A ? about siamesing L98 base....
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From: Austin Texas
A ? about siamesing L98 base....
I wanted to know if anyone has data on how far down to siamese the runners. I've seen as little as 3/4" up to 1.25" mentioned, but there is a point where you can go too far.
Figured I'd do this while everything is apart and then I can get some empirical data on what it will gain on a "slightly" built L98. :D
Figured I'd do this while everything is apart and then I can get some empirical data on what it will gain on a "slightly" built L98. :D
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From: Portage Mi
Re: A ? about siamesing L98 base.... (Joe90)
Maybe just no solid info. Somebody mentioned in one of the threads that people had more luck siamesing the stock base than the accel and big mouth bases. Don't know if you saw that, but just thought I would mention it.
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From: Santa Ana CA
Re: A ? about siamesing L98 base.... (Joe90)
I dont think you can go too far, but I think you can go too little. After I initially posted my results from this mod a fair amount of people tried it. One in particular, Mike Davis, tried cutting a little at first, then cut out more and got better results. I've figured for a while now that anything less than a couple inches wont do much, its like a window that the air is probably going to pass by with no real effect. The bad spot in the intake base is right in the middle too, so you havent touched that spot with such a short area removed. I cut 5" out of mine first shot, and I am quite happy with the change. Running a fairly decent cam (224/232 .497/.517) and it really woke up on the top end from the change to the intake base. I also ran this base on my 305 TA and it raised the RPM range where power is made at least 500RPM, if not more like 1000.
If youre at all worried about how much to cut though, keep in mind you can always go back in there later and cut more. I'd start with 2" though personally.
If youre at all worried about how much to cut though, keep in mind you can always go back in there later and cut more. I'd start with 2" though personally.
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From: Austin Texas
Re: A ? about siamesing L98 base.... (madmax0)
MadMax,
Did you lose any of the bottom-end torque on the engine when you did it? This is the main concern I have right now. I don't want to lose any, but if it was minimal (say 10-15 lb/ft) to gain some RPM then it would be fine by me.
[Modified by Joe90, 3:03 PM 7/12/2002]
Did you lose any of the bottom-end torque on the engine when you did it? This is the main concern I have right now. I don't want to lose any, but if it was minimal (say 10-15 lb/ft) to gain some RPM then it would be fine by me.
[Modified by Joe90, 3:03 PM 7/12/2002]
5th Gear
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From: Santa Ana CA
Re: A ? about siamesing L98 base.... (Joe90)
I'm sure there was some loss, but IMO nothing worth worrying about. I think low end torque is overrated anyway, just makes it harder to hookup. From 3150RPM up (where the before siamesing dyno results of mine started) I had more torque with the siamesed base. As a wild guess, the stock base probably had more torque at around 2500RPM and down. Take a look here for some more info, in case you havent seen this post:
http://www.thirdgen.org/techbb2/show...threadid=47263
http://www.thirdgen.org/techbb2/show...threadid=47263
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From: Austin Texas
Re: A ? about siamesing L98 base.... (madmax0)
MadMax,
THAT is the kind of information I was looking for!!! Thanks!!!!
From what I could surmise from the links on the 3rd Gen site, I MAY lose up to 20 lb/ft down low (with almost 500 lb/ft on hand, losing 20 won't EXACTLY kill me) but I'll gain about 750 - 1000 RPM of useable HP. What this means is I can stand on it a little longer between the turns without needing to grab the next gear, only to downshift shortly afterwards. It also broadened the torque curve some, made it very flat on some of those dyno graphs.
I just happen to know a few club members who have their own mills at home, and they run on BEER!!!
THAT is the kind of information I was looking for!!! Thanks!!!!
From what I could surmise from the links on the 3rd Gen site, I MAY lose up to 20 lb/ft down low (with almost 500 lb/ft on hand, losing 20 won't EXACTLY kill me) but I'll gain about 750 - 1000 RPM of useable HP. What this means is I can stand on it a little longer between the turns without needing to grab the next gear, only to downshift shortly afterwards. It also broadened the torque curve some, made it very flat on some of those dyno graphs.
I just happen to know a few club members who have their own mills at home, and they run on BEER!!!
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From: Santa Ana CA
Re: A ? about siamesing L98 base.... (Joe90)
Beer mills... those are the best kind!
Yea there is good info on that post. I'm glad I put it there :) Mike Davis' results are better than mine for an engine thats putting down the kinda power its supposed to... I'm still trying to sort out what the deal is with mine. I've done some mods since then though that would skew the results, so if I ever do get it running right, I'll have to swap on a stock base to get a non-siamesed result.
Oh and in case you havent already, read up on Mike Davis' results. He has alot more varied data on it (and other things) than I do. Theres a link to his website on that post somewhere.
[Modified by madmax0, 3:46 AM 7/13/2002]
Yea there is good info on that post. I'm glad I put it there :) Mike Davis' results are better than mine for an engine thats putting down the kinda power its supposed to... I'm still trying to sort out what the deal is with mine. I've done some mods since then though that would skew the results, so if I ever do get it running right, I'll have to swap on a stock base to get a non-siamesed result.
Oh and in case you havent already, read up on Mike Davis' results. He has alot more varied data on it (and other things) than I do. Theres a link to his website on that post somewhere.
[Modified by madmax0, 3:46 AM 7/13/2002]
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Re: A ? about siamesing L98 base.... (Joe90)
Before siamesing an '87 Vette intake base for my '88 I ran a very informative post on http://www.thirdgen.org that included much insight from Madmax.
My first cut only went 1" into the top end of the base runners; I wanted data on progressive cut depths. To date I haven't gotten reliable data for the "after" compare due to other issues. I just had a serious oil leak repaired along with a shift kit and 2,000rpm TC installed so won't have a true "after" data. I also had the shift points raised from 4,800rpm to abouty 5,500rpm to take advantage of the better breathing up top.
Since I have an A4 I can't get any realy low end torque readings from a dyno pull. But like Madmax I agree that there should be some due to the effective shorter runner lengths. Of course if you do an appropriate mod like exhaust, cam or heads you will likely have better than stock low end plus much better top end range.
My purpose was to stay in lower gears longer during a 1/4mi pass to raise trap speed and lower ET.
My first cut only went 1" into the top end of the base runners; I wanted data on progressive cut depths. To date I haven't gotten reliable data for the "after" compare due to other issues. I just had a serious oil leak repaired along with a shift kit and 2,000rpm TC installed so won't have a true "after" data. I also had the shift points raised from 4,800rpm to abouty 5,500rpm to take advantage of the better breathing up top.
Since I have an A4 I can't get any realy low end torque readings from a dyno pull. But like Madmax I agree that there should be some due to the effective shorter runner lengths. Of course if you do an appropriate mod like exhaust, cam or heads you will likely have better than stock low end plus much better top end range.
My purpose was to stay in lower gears longer during a 1/4mi pass to raise trap speed and lower ET.
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Re: A ? about siamesing L98 base.... (65Z01)
Madmax thanks for that link to http://www.thirdgen.org
I recently bought an already ported Plenum, AS&M LT runners and a ported stock base that's all been port matched.
I'm been thinking of siamesing the base and really open it up, but what about my runners? Should I modify them at all or just leave them alone?
Thanks,
Mark
I recently bought an already ported Plenum, AS&M LT runners and a ported stock base that's all been port matched.
I'm been thinking of siamesing the base and really open it up, but what about my runners? Should I modify them at all or just leave them alone?
Thanks,
Mark
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Re: A ? about siamesing L98 base.... (Mr. Magoo)
Hey Mark,
Theres no real gains to be had by sorta siamese the runners themselves by half an inch or less.Those large tubes will be fine as is...Just make sure theyre all round and consistent with the gaskets and etc...
also would not touch them since it should have better re-sale value later if you decide(well,I think you will) to sell them and get the SR or MR someday with more mods and money permits.
:D
Theres no real gains to be had by sorta siamese the runners themselves by half an inch or less.Those large tubes will be fine as is...Just make sure theyre all round and consistent with the gaskets and etc...
also would not touch them since it should have better re-sale value later if you decide(well,I think you will) to sell them and get the SR or MR someday with more mods and money permits.
:D
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Re: A ? about siamesing L98 base.... (Bill's86Coupe)
As I mentioned I have only a 1"x1" cut in my base but it seems to realy have helped top end breathing.
This afternoon I made some passes with the higher shift points; actually they read as 5,200 and 5,600 for the 1-2 and 2-3 shifts. The latter was a little too high but the former could have been a little higher. Try that with a stock TPI intake!
Of course with the 2000rpm TC I blew the tires off during burn off with hardly touching the accelerator.
The next step is to get some dyno pulls with this setup and then open up the siamese holes to 2" deep. I want to push the shift points up to high 5,000s to stay in lower gears longer for better ETs on street tires. So far it seems to be working.
This afternoon I made some passes with the higher shift points; actually they read as 5,200 and 5,600 for the 1-2 and 2-3 shifts. The latter was a little too high but the former could have been a little higher. Try that with a stock TPI intake!
Of course with the 2000rpm TC I blew the tires off during burn off with hardly touching the accelerator.
The next step is to get some dyno pulls with this setup and then open up the siamese holes to 2" deep. I want to push the shift points up to high 5,000s to stay in lower gears longer for better ETs on street tires. So far it seems to be working.
