Question for the camshaft experts
Thread Starter
Le Mans Master
Joined: Mar 2008
Posts: 5,948
Likes: 72
From: Oxford MA-----You just lost the game!!!!
Question for the camshaft experts
Hi guys! I have a basically stock L-48 engine in my 1980 Corvette, with the Corvette Central dual exhaust system (Patriot Tight Tuck block hugger headers with a 2 1/2" dual exhaust going through Magnaflow mufflers) I am contemplating new aluminum heads and a cam upgrade.I wouldn't call the exhaust system restrictive, but I do not get the scavenging effect of tuned long tube headers. The heads I/E ratio is above 75%. So, I have a relatively free-flowing exhaust and a good I/E ratio, which would seem to call for a straight grind cam with a tight LSA, but since I don't have the scavenging effect from long tube headers, will the valve overlap really do me any good? I'm thinking the I/E ratio points to a straight grind cam, but the lack of scavenging points to a wider LSA, What do you all think about it?
Scotty
Scotty
Le Mans Master
Joined: Apr 2011
Posts: 6,284
Likes: 1,171
From: Hermosa
How narrow LSA we talking? how much CR? How much overlap?
what a good IE ratio allows is for the overlap to be used during the induction phase to increase the fresh charge volume to your advantage vs Having to use the overlap during the blowdown phase to get the exhaust out due to poor flowing exhaust.
you don’t HAVE to have good exhaust scavenging if the exhaust already flows freely. There is such a thing as overscavenging.
Narrow LSA’s do not like exhaust restrictions however.
what a good IE ratio allows is for the overlap to be used during the induction phase to increase the fresh charge volume to your advantage vs Having to use the overlap during the blowdown phase to get the exhaust out due to poor flowing exhaust.
you don’t HAVE to have good exhaust scavenging if the exhaust already flows freely. There is such a thing as overscavenging.
Narrow LSA’s do not like exhaust restrictions however.
Race Director
Joined: Mar 2018
Posts: 10,705
Likes: 2,166
From: Golden Colorado
I would recommend doing it all at once. Another thing to consider, if your not really sure of what your doing (when it comes to specs and mixing parts) consider a top end kit like Edlebrock and others offer. They have taken the guess work out of it and developed a proven combination to go with what you’ve got. Just something to think about. 
Thread Starter
Le Mans Master
Joined: Mar 2008
Posts: 5,948
Likes: 72
From: Oxford MA-----You just lost the game!!!!
How narrow LSA we talking? how much CR? How much overlap?
what a good IE ratio allows is for the overlap to be used during the induction phase to increase the fresh charge volume to your advantage vs Having to use the overlap during the blowdown phase to get the exhaust out due to poor flowing exhaust.
you don’t HAVE to have good exhaust scavenging if the exhaust already flows freely. There is such a thing as overscavenging.
Narrow LSA’s do not like exhaust restrictions however.
what a good IE ratio allows is for the overlap to be used during the induction phase to increase the fresh charge volume to your advantage vs Having to use the overlap during the blowdown phase to get the exhaust out due to poor flowing exhaust.
you don’t HAVE to have good exhaust scavenging if the exhaust already flows freely. There is such a thing as overscavenging.
Narrow LSA’s do not like exhaust restrictions however.
My thinking is that if I find a mild straight grind cam with a 112 LSA, that will be the cam for me. I have an old Crane Energizer 272 H10. It's a straight grind cam with 216 degrees of duration at .050" and .454" of valve lift on a 110 LSA. I'm wondering if a similar cam on a 112 LSA would be a better choice for me, or if it will really make enough difference to even bother with.
Scotty
Le Mans Master
Joined: Apr 2011
Posts: 6,284
Likes: 1,171
From: Hermosa
That crane cam sounds like it would work just fine. The difference between 112 and 110 LSA is not great but may be significant for your use. With a 110 you'll have 52* of overlap and with 112, you'll have 48* of overlap. The primary difference being vacuum level and RPM range.
The 110* top end around 5400 RPM and the 112* around 5100 RPM.
If it were me I'd go with 110 every time.
Run that through a DCR calculator see where you're at.
The 110* top end around 5400 RPM and the 112* around 5100 RPM.
If it were me I'd go with 110 every time.
Run that through a DCR calculator see where you're at.
Drifting
Joined: Mar 2006
Posts: 1,263
Likes: 188
From: Wabasha Mn
Well, I'm thinking of 110 as being on the narrow side and 112 being on the wide side. Maybe that's not enough difference to make a difference. An optimistic calculation of the compression ratio using nominal figures is 9.4:1 I'm going to be using what most people would consider a fairly mild cam, maybe somewhere in the 215 at .050" range, so the overlap probably won't be excessive either way. Also, I'm looking for a broad flat torque curve rather than a peak number, and I'd like to keep the rpm below 5500.
My thinking is that if I find a mild straight grind cam with a 112 LSA, that will be the cam for me. I have an old Crane Energizer 272 H10. It's a straight grind cam with 216 degrees of duration at .050" and .454" of valve lift on a 110 LSA. I'm wondering if a similar cam on a 112 LSA would be a better choice for me, or if it will really make enough difference to even bother with.
Scotty
My thinking is that if I find a mild straight grind cam with a 112 LSA, that will be the cam for me. I have an old Crane Energizer 272 H10. It's a straight grind cam with 216 degrees of duration at .050" and .454" of valve lift on a 110 LSA. I'm wondering if a similar cam on a 112 LSA would be a better choice for me, or if it will really make enough difference to even bother with.
Scotty
Le Mans Master
Joined: Apr 2011
Posts: 6,284
Likes: 1,171
From: Hermosa
I ran the Isky 264 Mega cam 214 214 450 450 108 lsa in my 76 l82 through my stock single exhaust with cat converter. Much stronger low and mid-range power compared to the L82 cam. Had the 3.36 rear and t400. Great old school cam and can use the stock valve train. Had to pass emission tests too. L82 cam was a dog at low speeds compared to the L48 cam.
If you have a higher stall converter would probably work real nice. If you have stock stall for L-48, might be piggish until the RPM gets a bit higher. Especially if paired with a 3.08 rear diff. ratio on an automatic.
However it is higher intensity than either the XE series or the Voodoo series cams, and the lift is lower.
EDIT: actually ran the math on that Isky cam and due to the lower lift the intensity is slightly lower than the XE series cam in inches of lift per degree of rotation.
Last edited by REELAV8R; Feb 5, 2022 at 09:20 PM.
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