ls john simpson my ls roadster has a replacement block not a i have'nt pulled the heads or the pan to see whether it's a four bolt or which pistons it has it's probably a safe bet that if the block had to be replaced everything else in it was too assuming it has flat top pistons what would the compression ratio be with the heads also if i install intakes and exhausts does cutting into the intake seats to install the exhaust seats spell disaster
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Re: 70 LS-7
re ls joe lucia assuming that your engine has flat top pistons which is unlikely the compression ratio with cc heads would be approximately in the range of to as far as the increase in valve size mod goes which requires overlapping valve seats i wouldn't perform that mod on a bet if you have cast iron heads with integral seats you might get away with it if you have aluminum heads with insert type seats i wouldn't even try it the real question is why you would even want to increase valve size you can achieve well over hp with valves that is far more power than you could get to the ground with any available street tiresIn Appreciation of John Hinckley -
Re: 70 LS-7
re ls john simpson thanks joe they had that valve set up when i got it i'm a bit concerned about problems caused by heat expansion i'd hate to have those valve seats rattling around in my combustion chambers but it's a whole lot harder to go down a valve size than it is to go upComment
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Re: 70 LS-7
re ls joe lucia if the heads are aluminum you could remove the valve seats install new ones and return to the original valve size if the heads are cast iron with integral seats you could have the heads machined to accept valve seat inserts which is a good idea anyway if you have soft valve seats in the era of unleaded gas and install original size valvesIn Appreciation of John HinckleyComment
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Re: 70 LS-7
re ls john simpson heads are aluminum if i machined them for new valveseats i would have to weld up the seat area to be able to cut them for smaller seats sounds like an awfully expensive proposition don't you thinkComment
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Re: 70 LS-7
re ls rolf krueger john here are some things to consider the aluminum head was first used in l engines it was an open chamber design with cc and valves it had round exhaust ports with the high rise l pop up pistons the compression ratio was that head was also used in the ls with some combustion chamber recontouring with the the low dome ls piston the compression ratio was if you use a flat top piston the compression ratio would be less than note that while some early 's over the counter crate engines used the aluminum heads the late 's and 's ls and ls crate engines used cast iron heads it makes no technical sense to consider installing larger valves in an head unless your engine displacement is well over cid the valve sizes are not the limiting factor in air flow i have heard of people installing hardened seats in heads but it is a tricky operation and i have no information on the reliability the lifetime of the head was relatively short because gm recognized it had numerous design limitations and big blocks in hi po passenger cars disappeared after gm invented a very good replacement aluminum head that has the casting number or the head this head was an open chamber cc head with valves and hardened seats it has a letter d shaped exhaust ports but is usually referred to as the c port head this head has substantially reshaped intake and exhaust ports that allow it to flow more air than the head depending on the cam used because of the substantially better performance and durability most street engine builders use the head and do not mess with heads for racing gm had special bowtie heads with revised valve locations that provide even more air flow in one of your earlier posts you indicated that you had an ls intake manifold lacking other information i will assume that you have the casting number or maybe aluminum intake and the stock big block hood if that is the case it makes no technical sense to consider bigger valves heads different cam etc because that ls manifold design was very inefficient and can not support more air flow its primary virtue was that it fit under the stock corvette hood it was referred to by many gm engineers as a low rise manifold and by the more pessimistic ones as a no rise manifold if you really want to get some serious horsepower out of your hi po big block in a corvette you need to install a gm or aftermarket high rise intake manifold and that will require you to use a different l style big bulge hood i would recommend that you carefully think through what you really want to do with your car otherwise you could spend a large amount of money with little performance improvement and probably create other problems it may be that a thorough and careful rebuild with as little modification as possible is the most judicious course of action finally remember that the ls intake underneath a stock bb hood seriously limits your big block engine output potentialComment
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Re: 70 LS-7
re ls john simpson i've got no argument with any of your comments your description of heads sounds an awfully lot like heads but it's moot the valves are already installed my questeion is about whether or not heat expansion is going to pop the suckers outComment
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Re: 70 LS-7
re ls joe lucia generally the od of valve seat inserts is the same for different size valves in other words if you remove the valve seat inserts that you currently have and replace them with inserts for smaller size valves those inserts should fit in the same pocket as your existing inserts no welding should be required this would not work if the stock insert pockets were enlarged to accept your current inserts or if installation of the oversize valves required otherwise cutting into the aluminum head more likely though i expect that the original seats were merely enlarged to accept the larger valvesIn Appreciation of John HinckleyComment
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Re: 70 LS-7
re ls john simpson i only wish it were so but these are really big valves as i said in my original post the pockets for the exhaust seats cut into the edge of the intake seats that's what bothers me the question is will heat expansion pull the seats away from each other or closer to each other away is ok closer could pop them outComment
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Re: 70 LS-7
re ls rolf krueger could you elaborate on what you mean by a ls roadsterComment
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Re: 70 LS-7
re ls john simpson beat up convertible with fitted with heads same intake as an ls speed no air large tube headers about four or five coats of different color paint just a beater vette but fastComment
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Re: 70 LS-7
re ls rolf krueger there was no corvette with an ls engine produced by general motors in or any other year although gm had initially offered such an option in the ls engine that was developed could not pass federal emmissions requirements and gm killed the project for production application gm did offer all the parts it took to build an ls engine over the counter as performance parts in addition there were over the parts counter ls engines built for the racing fraternity it is always possible that someone got all the necessary parts or a crate engine and built his own ls corvette after the fact however no such vehicle was ever assembled and sold by general motors in gm did build and sell a corvette with an ls engine the ls was a detuned version of the ls with modifications to reduce compression ratio and meet emmission requiremets only corvettes were built in with the ls engine do you have a name it is customary to identify oneself on this listingComment
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Re: 70 LS-7
re ls john simpson because i'm not an ncrs member there is no provision for me to post my name other than in the body of the message my name is john simpson whether the factory an affiliate of the factory or an owner put the engine in is irrelevant to me i'm only interested in the answers to my questions none of which have yet been addressed allow me to digress for a moment years ago i built a national st aaca car a mgtd showing it was no fun although building it was on the other hand i once built an mgtf initially with a truck engine and speed w od and later with a hp fuelie a healey rear end and a torque flite tranny building it was fun beating up on vettes was a blast and listening to the purists whine was bearable this car zr should be much the same building it is fun driving it will be a blast and listening to the comments of the experts will be bearable now does anyone have knowledge to offer me about my questions or just opinions about the authenticity of my carComment
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Re: 70 LS-7
re ls tom freeman john no one is trying to avoid your question we just asking info about the engine so we can get the needed details to answer your question since there was not an ls we are in the dark if you could give the full specs for the engine maybe someone can come up with the answer for you note you don't have to me an ncrs member to post your name at the top under subject is a field for from where your name goes tomComment
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