L48 mods - 1979
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From: Frederiksberg, Denmark
L48 mods - 1979
Hi all,
I also posted this item in the 'modifications' section. But I thought I would also post it here, as you guys are terrific!
After an unfortunate incident with the crankshaft I have ordered a rebuild of the ol' trustworthy 350. My mechanic, who claims to know a lot about Vettes, has suggested the cylinders to be bored .030 over, installation of hypereutic pistons resulting in a compression of 10:1 and a new camshaft from a L 82-engine. I will retain the stock manifold and cylinder heads.
How does that sound for a first-time mild modification? Any alternate suggestions? And what might be next (besides the obvious Merlin502 purchase? ;)
I also posted this item in the 'modifications' section. But I thought I would also post it here, as you guys are terrific!
After an unfortunate incident with the crankshaft I have ordered a rebuild of the ol' trustworthy 350. My mechanic, who claims to know a lot about Vettes, has suggested the cylinders to be bored .030 over, installation of hypereutic pistons resulting in a compression of 10:1 and a new camshaft from a L 82-engine. I will retain the stock manifold and cylinder heads.
How does that sound for a first-time mild modification? Any alternate suggestions? And what might be next (besides the obvious Merlin502 purchase? ;)
Race Director
Joined: Apr 1999
Posts: 11,520
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From: CORVETTE 77 385 C.I. TEXAS
Re: L48 mods - 1979 (Vettelaw)
10 may be too high depending on your el. & gas octane- little to gain & a lot to lose. 9.5 is good w/ iron heads. Better heads rec.! Duals & headers rec.!
Cam- What's your trans. & gears?
:cool:
Cam- What's your trans. & gears?
:cool:
Thread Starter
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From: Frederiksberg, Denmark
Re: L48 mods - 1979 (Ganey)
I have considered the ZZ4 option. However, it's kinda pricey to ship a crate engine across the pond, plus the government is ripping people off by claiming an import tax of 6% and an additional VAT on 25%. Part of the reason why I'm considering emigrating to a more Vette-friendly country (Oh say can't you see...! :) )
The transmission is TH350. I am not totally clear on the gears but the car is a stock 1979 L48, and when I am doing 75 mph the engine runs at 3500 rpm (approx.)
The transmission is TH350. I am not totally clear on the gears but the car is a stock 1979 L48, and when I am doing 75 mph the engine runs at 3500 rpm (approx.)
Le Mans Master
Joined: Jul 1999
Posts: 9,206
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From: Sewell NJ
Re: L48 mods - 1979 (Vettelaw)
I agree with the others that 10:1 is too high. I would keep the compression in the 9 to 9.5:1 range. I would also look at a Comp Cams or Crane camshaft in the 260 to 268 degree range. Camshaft design has come a long way since the L-82 camshaft and a dual pattern cam might help the exhaust side if you're going to run stock manifolds.. There are also better heads available than the stock ones and the cost (I don't know how the shipping and taxes will effect this) is comparable to having your heads reworked. I have World Products SR Torquers with 2.02x1.60 stainless valves and they ran about $450 for the pair. Make sure you go with a double row timing chain also and a nice set of roller tip or full roller rockers would be nice too. It's fun spending other peoples money but these are suggestions that might save you in the long run. :D :yesnod:
Melting Slicks
Joined: Dec 2000
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From: Wichita, KS
Re: L48 mods - 1979 (Vettelaw)
Yes, the L82 cam would be a nice mild upgrade if you are going to retain the stock intake and exhaust manifolds and cylinder heads. Ask the shop doing the work about gasket matching the ports. As mentioned above 10 to 1 is too much compression for todays gasoline with a mild motor.
Other cams that you might look at are
Crane Powermax P/N 113901 Duration @.050 204 / 216
Comp Cams Extreme Energy XE256
Edelbrock Performer
If you've got a pocket full of money and want to retain the stock look you could look at a roller cam. I can't recommend any as I'm not too familier with the differances in the profiles to know what will work with a stock motor.
Your rear gears may be 3:55 to 1. That is what I have and with 255/60-15's I'm showing 3300 RPM at 70.
Other cams that you might look at are
Crane Powermax P/N 113901 Duration @.050 204 / 216
Comp Cams Extreme Energy XE256
Edelbrock Performer
If you've got a pocket full of money and want to retain the stock look you could look at a roller cam. I can't recommend any as I'm not too familier with the differances in the profiles to know what will work with a stock motor.
Your rear gears may be 3:55 to 1. That is what I have and with 255/60-15's I'm showing 3300 RPM at 70.
Safety Car
Joined: May 2001
Posts: 3,758
Likes: 3
From: Surrey
Re: L48 mods - 1979 (vettfixr)
Vettelaw:
Last night I discovered that there is a place near me who specialise in our favorite engines. The prices are much cheaper than I'd pay if shipping direct from the US (I also get clobbered with taxes) & I'm trying to get a brochure/price list from them. I'll let you know who they are when I get some more info. As we're both in the EU, then you shouldn't have to pay taxes if something is shipped from here (in theory :rolleyes: ).
Vettfixr:
Would a gear drive be better than a double row timing chain, or are there disadvantages to gear drives?
:cheers:
Paul
Last night I discovered that there is a place near me who specialise in our favorite engines. The prices are much cheaper than I'd pay if shipping direct from the US (I also get clobbered with taxes) & I'm trying to get a brochure/price list from them. I'll let you know who they are when I get some more info. As we're both in the EU, then you shouldn't have to pay taxes if something is shipped from here (in theory :rolleyes: ).
Vettfixr:
Would a gear drive be better than a double row timing chain, or are there disadvantages to gear drives?
:cheers:
Paul
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Joined: Jul 2001
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From: Frederiksberg, Denmark
Re: L48 mods - 1979 (UKPaul)
UKPaul:
Sounds exciting about that place in UK. I am looking forward to receiving more info.
Guys,
About compression I have heard that the gas being used here in Europe has a higher octane level that what they supply in the US. My mechanic has informed that it is possible to run a 10:1 engine with 95 octane pump gas with very little detonation. Also, he said something - that I did not fully understand - about the theoretical compression being 10:1 but the practical ration being closer to 9,5:1 due to the cylinder heads. Does that sound all too goofy? :confused:
Vettelaw
Sounds exciting about that place in UK. I am looking forward to receiving more info.
Guys,
About compression I have heard that the gas being used here in Europe has a higher octane level that what they supply in the US. My mechanic has informed that it is possible to run a 10:1 engine with 95 octane pump gas with very little detonation. Also, he said something - that I did not fully understand - about the theoretical compression being 10:1 but the practical ration being closer to 9,5:1 due to the cylinder heads. Does that sound all too goofy? :confused:
Vettelaw
Burning Brakes
Joined: Dec 2000
Posts: 1,183
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From: Des Moines Iowa
Re: L48 mods - 1979 (Vettelaw)
Compression ratio calculations must take into consideration block/pistion deck height, dish/dome or valve relief areas in pistions, cc area of head with valves and sparkplugs installed, cylinder bore and stroke, and lastly, cylinder head gasket compressed thickness and clearance between headgasket and cylinder walls.
Many compression ratios are estimates simply using a couple of the major factors above, like bore/stroke and cc area of heads.
Many compression ratios are estimates simply using a couple of the major factors above, like bore/stroke and cc area of heads.
Le Mans Master
Joined: Jul 1999
Posts: 9,206
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From: Sewell NJ
Re: L48 mods - 1979 (UKPaul)
Hi Paul
A gear drive will retain it's accuracy better than a chain but they are noisy. they whine like a blower. I think for the street a double row timing chain from a reputable manufacturer (Cloyes is one of the best) is more than sufficient. I'm also not sure whether you would have a clearance problem with a gear drive because of the short water pump . I know my double row chain fits behind the stock cover and I don't have a problem but it's very close to the water pump.
A gear drive will retain it's accuracy better than a chain but they are noisy. they whine like a blower. I think for the street a double row timing chain from a reputable manufacturer (Cloyes is one of the best) is more than sufficient. I'm also not sure whether you would have a clearance problem with a gear drive because of the short water pump . I know my double row chain fits behind the stock cover and I don't have a problem but it's very close to the water pump.
Race Director
Joined: Apr 1999
Posts: 11,520
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From: CORVETTE 77 385 C.I. TEXAS
Re: L48 mods - 1979
Vettelaw
Comp cams XE262 would work w/ fresh engine & a little lope at idle. Comp cams XE256 is min. cam, more low rpm power than the other & smooth idle.
Paul
A gear drive is not rec. for street, it is better to run a roller timing set.
Comp cams XE262 would work w/ fresh engine & a little lope at idle. Comp cams XE256 is min. cam, more low rpm power than the other & smooth idle.
Paul
A gear drive is not rec. for street, it is better to run a roller timing set.
Burning Brakes
Joined: Aug 1999
Posts: 774
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From: Palatine IL
Re: L48 mods - 1979 (Vettelaw)
Check out my signiture for another opinion. It has good low end torque and really comes alive around 3000 rpm. It has ~ 9.5:1 compression and I haven't got it on a dyno yet to figure out the actual torque and hp numbers.
I agree with the above posts to stick with 9.5:1 compression. I had a L-82 cam and went with a mild comp cam. There have been improvements over the last 21 years.
Have fun! :smash:
I agree with the above posts to stick with 9.5:1 compression. I had a L-82 cam and went with a mild comp cam. There have been improvements over the last 21 years.
Have fun! :smash:
Drifting
Joined: Jul 1999
Posts: 1,542
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From: Plano TX
Re: L48 mods - 1979 (Ganey)
I have a 1980 L82. The motor was replaced with a ZZ4 enigne because I didn't have the time for a rebuild and wanted more performance.
I will say this though. Why an L82 cam? The design is 30 years old so this is not the way to go!
If you must go with a flat tappet hydraulic design, at least get a new desing from Crane or Comp cams with new lifters and matching springs that matches your needs, type of transmission and rear gear. If you can afford a hydraulic roller (the reason I went with ZZ4) this is the best way to go because you get high lift with short duration for great power, without radical idle or poor low end response.
For compression, 9.5 to 1 should be max with iron heads. 10 to 1 is OK with aluminum heads because they remove combustion the heat quicker, reducing ping.
Dave
I will say this though. Why an L82 cam? The design is 30 years old so this is not the way to go!
If you must go with a flat tappet hydraulic design, at least get a new desing from Crane or Comp cams with new lifters and matching springs that matches your needs, type of transmission and rear gear. If you can afford a hydraulic roller (the reason I went with ZZ4) this is the best way to go because you get high lift with short duration for great power, without radical idle or poor low end response.
For compression, 9.5 to 1 should be max with iron heads. 10 to 1 is OK with aluminum heads because they remove combustion the heat quicker, reducing ping.
Dave
