resipsa

What is the maximum valve lift for an LT1 aluminum head with unmodified valve guides and adequate retainer-to-valve guide clearance? I just purchased an Comp Cams XFI 466 kit. The cam has .570 intake and .565 exhaust lift with 1.6 rockers. Two of the techs at Comp Cams told me that no machining is required, but one tech told me that the guides need to be machined to achieve adequate retainer-to-guide clearance and to make the beehive springs fit around the guides.

Kevin Woods

I recently pulled my AFR heads and replaced them with stock aluminum heads on my 396ci; AFRs went to my engine builder so that he could match up the valvetrain components for my next engine build !!!

Anyway.....with 1.6 RRs and the stock 3/8" studs, I'm at .564" on the intake and .586" on the exhaust. After about 800 miles, no apparent problems, so far.......

KW

resipsa

Thanks for the info. Did you check the measurement between any of the retainers and valve guide/seals? What springs are you using.

Thanks

Demonic85

Its the valve springs that are susceptible to breaking on engines with a high lift cam. Stock valve springs on an L98 can safely handle .550" and I believe LT1's can handle .600". To be safe though I would definitely upgrade your valve springs

Mojave

Whoa there. Stock LT1 springs will most definitely NOT handle .600" of lift. LT4 springs are good to .525", and stock LT1 springs are less (something around .500" sounds right, I think). I wouldn't run over .500" on stock springs.

Now, as far as how much lift can the heads handle with different springs, that is another question. I know people run that cam with stock heads with different springs, so it should work.

STL94LT1

I'm running 605/622 lift on my LT1 heads. I'm also running 918 Bee Hive springs installed at 1.8".

Kevin Woods

No.....I know of so many guys with the stock heads and .550"+ of lift, that I was not much concerned.

These heads have the CC 987 springs.


And I thought I was pushing the envelope .

The 918's are rated buy Comp Cams as having a .600" max lift.

By the way.....I run that same custom cam (224/230 duration lobes, yes?) in my Caprice but with 1.52 rockers.....with the 918 springs.

KW

resipsa

I assume that you didn't have to machine down the valve guides to prevent contact between the guides and the retainers?

Jonnymac

I know an F-body owner that runs .625 with stock heads.

STL94LT1

Nope.

STL94LT1

Originally Comp rated the 918's for .625 lift. PAC who made the original 918's for Comp now offeres a Nitride treated 918 that is good to .650. One of these days when I refresh my springs I"ll go with the updated version.

BTW: How does that cam work in a heavier car?

-Mike

Greg Gore

High quality springs are important. A broken cheap valve spring has the potential to take out the entire engine. Setting up spring heights is not hard but there are several things involved and it should be checked by someone who has the tools and experience to get it right. You will also need a spring tester or rater. Measure from the bottom of the retainer beside the valvestem to the top of the guide or seal and see how much room you have. Next measure from the spring seat on the head to the spring seat on the bottom of the retainer to see how much room for a spring you have. Use this number to see what the seat pressure will be on the new springs you are considering and compress the spring by your total lift to see what over the nose will be. These numbers are important to decide if you have the correct load springs for the intended purpose. The final thing that might need to be done is check piston to valve clearance in the split overlap position. This means when both valves are open at the same time. Exhaust valves will be closest to the piston at 10 degrees BTDC and intake valves will be closest at 10 degrees ATDC. You will need a minimum of .100 on both and maybe a little more on the exhaust. Actually if I saw .100 on the exhaust I would check them all to make sure there wasn't one closer due to production tolerances. If the valves touch the pistons they will break. Things that change piston to valve clearance is increasing valve lifts and changing cam timing. Advancing the cam places the intake valves closer while adding exhaust clearance and retarding the cam pushes the exhaust valves closer.

resipsa

The XFI kit includes new roller lifters, 26915 beehive springs and corresponding retainers and locks. Phoenix Auto in Palm PA is installing the this package for me.

STL94LT1

You need the 918's, not 915's for the XFI 466

resipsa

I know thats what the catalog says, but the 918s have been on backorder since early December and probably will not be available until well into February. My partially disassembled car has been at Phoenix since late December waiting for the cam and springs. I can't wait till February for the 918s. Two of the techs I spoke with at Comp Cams assured me that the 915s would work fine in my application (max rpm 6200 rpm - I dont trust rods/rod bearings beyond this). Both springs have the same spring rate of 313 lbs/inch although the 915s are rated 25 lbs lower at 1.8" (105 vs. 130) and 1.2" (293 v. 318) than the 918s. The 915s are rated to .600 lift. I'm thinking about shimming the springs .030 (installed height of 1.77") to give me about 115 lbs on the seat. I think this should work fine?

STL94LT1

PAC was the original manufacture for Comp's bee hive springs, before Comp sent there manufacturing to Mexico. You can still buy the original 918's made by PAC.

http://www.herronperformance.com/sto...&productId=183

resipsa

It sounds like you're not convinced about the use of the 915s with this cam. I kind of feel the same way. I'm going to call PAC tomorrow for availability. Thanks for the info.

STL94LT1

Comp advertises that the XFI series camshafts should be used with the 918 springs, and then because of a stock shortage they try to sell you the 915's. Personally, I don't think the 915's have enough seat pressure for the aggressive ramps of their XFI camshafts. I've even seen people shiming the 918's to get a higher seat pressure because of valve float.

Greg Gore

Endura Tech by NHK. Currently the best valve spring in the world regardless of price.

Kevin Woods

Interesting!

I had my lobes ground on a 110* ICL and a 114* LSA......works quite nicely in a stroked B-body (Mid-12's quarters and 21 MPG HWY) !

KW