Pat,

With the current combo
.043 quench, 65cc head
290-300 ADV
224-234 @.050
112 LSA, 107 ICL
you calculated 7.7 DCR.

with the comp cam
268-286 ADV.
224-236 @.050
113 LSA, 108 LSA ( straight up)
you calculated 8.10

I have 2 questions.
1- is this enough differenct to warrant a cam change ?

I read on your site advancing the cam raises the DCR ? What would the comp cam be if installed 4 deg adv.

The motor is on the stand, and nows the time to change cam if needed ?

Thank you

Mike

Is there a typo in the specs of the comp cam? 268-286 ADV.?

That's an awful big split. Usually about 10 degrees or so, that's 18 degrees?

Tom

The 7.7 was with a .035" quench and 64cc heads. With .043 and 65cc, DCR is 7.49. This is with 5º advance ILC at 107.

A cam with a 113 LSA is advanced 5 degrees if installed at 108. Straight up is 113 LSA installed at 113 ICL.

I calculated the NX cam at 4 degrees advance, 109º ICL. You could advance it to 107 for 6º of advance. With 6º advance the DCR is 8.18.

If I were going to spray this engine, I'd use the NX cam. Notice how much more exhaust duration it has. With nitrous, getting the spent gases out is a major issue. After all, you're filling the cylinders with, what amounts to, liquid air and fuel.

The shorter adv timing will help with reducing overlap, which is desirable with nitrous. The NX cam has 51º of overlap, the 290 cam has 71º.

With the big boost in torque that nitrous gives, I would worry too much about DCR. If you're in the 7.7 to 8.2 range, you'll be buying tires regularly smile.gif .

Tom, that is the correct duration. All Comp's nitrous cams are like that. The 284 cam has 305 on the exhaust.

thanks Pat.

the comp cam has 113LSA, but comp grinds 5 deg of advance into it.
It comes 113 LSA 108 ICL. I was curious as to installing it 4 deg advanced from that ( 104 ICL) to bring up the DCR. My main concern with the DCR is that 98 % of the time i won't be using nitrous ( these cams are supposed to work good off nitrous too ) ?? But i want to achieve the most out of the motor before i spray it.

I really appreciate your time and work

Mike

9º advance is a bunch. I've never ran one more than 6º. You know what, I'd just put it in at 5º and run it there. That gives a DCR of 8.125. You could install it at 9º but I wouldn't. I think that is just too much advance and you should go with another cam. I don't know what the down side of this much advance is but I wouldn't want to be the experimenter smile.gif . Don't forget that the whole cam is shifted this much. The exhaust will open very early (plus nitrous cams already open the exh quite early) and that could cost power.

You might consider the NX262H. With 5º adv it's DCR is 8.297. It peaks out only 300 rpm less than the 268.

Pat,

I will use the NX 268 H and install it at 108 ICL. The 8.125 will be the best it's ever been.

Thanks.

the motor before was .053 quench and 72cc head with the 290-300 cam and Dart iron Eagles (180).

the car is an 85 vette that made 325 RWHP with that set up and ran 12.75 @ 107. I think the cam, Canfields and intake ( stealth to RPM) will be a much better improvement.

thanks again, i couldn't have made this much of an appropriate change with out your help.Once again, i really appreciate the advice and work you have done for me. smile.gif
Mike

I'm sure it will work out great. Good luck with it.

Pat,

i was compairing the 2 cams and the DCR's, and since i only rev the car to 6K i decided to gowith the 262 cam and the better DCR. 99% of the time this car is driven on motor around town and to work.

I have heard several people talking about leaving as much as 40 HP on the tablw with the improper cam selection ? I'm assuming that's what this program helps to avoid. Do you think that say a DCR or 7.5 compared to 8.3 could actually loose that much HP ?

Mike

I doubt it is nearly that much. I think you could lose that much, or more, by overcamming a bunch. There are a lot of cars out there with big cams in low compression engines. I had an engine with 8.1 SCR and a 308 cam, I didn't build it. The DCR worked out to 5.67. The cam wanted over 12:1 (8.24 DCR). In this case it could very well be much more than a 40hp loss. It ran in the 13's but would have made a bunch more power with a much smaller cam or a lot more compression.

The 268 isn't nearly that far off. You're probably looking at a 10-20 hp difference. Maybe more with the nitrous. I think the 262 is a good choice especially with aluminum heads since they will draw off a lot of heat.

What exactly is quench again? And how do you figure it out or determine it?

Quench is the distance between the flat part of the piston and the flat part of the head. It is the sum of the deck clearence and the compressed thickness of the gasket. A piston down the hole .005 with a .040" thick gasket has a quench of .045".

thanks Pat,

the motor is going in thos week, i will break it in for about a week and then take it to the track and post the difference's.

Mike