On a rebuilt engine where block hieght and heads have been milled, what is the best way to check/decide if the intake manifold will need machined to fit properly. The way it looks from a test fit the valley or front and back of the manifold will need material removed to lower the sides for proper fitment. With the manifold sitting in place and no (manifold to head) gaskets on, Can I use a feeler guage to measure for a specified amount of clearance? Anyone know the desired clearance?

 

Clearance to what? Mine have been milled and I just port matched, didn't need to deck the intake.

 

In a perfect world - you'll want to mill the intake off the same amount as the heads.

How much were the heads milled?

I recommend that you set the intake on with the gaskets in place and see if the base bottoms out before the port flanges do.

 

.05 on a head clean up is so little though, haven't had any troubles with my engines. On one with a really thin head gasket I needed to round out the accessory bracket holes though.

 

most likely it will fit/run without issue if the gap is ~.05

 

C4vettrn,
Using feeler gages are possible but difficult to get in all manifold gasket and port areas for thorough measurements.Clearance at the china walls should be just enough to allow for a resonable layer of RTV sealer after being torqued.
Unless you have milled a lot off the heads other than just to straighten them such as angle milling, or done any serious porting of the intake to match the heads previously,probably nothing will need to be done. The stock intake ports are usually small enough to allow minor surfacing of block and heads and still align. If more has been done,you could mount the intake using old gaskets and torque it up dry to check (1)for any bolt to bolt hole interference with the manifold. (2) use an adjustable inspection mirror and flashlight thru the T.B.opening to see how all the ports align to the heads. If angle milling was done or you just want to know if the angles are right,I take a set of new metal 7777 sandwich intake gaskets,install, and torque them up. Then remove them and precision measure the thickness variance in crush between the top and bottom at the ports to determine if the manifold and head angles are close to the same or if machining of the manifold is required. Using paper gaskets would make doing this difficult without some kind of a crush surface for measuring.I do waste a set of gaskets doing this but it gives me actual gasket compression fit. I found this problem after assemble of my freshly decked LT1 block,new AFR heads, and a new LT4 manifold out of the box. It would be difficult to detemine at this point what part is actually off short of disassembly, unless you precision measured all angles prior to assembly, so machining of the manifold was done. I found .017" difference in a 2 1/2" length top to bottom on both sides so I had to angle mill the manifold to match. This had the potential for serious manifold vacuum leaks as well as oil intrusion from the gallery if not fixed. This removal amount did require slight clearancing of the manifold bolt holes to insure no interference. China wall clearance was still present but feeler gage checks showed a little over a 1/16" drop in the manifold so I took that off those manifold surfaces as well.
Rick

 

What manifold gasket are you guy's using? The one GOLEN engine reccomened has larger ports than my stock one did. These are it.
http://www.summitracing.com/parts/FPP-1284/

Next question: My FelPro head gaskets came with smaller than stock coolant holes for the middle two cylinders. I looked at my original gasket and the same holes on it were large diameter on the bottom only and the same smaller size on the top two. I drilled my new gasket to match my old one thinking I couldn't go wrong? Is this standard practice? THANKS!
http://www.summitracing.com/parts/FPP-1074/

 

Felpro make a boomerang shaped measuring tool to figure out if you need machining to correct a misalignment. Its felpro 2520, it measures the intake & heads(installed of course).

 

Ok I installed and tourqed my head gaskets then I layed the intake gakets on each side of the head and set the manifold down. I had 65-70 thousands of clearance between the china wall and manifold both front and back. Im sure when it's tourqed in place it may close up but that still seems like alot?

If I set the manifold in place without the gaskets it touches the china wall with clearance on both sides. Is there a recommened clearance one should have? My gaskets measure .69 crushed.

 

TTT

 

Did your intake bolts start easy? Usually when theres a problem, those bolt holes don't line up to the threaded holes. 65 thous. sounds ok for the end rails, you are gonna use rtv there.

 

Thanks that looks a neat little tool Looks like 2521 is for 1987 and later...and the 2520 is for 1986 and earlier...



Mike

 

Yeah, its a handy tool if you do alot of intake/heads swaps. It's made out of thick alliuminum, & has instructions. I had to clearence mine at the ends b/c the heads I'm running has raised v. cover rails. I't helped me figure out that my heads needed alittle taken off, so the intake bolt holes would line up,( I had an intake sucking oil & no matter how thick an intake gasket I used, it burned oil). Now that I think about it, those new heads I installed should've been put on an engine that is zero'd decked, mine wasn't. Hind sight 20/20 huh?

 

I have the same problem determining whether the cylinder head to intake manifold interfaces line up properly and how much if any needs to be milled off the intake on a 08 LS-3 that has had .020 milled off the heads and using .012 thinner head gaskets. The Jegs site says the fel-pro 2521 is for 1987 & later small block chevy engines with 23 degree angle. There is no further application information on Jegs site or on Fel-Pro's site for this tool. After much searching I finally got hold of Fel-Pro tech support and found out this is strictly a go/no go tool that does not apply to the LS-3 or for that matter any LS engine according to Fel-Pro.

 

Testing by FelPro - and maybe others - show that some stocvk size gasket holes should be made larger than stock while others smaller. Has to do with equalizing coolant flow and temperatures.

The Fel-Pro gaskets I used on the 415 I was building called for increasing the size of a couple of holes in the 400 BLOCK, which I did according to Fel-Pro's directions.

Standard Practice? I'd say "no", but you'd probably have to run a survey to get some representative results. Even then, I'd tend to trust Fel-Pro's engineers.

If you think about it, Fel-Pro is one of the best known, reputable gasket manufacturers - if not THE best - going. So you took what their engineers produced and chose to modify it by enlarging holes in the gasket. Is there any engineering science to support that decision?

Making changes like that without the supporting science is risky; not really knowing what the results will be.

Just me view.

Jake

 

Machine shops, especially those who specialize in racing engines, probably have a mathematical formula they can use to calculate how much material and from where it should be removed. The amount depends on the numbers involved. You know, how much the block was decked, how much the heads were surfaced, gasket thicknesses, etc.

It's been a LONG time since I've actually seen the formula but IIRC the amount of material removed differs depending on whether it's the China Wall areas or the Intake port areas. Different amounts are taken from each location.

Remember, it involves more that just bolt hole alignment, but port alignment and sealing as well. I left things such as this in the hands of my trusted machinist which is one reason he was chosen.

Jake