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Would L98 alum heads be good upgrades for an 82 Xfire?

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Would L98 alum heads be good upgrades for an 82 Xfire?

 
Old 05-24-2019, 08:29 AM
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Fast81
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Default Would L98 alum heads be good upgrades for an 82 Xfire?

Local set for sale for ~$300

Only hesitation would be their 58cc chambers putting compression up near 9.8. could the stock CPU handle the extra CR? would the stock cam be too small ?

Thanks
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Old 05-24-2019, 09:15 AM
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Good questions ... best left to Xfire guys ... not me.

If in good shape, those seem a good value.

But ... do those heads come with their self-guided/aligning rocker arms & centerbolt valve covers w/ vc bolts?

Last edited by jackson; 05-24-2019 at 09:34 AM.
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Old 05-24-2019, 10:23 AM
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Originally Posted by jackson View Post
Good questions ... best left to Xfire guys ... not me.

If in good shape, those seem a good value.

But ... do those heads come with their self-guided/aligning rocker arms & centerbolt valve covers w/ vc bolts?
If they’re complete with good guides that’s a good value. I don’t think they had self aligning rockers... the pair I just sold had ‘guide plates’. IDK just googled it and couldn’t find a quick definitive answer.

Last edited by jim2527; 05-24-2019 at 10:29 AM.
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Old 05-24-2019, 11:45 AM
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Originally Posted by Fast81 View Post
Local set for sale for ~$300

Only hesitation would be their 58cc chambers putting compression up near 9.8. could the stock CPU handle the extra CR? would the stock cam be too small ?

Thanks
They would put your CR around 11:1. If they are stock it will take another $300 or so to get them useable. You would be better off saving some money up for a good set of aftermarket heads like AFR or RHS.
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Old 05-24-2019, 11:49 AM
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Check out your local machine shops, sometimes they have gone through or ported heads for similar or not much more. Buying used heads is a huge gamble you never know what youre getting.
Taken the grinder to many heads and the owners knowingly skipped over the guides, proper valve job due to cheaping out....which means youll have to do all of it to make things right.
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Old 05-24-2019, 10:01 PM
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But if a XFire guy got his hands on a good pair, would they work ?
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Old 05-24-2019, 11:50 PM
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If the last three digits are 128, the head spec would be IN.1.94/EX. 1.56 valve size with a 58cc chamber. I also think those were the base heads for the ZZ4 same spec as 113 heads.

I think those runners are 163/165cc, but not 100% sure on that. Are we talking about a bone stock CFI motor or one that has been modded? If modded, what mods? OR are you just asking if they would work period? A 58cc chamber IMO would be too much on that motor if stock and 64/65cc would be a much better choice. Stock CR is 9:1.

A 170cc runner would be a better choice for a stock motor with a 64/65cc chamber, but NOT with the stock intake, it would kill any gains with those heads. A higher lift cam around the upper 400s around .488 or so would also be a better choice with using the stock ECM, but keep the duration closer to stock, if you stray too far, you WILL have issues with a stock ECM. This is just my opinion and I'm sure others will have different ones.

Last edited by Buccaneer; 05-24-2019 at 11:51 PM.
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Old 05-25-2019, 12:02 AM
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Originally Posted by Buccaneer View Post
If the last three digits are 128, the head spec would be IN.1.94/EX. 1.56 valve size with a 58cc chamber. I also think those were the base heads for the ZZ4 same spec as 113 heads.

I think those runners are 163/165cc, but not 100% sure on that. Are we talking about a bone stock CFI motor or one that has been modded? If modded, what mods? OR are you just asking if they would work period? A 58cc chamber IMO would be too much on that motor if stock and 64/65cc would be a much better choice. Stock CR is 9:1.

A 170cc runner would be a better choice for a stock motor with a 64/65cc chamber, but NOT with the stock intake, it would kill any gains with those heads. A higher lift cam around the upper 400s around .488 or so would also be a better choice with using the stock ECM, but keep the duration closer to stock, if you stray too far, you WILL have issues with a stock ECM. This is just my opinion and I'm sure others will have different ones.
Aren't you the only one here with a highly modded xfire? Pretty sure that makes you more of an xpert than anyone without.
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Old 05-25-2019, 09:46 AM
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Default Guide Plates: when they're not

My understanding --- L98/ZZ4 OE "guide plates" exist as solely an OE assembly aide to help locate the PR during OE motor assembly process ...
... their guides' fingers are not tight enough to be a real PR guide ... the heads' casting does not have an alignment hole that's tight enough either ... hence self-align rockers.

Those heads need one or the other ... real guideplates ... or ... self-align rockers ... but never both together.

perhaps 1'st year head production may be an exception ... use your eyes & your noggin.

Note: GM states do Not use self-align rockers with solid lifters.

Note: GM states do Not use guideplates with self-align rockers.

Years ago, bought a used set of ZZ4 (L98) heads from a lightly-used ZZ4 ... just as I expected, they were in great shape! But, project didn't materialize: I sold 'em ...
... and, just as I told him, the third-hand buyer got a great set of heads too. Almost as-new, perfect, ready-to-run.
Another time, bought a pair of filthy Vortecs. I broke 'em down, cleaned 'em up and checked 'em. One was cracked across seats ...
... Local seller worked with me and continued giving me heads (total of 6) until I had a good pair. Two out of three were junk. ...
... Took a bit of work but I was ok with the deal. Would do same again.

There's both sugar & sh7t out there ... use your noggin to figure out just how to check & how to trust etc ...
... or, if you ain't got the chops, just buy new stuff ...me and Lamonte 'll take those deals.

y'all have a happy & safe holiday ... please Remember who & how & why it's their day of decoration.
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Old 05-25-2019, 10:58 AM
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Were L98 heads from all model years the same? 1984 thru 1986 show 9.0:1 compression. 1987 thru 1990 show 9.5:1 compression. 1991 shows 10.0 compression. Don't know if the differences are all in the heads or are a combination of heads and pistons. You need to research WELL to get what you need.
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Old 05-25-2019, 11:53 AM
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Originally Posted by Kacyc3 View Post
Aren't you the only one here with a highly modded xfire? Pretty sure that makes you more of an xpert than anyone without.
Well, I'm not the only one that has a modded CF, but I only know of one other CF motor that is naturally aspirated twin TBs that is faster than mine and he is in Australia... Ben73 with a 84. There could be others, just don't know of any and I have been working with CFI specifically for 26 years now.
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Old 05-25-2019, 12:24 PM
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I'll just leave this right here. From 2012 testing with NOS.
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Old 05-25-2019, 12:37 PM
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Originally Posted by 7T1vette View Post
Were L98 heads from all model years the same? 1984 thru 1986 show 9.0:1 compression. 1987 thru 1990 show 9.5:1 compression. 1991 shows 10.0 compression. Don't know if the differences are all in the heads or are a combination of heads and pistons. You need to research WELL to get what you need.
Xfire or not ... other motors you see similar stated CR differences with one head ... likely chalk that up to different piston dome volume / compression height / gasket thickness.
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Old 05-25-2019, 02:51 PM
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Originally Posted by Fast81 View Post
Local set for sale for ~$300

Only hesitation would be their 58cc chambers putting compression up near 9.8. could the stock CPU handle the extra CR? would the stock cam be too small ?

Thanks
Well IMHO a head inspection and overhaul would be required and even new heads need an inspection with possibly a re-assembly due to lack of quality control in less expensive heads. But the L98 head only lacks in flow on the intake side that will respond to pocket porting so before using L98 heads I would overhaul with a valve job, pocket port and new springs with a surface shave to clean it.

So what size head chambers do you have now? I found 74cc chambers. So 74/58 = 1.28. Or rather 58/74 = 0.78. C.r. = 9.0 = (static volume + swept volume)/static volume. So static vol = vol head chamber + vol above piston.

[(74cc + above piston volume) + swept volume]/(74cc + above piston volume)= 9.0

(74cc+above piston vol+swept vol)=9.0(74cc+above piston vol)

swept vol = [(4/2)x(4/2)] x π x 3.48 = 43.73

Hmm! (74cc + above piston vol + 43.73) /(74cc + above piston vo) = 9.0cr

74cc = 4.52ci and 58cc = 3.54ci

4.52ci+ above piston vol + 43.73 = 9.0 x 4.52ci + 9.0 x above piston vol

43.73 = 40.68 + 8 x above piston vol

(43.73-40.68)x8 = above piston vol = 24.4

58cc+24.4 +43.73]/58cc+24.4 = cr = (3.54ci+24.4+43.73)/(3.54+24.4) = 2.57 which doesn't make sense so I have a math error somewhere - but don't have the time to find it.

Anyways the static compression ratio has to increase something less than 74/58 x 9.0 = 11.52. So you could try a dynamic cr for your cam and altitude to see the worse case for the swap. Dynamic cr <8.3 should be okay.

Good luck.

Last edited by cardo0; 05-25-2019 at 02:55 PM. Reason: Stupid auto correct!
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Old 05-25-2019, 03:21 PM
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Originally Posted by Buccaneer View Post
Well, I'm not the only one that has a modded CF, but I only know of one other CF motor that is naturally aspirated twin TBs that is faster than mine and he is in Australia... Ben73 with a 84. There could be others, just don't know of any and I have been working with CFI specifically for 26 years now.
That makes you the xpert.
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Old 05-25-2019, 03:36 PM
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Default For what it’s worth..........

May not be relevant but these aluminum heads are greatly under appreciated. I put a good set on a 350 with thin head gasket (CR 10.4) flat top pistons Duntov Comp cams hyd 30 30 with self align rockers 650 carb and headers. Ran like a bandit.
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Old 05-25-2019, 03:52 PM
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Default OE L81 CR=8.2:1 ... w/ 58cc = 9.74:1 CR

GM heritage center states 81 350ci C3 had 8.2:1 CR with combustion chamber volume = 75.47cc and its sump head piston 0.025" down in hole

do a quickie what-if back-calculate with summit basic CR calculator .... using 75.47cc and 4" bore & 3.48" stroke to attain 8.20:1 CR

then swap the 75.47 chamber for 58cc ........... pencils out to 9.74:1 CR

Given all else equal, ... you swap OE 75.47cc chambers to 58cc ... CR will increase from 8.20:1 to 9.74:1.

I wouldn't sweat that increase; I'd embrace it.

As before ... I leave the camshaft & ECM to Xfire guys.
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Old 05-25-2019, 04:18 PM
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Default OE L83 CR = 9:0:1 ... w/ 58cc = 10.95:1 CR

My mistake ... above post I considered an L81 Not L83

Numbers pencil out quite differently.

GM heritage states for '82 L83 350, same 75.47cc chamber also a sump head piston 0.025" below deck

given all else same OE L83 at 9:0:1 CR ... swap 75.47cc chamber for 58cc chamber ... CR will increase from 9.0:1 to 10.95 CR.

I'd be concerned with that CR ... a larger cam will likely effectively lower its DCR ... again, leave cam & ECM to xfire guys.
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Old 05-25-2019, 05:53 PM
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Originally Posted by Gunfighter13 View Post


I'll just leave this right here. From 2012 testing with NOS.
LMAO...So, using NOS is NOT naturally aspirated, that IS BOOSTED or a Power adder just like adding a turbo or SC. If your running just two TBs, turn the NOS off and see what it does. I would be very curious at the specs and I see you are running a 4.09/4.10 gear. Ha, I'm just running a punny 3.31.

Last edited by Buccaneer; 05-25-2019 at 05:55 PM.
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Old 05-25-2019, 05:59 PM
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Originally Posted by jackson View Post
My mistake ... above post I considered an L81 Not L83

Numbers pencil out quite differently.

GM heritage states for '82 L83 350, same 75.47cc chamber also a sump head piston 0.025" below deck

given all else same OE L83 at 9:0:1 CR ... swap 75.47cc chamber for 58cc chamber ... CR will increase from 9.0:1 to 10.95 CR.

I'd be concerned with that CR ... a larger cam will likely effectively lower its DCR ... again, leave cam & ECM to xfire guys.
Hence my statement that going to 58cc head would IMO not be a good idea in a 82 CF motor, but others have other ideas. Go for it and let me know how that worked out for you.
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