Hey Jay am I "in the ball park" or out in left fie

[1KWIK72]

I am putting together my new motor. 18* BMF heads 268cc runners 14:1 4.155" bore 3.75" stroke 406ci. The machine shop that did my work dealt with comp on the cam. To make a long story short I am having piston to valve clearance issues partly my fault because I had CFE mill the heads some. At this point I am having custom pistons made with big valve pockets and probably .043" rings with a back cut on the top one to make it all fit. I have had some people tell me the cam is not quite right but I am not sure just wondering your opinion. Grind is CS-1842-1846-R109 Adv dur 311 319 .050" dur 278 286 Lobe sep 109 ground on a .950 base circle 1.7 ratio intake 1.6 ratio ex .782" in .736" ex (.460" lobe on both) using a regular size SBC roller lifter. Any thoughts?

Thanks
Craig

[Chris Uratchko]

What is your valve to piston?

[Jay Allen]

Grind is CS-1842-1846-R109 Adv dur 311 319 .050" dur 278 286 Lobe sep 109 ground on a .950 base circle 1.7 ratio intake 1.6 ratio ex .782" in .736" ex (.460" lobe on both) using a regular size SBC roller lifter. Any thoughts?
I just don't get it? 278 at .050 is friggin HUGE! A 109 LSA means it probably goes in on a 106 or 105 knowing Comp and their cam cores. And there is no wonder you don't have much if any P-V.

278/2 = 139, assuming a 105 IC,
139 - 105 = 34 BTDC is where the intake valve opens.

286/2 = 143, if you have a 105 IC, then the exhaust center is 113.
143 - 113 = 30 ATDC where the exhaust valve closes.

34 + 30 = 64* of overlap at .050. That is not even in the ballpark. if you had like mildly done up 23* 210cc heads and tyou wanted 8000 RPM, then maybe, kinda, perhaps. That is a friggin TON of overlap.

***These numbers may change by a few points if the IC is 109 and the LSA is like 112-113 making the EC 116-117. That helps the overlap, but increases the RPM by a butt load.

I guess you want to turn this thing like 8500 RPM or more, like way more?

***Edit: I see the grind is -109. So the IC is 105-106.

[1KWIK72]

Well originally with the proposed flat top piston and 6.125 rod. Intake was about -.010" and ex was .050". That was no lash. I then switched to a JE small dome piston and 6" rod with lash clearance was .004" intake .065" ex. Because of the 2.180" steel intake valve we are shooting for a minimum of .080" intake which is going to be tough and should not be an issue to get .110 on the ex side.

[Chris Uratchko]

No need for .080 intake if your struggling to get ptov....

[1KWIK72]

Well we were shooting for trap RPM somwhere around 7800 the above mentioned P to V was with it installed @ 105.5 IC

[1KWIK72]

So Jay are you saying this thing is going to be a slug or just that I am going to have to turn 10k to get it to run???

[Jay Allen]

I am going to have to turn 10k to get it to run???
Bingo!

Lots and lots of RPM and lots and lots of NOS to utilize that thing. I air on the side of small in terms of duration at .006, .020, .050. I get the lobe area in areas that typical do not affect P-V. My cams will normally GIVE you MORE P-V and allow you to run a lot less NOS.

I don't buy into the *NOS* cam thing.......

[1KWIK72]

Well this is a 100% NA motor so No NOS. They Did say converter would have to be in the 6000-6200 range I can stand to give up a little on the bottom end as it is a small tire car with a TH400 as long as it makes up for it on the top end. This really sucks I am kinda stuck in the middle as the guys who do my machine work do really good work and they along with comp say this cam is it. On the other hand my cyl head guy at CFE also thinks they missed the boat on the cam, but he was wondering why so much lift? Which makes me wonder why flow a head and stick springs on it that are good to .800+ if your not going to use it? I am just plain confused everyone has different opinions but come on! seems like everyone I talk to has a way different opinion.

[Chris Uratchko]

Well the writing is on the wall.

You have a Machinst, and a Cam Grinder telling you what you need, and you have a Cam Designer, one of the top 5 cylinder head shops in the world, and an engine designer telling you that cam is way off....

That's a no brainer. No offense, that's just the way I see it.

[Jay Allen]

Well the writing is on the wall.

You have a Machinst, and a Cam Grinder telling you what you need, and you have a Cam Designer, one of the top 5 cylinder head shops in the world, and an engine designer telling you that cam is way off....

That's a no brainer. No offense, that's just the way I see it.
I said NOS because that thing is so big if you don't spray it, then its a slug for what it is.

Dude, you came here looking for unbiased opinions. That is what you were given. Just because they do not line up with a 10/hr phone guy at Comp (who sold you the cam, what's he supposed to say) and a machinist who bought the cam (and doesn't want egg on his face because he's wrong and actually knows ZERO about cams) what do you want.

CFE is a PREMIERE cylinder head shop.
Chris Uratchko is one of the smartest engine guys I know.

The problem with the cam ain't the lift. Its too big at .050. It has too much overlap. The events are wrong and thus that makes the LSA off for that type of engine.

If you did not have doubts, you would not have been here. Its your engine. Its your money. As long as you are happy, that is all that counts.

Good Luck.

[1KWIK72]

Jay, first off I apreciate you (and Chris) taking the time to respond. My previous comments were in no way meant to imply you guys were wrong or off the mark. If I upset you I apologise. As for my machine shop guy, he isn't the type of guy to not want to admit he is/was wrong. He actually suggested I get other opinions on cams as he was relying on his contact at Comp to suggest a grind. He did think it was pretty close but admittedly he is a roundy round guy. You are probably right on about Comp the guy I spoke with on the phone. He didnt want to make a recommendation he wanted the grind# first then said yea it is what I would have recommended. I never dealt directly with CFE I have a friend who works there. He was the one who suggested the cam needed more lobe separation and didnt think it needed that much lift. He had previoulsy said the same thing on my 23* motor and loaned me a cam with the same .050" dur #s but on a 110 instead of a 106 lc. The car lost over a tenth and was a complete turd. Granted it may not have been the optimum cam for my app but it was an A,B,A test as I swapped the cam back at the track and it went back to where it was. So his advice I take with a grain of salt. You are right I do have my doubts that is why I am here asking, it is my money and I am quickly running out of it on this project. I guess at this point my questions to you are 1. Can you design me a cam that will work without extensive reworking of the rest of my stuff? 2. How long will the springs live and due to having a large steel valve will I have stability issues there? 3. What kind of power would you anticipate this thing making and due to traction issues could it be taylored slighly to help this?

Thank you for your time
Craig

[buschracing]

probably the reason you slowed down going from 106 to 110 was the intake centerline. Your cam was already too big at .050" on intake for your compression ratio and rpm potential, so it needed the more advanced intake events to keep cyl. pressure up.

I can tell you what you will need for that 2.180 steel valve...lots of spring pressure on the intake side!! If you end up at .800" with shaft rockers and a shift near 8000 rpm, you will want either a Comp 947 or 948 triple spring to cope with that heavy valve.

go with Jay on this one...you will NOT regret it!!!

[1KWIK72]

I agree the intake events not being optimum. I noticed they were quite different on the 110lc cam even installing it advanced a couple degrees. That is all water under the bridge though at this point the old motor is history. I will probably have to stick to the springs that came with the heads (Manley Nextecs) for a while due to buget issues but the plan was to shim them to bump the pressure. If this thing runs like it should I was hoping for some 9.70s or so at about 140. That should put me through about 7800 or so. I was hoping to shift somwhere around 7500.