.
L98 Heads
Le Mans Master
Joined: Jun 2004
Posts: 6,231
Likes: 65
From: Seattle WA
St. Jude Donor '14
If you don't need it right away, I'm going to do a FAQ on doing this as part of a general top FAQ. Otherwise I'll send via PM to keep from going OT - just let me know 
I have to admit that the numbers aren't adding up from my perspective
I would tend towards making another choice; the L98 heads really aren't great from a flow perspective, and all this monkey business seems like a lot of work and expense to make something work vs. picking the right parts for the application.I'm not a big fan of using DCR as an offset to a too-high SCR; from my perspective this is a racing design approach that doesn't work well on a street-driven engine as in the end it's a "too big" cam to bleed off CR at low RPM. It does work, but at the cost of low-speed throttle response and fuel economy.
But...I'm a pretty conservative guy and virtually all of my builds are < 1.2 HP/CID
Thread Starter
Safety Car
Joined: Mar 2009
Posts: 3,558
Likes: 4
From: Oakland California
Well just checked duration numbers on the factory L82 cam. Came up with
312/312 advertised duration
222/222 duration @ .50.
450/460 lift
114 LSA.
This might just work as 312 advertised is really huge and the dcr is based on the intake closing point that is obtained from the advertised duration. Factory slow ramp just might make it work. Would need to do a little more research.
312/312 advertised duration
222/222 duration @ .50.
450/460 lift
114 LSA.
This might just work as 312 advertised is really huge and the dcr is based on the intake closing point that is obtained from the advertised duration. Factory slow ramp just might make it work. Would need to do a little more research.
http://www.jegs.com/i/JEGS-Performan...ductId=1215318
Is there a cam(flatt tappet hydraulic) that will work?
Drifting
Joined: May 2005
Posts: 1,258
Likes: 38
From: springtown Texas
Intake Exhaust
Advertised Duration 292° 302°
Duration @ .050" 234° 244°
Valve Lift w/ 1.5 Rocker Arms 0.488 0.510
Valve Lift @ Cam 0.325 0.340
Max Lift Angle 109° 119°
Lobe Separation 114°
Cam Timing @ .050" - Opens 8° ATDC 61° BBDC
Cam Timing @ .050" - Closes 46° ABDC 3° BTDC
thats alot of duration. do you have a stall convertor. @2000-2500 would work. that cam also has a wide seperation which builds cylinder pressure.
my motor has 11.1:1 comp. but my cam has 107 seperation. lots of overlap. maybe it helps bleed of some cylinder pressure. and my my cam is alot smaller. 227/241@.050 with @ the same lift as that one. the l98 heads don't flow that well after .500 lift. not much gain going past that.
billa would know more about this, but you can advance or retard the cam to increase or decrease cylinder pressure. i don't know if i would go with that cam. and 64 or larger heads might be a better choice if you can't get 93 gas there.
Advertised Duration 292° 302°
Duration @ .050" 234° 244°
Valve Lift w/ 1.5 Rocker Arms 0.488 0.510
Valve Lift @ Cam 0.325 0.340
Max Lift Angle 109° 119°
Lobe Separation 114°
Cam Timing @ .050" - Opens 8° ATDC 61° BBDC
Cam Timing @ .050" - Closes 46° ABDC 3° BTDC
thats alot of duration. do you have a stall convertor. @2000-2500 would work. that cam also has a wide seperation which builds cylinder pressure.
my motor has 11.1:1 comp. but my cam has 107 seperation. lots of overlap. maybe it helps bleed of some cylinder pressure. and my my cam is alot smaller. 227/241@.050 with @ the same lift as that one. the l98 heads don't flow that well after .500 lift. not much gain going past that.
billa would know more about this, but you can advance or retard the cam to increase or decrease cylinder pressure. i don't know if i would go with that cam. and 64 or larger heads might be a better choice if you can't get 93 gas there.
Thread Starter
Safety Car
Joined: Mar 2009
Posts: 3,558
Likes: 4
From: Oakland California
It's a manual transmission. I'm going to give these heads a try. I see people here running them on their motors with a similar setup. I just don't have the budget for any other aluminum heads.
Instructor
Joined: Nov 2011
Posts: 183
Likes: 0
polish the combustion chambers and round the edges off it will reduces detonation youll be around 10.1 but alum heads let heat out quickly so 91 should be ok if carbs tuned correctlty going with a better cam would be good one with split duration i like the luniti voodoo cams if u dont wanna do the cam swap 1.6 rockers would be good to do it will in crease your lift by .30
Race Director
Joined: May 2005
Posts: 10,674
Likes: 122
From: Millington Illinois
St. Jude Donor '08-'09
I have to admit that the numbers aren't adding up from my perspective I would tend towards making another choice; the L98 heads really aren't great from a flow perspective, and all this monkey business seems like a lot of work and expense to make something work vs. picking the right parts for the application.
I'm not a big fan of using DCR as an offset to a too-high SCR; from my perspective this is a racing design approach that doesn't work well on a street-driven engine as in the end it's a "too big" cam to bleed off CR at low RPM. It does work, but at the cost of low-speed throttle response and fuel economy.
I would tend towards making another choice; the L98 heads really aren't great from a flow perspective, and all this monkey business seems like a lot of work and expense to make something work vs. picking the right parts for the application.I'm not a big fan of using DCR as an offset to a too-high SCR; from my perspective this is a racing design approach that doesn't work well on a street-driven engine as in the end it's a "too big" cam to bleed off CR at low RPM. It does work, but at the cost of low-speed throttle response and fuel economy.
It might work but I would look to a bigger chamber head. I don't see a lot of upside for the work and hastle and a good chance you could have detonation issues. Not much power gain and could actually lose power if you have to dial your timing back to avoid detonation once it is together.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
2027 Corvette vs The World: Every C8 vs Its Closest Competitor
Joe Kucinski
10 Most Common Corvette Problems of the Last 20 Years!
Joe Kucinski
5 MOST and 5 LEAST Popular Corvette Model Years in History!
Joe Kucinski
2027 Corvette Buyer's Guide: Everything You Need to Know!
Joe Kucinski
Le Mans Master
Joined: Oct 2002
Posts: 7,098
Likes: 378
From: Las Vegas - Just stop perpetuating myths please.
I never found reliable piston volume numbers for my crate 350".
I looked all over but nothing seemed match the pistons in my "Hecho in Mexico" crate GEN I motor. And i even tried to measure piston volume with short block in the car - lost the seal every try. But heck of coarse if u have the engine out of the car then measure the piston volume.
I think your easiest measurement would be compression. It should be something like 160psi or less while cold for a stock L82. Once u install the L98 head u could test compression again and anything less than 200psi cold will work on 91 pump gas, maybe even 210psi.
Just one caution is u need a smoother deck finish on the block for aluminum heads. Some thing like Ra 25-30 where iron heads need more like 50-60 Ra finish on the block deck surface. This allows the alum heads to slide around more due to the greater expansion and contraction rates. The GEN I sb motors came with some pretty rough looking decks. U can search here on the forum to find others running the L98 head having gasket leaks.
Hope this helps,
cardo0
I think your easiest measurement would be compression. It should be something like 160psi or less while cold for a stock L82. Once u install the L98 head u could test compression again and anything less than 200psi cold will work on 91 pump gas, maybe even 210psi.
Just one caution is u need a smoother deck finish on the block for aluminum heads. Some thing like Ra 25-30 where iron heads need more like 50-60 Ra finish on the block deck surface. This allows the alum heads to slide around more due to the greater expansion and contraction rates. The GEN I sb motors came with some pretty rough looking decks. U can search here on the forum to find others running the L98 head having gasket leaks.
Hope this helps,
cardo0
Le Mans Master
Joined: Jun 2004
Posts: 6,231
Likes: 65
From: Seattle WA
St. Jude Donor '14
Just one caution is u need a smoother deck finish on the block for aluminum heads. Some thing like Ra 25-30 where iron heads need more like 50-60 Ra finish on the block deck surface. This allows the alum heads to slide around more due to the greater expansion and contraction rates. The GEN I sb motors came with some pretty rough looking decks.
Thread Starter
Safety Car
Joined: Mar 2009
Posts: 3,558
Likes: 4
From: Oakland California
Umm...did you try to cc the bore with the engine in the car, i.e. plexi plate, etc.?
This isn't really about the heads, but the gaskets - steel shim gaskets commonly used with aluminum heads require a very smooth deck. This isn't really an issue any more now that we have the rubber-coated Multi-Layer Steel (MLS) gaskets from Fel-Pro and Cometic. They're not cheap, but they'll seal on just about any deck
This isn't really about the heads, but the gaskets - steel shim gaskets commonly used with aluminum heads require a very smooth deck. This isn't really an issue any more now that we have the rubber-coated Multi-Layer Steel (MLS) gaskets from Fel-Pro and Cometic. They're not cheap, but they'll seal on just about any deck
Le Mans Master
Joined: Jun 2004
Posts: 6,231
Likes: 65
From: Seattle WA
St. Jude Donor '14
The thicker the gasket the more options you have...and the less you'll pay for the gasket.
Any P/N would be specific to compressed thickness
Here's a PDF link to the marketing sheet for the Fel-Pro:
http://www.jegs.com/PDFs/375mls.pdf
And the FAQ for Cometic:
http://www.cometic.com/faq.aspx
Le Mans Master
Joined: Oct 2002
Posts: 7,098
Likes: 378
From: Las Vegas - Just stop perpetuating myths please.
Umm...did you try to cc the bore with the engine in the car, i.e. plexi plate, etc.?
That is a YES. How did u do it with the engine in the car??? Do u have anything useful to say here that would help the OP measure/cc his??? Just curious.
This isn't really about the heads, but the gaskets - steel shim gaskets commonly used with aluminum heads require a very smooth deck. This isn't really an issue any more now that we have the rubber-coated Multi-Layer Steel (MLS) gaskets from Fel-Pro and Cometic. They're not cheap, but they'll seal on just about any deck
That is a YES. How did u do it with the engine in the car??? Do u have anything useful to say here that would help the OP measure/cc his??? Just curious.
This isn't really about the heads, but the gaskets - steel shim gaskets commonly used with aluminum heads require a very smooth deck. This isn't really an issue any more now that we have the rubber-coated Multi-Layer Steel (MLS) gaskets from Fel-Pro and Cometic. They're not cheap, but they'll seal on just about any deck
cardo0
Le Mans Master
Joined: Jun 2004
Posts: 6,231
Likes: 65
From: Seattle WA
St. Jude Donor '14
My facts are just fine; as an example from the Cometic link I posted above:What surface finish is required to us an MLS head gasket?
A surface finish of 50 RA...
These gaskets are specifically intended to offer the benefits of a steel shim gasket while sealing to a stock-type finish on the block and head deck - hence the rubber-coated MLS.
Last edited by billla; Jan 15, 2012 at 11:29 PM.
Le Mans Master
Joined: Aug 2008
Posts: 5,578
Likes: 61
From: Austin TX
I also seem to remember the combustion chamber having some sort of square obtrusion right on the edge of the chamber. My porter/machinist had no idea what it was there for, but we decided to leave it. The car ran great otherwise.
Le Mans Master
Joined: Jun 2004
Posts: 6,231
Likes: 65
From: Seattle WA
St. Jude Donor '14
Le Mans Master
Joined: Oct 2002
Posts: 7,098
Likes: 378
From: Las Vegas - Just stop perpetuating myths please.
Graphite better than MLS for this.
That's good advice My facts are just fine; as an example from the Cometic link I posted above:
What surface finish is required to us an MLS head gasket?
A surface finish of 50 RA...
These gaskets are specifically intended to offer the benefits of a steel shim gasket while sealing to a stock-type finish on the block and head deck - hence the rubber-coated MLS.
My facts are just fine; as an example from the Cometic link I posted above:What surface finish is required to us an MLS head gasket?
A surface finish of 50 RA...
These gaskets are specifically intended to offer the benefits of a steel shim gasket while sealing to a stock-type finish on the block and head deck - hence the rubber-coated MLS.
I don't know how you can recommened aluminum heads on a stock '74 deck surface.
Let me try this one more time. Max roughness for a FelPro MLS is 60 Ra. Stock '74 blocks are decked for iron heads with a surface greater than 60 Ra.
Try it for yourself and let us know but to recommend that for someone else is a brainless set-up.
Unless your trying to ruin someones elses build - then it would be very deceiving.
cardo0
