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Your thoughts on a high revving LS2

This is a discussion on Your thoughts on a high revving LS2 within the Internal Engine forums, part of the LSx Technical Help Section category; I've been thinking about utilizing an LS2 for an FD chassis RX7. My thoughts were to create a lightweight, high ...

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    Your thoughts on a high revving LS2

    I've been thinking about utilizing an LS2 for an FD chassis RX7. My thoughts were to create a lightweight, high revving car to emulate a Porsche GT3 RS or a BMW M3 CSL. To me, a higher revving engine is more exciting in this type of car and better suited. With such a short wheel-base, I want a broader torque curve and more peak horespower. I think gobs of down-low torque will upset the car more because of it's short wheel-base and low weight. So, I was curious if anyone has gotten these LS engines to put out 8000 RPM in a streetable package? I want to be able to maintain good fuel economy and durability as well.

    I do wonder however, if the engine design being a pushrod V8, just doesn't lend itself to high RPM applications?

    Any help would be appreciated. Thanks in advance.

    Nick

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    Senior Member redbird555's Avatar
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    In short no that's not a good idea. Ls engines make great power under 7k I realize it would be a small car but I think a motor with a 6800 redline with 4.10s in the rear would be very fun. To turn that kind of rpms you would need forged internals all around along with arp rod bolts and one hell of a valvetrain ie titanium valves, hardened pr's and maybe even convert to a solid roller cam. IMO it's not worth it you can still have a fun motor with just a can and spring swap and spin it to 6800

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    Moderator Firebirdjones's Avatar
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    As with any pushrod V8, it would have to be built with rpm in mind. 8,000 rpm isn't hard to achieve, we used to do that with stock Gen 1 cranks and rods and a big solid cam back in the day with a fair amount of success I still have a couple of those sitting here.

    Doing it with an LS engine wouldn't be tough, but I don't care for the snap cap rods to start with. A good rotating assembly along with a stable valve train setup and it will turn rpm. You have to think "light weight" and that includes the rotating assembly as well as the valvetrain.

    An LS2 would be a good start with it's 4" bore. You could even source a short stroke crank to drop the piston speed down.

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    Thanks for the replies guys.

    Firebirdjones, in your opinion which LS engine would be the best to start with? My research has told me that rod bolts are absolutely necessary to upgrade in order to obtain those higher RPMs. I also hear you when you say the rotating assembly needs to be lightweight. But I've also heard that the crank is hollow from factory, so what other steps would I need to take to lighten the rotating assembly sufficiently?

    Second question, does my logic hold any water here? Will I be eliminating some of that low end 3000 RPM torque and make it less frisky by getting her to rev higher?

    Thanks again guys.

    Nick

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    Moderator Firebirdjones's Avatar
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    Hp is a product of RPM. You'll still have torque, it will just be higher in the rpm range, that's the trade off. I assume that's what you want.

    We used to use stock GM rods when doing this on gen 1 stuff and even BBC's years ago. Nowadays I'd rather use aftermarket lighter weight rods that are stronger. Pistons are also lighter now with better skirt and pin designs, small ring packs, etc..
    Most old school engine builds now, including chrysler, pontiac, chevy and ford are also using sbc sized rod bearings and smaller diameter main bearings for less friction and heat as well as lighter weight. Reducing friction makes HP, and there is alot of that to be found in the short block. The LS engines are good at doing that in stock form as they already have smaller diameter bearings, small ring packs, short skirt pistons etc...The rods are a weak point however and a forged piston is a must.

    As far as what LS engine to start with. I don't really know what your goals are but I assume being a small car that keeping weight down is a priority. Stock aluminum blocks would work fine. I'm a fan of a 4" bore, which has been the basic starting point for making HP for 30+ years. The larger the bore the better the cylinder head will flow. Depends on how much you really want to spend on a project like this.

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    Senior Member Shermanator86's Avatar
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    I'd like to see this idea come through, I've liked the idea ever since I read an article on someone (can't remember now) building a 302 ls1 de-stroked motor don't know why just sounds like a fun motor to twist out at high revs

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    Sherman, you're in-line with my thoughts man. It's not about power to me, really...a 2800 lb. car with 400 HP will be fast, there is no question about that. And really, HP isn't the goal necessarily, but it will be a bi-product. The experience is what I'm after.

    Firebird, thanks for the insight. In response to your question of how much I wanted to spend on this project; I'd like to tell you that I will spare no expense, but of course, everyone's got a budget. I will say this though, I am committed to the end product and I'm a very patient man. I can spend a year building this engine if I feel like the end result will be worth the time, effort and money. To the point I was just making, I'm not really chasing HP, so I won't be looking for necessarily the most radical components for this build. I know HP will be a bi-product of the weight reduction to the rotating assembly and the reduced friction you spoke of and truthfully, I'd like to see around 500 HP to the crank, which is probably relatively easy with 6 liters of displacement, an extra 1-2k RPMs, lightweight rotating assembly and a great flowing head.

    Looking around there are definite price gaps between the LS1, LS2 and LS3. All of which are swappable into the 7, so the block itself is nearly identical, if I'm not mistaken. But, if I'm going to need new rods and pistons anyway, why not pick up a cheap LS1 with a million miles on it, bore it out to 4" and find an LS7 head or LS3 heads and take care of my valvetrain? Does that make sense to you? How would you approach it, now knowing that I am targeting about 500 BHP and want to turn out 7500-8000 RPM safely? Durability in my engine build is an absolute MUST. I won't sacrifice that for an extra 500-1000 RPMs.

    I hope that all makes sense. Again, thank you for your time with this, I appreciate the help guys.

    Nick

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    Moderator Firebirdjones's Avatar
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    Quote Originally Posted by nickdex87 View Post
    Sherman, you're in-line with my thoughts man. It's not about power to me, really...a 2800 lb. car with 400 HP will be fast, there is no question about that. And really, HP isn't the goal necessarily, but it will be a bi-product. The experience is what I'm after.

    Firebird, thanks for the insight. In response to your question of how much I wanted to spend on this project; I'd like to tell you that I will spare no expense, but of course, everyone's got a budget. I will say this though, I am committed to the end product and I'm a very patient man. I can spend a year building this engine if I feel like the end result will be worth the time, effort and money. To the point I was just making, I'm not really chasing HP, so I won't be looking for necessarily the most radical components for this build. I know HP will be a bi-product of the weight reduction to the rotating assembly and the reduced friction you spoke of and truthfully, I'd like to see around 500 HP to the crank, which is probably relatively easy with 6 liters of displacement, an extra 1-2k RPMs, lightweight rotating assembly and a great flowing head.

    Looking around there are definite price gaps between the LS1, LS2 and LS3. All of which are swappable into the 7, so the block itself is nearly identical, if I'm not mistaken. But, if I'm going to need new rods and pistons anyway, why not pick up a cheap LS1 with a million miles on it, bore it out to 4" and find an LS7 head or LS3 heads and take care of my valvetrain? Does that make sense to you? How would you approach it, now knowing that I am targeting about 500 BHP and want to turn out 7500-8000 RPM safely? Durability in my engine build is an absolute MUST. I won't sacrifice that for an extra 500-1000 RPMs.

    I hope that all makes sense. Again, thank you for your time with this, I appreciate the help guys.



    Nick
    With rpm the goal, and a 4" bore, you can use the 15 degree LS3 head. Those large ports on a relatively small motor are going to like rpm. The 12 degree LS7 heads would be even better for making power if you can afford it.

    The LS1 won't go to 4" however unless you sleeve it. Gets a bit pricey that way. A high mileage aluminum LS2 would be better suited for your 4" bore goal with a light hone (clean up) since they are a 4" bore to start with.

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    Moderator Firebirdjones's Avatar
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    Quote Originally Posted by Shermanator86 View Post
    I'd like to see this idea come through, I've liked the idea ever since I read an article on someone (can't remember now) building a 302 ls1 de-stroked motor don't know why just sounds like a fun motor to twist out at high revs
    I haven't seen that done with an LS motor (yet) but it sounds interesting. Should make silly power with a good head. I have a real 69 Z with a 302 here and they do love rpm. With 4.88 gears it keeps you busy

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    Senior Member Shermanator86's Avatar
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    that is one of my dream cars btw (69 302) I'll try to dig up the article I know its old cause I was in middle school i think when I read it haha

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    Senior Member Shermanator86's Avatar
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    here is the car I'm thinking of but I'm for sure I read it in either hot rod or car and driver though originally
    Chevrolet’s 302 Camaro SEMA Show Car | CamaroZ28.Com
    Chevy Camaro Feature -- Super Chevy

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    Moderator Firebirdjones's Avatar
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    Nick,
    For what it's worth, you don't really HAVE to have the 4" bore. Since LS1's are becoming more pleniful in used condition, it would be a cheaper way to go. The 3.9" bore is fine, and would easily make your HP goal. You would have to stick with a cathedral port head, but that's not going to hurt the rpm potential.

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    Moderator Firebirdjones's Avatar
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    Quote Originally Posted by Shermanator86 View Post
    here is the car I'm thinking of but I'm for sure I read it in either hot rod or car and driver though originally
    Chevrolet’s 302 Camaro SEMA Show Car | CamaroZ28.Com
    Chevy Camaro Feature -- Super Chevy
    That's interesting that it's been done. They didn't go into much detail as to the crank used though or any other details of the engine, unless I missed something?? It made 435 HP but I'm surprised they measured that at only 6,000 rpm. You can spin a stocker 346 to 6,000, and make power beyond that with a camshaft swap.
    With that said, it sounds like this 302 was a rather "mild" build.

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    Senior Member Shermanator86's Avatar
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    Yea from what I remember its wasn't very crazy of a build, like I said I read this article about 10 or 11 years ago so i'm a bit foggy on the specifics of it all.

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    Quote Originally Posted by Firebirdjones View Post
    Nick,
    For what it's worth, you don't really HAVE to have the 4" bore. Since LS1's are becoming more pleniful in used condition, it would be a cheaper way to go. The 3.9" bore is fine, and would easily make your HP goal. You would have to stick with a cathedral port head, but that's not going to hurt the rpm potential.
    In truth I'm somewhat partial to an LS2. I have always viewed the LS1 as the weak link since I associate with a number of Goat owners. They always bash the old 5.7...but truthfully I don't care about having the extra .3 liters of displacement. However, what I do care about would be a new technology or maybe just an overall better engine design.

    So, if you were in my shoes would you feel it justified, or "worth it" to go LS2 over LS1?

    Thanks again guys, you've been very helpful!

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    Senior Member Shermanator86's Avatar
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    to my knowledge there isn't any real technology jump in the to ls2 mostly just a size difference. as far as a 5.7 gto full bolt ons will put it right with an ls2 power wise

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    Moderator Firebirdjones's Avatar
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    Quote Originally Posted by nickdex87 View Post
    In truth I'm somewhat partial to an LS2. I have always viewed the LS1 as the weak link since I associate with a number of Goat owners. They always bash the old 5.7...but truthfully I don't care about having the extra .3 liters of displacement. However, what I do care about would be a new technology or maybe just an overall better engine design.

    So, if you were in my shoes would you feel it justified, or "worth it" to go LS2 over LS1?

    Thanks again guys, you've been very helpful!
    The only physical difference between the 5.7 and the 6.0 is the bore. 3.9 verses 4.0. They use the same crank. Of course there are camshaft differences, and cylinder head differences, but I'm talking about the basic package, not the changable parts.

    With that said it's really a matter of personal preference. In theory, the 4" bore has the potential to make the most power due to it's ability to unshroud the valves better than the smaller bore.
    But,,,,I see these 5.7's make silly power, thanks to the phenominal cylinder heads nowadays being offered. With such a small difference, and since either package would meet your HP goals, I'd go with which ever one fits your pocket book.

    I had to make a similar decision on a retro swap in a 72 blazer. I wanted a cast iron block, so it was either a 5.3 or a 6.0. Not as tough of a decision here though I ultimately went with the 6.0 LQ4 and I don't regret it one bit. Great running engine package for what I'm doing with plenty of grunt to move around a 4700 lbs. truck. I don't think I'd have been happy with the 5.3

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    Yeah, it's kind of like splitting hairs huh? 5.7...6.0...? I figure both will, as you said, get me to my HP goal with the same head/cam/valvetrain/tuning. So, I suppose, what it comes down to is, which one has the better sleeves? I know other auto manufacturers can make two engines from the same family with very different inards. For example, my daily driver has a J30A1 engine, which is virtually identical to the J32A2, aside from the head and displacement. But the sleeves in the J32 are far superior and can take higher rev applications, which my J30 engine cannot.

    Also, since I'm getting more aggressive with my RPMs, would you suggest a different oil pump or oil pan? I want to have that longevity built into the motor and ultimate reliability. But, I may be limited with oil pans because of course, the engine wasn't designed to sit in an RX7 and the "special" sub-frame and engine mounts may put the engine too low in the engine bay for a massive oil pan.

    Oh so many things to figure out huh...? :-)

    Thanks dude!

    Nick

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    Moderator Firebirdjones's Avatar
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    I honestly don't know if there is any difference in the sleeves with the 5.7 and 6.0. They generally only take a mild hone or a slight overbore of about .010 to stay safe. Which leads me to believe they are similar. Resleeving for more overbore is very expensive.

    I've never done an RX7 swap so I'm not sure what you are dealing with as far as oil pans. I would assume ground clearance would be key so you might be stuck using the F-body pan or even the corvette pan since it's baffled from the factory. That's a cheap way to gain some oil control without breaking the bank if you plan to road race. I see the vette pans occasionally at swap meets complete with the pickup tube for cheap. With a high volume pump I would be comfortable with what you are doing.

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    OK cool thanks again for all of the insight guys!

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