LS that revs to 7500 RPM

[Vicinity]

I'm going to start building my engine later this year. I really don't care how many cubes (so any block will do), but since I've been driving my 944 I've gotten really used to the higher RPM's. I'd like to build an LS that revs to 7-7500 RPM. From what I understand a stock LS1 in the Vette was limited to something around 6.2k so I don't think my goal is unreasonable.

I've never build an engine before. I've messed around with the internals of an LS1, but I've never really "gotten into it". So this will be a learning experience for me.

Where should I start to attain my goal?

[Flash68]

I assume you spend time on ls1tech.com? That's where I'd be asking questions, not here.

Agreed on loving the 7k+ rpms!

[Z06vet]

I used to shift my Z06 with cam & headers at 6850, and my current heads/cam LS1 will easily hit 7K. I havent dyno'd it yet to see if its still maing power up there. Some of the LS3's with a cam & exhaust advertise 7K rpm redline. Can't speak from experience on that one though. What kind of driving do you do?

[AKlowriderZ71]

I spin my 5.3 to 6400 regularly, with a mild cam & stock heads. With the right combo, many guys are spinning the LS engines to 7500 rpm, but it takes the right combo. 7000 rpm is pretty common with aftermarket heads, matched cam, and a well built shortblock.

[Ron.in.SoCal]

High Rs in a V8 is loads of fun, but...pushrod engines have a hard time w high RPMs due to valve float. Not that this cannot be done, but the resulting stress on your valve train over the long haul is a motor issue waiting to happen. This is one of the reasons MSD makes rev limiting a simple adjustment and many keep it below 7k. Now if you're building the motor for drag or road racing and do not care so much about longevity, I say go for it...

http://www.youtube.com/watch?v=_REQ1PUM0rY

[Flash68]

^^ Good stuff Ron... also, I would consider a solid roller cam if you want to rev that high.

[Ron.in.SoCal]

^^ Good stuff Ron... also, I would consider a solid roller cam if you want to rev that high.

Thanks Dave. I came back to this thread to clarify a bit as I was looking at it from my own LS perspective. You are correct on soild rollers. Also, for those that don't know - and I'm no engine builder expert - DOHC motors don't suffer as much from this same issue.

[Gitter Dun]

High Rs in a V8 is loads of fun, but...pushrod engines have a hard time w high RPMs due to valve float. Not that this cannot be done, but the resulting stress on your valve train over the long haul is a motor issue waiting to happen. This is one of the reasons MSD makes rev limiting a simple adjustment and many keep it below 7k. Now if you're building the motor for drag or road racing and do not care so much about longevity, I say go for it...

http://www.youtube.com/watch?v=_REQ1PUM0rY

Agreed to a certain extent. If you pick a cam that ran around 280 duration at .050 it shouldn't be too bad. Big bore short stroke is the way to go IMO.

[67camaro*z]

Use a 4.8l crank in a 6l block. I think the real limitation aside from a stout valve train would be the stock style intake mani.

http://ls1tech.com/forums/generation...l#post10452939

[67camaro*z]

Or this:

http://i31.photobucket.com/albums/c3...9Camaro013.jpg

[Nessumsar]

Dan, I have been bench-building my next engine. What I have so far is an LS1/6 engine, with a 4.8 crank, carb'd Victor Jr intake, ls7 lifters, comp pushrods, beehive springs, and ls7 rockers. Comp makes a cam that should make peak power at 7500 with this combo; I plan to shift at 8000. With the short stroke of the 4.8L crank (3.25"), even at 8000rpm the mean piston speeds won't be that high.

Using Comps engine program this engine should make ~540hp with stock head flow numbers. Granted, this is simulated, but I have found this program's number to be close to real; if anything a good idea to go off of.

edit: I'm still toying with the idea of piston oilers. Some cheap insurance...

[Flash68]

Yeah that is a short stroke! What are the specs on that cam Jon?

[Nessumsar]

I'll have to get the specs tonight. I want to say it was one of their 293 cams.

[parsonsj]

Factory redline for an LS7 is 7000 rpm. Maybe you start there?

[funcars]

A lot of things to consider: adequate oiling for what you are doing with it, valvetrain set up to handle rpms (solid rollers, good springs, good rockers, correct pushrod length/valve geometry, cam with appropriate lobes, etc.), and the rest of the parts selected properly to run reliably at those rpms. More rpm costs more dollars for valvetrain parts. Rpm also causes the largest tensile loads on rods too (combined with rod/stroke ratio and how fast the pistons have to be accelerated).

[chicane67]

There are peticular reasons that -most- 427cid (and/or larger) packages dont really rev over 7-7250 RPM. The biggest reason of all of the inclusive issues just happens to be... ring speed.

That is one peticular reason that the OE doesn't put more camshaft into the LS7 to make even more power... because it is possible.... and that is easily proven.

The longer the stroke of the package, the higher the instantaneous ring speed. All the way to the point that if you spend much time there... you will eventually induce damage to either the ring lands of the pistons... or you will melt the rings into the pistions.

If you want larger displacements to buzz much more than 7250-7400'ish and live... all you need to do is change the bore and stroke combination.

For rough example:
4.125 x 4.000 = 428 cid (max 7250-7400'ish)

4.225 x 3.819 = 428 cid (max 7550-7700'ish)

Both the 4.000 and the 3.819" are common LSx crank shaft strokes.



And yes, piston oilers would be considered mandatory... in my book.

[93Polo]

You can spin any of the LS motors that high assuming the top end is flowing the air to support the rpm and the valve train is stable. My '00 LS1 with TEA stg 2 5.3 heads running comp 987 springs, Yella terror rockers, stock lifters and Futral 228/230 cam saw 7k many times. The car was sold and the new owner backed the rev limiter down to 6,700?. I was collecting parts for a 388 all bore motor back then and wasn't that concerned with the lifespan on the stock shortblock. We changed the springs at 25k miles and never had a problem. I would add a forged bottom end to handle 7,500 rpm as the stock bottom would be a gamble spinning that fast, as mentioned above stock rings/ringlands are at risk.

Phill99vette was one of the early ones to try to spin a hydraulic lifter LS that high. I know he went to 7,200 on a forged bottom end.

http://www.ls1tech.com/forums/genera...9-untuned.html

If you want more of his topics I would limit your search to his screenname, posts a year and older, and Gen III internal tech.

I am sure with the lifter and spring selections out now it would be easier to setup.

[chicane67]

You can spin any of the LS motors that high assuming the top end is flowing the air to support the rpm and the valve train is stable. My '00 LS1 with TEA stg 2 5.3 heads running comp 987 springs, Yella terror rockers, stock lifters and Futral 228/230 cam saw 7k many times. The car was sold and the new owner backed the rev limiter down to 6,700?. I was collecting parts for a 388 all bore motor back then and wasn't that concerned with the lifespan on the stock shortblock. We changed the springs at 25k miles and never had a problem. I would add a forged bottom end to handle 7,500 rpm as the stock bottom would be a gamble spinning that fast, as mentioned above stock rings/ringlands are at risk.

Phill99vette was one of the early ones to try to spin a hydraulic lifter LS that high. I know he went to 7,200 on a forged bottom end.

http://www.ls1tech.com/forums/genera...9-untuned.html

If you want more of his topics I would limit your search to his screenname, posts a year and older, and Gen III internal tech.

I am sure with the lifter and spring selections out now it would be easier to setup.

To expound on this a little more...

You dont need the airflow of TEA STGII cylinder head to do this... and the fact(s) to support that... start some 45 plus years ago, with a little engine known as the 302 (available in the 67-69 Camaro)... a production engine from General Motors.

Considering that the "186" casting cylinder head flowed around 250+/-cfm (it has a 170cc intake runner, heavily ported)... yet would spin to 7800-8000+ rpm with ease... is just scratching the surface. There is much, much more to an engine than stuffing a cylinderhead on top with the most cfm into it with a forged bottom end. Hell... you can change just the camshaft and springs in an LS1/2/3 and spin it to 8K... without blinking an eye (and this is where you would need to use the good parts to keep the bottom end together.) Katech has also proven this... with a little engine that they affectionately refer to as the "Sneak Attack"... a 346 cid engine that will pull through 8000+ rpm... all the while running an LC of 112 to 116.

Now... THAT's F'in crazy with a 112 - 116 LC... but it also provides a little more to the theory I explained above. That peticular build is a 4.125" bore with a 3.25" stroke.

The biggest single items in the equation are... the camshaft (more specifically, the duration of said camshaft)... and the mechanical limitations to the parts envolved. The total duration and LC are going to play the biggest roles in the engines rpm in dealing with the camshaft... well over that of total intake cfm. Not to mention, that specific mechanical limitations in specific components of the bottom end, being the other. This is where forged and billet bottom end parts come into play, because it adds to the longevity to something that is coming into its mechanical limitations.) I mean, you could stuff a cylinder head on a given package that flows eleventy billion cfm... but you are still going to melt the ring lands if you come within the mechanical limits of that specific component.



Building an engine with mere intake cfm alone... is at best... bench racing, in its most primative form. However, having a cylinder head that will flow larger numbers... does make it easier to build power... yet however, you still need to spend the money on the parts that will keep it together in the long run when dealing with elevated operational rpm.

Cheers.

[Flash68]

Katech has also proven this... with a little engine that they affectionately refer to as the "Sneak Attack"... a 346 cid engine that will pull through 8000+ rpm... all the while running an LC of 112 to 116. .

Now that would be a fun motor on a road course... but at $17k starting price.. ouch!

[93Polo]

To expound on this a little more...

You dont need the airflow of TEA STGII cylinder head to do this... and the fact(s) to support that... start some 45 plus years ago, with a little engine known as the 302 (available in the 67-69 Camaro)... a production engine from General Motors.

Considering that the "186" casting cylinder head flowed around 250+/-cfm (it has a 170cc intake runner, heavily ported)... yet would spin to 7800-8000+ rpm with ease... is just scratching the surface. There is much, much more to an engine than stuffing a cylinderhead on top with the most cfm into it with a forged bottom end. Hell... you can change just the camshaft and springs in an LS1/2/3 and spin it to 8K... without blinking an eye (and this is where you would need to use the good parts to keep the bottom end together.) Katech has also proven this... with a little engine that they affectionately refer to as the "Sneak Attack"... a 346 cid engine that will pull through 8000+ rpm... all the while running an LC of 112 to 116.

Now... THAT's F'in crazy with a 112 - 116 LC... but it also provides a little more to the theory I explained above. That peticular build is a 4.125" bore with a 3.25" stroke.

The biggest single items in the equation are... the camshaft (more specifically, the duration of said camshaft)... and the mechanical limitations to the parts envolved. The total duration and LC are going to play the biggest roles in the engines rpm in dealing with the camshaft... well over that of total intake cfm. Not to mention, that specific mechanical limitations in specific components of the bottom end, being the other. This is where forged and billet bottom end parts come into play, because it adds to the longevity to something that is coming into its mechanical limitations.) I mean, you could stuff a cylinder head on a given package that flows eleventy billion cfm... but you are still going to melt the ring lands if you come within the mechanical limits of that specific component.

Building an engine with mere intake cfm alone... is at best... bench racing, in its most primative form. However, having a cylinder head that will flow larger numbers... does make it easier to build power... yet however, you still need to spend the money on the parts that will keep it together in the long run when dealing with elevated operational rpm.

Cheers.

My main point was you do not need an exotic bore/stroke combination, LS7, or solid lifters to enjoy over 7k rpm with a LS motor. Phil's motor was a standard forged 347 shortblock with a well researched/setup top end. Also he built this motor 5+ years ago.

Agreed there are many variables ICL, LSA etc can be manipulated to move the power curve and dynamic compression ratio. Lobe design also comes in play with keeping everything stable. The little Futral cam I ran was soft compared to the Comp XE-R Phil ran. The valve trane otherwise used the same parts, he had float at 6,100 and mine was fine to 7k using comp 987s.

CFM alone is also benchracing as velocity is important. The TEA stg 2s I ran and the TEAs that Phil ran with extra port work are still solid but the new TFS casting would in theory yield more power. I am not a big fan of the LS3/L92 top end everyone is so eager to jump on but the TEAs are dated. Again it was more to the point of nothing exotic.

When stroker LS cranks were still very expensive many guys built all bore 382s and 388s with 4.1-4.125" sleeves and a stock 3.622" crank. I was always interested in what that setup would do with the big LS7 heads. 525-550 rwhp with this setup in a motor that spun to 7k rpm was not uncommon on ported 243 casting LS6 heads. The HP potential would be big with the extra CFM but would the velocity be there to build tq down low, how would the tq curve be?

As with any setup or desired result the total package must be thought out to get the best results for the money.