Ok, I'm reading everything I can on finding the correct geometry and getting the right pushrods. I like the Comp Cams adjustable pushrod length checkers, the ones that move in .050 increments to make it easier to measure. I haven't figured out yet exactly how to measure everything yet but that's why I'm still reading and researching.

Anyway, I just saw in the Comp Catalog where they recommend specific pushrods for this cam (XE274H). They recommend the #7812-16 rods which are 7.794" in length. It's not that easy is it? Even if I'm using their suggested lifters, the Pro Magnum full roller rockers and the suggested Comp springs I can't just pick a 7.794" pushrod without checking the geometry first can I? I already have a set of new Summit 7.794" pushrods if that's the case.

So, the question is, what do they base this recommendation on? I'm using a .015 compressed gasket and Trick Flow aluminum heads on a stock deck height. I thought all that played into the geometry as well.

One of you guys surely knows this answer. Thanks in advance!!

 

It does all play into the geometry. Get a pushrod length checker and use it as the instructions tell you. No one can tell you the exact length you need without measuring with a checker on a modified engine with different gaskets and aftermarket heads. It is the only safe way to do it.

 

I would never just go and buy a recomended pushrod length. There are way too many variables not taken into consideration by the manufacturers.
Here's a good instructional on how to.
http://www.carcraft.com/techarticles...pushrod_length
Eddie

 

Ok, that's what I figured. The Hi-Tech line of Comp's pushrod length checkers come in different sizes. Each one measures up to an inch. So they have one that starts at 6.800" and goes to 7.800", the next size starts at 7.800" and goes to 8.800". They have longer and shorter as well.

Should my pushrods be between 7.800" and 8.800" or do I need to get the smaller one too?

I read the info on Comps website about how to check the length using their adjustable checkers and like the idea of these having the .050" increments to go by. I just don't know what range I should be in.

Thanks!!

 

Looks like your right on the Margin with the Length checker. Get them both or use your best hunch and if its not right get the other One.


You need to get the pushrods that are exactly Correct length or the consequences are early Guide wear ect.
Heres one way to do it: pre pump up a lifter, then Put some ink on that valve stem tand Use the adjustable rod to set up one of the rocker arm rollers on the stem. Then with the coil disconnected crank the engine over a few times. Pull the rocker arm back off and look at the trace mark on the valve stem. If the mark is narrow, and takes up about 1/3 of the whole dia. of the valve stem and "traces right on the center" measure the adjustable Push Rod , round off to the closest .050". Thats the ones to order. If the mark isnt where it should be, adjust the Pushrod till you get it..Hope this helps..

 

How do you do this? Remove and soak the lifters in oil or will running an engine pre-oiling tool do the job?

 

Sorry, I should have said a hyd. lifter must be pumped up full for the results to be accurate. Im not sure if filling one up by hand will work ? I doubt it will , so If you dont have the dist. installed , probably best to get a solid lifter to do the length check.

Edsred72's link to carcrafts article is a great one, it details this procedure very well.

 

It's definitely a good article on how-to but I'm still missing the lifter thing. I'm in the process of building the engine so I definitely don't have the dist in place. I have hydraulic lifters and it sounds like I can't pump them up manually. So, how do I know what solid lifter to use; doesn't it have to be a specific size?

 

Use light checking springs and no need to pump up the lifter

Also check Crane's adjustable rods, might be more adjustment in theirs than Comps

 

If you really think you need pushrod length checker .....
Star Racing www.starperf.com has em for about $11 each or a set 5 for about $50. Their P/N REN.7901 has range 7.500 - 8.700 (~$11). No argument ... not gonna ... but hope your Alum heads like the shim gaskets.

 

Thanks for the info on the checker; I'll look into it.

On the gaskets, all I can say is that the Fel-pro 1094 says it can be used with aluminum heads. It's a rubber coated gasket on both sides and is meant to be installed completely dry.

I did my homework on this before going that route and found a lot of people using them with aluminum heads with no problems. I searched a lot of different forums (even non-corvette) and also read everything I could online.

Yes, I have concerns about brinelling the heads but after double checking all my piston heights again I found some as much as .028 in the hole. Put that with a .028 gasket and I'm looking at a .056 quench distance. I'm just not comfortable running that quench with an 8.1 DCR and 10.05 static. Apparently the VR 5746 .026 gasket cannot be purchased any longer. The only place I found (thanks to Rich) that had it listed was NAPA and after a week of it being in a "picking parts" status I cancelled the order.

So, I either have to run the .056 quench, use the shim gaskets, or have my original numbers matching block decked and use a thicker gasket. I don't particularly like any of those options but the shim gasket is the one I've picked (subject to change )

I do appreciate your input and pointing out that the shims are usually not good for alum heads.

 

28 or 26 ... insignificant diff ... but regardless if on website www.competitionproducts.com (800-233-0199) used to sell VR5746 ... any local parts house that currently carries VR has/can get.

 

I definitely agree .002 is insignificant. My concern was going back and finding that I had pistons as deep as .028 in the hole. .054 or .056 quench either way just seems like a lot when I'm running such high DCR and SCR numbers unless I'm missing something.

I was on the edge of thinking it was just barely OK when I was going to be .022 in the hole and a .048 quench distance with the .026 gasket. I don't want detonation but want to use the heads and pistons I already own. This is really limiting me on what I can put together.

 

My quench is ~.060", went thru the same thing as you and also had the added headache of piston to valve clearance which would have been too dangerous if I lowered the quench.

My compression ratio is 11:1 and my DCR is 8.5 and I made 550HP with no detonation problems on 91 octane. Quench is overrated IMHO, if you can lower it fine, if not no biggy. I would love to see a comparison of the same engine with .050" and .060" quench, I would bet there wouldn't be any measureable difference

 

This helps a lot. Thanks for posting! I've changed my combo so many times based on things I've read that I may have gotten too caught up in some of the numbers.

I was originally going to run the Comp XE268H cam which put my DCR at 8.32. Wasn't comfortable with that but some people thought it would be fine as long as I kept the quench small. I think that's how I got so stuck on quench.

Well, now I'm leaning toward the XE274H cam which lowers my DCR. If I stick with the 274 and go with the .028 composite gasket, my DCR comes down to 8.1 and SCR comes in at 10:1. My quench will still be at .056 in the worst cylinder and it sounds like that's OK. A few people have agreed here that I shouldn't get too concerned about this quench.

Add that to the even slight possibility of brinelling my alum heads with a shim gasket and I think I'm convinced that I should go with a composite gasket. Since the .028 is readily available from Summit and I'm getting other stuff there; that's what I'll get.

I think its very easy to read too much information on the Internet. I have gone from not very educated when it comes to engine building to knowing way more than I think I want to know. Hopefully I'm on the right track now.

Now, time to put my head back into the original question and figure out my pushrods.

Thanks guys!!!