carb jets, 454 assembly, and th400 questions.

[curtis73]

Just finishing up a project and need a few little helps. This is a basically stock reman longblock that is getting a mild comp 212/218 cam and 049 heads. The heads are on, the cam is in, and tomorrow I'm finishing it up. The vehicle is a 73 Impala Wagon that currently has a sick 454.

1) the stock-style rocker assembly has the stock-style acorn-shaped friction-locking nuts on it. Are those nuts designed to be used as adjustables, or are they only intended to torque down? If they're adjustable, my life is easy. If not, I have to go through each one and check for proper .020-.040 preload on each and maybe have to get custom pushrods. I'd just get polylocks, but I have to keep my stock valve cover height to keep the A/C.

2) If they are adjustable, how much preload goes on the lifters? Comp told me 1/2 turn for their lifters. Crane told me 1/4-1/2, but the chevy rebuild techbook says one turn. I'm using stock replacement lifters from an unknown source; How much is right?

3) The car is a 73 with 60k original. The stock th400 in there has good red fluid, but shifts like a stocker. Should I rebuild before a shift kit, or should I just throw in a B&M kit and flush and fill? It would make my life easier (time is of great importance right now) to avoid a full rebuild.

4) The engine was purchased as a reman longblock by a guy who sold it to me. It came with 049 heads on it and it was sold as a generic 454 stock replacement for 1965-1984 vehicles. Is there any way to tell compression ratio without pulling the heads to do a full measurement? Since I know the swept volume, could I fill a BDC cylinder with a measured amount of oil and subtract the swept volume? Is there an easier way?

5) The "new" engine was purchased for a truck, but was listed generically for all 65-84 vehicles. Is the "new" engine's oil pan going to be the same as my Impala's? Or do I need to swap the old pan/pickup onto the new engine? This is something that I can find out on my own with the engines side by side, but I only have a friend's garage for one day to do the swap. Knowing this ahead of time will help me streamline the effort.

6) Is there a magic way of finding carb jetting for a combo? In the past I've sent my Q-jets away to Jet Performance and got back perfectly tuned pieces so the seem to have the secret formula. Unfortunately I don't have time to use their services this project. How will I be able to tell what jets to use? I might be close since the current combo runs rich and the new cam is only a mild step up, but I want it to be spot-on. The carb is a Q-jet in this case by the way.

Lots of questions--I know, but I'm the ultimate bench engine builder. I have read every Car Craft, Hot Rod, and PHR magazine every published for the past decade or more, as well as most of the SAM texts and ASE texts, and yet to date have only built three engines. Most of it is like second nature, but some things still are cloudy. Thanks so much

Curtis

[pind]

compression ratio should be about 8.6:1 ( swept volume + chamber volume/ chamber volume )

one full turn on the lifters for preload is something I have always used on chevys, although I do know guys who use 3/4 turn with success. If in doubt, do a running set on the valve lash.

if the tranny shifts well, go with a flush/fill and a shift kit. the 400 is a pretty strong unit.

[68chevelle]

the only question in going to adress is the carb question. for the time being i would run the same carb as you have on the old engine. when you can i would sugjest having it tuned at the least but perferably sending it to Jet to have them tune it. it should work about the same but as you said with the cam being a little bigger and it running a little rich you might be about right. but the only way to find out is to try it, or call Jet and ask them. they should be able to tell you over the phone what jets they would run if you give them info like cam specs, car, and all the other info that you have to give them when you sent your other carbs off. one thing you do need to realize is that when you send a carb to Jet to have it rebuilt and tuned they do more than just jet it and rebuild it, so if you rejet your old carb for the new engine it probably wont perform as well as if you sent it to Jey but if you had them do this carb that will be going onto that new engine it should be pretty close to perfect still. when you send a carb to Jet they change all the important springs that control opeing rates and sutch things. they tune ever aspect of the carb down to drilling out a few pasages and whatnot. basicaly the only things that are the same when you get it back are the main body of the carb. evrything else has been adjusted or replaced as to best suit the spacific aplication it is being built for. they do the absolute best work on carbs and what they turn out is some of the best carbs you can get.

[MagicRat]

For the lifter pre load, your rocker arm nuts are adjustable. Use Crane specs, not your rebuild manual specs. I have used 3/4 turn. Play it safe. If there is too little pre load, the valve gear is just a bit noisy. Too much preload might burn your valves.

Just bolt your stock carb on and see how it goes, before tuning. Quadra jet carbs sometimes do not like long duration camshafts. The venturis work best on engines that have stock cams with lots of vaccuum. As the cam gets lumpier, they do not work as well. Chances are, your carb will be fine as is, but if it runs poorly, consider a Carter AFB (Edelbrock) or Holley, instead of tuning it.

Finally, when you say your new 454 is for a truck, do you mean light truck (pick up?)
There are lots of 366, 427 and 454 engines that were used in medium duty (5 ton) trucks. All these engines look almost the same as the auto and pick up truck 454, but the deck height is an inch taller, they have low compression and huge, heavy pistons. Lots of people have mistaken these for a car big block. However, they don't make much power and won't fit into a car.

[curtis73]

Nope, its definitely a car block with a standard deck height. It is a two bolt block cast in October 76 that has been taken .030" over. I asked about the compression to fine tune things. I knew it would be between 8 and 8.7, but wondered if I could use something to really tighten up that gap. It would really help me tune the spark curve. It gets fired up tomorrow! Wish me luck!

By the way, one for the Hollander book. I put the "new" engine in with the truck pan to see how it fits. The stock pan I could fit a hand between the pan and the crossmember. The new pan is a nice tight 3/8 inch above the cross member and slopes EXACTLY with the curve of it. The sump is about even with the bottom of the crossmember and tranny, and with the wagon's altitude its never going to be a problem. Its a bigger capacity pan with a better windage tray. What more could I ask from a mistake?