Loooooow compression cam conundrum

[HT413]

Hey fellas, I want to know what you guys think about the cam recommendations I just received and your thoughts on the rest of the combo as well. As some of you guys may remember, I'm running a low compression 413 out of a 1972 RV. I was planning on building a new motor, but what can I say, IQ52's low compression 440 tests have changed my mind.

What I have: 413 that I measured to be about 7.2:1 :sleepy1:, bone stock 906 heads, Torker2 440 intake, Comp XE268H cam, headers, 727, 8-3/4 (3.23 sure grip). Oh, and the previous owner also thought it best to pair this RV motor with a 4500 stall converter. :eusa_think: It's in my 69 belvedere, mini tubbed, 4 link, 30" ET streets. It's been lightened somewhat (light weight seats, fiberglass bumpers, hood, deck lid). It's a weekend only street cruiser that will see a couple of weekends of track time a year. Will never see north of 6000 RPM's. Maybe 5700 is more like it.

So here's all what Lunati, Hughes and Howard's have recommended. They recommend some 75cc heads to get me over 8:1, (leaning toward 75cc RPM's that I can bolt onto a future build), RPM intake, some more gear (I was leaning toward 4.10's), a converter around 2800-3000 stall, and of course a cam. That way, if or when I do build a new motor, all I'm out is a cam and some gaskets.

So we have some small hydraulics on 106 LSA's, a whiplash (which has some lovers and haters), a comparatively large solid and a 40 year old purple shaft to boot.

Help me make some sense of it all. :eusa_think:

As always, thanks for your help. :headbang:

 

[Kern Dog]

That is an impressive page of information!

From what I understand, the lower compression will want a cam that builds more cylinder pressure if you want more torque. You state that you don't intend to spin the engine past 5700. A low CR with a big cam will need more rpm to overcome the loss of efficiency at low rpms. This leaves the Lunati out as a sensible choice. I ran a MP 280/474 in a 9.0 to one 440 and that engine flat out screamed! Nice idle, great street manners with decent mileage and great power.
The recent Mopar Muscle article showed that their 383 gained a full point of compression when going from their 88 cc iron heads to the 75 cc E-street heads. The 915/516 heads are about the same cc range, right?
































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[HT413]

That is an impressive page of information!

Lol, thanks. You should see, I made a table of like 20 cams so I can see how they all compare. Kind of a geek that way.

You state that you don't intend to spin the engine past 5700. A low CR with a big cam will need more rpm to overcome the loss of efficiency at low rpms. This leaves the Lunati out as a sensible choice. I ran a MP 280/474 in a 9.0 to one 440 and that engine flat out screamed! Nice idle, great street manners with decent mileage

Thanks, that's a great point. I was thinking that lunati sounded maybe a bit too big for what I intended.

The recent Mopar Muscle article showed that their 383 gained a full point of compression when going from their 88 cc iron heads to the 75 cc E-street heads. The 915/516 heads are about the same cc range, right?

Yup, and now RPMs are available in 75cc. Indy EZ's are 75cc as well I think. Overkill for this for sure, but maybe not for the next one.

 

[Banzaiii67]

So here's all what Lunati, Hughes and Howard's have recommended. They recommend some 75cc heads to get me over 8:1, (leaning toward 75cc RPM's that I can bolt onto a future build), RPM intake, some more gear (I was leaning toward 4.10's), a converter around 2800-3000 stall, and of course a cam. That way, if or when I do build a new motor, all I'm out is a cam and some gaskets.

Personally, I'd keep the cam you have (same one that mopar muscle used with the e-street heads) and change your gears and converter and see how that works. Than if you feel you need more power put the 75cc heads on.

 

[Meep-Meep]

While IQ demonstrated good HP numbers with bigger cams and low CR, that doesn't mean it will be a joy to drive in commute traffic. Low RPM performance will suffer and out of the box components like carbs and distributors will need tweaking to make then work well. My approach will be to make the most average power you can from idle to about 5000 RPM, and by matching up the cam and compression you can really make a nice driver. Factory tuning tends to be very conservative but just a slight bump in the cam can make a huge difference. I'm not crazy about any of the cams on that list for an 8.0:1 engine.

 

[Cornpatch MO]

You may consider steel shim head gaskets to raise the compression a bit more..........................MO

 

[HT413]

While IQ demonstrated good HP numbers with bigger cams and low CR, that doesn't mean it will be a joy to drive in commute traffic. Low RPM performance will suffer and out of the box components like carbs and distributors will need tweaking to make then work well. My approach will be to make the most average power you can from idle to about 5000 RPM, and by matching up the cam and compression you can really make a nice driver.

You pretty much nailed what i'm trying to do. I'm certainly not going to attempt to chase iq52's numbers or any of the other guys i've read. Just that i've learned an awful lot from them and it seems that building a fresh 440 with about 500HP would be like $8k spent on less than 100hp.

I'm not crazy about any of the cams on that list for an 8.0:1 engine.

That's my impression too, meep. I'd guess the extra lift and less duration of the howards 220 cam should give a significant kick in the pants, but not sure what to think about the 106 lsa.

- - - Updated - - -

Personally, I'd keep the cam you have (same one that mopar muscle used with the e-street heads) and change your gears and converter and see how that works. Than if you feel you need more power put the 75cc heads on.

That may be just what i do. I'm thinking that howards 220 cam might be a step in the right direction but not sure it'll make that big a difference.

 

[Meep-Meep]

Just about any one of these under the .500" lift mark should do nicely http://www.summitracing.com/search/...s?SortBy=BestKeywordMatch&SortOrder=Ascending
You are cursed with low compression, and if you kill all your cylinder pressure with a big cam, or have too much overlap, you won't be a happy camper. The ones listed here will work with a stock intake.

 

[HEMI-ITIS]

That kinda compression is IDEAL for BOOST!!!!!!!!!!!!!!!!!!!!!!!!:blob1:

 

[Tempest 455]

Also advance the cam. Get a degree wheel and advance the intake centerline. If you don't know how to do this a local machine shop can. It's not that hard. That will help w/ cylinder pressure and low speed TQ.

 

[Meep-Meep]

That kinda compression is IDEAL for BOOST!!!!!!!!!!!!!!!!!!!!!!!!:blob1:

Agreed! But that requires cubic dollars.

 

[HT413]

Agreed! But that requires cubic dollars.

Lol, you got that right. I thought about turbo, but just being honest, that's WAY out of my league...

 

[HEMI-ITIS]

Lol, you got that right. I thought about turbo, but just being honest, that's WAY out of my league...

What kinda power would you like to have?? I'm a boost junkie,but there's many ways to make power.:blob1:

 

[99ss]

Agreed! But that requires cubic dollars.

Not necessarily. But 3500 is a minimum place to start

 

[HT413]

What kinda power would you like to have?? I'm a boost junkie,but there's many ways to make power.:blob1:

I can't say. With this low compression motor, i'm just trying to maximize it for what it is. The motor runs pretty good despite the terrible combo, so with what I've read other guys doing, I'm thinking a better combo will make this thing a fun car to drive and terrorize the mustang crowd with.

 

[HEMI-ITIS]

Get what you have to run the best it can,Then try nitrous:naka:

 

[HT413]

Get what you have to run the best it can,Then try nitrous:naka:

Hmm, hadn't thought of the bottle before. Food for thought.

 

[HEMI-ITIS]

Get it to run well,you might get 15 MPG cruzin,then turn the hose on when you feel the need:eusa_angel:

 

[MikeyT]

First off Ht413, I think you are doing a great thing with asking and building your base of knowledge... I guess for me the big elephant in the room is that compression. Anything less then 9:1 with those aluminum heads will suffer with dynamic compression. I would look at two routes.... You would be better off spending the money on a nice set of 516 or 915 heads that are milled down a bit more oh 73 or 72 cc.. I would go with the 268 XL cam and a holley street dominator intake.

Or...

Pop the slugs out and go with higher compression ones and get it to 10:1, do a decent job on those 906 heads and run the solid roller with again a street dominator intake...


Personally if it was me, I would do the latter.

Good luck
Mikey

 

[99ss]

Comes down as always to budget. How much do you have to spend is the question.