Advice on camshaft choice for my sbc......

Hello all, my '51 styleline is coming along well and I'm currently doing the engine, giving it a freshen up and a small amount of modifying, I have a 1989 hencho Mexico 350 4 bolt main engine with what I believe is an 8.5:1 compression, I've given the heads a decoke and mild port job (smoothed the bowls and gasket matched the ports) and now I'd like to get some feedback on best way to go cam wise. She will be running a Shaun Murphy induction stage 2 quadrajet, with tubular rams horns exiting out of a 2.5 or 2.75 exhaust. I would like to get a nice lumpy tickover so it sounds like it's running a hopped up mill, and also like it to have a bit of go but don't want to sacrifice low down power for when I'm cruising round the campsites at the shows In the summer! Now I'm drawn to the comp cams line up and see that a 268H is probably best for what I have but I don't think this will give me the rumpty tump I'm after, so the 280H or 270H might be better but what I've read on some threads is these are no good for my compression ratio, I could get my heads machined down a bit to raise the compression as they are all in bits at the moment but again I don't know by how much I should go, was thinking as much as 60 thou, but again this is just from looking online so if anyone has had experience that would be great. I'm over in the uk so parts are far and few between over here I have a company that supplies comp cams over here or as an alternative there is a firm local to me that can custom grind a cam for me, but what specs should I be looking at etc.

I've looked on the hamb and the net and there's a lot of good info but also a lot counteracts each other. So if any of you hambers can help me out that would be great.

Cheers and happy new year Jason.


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you are right , about 8.5:1. in my opinion about 9:1 is about the maximum to use on the street around here with regular gas.

i've never been a fan of milling a sbc heads for compression , especially that much...makes for other issues. if you want more compression ratio swap the heads for smaller combustion chambers or put in flat top pistons

as for camshaft , you will get about 10000 suggestions...my suggestion is it is easy to over cam an engine. i would recommend the Edelbrock Perfomer ... and everyone makes a copy of it too. like Summit #SUM-1102

 

The Comp Cams 268H would be a great choice for your engine. You don't mention what you're runnung for a transmission or what the rearend ratio is. It would be really easy to overcam just for the lumpy idle. The best deal would be to get a hydraulic roller setup with close to the same specs as the 268H.

 

Maybe the edelbrock performer RPM cam 488-510 lift.

 

Lumpy cam and low down power do not go together.

 

The cam alone won't give you the "rumpty tump" you are after.
Compression is what you want, and tight quench is what you need so it keeps detonation at bay with pump gas. Forget about 87 but 93 is real doable.

Stick a lumpy cam in with no compression and you'll loose all your low end power.

 

Thanks sorry I'm running a th350 with a 10 bolt rear but unfortunately I don't know the ratio of the rear as there was no tags on it when I got it, also I will be running a high stall converter.


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If you are mostly interested in the Lumpy sound, go with a Comp Cams Thumper - they actually work pretty good for what you are trying to do. But as others have said you really need some compression in order for it to really sound right.
You can run a lot more than 8.5 or 9:1 on the street with pump gas if you have enough cam overlap to bleed of dynamic compression at lower RPM.

 

I ran basicly the same 350 as yours,the tried and true L-79 Grind is probably a good choice.Give this a listen:http://www.youtube.com/watch?v=Ywe6oDkkEJE there may be more on youtube. Here is what you may want to order:http://www.ebay.com/itm/Cam-And-Lif...Parts_Accessories&vxp=mtr&hash=item461807088f Hard to beat this deal!

 

x2.

the new thumpr cams are built for this.

Great sound and a lot better power than the old radical cams of yesteryear.

 

Thanks, just looked and yes the l79 seems great value, as do the thumprs, it's certainly more like the sound I'm after. I'm pretty sure I have to raise my compression now to get it how I want.


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Thank you yes I realise that but meant that I did want it to be slow as off the line if you know what I mean maybe a 2500 stall might help


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With the savings on the L79 cam & lifters I posted give this a read and see what fits the budget: http://www.carcraft.com/techarticles/ccrp_1209_eight_budget_sbc_head_shootout/viewall.html or http://www.ebay.com/itm/327-350-CHE...Parts_Accessories&hash=item53fbb5936f&vxp=mtr

 

Why are you running a high stall converter?

 

Stick with the 268H. Your choices are limited by your compression ratio. Do you know the CC of the heads? 76cc or larger I'm guessing.
You wont be able to take enough off the heads to get to the necessary compression for the larger cams. Plus, you will have to have the intake cut, or sealing the intake will be a pain in the ass.

 

Get a comp cams thumper , IMHO I would stay away from any of that old L-79 stuff , it was designed for 11:1 comp and really high octane fuel, just because something worked in the 60's does not mean it works in 2013 ! Good luck and call comp cams

 

You can not pick a cam by sound.
The sound is a by product of a high stepping engine struggling to stay running at low Rpms.

At 2500 Rpms I doubt that you'll be able to tell by listening alone if it has a lumpy cam or not.

 

The Comp Cams Thumpr Series love compression. You're too low to utilize those. Comp will tell you the same thing. The most cam I would put in it would be the SUM-K1104 (.465 lift 224* duration.) or a Comp 268H. I have used many of the Summit cams and had success with the similar compression ratio you are talking.

 

Ok thanks for all the replys, I'm really stuck with what I have so far head wise, the only other thing I have found is these pistons..... http://www.summitracing.com/int/parts/slp-h617cp/overview/
They are domed and seem to raise the compression with my 73cc heads (although until I get back to the shop where my engine is I'm only guessing I have 73cc heads as it's a standard '89 crate 350). I could get a set of these but again there's mixed reviews, I guess they would work and bring compression up to 10:1(ish) then allowing me to use a lumpy idle cam.

Would appreciate any views on these? Thanks again Jason.


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Thanks for that, very interesting read shows I'm battling against all sorts here, those alloy heads look great for the money.....


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Maybe you should plan from a performance perspective and let the exhaust handle itself.

 

Those heads look like a steal @ 620 with free shipping!!!
Just got my vortec heads out of the shop.
Valve job, 1new valve, cut down guides, screw in studs, high lift beehive springs, and a couple misc things was 450.00 on my heads.

Now have you used them ?

 

The pricing is attractive, but there have been a lot of issues with the overseas castings on the cheap aluminum heads. I think the $450. you have in the Vortech's is a better deal for longevity and piece of mind.

 

Run an Isky 262 Supercam.

 

I used these thin .015" head gaskets on 2 engines. Both still running good. Will bump up your compression .5 to .6 over a std .039/.041.

http://www.summitracing.com/parts/FEL-1094

A comp cams XE268H is a great cam. I have one in my car

 

I used a CC 268 in a 69 impala 327 originally 2v carb. I added edlbrock 2 plane alum. intake holly 600 4v,.headers 1800 or so stall th350, stock rear end and suspension. The compression was suppose to be about 9.5 to 1 but it didnt seem like it. It ran 15.9 in the 1/4 mile. There was enough lumpy lump to notice but not choppy. Its a good street cam though.

 

Four strokes, intake, compression, power, exhaust, in that order. Overlap occurs where? And increased overlap is gonna bleed cylinder pressure how?? Please explain Don, in terms of valve events.

 

The Intake closeing event in the biggest

 

I'll just leave this here:

http://www.dragzine.com/news/thumpin-power/

 

The Thumper cams require compression. The 327/350, the L79, the LT1 all had compression. Either stick with the 268H, or put some wind in your engine.

Flat top pistons are cheap. You can achieve 9.5 compression, and run it on pump gas with your heads.

For what you have, CC 268H will supply the fun you are looking for.