.

AFR makes a 227cc altered valve spacing LT4 type head that will make serious power on the right combination... think 383-396" and higher rpms. Needa well balanced, very lightweight rotating assembly for this however with the long stroke, but a solid roller LT1 using a head like that can rival most similar cubed LSx motors but the LS1 based motors still can get better heads.

Bad Karma

I think the biggest amount of work went into the intake port design of the heads. It is night and day difference from the Gen-1 heads, even under a carb manifold they perform well.

383vett

The larger ports do make a difference, but the main hp increase is due "cathedral" port design which allows the intake charge to take a straight shot to the valve and combustion chamber.

SJW

Stock LS1 and LT4 dyno curves are very similar. Not a lot of difference there.

LT1 and LT4 intakes are dry. I suppose it's possible that you could make one from plastic, but bear in mind that it needs to be able to seal oil within the lifter valley.

Live well,

SJW

FLASH92LT1

Size doesn't matter!!! (I've heard that before!)

cuisinartvette nailed it. The LS heads are 12 degree valve angle design with high ports for a straighter shot into the combustion chamber.

Some race SB1 heads are 18 degree but there's only so far the intake port can get raised to compliment them. You can't even get close to the LS design with them.

The shallow valve angle along with high ports flows way more air than even large SB1 ports can flow.

-- Rick '92 LT1

Fastbird

Fixed.

Factor in a superior runner design in the head coupled with the 18* vs. 23* valve angle, and improved runner design in the manifold and you get why the LS1 is more powerful than the LT1. It's just a factor of evolution. The cathedral port itself isn't the main factor, it was more of a by product of the design. The LS7 and LS3/L76 all have rectangular ports like it's Gen II Predecessor though, and they DOMINATE the LS1/6/2 cathedral port design. The simple fact is the valve angle and overall runner design lends itself to a vastly superior flow without a greatly increased volume, promoting higher velocities with an easier entry angle.

The LT4 head stands up initially, but it's 23* design limits it's ability to respond to mods and it's ability to keep up with it's younger brothers.

SJW

We have a winner. Stock, the LT4 stacks up well against the LS1. With mods, the differences show up quickly.

Live well,

SJW

pmihaltian

Very interesting post. Thanks to all for the information

lt4obsesses

The intake manifold on the LS1 does a much better job of channelling the air flow and maintaining air velocity to the ports compared to the LTx manifolds. Larger single TB aids in this as well, far less air turbulance.

It also doesn't hurt the LS1 that each spark plug has it's own coil a mere 6" away.

Stock rockers at 1.7:1, and redline at 6800 also gives the LSx a distinct advantage.

cv67

Just to give an example of the power potential of the LSx check this out.

Started with a 12:1 327 big solid flat tappet, old school iron heads then to 195 AFRs. Heavy car that struggled to get in the 12s I believe and with the 195s dropped some more, cant recall if he hit 11s or not.

Now took a junkyard LSx shortblock had the stock heads ported, 230ish cam/carb and is going 10s with trans slippage.

Hard to do that with a Gen 1 Chevy esp the mph.
If I ever build another mill it will be a LSx its simply easier to make big power thats driveable.

http://www.chevelles.com/forums/showthread.php?t=331501

mcm95403

And keep in mind that anything Gen 1 is all based on the same design from 50+ years ago. You can improve the basic design just-so-much and then after that you have to start making major changes to get muhc more of an improvement. The SBC has always had a problem with the pushrods passing through the port area making that big bulge in the port. The only real way to get around that is a total re-design.

Frankly, I'm amazed at how much power you can make out of a Gen 1 engine nowadays. With the recent (last 15 years or so) computer designed HR cams, heads and intakes, you can now make WAY more power and get better mileage than what we could when my 84 was a new car. That's saying a lot for an engine that had already been around for 30 years 1/4 of a century ago.

The new engines are just a wonder to behold. My best friend Mike has a new Z06. That thing is a total MONSTER when you get on it, yet it idles smooth, has A/C, is totally quiet cruising on the freeway and gets 27mpg. If you'd told me 20 years ago that I could have a 505 hp 427 with manners like that and that kind of mileage, I'd have written you off as being on drugs - now it's a reality. Totally amazing. My 70 Super Bee 440+6 made about 425 hp and got 6 mpg when you drove it "normally" and only once did I get 10 mpg. That car was no where NEAR as quick as most of these new cars and sure wasn't as comfortable and couldn't handle well at all.

Technology marches on..........

96 lt-4

Yeah but I would rather have the Superbee

lt4obsesses

The SuperBee could fund your retirement. The Z06 will put you back to work.

mcm95403

I just remind myself that the cars would never have survived the divorces.............

Here is the only picture I have of it. In the background in my friends 69 Hemi Road Runner and in the driveway is his 500" Hemi Demon drag car - it ran 8.55 @ 155 back in 1985

Shaf1970

Ok, so are these worth anything to an LT4 owner, are you going to see a worth while performance increase over a stock ported head.


http://www.trickflow.com/egnsearch.a...8&autoview=sku

cv67

LT4 head is 195cc If Im not mistaken flow #s arent too far apart on them.

Shaf1970

Thanks, I did not understand why Trick Flow would go to the trouble of making a 21 degree head and then it only be 185cc.

Fastbird

It's not all about volume. Let's look at some Gen III stuff. Take a stock LS6 head and port it.......you're entering into runner volumes of 225-230cc's and peak flowing (it's not about peak either, but I'm using this as a broad example) around 230 CFM at say .600 lift. Now take a set of AFR 205's. Those are 205cc runners, and flow about 235 CFM at .600. The design of the runner, shape of the bowl, area around the valve guide, transitional areas all play into how well a head flows. The AFR's make more power than the LS6's because they carry a higher port velocity and thus flow more air due to a superior design.

LT4 head vs. box TFS GenX = GenX by a little. Ported, the GenX will murder a ported LT4. Even the original TFS heads (the 195 that are 23* like what I have on my LT1 Trans Am) were superior to the LT4's. The aftermarket doesn't just copy the original design, they make improvements here and there that add up to noticable gains.