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Corvette
C4 Forum
1988 Convertible for sunny day drives
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<blockquote data-quote="Tourmax" data-source="post: 175803" data-attributes="member: 5304"><p>continued from: <a href="https://canadiancorvetteforums.com/threads/about-4-weeks-in-having-some-serious-thoughts-about-modifications.30432/#post-175718" target="_blank">About 4 weeks in, having some serious thoughts about modifications......</a></p><p></p><p>So i'm looking at options to modify the L98. I don't particularly want to take too much away from it on the bottom end to reach an ultimate HP number, so there's going to be compromises somewhere.</p><p></p><p>I'm shooting for around 300-350 at the crank, so my goals are fairly modest. somewhere around stock LT1 numbers. But this is a street car and I want it to stay that way so a high reving screamer is out of the question. No sense making 400 HP if you have to spin it to 6G to get it. that's not where this car will live.</p><p></p><p>Aftermarket stuff like a FAST TPI setup would be great, but I don't really have that kind of money to drop all at once. The FAST system is going to tickle 2G CAD by the time I get it at my door and I'm (IE: bank account) not up for that.</p><p></p><p>I've got a complete LT1 intake:</p><p></p><p>[ATTACH=full]31231[/ATTACH]</p><p></p><p>I grabbed it used for 75 bucks. Intake, rails, injectors, etc. Couldn't pass it up at that price. I am considering altering as required (distributor hole, water ports, bolt holes, etc) and using it, but with 3.5" long runners, I'm worried it will adversely effect low end torque production, where the car spends most of it's time. I'm also not thrilled with the thought of using a remote thermostat housing and I don't particularly like the fact that you have to take the water from the heads from either the front of the rear of the heads when the L98 has coolant crossovers in front and back of the L98 TPI lower. Using the HEi distributor also means loosing all the EGR stuff (no room), which doesn't give me that good "no smog" feeling.I live in atlantic Canada and have experienced being the USA's "tailpipe"more than once in the summers and don't wish that crap on anyone. The good news is even if I loose the EGR stuff, I can get it back by using a cam that allows enough overlap to perform the same function as the egr valve (IE: LT4 has no egr valve, all done in cam design).</p><p></p><p>I'm also now considering altering the LT1 rather radically". I'm thinking to chop the front and back off the LT1 intake, take one of the spare TPI lower manifolds I have lying around and chopping the front and back off that. Then, once bolted firmly in a jig, wled the L98 pieces to the LT1 piece. That will give me an LT1 style runner/plenum piece, yet retain the water passage crossovers, the front mounted thermostat hosing and the rear distributor hole. I'd still loose the EGR bits, but again, I can handle that with cam timing.</p><p></p><p>the next option is to "customize" the OEM L98 TPI stuff. I'd take another spare TPI lower I have and port it out as much as possible. Then, after a tedoulsy long set of calculations, decide on a runner length and diameter that will put the power curves where I want them. The OEM runners are about 21" in length (to the intake valve), which is tuned the way GM engineers wanted it. I've also done some quick calcs and the OEM TPI is indeed sized for a 305, so it's leaving something on the table on a 350. Calcs seem to indicate I need a 1.7" runner instead of a 1.5" runner to feed a 350 rather than a 305. Calculating out the runner length will put the torque and HP at the rpm ranges where I decide I want it. Shortening the tube runners isn't a big issue. I'll just machine off the oem tubes, open up the flanges and weld in new mandrel bends. To deal with shorter runners, I'll just cut the sides off the OEM plenum and add "filler material" to bring the sides of the plenum down to meet where the runners end. Effectively, I'll be adding to the plenum volume while simultaneously shortening the runners. I'm hoping to end up with runners somewhere around LSx territory (around 12"), but I'll have to see what the formulas spit out. On the plus side, it will look nearly stock and mostly retain the TPI look (which I like, it's period correct).</p><p></p><p>The Last option is to just port out the OEM TPI and try and see if I can source some larger runners. I could make them, but if they are going to be stock lengths, I'd just a soon buy a pair, port match them to the upper/lower and bolt it togther.</p><p></p><p>An aftermarket lower would be nice, but they're no longer made and anything used seems to be asking OH MY GOD! prices.</p><p></p><p><img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite1" alt=":)" title="Smile :)" loading="lazy" data-shortname=":)" /></p></blockquote><p></p>
[QUOTE="Tourmax, post: 175803, member: 5304"] continued from: [URL='https://canadiancorvetteforums.com/threads/about-4-weeks-in-having-some-serious-thoughts-about-modifications.30432/#post-175718']About 4 weeks in, having some serious thoughts about modifications......[/URL] So i'm looking at options to modify the L98. I don't particularly want to take too much away from it on the bottom end to reach an ultimate HP number, so there's going to be compromises somewhere. I'm shooting for around 300-350 at the crank, so my goals are fairly modest. somewhere around stock LT1 numbers. But this is a street car and I want it to stay that way so a high reving screamer is out of the question. No sense making 400 HP if you have to spin it to 6G to get it. that's not where this car will live. Aftermarket stuff like a FAST TPI setup would be great, but I don't really have that kind of money to drop all at once. The FAST system is going to tickle 2G CAD by the time I get it at my door and I'm (IE: bank account) not up for that. I've got a complete LT1 intake: [ATTACH type="full" alt="3.jpg"]31231[/ATTACH] I grabbed it used for 75 bucks. Intake, rails, injectors, etc. Couldn't pass it up at that price. I am considering altering as required (distributor hole, water ports, bolt holes, etc) and using it, but with 3.5" long runners, I'm worried it will adversely effect low end torque production, where the car spends most of it's time. I'm also not thrilled with the thought of using a remote thermostat housing and I don't particularly like the fact that you have to take the water from the heads from either the front of the rear of the heads when the L98 has coolant crossovers in front and back of the L98 TPI lower. Using the HEi distributor also means loosing all the EGR stuff (no room), which doesn't give me that good "no smog" feeling.I live in atlantic Canada and have experienced being the USA's "tailpipe"more than once in the summers and don't wish that crap on anyone. The good news is even if I loose the EGR stuff, I can get it back by using a cam that allows enough overlap to perform the same function as the egr valve (IE: LT4 has no egr valve, all done in cam design). I'm also now considering altering the LT1 rather radically". I'm thinking to chop the front and back off the LT1 intake, take one of the spare TPI lower manifolds I have lying around and chopping the front and back off that. Then, once bolted firmly in a jig, wled the L98 pieces to the LT1 piece. That will give me an LT1 style runner/plenum piece, yet retain the water passage crossovers, the front mounted thermostat hosing and the rear distributor hole. I'd still loose the EGR bits, but again, I can handle that with cam timing. the next option is to "customize" the OEM L98 TPI stuff. I'd take another spare TPI lower I have and port it out as much as possible. Then, after a tedoulsy long set of calculations, decide on a runner length and diameter that will put the power curves where I want them. The OEM runners are about 21" in length (to the intake valve), which is tuned the way GM engineers wanted it. I've also done some quick calcs and the OEM TPI is indeed sized for a 305, so it's leaving something on the table on a 350. Calcs seem to indicate I need a 1.7" runner instead of a 1.5" runner to feed a 350 rather than a 305. Calculating out the runner length will put the torque and HP at the rpm ranges where I decide I want it. Shortening the tube runners isn't a big issue. I'll just machine off the oem tubes, open up the flanges and weld in new mandrel bends. To deal with shorter runners, I'll just cut the sides off the OEM plenum and add "filler material" to bring the sides of the plenum down to meet where the runners end. Effectively, I'll be adding to the plenum volume while simultaneously shortening the runners. I'm hoping to end up with runners somewhere around LSx territory (around 12"), but I'll have to see what the formulas spit out. On the plus side, it will look nearly stock and mostly retain the TPI look (which I like, it's period correct). The Last option is to just port out the OEM TPI and try and see if I can source some larger runners. I could make them, but if they are going to be stock lengths, I'd just a soon buy a pair, port match them to the upper/lower and bolt it togther. An aftermarket lower would be nice, but they're no longer made and anything used seems to be asking OH MY GOD! prices. :) [/QUOTE]
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1988 Convertible for sunny day drives
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