Question about Comp Cam XE256H, low compression 383, and valve spring shims

[Triple Black 73]

I bought the wrong cam for my low compression 383. The CompCam Camquest tool says the XE256H (21-221-4) is a "great fit" for the engine. I plan to buy the whole kit: https://www.summitracing.com/parts/cca-k21-221-4 Will this cam work good for me? Is there a better cam for the engine?

Here are the engine specs:
Block: 9.985 (Decked .005)
Piston Compression Height: 1.848 (Cast Silver-o-Lite flat top)
Bore: 4.310
Stroke: 3.375
Gasket: 0.020 (Mopar steel shim head gasket)
Heads: 346 milled 0.010 ~78.5 cc
Compression Ratio: ~8.75
Other parts: Headman headers, 2 chamber mufflers, stock intake, 850 CFM Thermoquad, Autolite AP-86 spark plugs, MSD 8mm wires

The CamQuest tool says this will make 350hp @4500 and 465tq @ 2500 (yeah right!)

Cam specs:
http://www.compcams.com/(S(vuszczyg...mpany/CC/cam-specs/Details.aspx?csid=705&sb=0

Also, my dad says I need to get valve shims to ensure the installed spring heights are correct. (We had an issue of one cylinder having 125 psi due to the valve not closing completely due to weak spring/wrong installed height) Will these work?
https://www.summitracing.com/parts/cca-4755

 

[lewtot184]

i'd use the comp cams 21-305-4.

 

[texas69bee]

That carb is way to big for that setup.
I'd go a 680 vac sec at best. Lewtots suggestion on cam is better than what you selected. As far as shims, take those heads to a builder and have him pressure check those springs. He will know what to do from there.

 

[Triple Black 73]

I hear you. The 268AH-10 and the XE268H both sound great and make good power, buuuut, how well will it work with clapped out 342 heads and 8.75 compression?

 

[66Satellite47]

I agree with lewto the cam you selected is really small, his choice is like the stock 383 HP cam which isn't really very big either. The 346 heads are a decent casting. You need to check the installed height with spring height tool and then shim to obtain the desired seat pressure with the springs you use.

 

[65-440]

where did you come up with that compression ratio ? You've milled the heads, deck and .020 gasket. My 383 build I didn't cut the deck, or heads, running .040 felpro blue and came out to 9.44:1 .... comp xe268h cam ...

 

[65-440]

use this and input your #'s ...

 

[66Satellite47]

use this and input your #'s ...

View attachment 420497

Not sure about this, but it looks like your formula is mixing metric & English units. I do mine all in English and only need to convert the head CC & dome or dish from CC's to cubic inches. Just my way.

 

[Triple Black 73]

where did you come up with that compression ratio ? You've milled the heads, deck and .020 gasket. My 383 build I didn't cut the deck, or heads, running .040 felpro blue and came out to 9.44:1 .... comp xe268h cam ...

Your deck clearance is 0.019. I measured mine at 0.087(!!) in the hole. Thus 0.020 gasket... Arp bolts... just to get 8.75:1. Wrong piston. Wrong cam. SOB.

 

[Triple Black 73]

I agree with lewto the cam you selected is really small, his choice is like the stock 383 HP cam which isn't really very big either. The 346 heads are a decent casting. You need to check the installed height with spring height tool and then shim to obtain the desired seat pressure with the springs you use.

Does the shim go on the base near the seals or on the top under the spring retainer?

Hmmmm.... Maybe I should Google that question....

http://www.superchevy.com/how-to/engines-drivetrain/1604-heres-how-to-set-proper-valvespring-height/

 

[moper]

I just did a '65 383 that is all stock. The XE256 is the right choice. You need to replace the springs with the ones Comp recommends. The Thermoquad is also a solid choice. My customer runs the 6bbl, with modified HP manifolds (it's in an A body). It pulls great, and it's a 3.23 geared 4sp car. I have used the XE268 many times too, but I think given what you're doing the 256 is a solid choice.

 

[65-440]

Your deck clearance is 0.019. I measured mine at 0.087(!!) in the hole. Thus 0.020 gasket... Arp bolts... just to get 8.75:1. Wrong piston. Wrong cam. SOB.

Yes, there's the difference !

 

[miller]

Does the shim go on the base near the seals or on the top under the spring retainer?

Normally, you don't use spring shims. I have used them in the past, but only for two different reasons. They always go at the base of the springs.
If your using used springs, and they fall short of the free standing height measurement, the right thickness shim is used to take up what's missing. Or, if the head's spring base surface has to be cleaned up, because of wear...shim for that.
New springs don't normally take shims. Main thing is the installed spring height you get.

 

[66Satellite47]

For a performance build, when a head has had a valve job the installed height will change a bit depending on how much was taken off both the seat & the valve. That's reason one for shimming and you need to measure to find out where each valve really is in terms of installed height. The other reasons are to obtain the desired seat pressure with the selected spring, again the spring pressure needs to be measured. Another is to correct for any spot facing done to correct for wear under the spring. The shims go under the valve spring. reason. You don't need to go through all this if it's a backyard build and you can hope for the best.

 

[Triple Black 73]

Great advice guys! Y'all gave me a lot to think about! This engine build has been a mess. I'm all high performance and my dad is bone stock. This 383 is a blend of both and we ended up with a turd sandwich. Many thanks for helping us get on the right track.

The heads has been worked over at least three times ('82, '94, & '12). The concerns with the valve springs is due to the valves being deep into the seats. We tested three cylinders. Number 1 and #3 was showing 150 psi while #5 was showing 115 psi. The seats look great and held water. However, the installed height of cylinder #5 is much higher (~0.030") than #1 & #3. The heads need new valve seats to get the springs back to where they should be, but I think that money would be better spent on 440 Source Stealth heads. So, shims it is. Also, I don't trust the stock springs as they might have over 300K miles on them. My dad daily drove this engine in his '71 Satellite from '77 until the mid '90, then I drove the hell out of it in '95 and '98 in my '73 Charger.

The CompCam CamQuest tool says the XE268 would make 20 more HP 500 rpms higher and 20 less torque 1500 rpm higher. I think I'll stick with the XE256 for the low end torque to overcome the 2.76 highway gears. If you guys say the XE268 could work then I know the XE256 will work!

 

[66Satellite47]

IMO a new stock style spring made for the XE256 is inexpensive enough to go for. I'd never consider using a heavily used stock spring with a fresh rebuild. Good luck.

 

[Triple Black 73]

IMO a new stock style spring made for the XE256 is inexpensive enough to go for. I'd never consider using a heavily used stock spring with a fresh rebuild. Good luck.

Yup. Everything I read said cry once and spend the money to get the complete kit. I just placed an order for this kit: https://www.summitracing.com/parts/cca-k21-221-4

 

[Lazerwolf]

There is no correct answer on cam choice. Do the research and find one to match what your looking for and your parts. For a street cruiser, that XE256H should work well. When I bought my 74 Charger (400 engine), it had the Comp Cams XE268H. I hated it but others here love that cam. Below 1500 RPMs, it was totally useless and only showed promise 60+ MPH. Great if only driving highway. Part of my problem was incorrectly installed parts and mismatched parts. I rebuilt top end using a Voodoo cam, fixed the issues and much happier. Still a work in progress, but that will always be. Buddy of mine with similar build went with the Thumpr cam since that was the performance and sound he wanted. As long as it runs the way you want it, no right or wrong choice.

 

[moper]

It sounds like the heads are clapped out... Stealths might be an option, but if you can find a set of 516s locally you could have them redone for less coin. The Stealths need to be checked by a reputable performance shop and the valve job fixed, and if you don't order them with the Comp spring option you should reaplce the springs too.

 

[Garys1969RR]

Your deck clearance is 0.019. I measured mine at 0.087(!!) in the hole. Thus 0.020 gasket... Arp bolts... just to get 8.75:1. Wrong piston. Wrong cam. SOB.

If you use the United Engine and Machine C Ratio calculator, you can input all your data, and get to the C/R you want. I'm getting you at 8.6 to 1, at best. Those heads may be closer to 88 ccs. And if there are valve reliefs in the piston, you have to add that to your compressed volume. Some KB pistons can have 4 to 7 cc of valve relief. You need at least a true 10 to 1 to get decent torque/horsepower.