L-98 valvetrain questions
Corvette Enthusiast
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From: So. Cal.
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Educate me on roller rockers. I know what they are. I have had them on my 396 for 15 years. Back then they just called them roller rockers.
So what does ths 1.6 or 1.5 mean?
Thanks
Mike
So what does ths 1.6 or 1.5 mean?
Thanks
Mike
Burning Brakes
Joined: Feb 2010
Posts: 1,013
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From: California City Ca
Mike
Ratio the 1.5 are stock raito on SBC the 1.6 give you .030 more lift.
I was looking to replace mine on my build after i Purchased my 1.5 R/R arms.
On the intake side ONLY to pick up some topend H/P numbers and leave the Ex side 1.5 so I will not lose any low end power.
But for the cost $150.00 or so to gain 3 H/P not worth the money for me.
I did the figuring on a online dyno to see if spending the extra cash to change them out I can't see it.
But if you'r planning to just replace the stock stamped steels any way mite as well I already have the ones I purchased duing the Build.
And on the stock heads I read you need to open up the push rod though holes going though the heads or they will bind up and bend the push rods.
Also you mite have to change the push rod lenghts for the 1.6 rocker arms.
But what I read it harder on the cam and valve seats you mite need higher valve spring rate.
Higher vavle spring rate hard to open the vavle and slams the valve closed harder on the vavle seats puts more pressure on the liffters push rods and cam makes them wear faster.
Ratio the 1.5 are stock raito on SBC the 1.6 give you .030 more lift.
I was looking to replace mine on my build after i Purchased my 1.5 R/R arms.
On the intake side ONLY to pick up some topend H/P numbers and leave the Ex side 1.5 so I will not lose any low end power.
But for the cost $150.00 or so to gain 3 H/P not worth the money for me.
I did the figuring on a online dyno to see if spending the extra cash to change them out I can't see it.
But if you'r planning to just replace the stock stamped steels any way mite as well I already have the ones I purchased duing the Build.
And on the stock heads I read you need to open up the push rod though holes going though the heads or they will bind up and bend the push rods.
Also you mite have to change the push rod lenghts for the 1.6 rocker arms.
But what I read it harder on the cam and valve seats you mite need higher valve spring rate.
Higher vavle spring rate hard to open the vavle and slams the valve closed harder on the vavle seats puts more pressure on the liffters push rods and cam makes them wear faster.
Thread Starter
Le Mans Master
Joined: Nov 2009
Posts: 6,882
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From: Bangkok, Thailand
Be sure to use the correct "flexplate" that belongs on the L-98 engine. From the factory, they were externally balanced on the tail of the crank. If it comes with the engine, no worrries. It will have the correct bolt pattern for your converter. If you buy an aftermarket flexplate, be sure it is the correct factory replacement in regards to balance, and it should have dual bolt patterns for the converter to bolt up.
Why are you trying to drop compression? Compression (to a point) is all good. Good for power, and good for emissions. If it were mine, I would put as thinner head gasket, if anything. This raises compression, and improves quench, all in a positive, efficient way.
Why are you trying to drop compression? Compression (to a point) is all good. Good for power, and good for emissions. If it were mine, I would put as thinner head gasket, if anything. This raises compression, and improves quench, all in a positive, efficient way.
My concern would be having knock issues with too much CR, a relatively small cam, an automatic, etc. and using the stock computer - even with a DCS chip. I'd rather drop it a little bit (9.5:1 should be fine I think) and have the timing right than have to back it off or figure out a custom tune to avoid knock.
Last edited by mcm95403; Oct 25, 2010 at 12:29 AM.
Race Director
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Hi Pete,
My concern would be having knock issues with too much CR, a reltively small cam, an automatic, etc. and using the stock computer - even with a DCS chip. I'd rather drop it a little bit (9.5:1) should be fine I think) and have the timing right than have to back it off or figure out a custom tune to avoid knock.
My concern would be having knock issues with too much CR, a reltively small cam, an automatic, etc. and using the stock computer - even with a DCS chip. I'd rather drop it a little bit (9.5:1) should be fine I think) and have the timing right than have to back it off or figure out a custom tune to avoid knock.
Besides, L-98 engines with 113 heads run a .051 gasket. I am not aware of any thicker gaskets out there.
Le Mans Master
Joined: Feb 2000
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From: Kempner Texas
I wonder if a couple of you guys realize that the use of words like "tiny" and "wimpy" carries with them a negative connotation. Also, to me, the use of those kinds of words perpetuates the "bigger is better" problem so many guys have when selecting a cam.
It's also what the cam tech gurus are referring to in their interviews when they say things like "The biggest problems we find is when the caller orders a cam with too much duration and then calls back, dissatisfied with how it performs in the engine" - and words to that effect.
A short duration cam is simply that, a short duration cam. I don't feel they should be referred to negatively or "put-down" simply because they have a short duration and/or low valve lift, that is unless you actually want the guy to buy the wrong cam for his application.
It's what's best for the application and what the user wants that really matters.
Just my view.
Jake
It's also what the cam tech gurus are referring to in their interviews when they say things like "The biggest problems we find is when the caller orders a cam with too much duration and then calls back, dissatisfied with how it performs in the engine" - and words to that effect.
A short duration cam is simply that, a short duration cam. I don't feel they should be referred to negatively or "put-down" simply because they have a short duration and/or low valve lift, that is unless you actually want the guy to buy the wrong cam for his application.
It's what's best for the application and what the user wants that really matters.
Just my view.
Jake
Thread Starter
Le Mans Master
Joined: Nov 2009
Posts: 6,882
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From: Bangkok, Thailand
I wonder if a couple of you guys realize that the use of words like "tiny" and "wimpy" carries with them a negative connotation. Also, to me, the use of those kinds of words perpetuates the "bigger is better" problem so many guys have when selecting a cam.
It's also what the cam tech gurus are referring to in their interviews when they say things like "The biggest problems we find is when the caller orders a cam with too much duration and then calls back, dissatisfied with how it performs in the engine" - and words to that effect.
A short duration cam is simply that, a short duration cam. I don't feel they should be referred to negatively or "put-down" simply because they have a short duration and/or low valve lift, that is unless you actually want the guy to buy the wrong cam for his application.
It's what's best for the application and what the user wants that really matters.
Just my view.
Jake
It's also what the cam tech gurus are referring to in their interviews when they say things like "The biggest problems we find is when the caller orders a cam with too much duration and then calls back, dissatisfied with how it performs in the engine" - and words to that effect.
A short duration cam is simply that, a short duration cam. I don't feel they should be referred to negatively or "put-down" simply because they have a short duration and/or low valve lift, that is unless you actually want the guy to buy the wrong cam for his application.
It's what's best for the application and what the user wants that really matters.
Just my view.
Jake
And in my case it's also an apples to oranges comparision since the hydraulic roller cam lobes are much more rounded than the early flat-tappet style lobes. Kind of like the difference between a V and a U. So the roller has a lot more effective duration than the non-roller even though they are both almost the same at .050"
Le Mans Master
Joined: Aug 2000
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From: Australia
" the stock wimpy cam designed for the restrictive CFI intake"
OP has changed intake and stock cam is now not " optimum" for new combo
Race Director
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It would also be fine (better) if you took Pete's advice and dropped to a thinner head gasket. Even 10:1 is not high if you quench it right. People with larger cams land in the 11:1 and higher range.
Learn about quench and DCR. You'll get some nice info out of it.
Learn about quench and DCR. You'll get some nice info out of it.
Le Mans Master
Joined: Aug 2000
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From: Australia
Thread Starter
Le Mans Master
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From: Bangkok, Thailand
Yes, but the more CR you have, the more the emmissions go up - NOx I think - and since I have to deal with CA smog, the 9.5:1 should be plenty.
I do understand about quench, etc. but I'm also limited by smog rules and requirements, the need to stick with the stock computer which is a very early version and not nearly as capable as the later ones, etc.
Remember, I'm not going for anything wild, just a solid L-98 with the LT-1 cam and the Renegade. If I get into the 275-300 HP level at the crank, I'll be a very happy camper.
I do understand about quench, etc. but I'm also limited by smog rules and requirements, the need to stick with the stock computer which is a very early version and not nearly as capable as the later ones, etc.
Remember, I'm not going for anything wild, just a solid L-98 with the LT-1 cam and the Renegade. If I get into the 275-300 HP level at the crank, I'll be a very happy camper.
Drifting
Joined: Nov 2009
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From: Perth Western Australia
St. Jude Donor '10
Something doesn't add up with me.
If my 87 has the same volume 58 cc heads as a 90 yet my 87 has dished pistons and the 90 has flat pistons, how could both engines have a compression ratio of 9.5?
PS: The deck height may be higher in the 90 than the 87.
If my 87 has the same volume 58 cc heads as a 90 yet my 87 has dished pistons and the 90 has flat pistons, how could both engines have a compression ratio of 9.5?
PS: The deck height may be higher in the 90 than the 87.
Last edited by Lemme; Oct 26, 2010 at 07:10 AM.
Le Mans Master
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From: Houston Texas
I donno either it is listed the same from 87 to 90 9.5:1 jumps tp 10:1 for 91.
Instructor
Joined: May 2008
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From: Midland Texas
On my 113 heads from a 90 L98 the valve retainer was hitting the valve seal at .48 valve lift so I bought a valve boss tool from Comp cams that removed the valve boss and resized it for the comps cam valve seal as well as far as your springs? I used beehive I can't tell you anything on that.
Race Director
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From: WI
More compression/better quench also relates to increased MPG. Even if all these mods made emissions worse, you will still pass. The combo is pretty close to stock, stock setups pass with numbers so low that there is a ton of room. You don't need narrow body rockers unless you're not willing to check clearance. Minor grinding of the center bolt bosses may be required.
Le Mans Master
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Last edited by engle1147; Oct 26, 2010 at 03:49 PM. Reason: 1990 was still 9.5 : 1 CR
Le Mans Master
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In '90 they went to the "flat" top pistons (.5 increase in CR) instead of the "dished" ones in the years just prior. Below is pic of 2 pistons a "used/beat to death" stock '89 (dished) and a new (flat top) '90 style pistion. With aluminum heads - keep the CR @ or under 11:1 and you'll be fine filling up at the pumps.
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BTW: IIRC, my 89 had something like 9.3:1 compression with a low 7.9:1 DCR. (I calculated it once using an SCR/DCR calculator). I think they rounded UP to 9.5:1 SCR. Also, the DCR is so low, there's plenty of room to raise compression with a head gasket w/o running into any operational issues.
Last edited by GREGGPENN; Oct 26, 2010 at 01:56 PM.