467-Ratman

I am sick and tired of the way my motor is running, it is very weak at off idle and does not come to life untill 3000. I am not sure if its the cam or carb or what but its time to start over. The other more major problem that we discoverd this spring is the wrong flywheel on the motor and a big out of balance vibration. I have another shop who is doing the work to cure that, but here is what I am looking to finish with. I want strong low to mid rpm performance, not peaky like now. 5500 rpms would be a good max range, I dont need a drag motor. My cam now is a 296-2 with 296\306 duration. I am looking for tips on a new cam, intake and carb. Compression is about 9.1-1. Thanks for the help!!!!! :mad

Corey_68

Damn, sorry you tearing her down already. :( But you sound like me. In my family one of our mottos is "If it can't cut it it can't stay". I too would ante up the time and $$$ and be satisfied than save a few pennies and be miserable.

Best of luck man :cheers:

norvalwilhelm

Why start over. Sure it could be the rings but if not you are tearing it down for nothing. The cam or heads can make the motor soft at the bottom and really come on strong on the top end.
I would start with a leak down test. If you have a trained ear you can easily apply pressure to each cylinder and see if it is leaking.
Every year I run the shop 135 psi air pressure into each cylinder with the valves backed right off and check the sealing of each cylinder. After doing this for years you really get a feel for it. I do have a very good leak down gage but have learned how to hear if a cylinder is good or not.
Anyway if the heads are too big it will act the way you say as well as a cam problem.
As for a carb borrow one.
First establish if the motor is sealing and if it is don't redo it for nothing. I have been where you are before and it was too big a set of heads that was doing it.

467-Ratman

I have learned alot over the last two years and probably the most obvious thing are the heads are wrong! I thought it would be real cool to have these monster heads, Grumpy Jenkins and all, oh well live and learn. I think its time to sell the heads and my beautifull gold finish 850DP and live in the real world!

norvalwilhelm

The heads may be wrong but not the carb. You have 468 cubic inches and it should handle the 850. I run 2 of them without a problem and all my past big blocks have had 850 double pumpers.
The heads for sure cause this problem and it don't know the duration at .050 and the lobe centers of your cam. Advertised duration mean nothing.
A easy cam in the 236-244 range 112 lobe centers has good idle vacuum , good off the line but runs out of breath on the top end.
A cam in the 256-264 range 108 lobe centers is great mid and top end.
What do you have?

467-Ratman

My cam has 236/246 duration at .050, I think the lobe centers is 112, and the vacuum at ldle is about 8 to 9.

69 N.O.X. RATT

First I agree with everything Norval says, however, if you want a very snappy great throttle response motor that will top out at about 5500 rpms, I make the following suggestions.

Get rid of your heads and get a pair of Chevy 049's or other 260 cc intake oval port Chevy heads. Make sure your pistons will fit with the new heads and give you 9.5 to 1 compression max.

If you want to go to aluminum look at the Brodix OEFI's or the new Brodix race rite oval port heads, the Dart ovals are very good. The Edelbrock or Chevy aluminum ovals have 2900 cc intake ports and will be a little less torquey at the lower rpm range

Put a solid flat tappet cam in with less than duration at .050 than you have. I would go with the Comp 282S, 236 at .050 .561 on a 110. Your 294 S is 248 at .050 .595 lift on a 110.

Get a 750 DP, and a performer rpm intake.

This motor will have great throttle response, and great street power, but will not want to rev above 5500 or so and will not make the rwhp your other one did.

This motor would love some 3.55 rear end gears


[Modified by 69 N.O.X. RATT, 5:37 AM 10/19/2003]

467-Ratman

Anbody want a great set of Merlin heads? They belong on someones drag car!

427Hotrod

There's another saying...."you don't have too much head...(or insert cam here too) you just don't have enough motor!"

Seriously, for the way you describe what you want, I'm sure the rectangulars are a little more than you want. But there are other ways around it without going crazy. But they aren't "that" big to be ridiculous. Factory LS-6's had larger heads tha tflowed much worse. They did it with cam and intake.

If you can sell them for a good price, I could see it, but otherwise I still wouldn't give up completely on them. Dart for years has recommended using oval port intakes on rectangular port heads to help them out. You have to think of the total airflow path from carb to valve.

I think the RPM airgap idea is a good one and for sure a nice small solid street roller would be great. I still like that Comp 288 street roller, but make sure you get the 110 LSA version...NOT the 112. It will make peak power around 5500-5800 probably yet still pull to 7000 if you want to and with your heads will not lose power on the top end at all. It holds tons of vacuum as well to help street driveability.

But "IF" you go into the engine...just stick a low cost 1/4" stroker kit in it assuming you're buying pistons and all anyway. You can handle the balancing issue at the same time and pick up 28 cubes as well as lots of low end TQ. Stroker cranks are great for that and will help those big heads work in the range you want to be in.

The flow numbers of those new Brodix ovals are great as well as some of the smaller AFR's. But frankly I don't think your heads are killing you too bad and could be made to work. I think we still have some tuning to do as well as I think you could optimize that cam pretty cheaply.

Try the RPM air gap first and then a different cam. If you want to stay with a solid flat tappet, I have a few favorites that I know work excelellent.

And your 850 carb size is alright...something is still weird with that dude.


JIM

467-Ratman

Thanks for the input Jim, I am going to talk to a guy on Monday who is about 70 years old but according to everyone in town knows how to really tune a Holley. Should be interesting.......

Guru_4_hire

I made a excel graph of alot of big block heads and their flow numbers and port sizes and valve sizes and such stuff. If any of you guys want it let me know and I will email it too you.

My e-mail is in my profile.