As I have mentioned in a a few threads, my son and I are building a 350 to drop in his camaro. It is a 350 from a 84 crossfire vette, 2 bolt main, 426624 crappy heads that nobody seems to like. We are throwing in a isky 280 mega cam kit, edelbrock rpm intake, and are topping it off with a holley 650 dp. I have been porting the heads quite a bit, and my local automotive machine shop tells me that so far I havent screwed them up, and they should actually flow pretty well. Our choice for the rockers are the 1.6 ratio with new springs to match.

The bottom end had a rebuild about 2 years ago, and all seems fine there. Bored .030 over, crank reground, line bored, new cam bearings. I have become increasingly concerened over the heads. I took pictures of the porting job I am doing to my buddy at the shop, and he is telling me this.... With what I have done, and plan to do, the motor will be a bit flat up to about 2800 rpm, the start to pull extremely hard up about 5200, then go flat again. That is if the whole thing doesnt blow up. I would like to put some low end into it so I am looking for some advice on this point, as well as any other suggestions you folks may be able to send my way. I am at the point where I can switch any combo except the crappy heads, the carb.

Thanks folks.

 

Well the first thing a i saw that might limit you is the 2 bolt main but i bet you have been told that all ready. Any machine shop could convert that to a 4 bolt. I would drop in a 3.75 stroke crank with 5.7 rods. Then have COMP ratio of 10:1 that is if those heads aluminum. Or you can convert that holley to e85 and run 11:1 with iron heads. or 12:1 with aluminum heads and e85. Use a 1 inch spacer that has 4 holes in it and has a spiral taper on in side. Not a open plenum one. Headers that are same length and tuned. Duel with no cats if possible. Hay I am not a master engine builder so this is could help or it could be wrong. Its what i wold do.

 

for what you're doing, a 2 bolt main will hold up just fine.

 

Any thoughts on possibly improving the low end power curve?

 

what are your cam specs?

 

That has to be one of the least knowledgable regurgitation of magazine facts I've seen in a long time.

As for the question at hand,I stated in another thread and I'll say it again,that's an old cam grind that leaves a lot on the table,as opposed to the modern grinds like the extreme energy,Voo Doo,etc.A properly matched camshaft will make all the difference in the world when it comes to a usable powerband.

 

an XE268 and that combo would make power hand over fist over the old school 280 cam you're thinking about running. the XE268 has abit less duration, advertised and @ .050, but much quicker ramp rates. the valve action of the XE grinds is much more aggressive, even with less duration or lift numbers. thus, giving more power than an old skool grind with slower ramp rates. the XE268 is going to want to start building power around 1500 and will want heads that are able to flow till 5500 or so.

the RPM intake and holley carb will work well, and i'd say that if you're using an auto, that a 2500rpm stall speed converter and 3.42 gears would make this a really fun ride.

 

I almost asked if he had his own show on the powerblock!

To the OP,

How much $$$ do you have in the shortblock?

 

Money in the block is nothing except the oil pump. The block was redone a couple years ago, and only has about 6000 miles on it. I didnt plan on doing anything to it, except a good clean up. It measures 4.030 on the button using my indicating bore gage. The crank has been reground, the block line bored. The bottom end looks really good. The heads are the crappy 624's but I have to use them with the budget I have. I have been doing the port work myself, and it all looks really good so far. I will be finishing them up in a couple days, and sending them to have them tanked, blasted, and the seats re-done. I am not sure about reusing the valves even though they look fine. If anyone has any specs on undercutting them, please let me know. I can bring them to my shop and gring them however I want. Being a toolmaker has its advantages at time.

 

I have this cam in a 350 and it pulls harder then stock over the entire range. It is matched with a Performer EPS and 600cfm performer carb as well as World Products S/R heads on a stock 4bolt short block. Make for a nice torquey and very driveable motor.

 

Just a thought, you might see if you can nab a later model block with a factory roller cam, then you don't have to worry about break-in problems or wiping a lobe. retro roller work great too, but $$$. also, have the heads been magnufuxed yet? if not I hope you aren't done with your port work, because if they're cracked you'll have wasted alot of effort.

 

They havent been tanked yet, but I didnt go too crazy. The motor ran great when it was pulled. It came with a mild build...performer intake, .442 lift cam, aftermarket rockers, springs. The guy just didnt want to put time and money into a motor so he bought a crate jobber to be done with it. The heads go in next week, so I will find out then. So far I only have my time into them, which I have plenty of. If they get trashed in a few months, it will just give my kid time to save up for a nice set. We are attempting this build on a 500.00 budget. So with the motor we will be 650 in.

I would like to re-use the valves, they are stainless, but not undercut. They also have the double retainer grooves. I havent seen the little lower retainers for sale anywhere. Can i use just the top retainer, or do I have to find the little plastic ones somehwere? I can also grind these valves anyway I want, so if anyone has info on how they should be undercut, please let me know. I would like to use as much as I can, but still put as much power to the pavement as i can.

 

I had n XE274 (which is one 'step' bigger than your XE268) in a 10:1cr 350, and even though it didn't really get into its powerband untill about 2500 or so, it wouldn't at all call it flat below that... from about 1300 and up was pretty decent. A little soft, but not bad at all. Power did not start to fall off till near 6000rpm.

Your XE268 will be a little sharper than my 274 off idle, because it is a bit smaller. But I wouldn't call it 'flat' at all.

That cam is similar, though a bit more aggressive, than the L82 cam that GM used in the mid-70s, which used basically the same shortblock at heads that you are using. It was also a little soft off idle, but from about 1500 and up it was pretty good, especially for the low compression motor that it was. Yours will be better with the Holley carb and probably more compression (same heads, but I'd assume you would go with flat top pistons, whereas the L82 had dished pistons).

 

Can you post a pic of the porting? and have you messed round with the intake runners? or have you been porting out the combustion chambers? as long as you have made the intake ports to big then you should be fine, it MIGHT e a lil doggy on bottum end but once you get up there she will rip. um to help lower end power, compression would help. if you are putting more air into the cylinder you wanna get it out here are some headers http://www.summitracing.com/parts/HED-68460/ 167$! long tubes so i would do stuff like that port match gasket match all that lil stuff helps a ton! but yea post up some pics and that will help too

 

I have actually done both. I have smoothed out the runners, and radiused the corner transitions, got rid of all the casting ridges, gasket matched them. I shaved down the guild bosses, and channeled the transition ridges there as well. I did some work on the exhaust side as well, pretty much the same thing as the intake side except for a near mirror finish on the runners, and boss guilds. All I did inside the chamber was clean up the casting a bit, take out the large hump under the plug boss, and smooth the radius transition there as well. I didnt want to add alot of area to the chamber so I didnt do any deshrouding. There are no sharp transition angles at all in there anymore, and the radii are nice and clean. I used a whip lap to add a little coarseness to the runner section as well, and it will get a touch more during blasting.

 

Called the machine shop this morning, and they will rework the heads for 180.00 bucks. That doesnt seem too bad for the pair. They will tank, mill em, grind the seats, replace the guilds, seals, and assemble the whole mess. This puts a damper on the 500.00 build, but for 180 bucks its worth it. Hopefully there are no cracks. I am having a hard time finding a cheap rpm intake, so I am considering a holley street dominator Im watching on ebay. Its old, but seems comparable. Carb rebuild kit should get here soon, as well as the head bolt kit, and gasket set. Someone mentioned that I need to use the same oil pan that I have on the 305 because of fit issues. True/false?

Thanks for all the input.

 

i thought i would run this by ya you said something bout the mirror finish. On the intake you dont wanna make it real smooth, it needs to be kinda rough not to rough but not really smooth, on the exhaust yea but not on intake make the chamber and exhaust as smooth polish um up so that the fuel and residue doesnt stick to the head so thought i would mention that

 

Only the ex side is polished, the intake sides are lap honed to about a 128 finish. The blasting will also add a little texture. I considered getting a bit fancy by polishing the runners, but leaving a scallop for about 3/4" on each side. Lap honing was easier, and proven to work though.