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Improving the L98

Old 05-12-2018, 12:36 PM
  #61  
aklim
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Originally Posted by DMITTZ View Post
Maybe a accel/lingenfelter Super Ram intake with a cam swap, headers and a tune would accomplish the OP's goals. Should still have lots of low end power and extend the power band at least 1000RPM higher....
It is a good start and not too invasive where concerning an older motor
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Old 05-15-2018, 04:24 PM
  #62  
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Some of you need to have a Coke and a smile. It would be wise to agree to disagree and keep the drama down.
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Old 05-16-2018, 01:59 PM
  #63  
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Originally Posted by Space387 View Post
..... Do you know what the max lift and duration can be run?

Max lift for factory, non-modified 113 casting heads from a mechanical perspective is 0.520" lift.


Max duration is dependent upon ability to tune the combination. My experience is to keep it between 215-225* for the most radical combinations. Drivability and idle quality are sacrificed as duration is increased past 225*.
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Old 05-16-2018, 11:57 PM
  #64  
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Originally Posted by thurman_merman View Post
Oh I agree, that's why I went with a miniram. OP wants more punch on the low end AND more top end, I wanted to point out that you trade low end torque for top end power.
Actually, by ditching the TPI and going with a Miniram or LT1-style intake, you don't lose bottom-end torque. What you lose is the silly mid-rpm torque peak-then-fall-off-a-cliff that starts roughly at 3000rpm. At 1500rpm I don't think there's much if any difference between the two intakes, and at 5000-6000rpm there's a huge difference in favor of the LT1 style. So, if the OP wants a wider torque curve (which is generally a good goal to shoot for), then the short-runner intake is the one to use.

Depending on whether he is rebuilding the bottom end or not, a bonus for ditching the TPI intake is the ability to run more compression ratio since there is no stupid hump in the cylinder pressure (which is where the torque hump comes from). There are all manner of quotes for CR on L98 engines, but I believe they were probably 9.5:1, whereas the LT1 was 10.5:1. That would actually allow a boost in cylinder pressure at all rpm. Also, depending on how much money the OP wants to put into this, he could do a lot better than the stock L98 heads. The Vortecs are better flowing, but the Fast Burn heads are considerably better flowing yet (at all valve lifts, not just high lift) while not losing any low-rpm performance.

cardo, you're just wrong on several things. The TPI intake's main limitation on rpm is caused by its length, not its runner cross section. You even mentioned the Helmholz effect it creates. Again, I think this peaks at around 3200rpm on a stock TPI intake, and that is caused by the resonance happening in phase with the intake valve's opening event. But what happens at an rpm where the resonance is 180* out of phase with the intake valve's opening - i.e., the rpm at which the resonance is now reducing intake pressure rather than increasing it? Yep, the increase in intake pressure now becomes a decrease of equal magnitude, at 50% more rpm than the torque peak. Cylinder pressure (and therefore torque and therefore power) falls off a cliff due to that resonant restriction. And that's exactly why an L98 is all done before 5000rpm. Helmholz theory holds that massively increasing the runner cross section can raise the resonant peak and cliff, which is what the FIRST unit accomplishes. But of course it will also lose something below the peak due to the slower flow velocity of the larger runners. And it won't widen the torque curve: it just moves everything higher, and you still have the unhelpful peak and cliff.

You're also wrong about dual-planes being useful for torque on a port-fuel-injected engine. The key to whether an intake is single- or dual-plane is how many intake valves "see" each throttle blade. If 100% see all the blades, then it's single-plane. If only half the valves see each blade, it's a dual-plane. If only a quarter of the valves see each blade, it would be a four-plane, and if only 1/8 of the valves see each blade (e.g. individual stacks with throttle blades in each), it's an eight-plane intake. Here's a tip: if the throttle body only has one blade, then by definition that intake is a single-plane intake. It can be no other way, because all the runners and valves "see" 100% of the throttle blades (because there's only one blade!). The only way to have a dual-plane intake is to have a two-barrel or four-barrel carb or TB that is physically separated all the way to the blades, such as on that Chevy performance piece you linked. In that setup, each valve can only see 50% of the throttle blades. No divider, no dual-plane. It really is that simple.

So the T-ram, convoluted though it is, is absolutely still a single-plane intake. A tunnel ram - even with its large plenum, and regardless of how many carbs/TBs sit on top of it - is still typically a single-plane intake. You could put a divider in the plenum and make it a dual-plane or even a four-plane, but I don't know why anyone would do that. All factory port-FI intakes I know of are single-plane, with the only exception being the very few that have individual stacks and throttles for each cylinder (E30 M3 comes to mind, but there haven't been many). There just aren't compelling reasons to make things more complicated.

That Chevy performance piece you linked is surely intended to be used mainly with nitrous injectors in the bosses, not fuel injectors. There are multiple reasons it would be kind of silly to use it as an EFI intake. Not the least of those reasons is the four-barrel throttle body that would be required. Surely GM intends this mainly for those that want to use a carb on an LS engine? I know some very, very highly placed LS builders, and they wouldn't use this intake for EFI on a dare. Using a dual-plane carb intake converted to EFI on an L98 to increase "torque" would just be dumb.
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Old 05-17-2018, 12:34 AM
  #65  
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Originally Posted by MatthewMiller View Post
Actually, by ditching the TPI and going with a Miniram or LT1-style intake, you don't lose bottom-end torque. What you lose is the silly mid-rpm torque peak-then-fall-off-a-cliff that starts roughly at 3000rpm. At 1500rpm I don't think there's much if any difference between the two intakes, and at 5000-6000rpm there's a huge difference in favor of the LT1 style. So, if the OP wants a wider torque curve (which is generally a good goal to shoot for), then the short-runner intake is the one to use.

Depending on whether he is rebuilding the bottom end or not, a bonus for ditching the TPI intake is the ability to run more compression ratio since there is no stupid hump in the cylinder pressure (which is where the torque hump comes from). There are all manner of quotes for CR on L98 engines, but I believe they were probably 9.5:1, whereas the LT1 was 10.5:1. That would actually allow a boost in cylinder pressure at all rpm. Also, depending on how much money the OP wants to put into this, he could do a lot better than the stock L98 heads. The Vortecs are better flowing, but the Fast Burn heads are considerably better flowing yet (at all valve lifts, not just high lift) while not losing any low-rpm performance.
I just want to make sure I'm on the same page, you are referring to the dynamic ( running) compression ratio correct? Where the 10.5:1 of the LT1 is the static? I have dabbled into this but I always over look the dynamic when thinking of bumping compression. At the moment I am not planning to tear down the engine for a while, unless I find a reason If so I will surely go for this intake and look to a higher CR. I will dig into the specks on head options and pare them with what intakes make the most sense.

The long term goal for this car is to have fun and travel in it. So a little wider power band sounds good, reasonable drivability and maintain the same or at least similar fuel consumption. I know the last one is very directly tied to my driving.
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Old 05-17-2018, 09:35 AM
  #66  
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Originally Posted by Space387 View Post
I just want to make sure I'm on the same page, you are referring to the dynamic ( running) compression ratio correct? Where the 10.5:1 of the LT1 is the static? I have dabbled into this but I always over look the dynamic when thinking of bumping compression. At the moment I am not planning to tear down the engine for a while, unless I find a reason If so I will surely go for this intake and look to a higher CR.
No, I was strictly talking about raising the static CR if you go with a short-runner intake. I wasn't sure if you were planning to rebuild the long block or not. If not, this gets harder to do. And in fact, if your current heads are the later 58cc version, you could even accidentally decrease your CR if you change to other heads (most of which will have larger chambers). I don't know how much can safely be milled off the decks of your current heads, but maybe doing that plus using a thinner gasket could gain you a bit of CR.

The long term goal for this car is to have fun and travel in it. So a little wider power band sounds good, reasonable drivability and maintain the same or at least similar fuel consumption. I know the last one is very directly tied to my driving.
Those are all reasonable goals. I'm a fan of wide powerbands (i.e., flat torque curves), especially for street driving and autocrossing, which is mostly what I do. The short-runner intake is your easiest route to getting that. By itself it won't improve mileage, but it won't hurt it either. Improving efficiency from this would come from an increase in CR, or a change in cams - basically anything you can do to increase cylinder pressures at cruising rpms (so this isn't about peak torque, but rather your torque at teeny throttle openings and low rpms). What you mainly will change with just the intake is that you'll eliminate that cliff your TPI setup falls off of at higher rpms.
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Old 05-17-2018, 01:17 PM
  #67  
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From what I could find is that I should have the 58cc heads and the only option for a smaller chamber is the LT1 aluminum heads at 54cc. I would like to go this route, if its not too much for the engine, after refreshing the lower end to get the most life out of these changes. I guess I will have to wait until I get the engine apart to measure the deck clearance and see how much of a change in compression I am actually going to. I tried looking for measurements and it seems that most everyone is getting different numbers.

If my sources are right by reverse engineering the sizes based on assumed/ known values:
Stock is 10.25 for my 1990 engine with 7cc in reliefs on the flat top pistons. I am fairly sure these are the same ones used on the F-body LT1 engine. Working from an assumed .040 compressed thickness gasket at 4.01 diameter yields a deck clearance of 0.02". If you carry these values to using LT1 heads on a stock gasket puts the engine at about 10.7:1 and if I run the same thickness 0.026 gasket I have on my LT1 now it puts me at about 11.2:1. I run 92/93 octane only so with some conservative tuning I don't foresee a huge challenge avoiding knock. The more I play with the numbers the more I like where this is going.

Last edited by Space387; 05-17-2018 at 01:37 PM.
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Old 05-17-2018, 02:27 PM
  #68  
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If you want accurate volume numbers you need to measure them yourself using liquid. Published numbers have never been reliable or accurate enough for me. And it's good experience once you do it enough to get repeatable results. May take several tries but a good skill worth learning.
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