Thoughts on a lunati SFT camshaft

I am building a 460 cu.in. bracket engine for my 3400 lb comet with a c6 8" convertor .I bought a set of the new afr 280 heads 75 cc .These will replace my edelbrocks .This Lunati cam I am looking at PN 30340743 257-265 649-649 ICL 106 LSA 110 I had RM grind me a cam for my other 460 but this is going to be a similar 460 with the exception of the afr heads . I have flat top pistons and a milled block .My edelbrock heads are the cj version all my machinists that looked at the edelbrocks feel my ports are to big .So wanting to run 6.40-6.50 in the 1/8 maybe the afrs will do the job .On a cool day I went 6.77 with the eds .So what LSA would you all recommend it comes 110 I was thinking 108 What are your thoughts on this ? I am at 11.67 on my compression ratio after I notch my pistons for that big 2.250 intake valve I will lose some compression would you advance the intake centerline to 104 to make up the difference ?By the way these afr heads look really good and they were good to speak with on the phone .They shipped them out on time and a little bit before actually .Sometimes my buddies at the track think I need a Windsor .My comet runs good for 3400 lbs and a heavy c6 .My best 1/4 10.72 @124 it just is slow in the 1/8 .

http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=1021&sb=2

http://www.lunatipower.com/CamSpecCard.aspx?partNumber=61643


You know how cam opinions around here are Doug but, for what it's worth I like the Comp Cams 294B8 myself.

I ran the Lunati in the Wallace Dynamic Compression Calculator and it showed 9.6DC and 202 PSI cranking compression with your deal but, I think Lunati's ABDC number is checked a little tighter ( on the small side ) then Comps cam card numbers?

I like the Lunati's Lift number better though.

PS: The Old Number for the Lunati you posted is 61643

Why don't you just get a cam ground specifically for it?

The head will fool you on how big it is. For the CID cam needs to be smaller.

Dave I have to purchase pushrods and rockers my money is tight right now Straubtech maybe a little less duration ? I want some lift so the heads will flow .

manofmerc wrote:Dave I have to purchase pushrods and rockers my money is tight right now Straubtech maybe a little less duration ? I want some lift so the heads will flow .

Last time Blake had a custom grind for me I don't recall it costing anymore then a regular cam. It just took a few weeks. Maybe there is a price difference between Lunati and Comp Cams but after having a custom cam vs a shelf cam it was so much better I couldn't see ever using a shelf cam again.

Custom cam is normally ground in two days. I don't remember why or what happened on yours Jason.

manofmerc wrote: I want some lift so the heads will flow .

In an NA engine you only want to lift the valve based on piston speed to max velocity. You over lift the valve based on the demand then the column of air stalls out. I've taken .100 of lift and 20 degrees of duration out of an engine and made more power. This industry's marketing theme is "Bigger is Better" when it should be "Combination is King".

IDT-572 wrote:Custom cam is normally ground in two days. I don't remember why or what happened on yours Jason.

I think it was just shipping. Shipping money to you, grind, then shipping to me. Maybe it was a week or two. I don't remember exactly but it was well worth the wait.

I'm 3 to 4 weeks during this time of year.

After talking with lunatis tech and thinking of straubtechs post a cam with less duration might be what I need Lunati 30340743 249-257 623-649 110ls 106il The afr guy preferred this cam over my other pick I haven't pulled the trigger yet but what about having it ground on 108 instead of 110 ls.Just asking.Primarily concerned about 1/8 times .Thanks everybody .

Straubtech wrote: I'm 3 to 4 weeks during this time of year.  

YES ... this time of the year it is usually about 15 working days or a bit longer.

The line-up for grinding gets to be pretty long in the spring.

If you are going to make a catalog cam into a special ground cam you may as well get something custom and be near exact.

manofmerc wrote:After talking with lunatis tech and thinking of straubtechs post a cam with less duration might be what I need Lunati 30340743 249-257 623-649 110ls 106il The afr guy preferred this cam over my other pick I haven't pulled the trigger yet but what about having it ground on 108 instead of 110 ls.Just asking.Primarily concerned about 1/8 times .Thanks everybody .

A dead giveaway 99% of the time that cam is wrong is the fact it has more lift on the exhaust. Exhaust is under pressure, max velocity happens as soon as you open the valve and at the lower lifts. In your case the camshaft is not correct. Will it run. Sure. Will run to its potential. No.

Straubtech I imagine most of these cams were designed around stock heads with their poor flowing exhaust ports . That is the reason for so much more lift and duration a common split pattern camshaft.So you are saying with more lift you lose velocity .My thought is on the exhaust side you just want to get it out .I understand velocity on the intake side most do .But one would think getting the exhaust out and ready for the next intake charge would be sufficient . Thanks for your time I am learning something .Doug

manofmerc wrote:Straubtech I imagine most of these cams were designed around stock heads with their poor flowing exhaust ports . That is the reason for so much more lift and duration a common split pattern camshaft.So you are saying with more lift you lose velocity .My thought  is on the exhaust side you just want to get it out .I understand velocity on the intake side most do .But one would think getting the exhaust out and ready for the next intake charge would be sufficient . Thanks for your time I am learning something .Doug

Doug,
Your favorite carbonated beverage....do you have to pull the pop top all the way to get the gas out or does the majority escape as soon as you crack it open? The reason more lift was on the exhaust for decades is because the lobes were in the same family and naturally since "big brother" was on the exhaust it had more duration and more lift. It wasn't until lobe families started getting mixed up and the understanding that lift on the exhaust is not as important on the exhaust side as duration did we see cam profiles with less exhaust lift.

The main reason a lot of large flat tappet cams have more exhaust lift is because they just can't get any more lobe lift for that given duration for that lobe profile used on the intake side; they probably would like to have more lift but, just can not get it without edge loading the lifter.
That extra needed lift can be gotten with the increase in duration on the exhaust side.  The exhaust lobe is not goiug to be made worse intentionally just because the intake lobe can't physically acquire that amount of lift.

Use a different ratio rocker arm to get the intake valve lift you want, if you need it. When the necessary intake lobe lift can be gotten, then the exhaust lobe lift is usually less, (or near the same), than the intake.

Straub and Randy thank for the info .Here is a grind with less exhaust lift Lunati 30340514 633/636 253/259 108 lsa 102 I C Kinda understanding the exhaust better remember I have these afr heads so the heads should take care of the exhaust .What do you all think of this last camshaft pick ? I know everybody wants me to chose a custom grind but right now that isn't happening .The cam Randy had ground for me has .019 less ex. lift than in. Maybe you guys know something after all .I believe these camshaft companies are living in the past not many use OEM heads any more and if they do they have been ported and that would require a completely different camshaft as well .And another case for a custom ground camshaft . Really good of you all to share your thought on this .Doug.