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Small cams on 106-108 LSA’s

General engine tech -- Drag Racing to Circle Track

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frnkeore
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Re: Small cams on 106-108 LSA’s

Post by frnkeore »

This tread is kinda timely for me, as I'm going to order a cam, next week. The engine is a 419 FE (4.092x3.984). The cam I'm going to order is In .609 - 230 @ .050 x Ex .606 - 239 @ .050. Heads flow In 250 x Ex 185 @ .600

The car is a 4000 lb Galaxy, w/C6 and 3.00 rear.

I was going to order it with a 112 LSA, 106 In CL, thinking I would have about the best off idle performance, with a stock TC but, after reading the input here, I'm wondering if a 108 LSA, 103 In CL, wouldn't be a better choice.

I also, echo the fuel mileage request, regarding the tight LSA.
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Re: Small cams on 106-108 LSA’s

Post by enigma57 »

When I was researching Rhoads lifters and reading over their applications for patents, I ran across a SBC hydraulic flat tappet cam Rhoads designed to work with their lifters. Their duration @ 0.050" was within a couple degrees of Mike's outstanding cam grind for his boat engine, but LSA was tightened up to 104 deg. Can't recall valve lift now, but being a flat tappet cam, I am sure Mike's hydraulic roller lobe profiles allowed for higher lift. The idea was apparently to boost low end with the tight LSA whilst pulling 10 - 15 deg. duration and some lift out at lower engine speeds. And when the Rhoads lifters pumped up in the mid range and added lift and duration, the power band would be extended. Not sure if the Rhoads lifters when pumped up functionally affect (extend) LSA, but that would be interesting to learn.

Interestingly, the last (latest dated) Rhoads application for patent was for running a cam having 'normal' intake profile and conventional lifters, with Rhoads lifters on the exhaust side only. LSA was in the 108 to 110 degree range, I believe. This would effectively extend the powerband by allowing a straight pattern cam to build torque at lower RPMs and add duration and lift (only on the exhaust side) when the Rhoads lifters pumped up. This cam was for a low to moderate compression ratio (9.00 - 9.50:1) whereas the earlier Rhoads cam was for engines having a bit higher static comp ratio (10.00 - 10.50:1, I believe).

Anyway...... I found all this quite interesting and would appreciate your thoughts on the thinking behind these two Rhoads cam designs / methodologies.

FWIW...... The solid lifter flat tappet cam I had Isky grind for my 9.5:1 Chevy 292 inline 6 tow engine was 210 / 216 deg. duration @ 0.050", 0.495" lift (both, running big block 1.75 rockers). Ground on 108 deg. LSA with 108 deg. ICL. The idea being to make the most average power from off idle to 5,000 RPMs (the point at which bad harmonics rears its ugly head with the long stroke 292 inline 6).

Had this cam ground before I ran across the Rhoads cam design papers. IVC being 56 deg., DCR is right where I want it for what passes as pump gas now of days. So I don't want to run Rhoads lifters on intake, as the shortened duration priour to them pumping up would likely cause detonation when pulling a load at low to mid RPM range before they are pumped up. However, I have been considering running Rhoads V-Max lifters on the exhaust side only to see if restoring full duration and lift from 3,500 to 5,000 RPMs would extend the powerband and / or increase power slightly in the upper rev range for this engine. This would be like running a straight pattern cam at low RPMs with variable duration lifters (only on exhaust side) which restore / increase lift and duration and transitions cam function to a split pattern cam in the mid to upper RPM range.

This cam is much like the old Isky E-4 grind from the mid-'50s. In fact, I spec'd the E-4 exhaust lobe and same 108 degree LSA but used a different intake lobe having 6 degrees less listed duration @ 0.050", but similar duration at 0.100" lift (-3 deg.) and at 0.200" lift (+3 deg.). Lobe lift for each (int. and exh.) is only 0.283" so no duration listed for 0.300" lift.

Exhaust is not restrictive. I am running a set of Tom Langdon's split exhaust manifolds which I have opened up to 2-1/2" outlets. Running 2-1/2" dual exhaust with crossover (balance) pipe and 2-1/2" ID chambered exhaust sections welded in wherever I can fit them.

Intake is free flowing as well. Fitted some pieces together to make a long runner intake based on the Brazilian triple sidedraught intake (adds 5" to intake runner length) and converted it to fit 3 Weber DCNF downdraught carbs. My friend Nick Smithberg did the welding and machine work. Its almost too pretty to hide under a hood.

In the event the long runner intake will not clear my steering column and master cylinder (this engine is going into my '57 Chevy sedan which is a driver and will be used to pull a boat trailer from time to time), Plan B is to run a Clifford dual carb intake with a hardwood plenum stuffer to reduce plenum volume and aid fuel distribution along with a pair of larger Weber DCNF carbs.

Head is a brazed lump ported iron casting from Sissel with larger valves and a little portwork.

So what do you think? Would running the Roads V-Max lifters (on exhaust side only) help this low RPM tow engine? (I already have a set of Isky solids and Rhoads V-Max lifters so can go either with solids on both intake and exhaust or solids on intake and Rhoads on exhaust.)

Best regards,

Harry
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Re: Small cams on 106-108 LSA’s

Post by mopardave »

Bullet racing cams will tell you a 108 lobe sep is better for a heavy car like yours. 4000# is heavy. Even 3400# would still be a heavy car.
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Re: Small cams on 106-108 LSA’s

Post by Walter R. Malik »

travis wrote: Thu Nov 19, 2020 5:10 pm
Walter R. Malik wrote: Thu Nov 19, 2020 12:52 pm

Years ago I bought and used many 302 Ford "Street Rod" cams from LAZER.
His cams were all ground in house because he was really a smaller, single person, business.
"Chief Cook and Bottle Washer" was the heading on Bill Metzger's business card. (He hosted many PRI conferences).
Looking into my past records ...that Small Block Ford 302 Cam was 205/210 @.050" ; .291"/.297" lobe lift, on 104 degree separation.
Did you ever have detonation issues with a cam like this on pump gas? And did they fall on their face around 4000-4500?
Never, when the compression ratio was less than 9.5/1; even a bit higher with aluminum heads.
Maybe if someone tried to run to much ignition timing there could be an issue.

RPM level was not an issue either. The cam you mention is 11 degrees smaller at .050" and that engine is 50 cubic inches larger.
One thing you have to remember is that this is meant for a "Street Rod" type vehicle where power upstairs is not a priority.
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Re: Small cams on 106-108 LSA’s

Post by novadude »

n2omike wrote: Thu Nov 19, 2020 7:32 pm I believe the rest of the combo needs to be taken into account when discussing LSA.
Tight LSA cams generally work with FREELY flowing exhaust systems. A restrictive exhaust KILLS a cam with overlap. Small cams are often used with stock exhaust manifolds and small exhaust systems. Overlap is bad with these, as all it does is cause reversion back into the cylinder. I've literally seen engines with carb bodies that were BLACK with soot from using a tight LSA cam with a restrictive exhaust. Tight LSA's need to BREATHE FREELY in order to work their magic... else, they are a step in the wrong direction.
Is this more related to overlap, or LSA?

I believe the OP was talking about short cams with less than ~50 deg overlap. As long as overlap is held to a minimum, why would it matter what LSA the cam is ground on?

The (typically) later EVO might make the power fall of fast at high rpm, but I can't imagine there is any problem using stock manifolds and dual exhaust (for example) with tight LSA, so long as the overlap doesn't get crazy.

Am I wrong?
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Re: Small cams on 106-108 LSA’s

Post by skinny z »

That would be my (unanswered) question asked in a different way.
Isn't it overlap rather than LSA that's often the deal breaker between what gives the greatest output compared to something that "OK"?
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Re: Small cams on 106-108 LSA’s

Post by Orr89rocz »

I recall gm’s 305 tbi “peanut” cam being a 178/194 at .050 and 109 lsa 106 icl.

With tpi and the bigger 207/213 117 lsa cam it made alot more power but i think the off idle torque on the old tbi motors wasnt terrible by any means.

Always was curious how those motors would do with a much tighter lsa than oem cams offered
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Re: Small cams on 106-108 LSA’s

Post by RevTheory »

novadude wrote: Fri Nov 20, 2020 1:37 pm
n2omike wrote: Thu Nov 19, 2020 7:32 pm I believe the rest of the combo needs to be taken into account when discussing LSA.
Tight LSA cams generally work with FREELY flowing exhaust systems. A restrictive exhaust KILLS a cam with overlap. Small cams are often used with stock exhaust manifolds and small exhaust systems. Overlap is bad with these, as all it does is cause reversion back into the cylinder. I've literally seen engines with carb bodies that were BLACK with soot from using a tight LSA cam with a restrictive exhaust. Tight LSA's need to BREATHE FREELY in order to work their magic... else, they are a step in the wrong direction.
Is this more related to overlap, or LSA?

I believe the OP was talking about short cams with less than ~50 deg overlap. As long as overlap is held to a minimum, why would it matter what LSA the cam is ground on?

The (typically) later EVO might make the power fall of fast at high rpm, but I can't imagine there is any problem using stock manifolds and dual exhaust (for example) with tight LSA, so long as the overlap doesn't get crazy.

Am I wrong?
You're not wrong. That AMC cam I mentioned earlier only had 43* of overlap and a pretty early IVC so it "cammed up" right away and idled like a baby. AMC has a pretty good exhaust manifold and his rpm was so low that I didn't worry about it too much at all.
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Re: Small cams on 106-108 LSA’s

Post by steve cowan »

skinny z wrote: Thu Nov 19, 2020 4:04 pm Maybe drifting a little off topic but what if the goal is the most lbs-ft per CID? Not the broadest or "area under the curve" but the greatest peak? (All else being equal)
1.4 -1.45 for pump gas is what people should aim for,very few hit that target.
For a NA unlimited engine EG - pro stock 1.65- 1.67 ft/lbs per cube
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Re: Small cams on 106-108 LSA’s

Post by mt-engines »

steve cowan wrote: Fri Nov 20, 2020 10:20 pm
1.4 -1.45 for pump gas is what people should aim for,very few hit that target.
For a NA unlimited engine EG - pro stock 1.65- 1.67 ft/lbs per cube
[/quote]

wow!! 1.45 lbft/ci na?
pump gas?
not happy dyno?
I'm happy when i get 1.3.

For me aiming for 1.4 would be setting the bar pretty high. I mean 695lb ft of torque from a 496, wouldnt be a walk in the park. 13:1+ a tunnel ram and 2x4s would pretty much be required.
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Re: Small cams on 106-108 LSA’s

Post by EDC »

"Quality" is like buying oats. You can pay a fair price for it and get some good quality oats,
or you can get it a hell of a lot cheaper, when it's already been through the horse.

Nil Satis Nisi Optimum

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Re: Small cams on 106-108 LSA’s

Post by cv67 »

Id think that would make a good TPI Cam idle-5000. Thoughts?
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Re: Small cams on 106-108 LSA’s

Post by skinny z »

mt-engines wrote: Sat Nov 21, 2020 12:36 am
steve cowan wrote: Fri Nov 20, 2020 10:20 pm
1.4 -1.45 for pump gas is what people should aim for,very few hit that target.
For a NA unlimited engine EG - pro stock 1.65- 1.67 ft/lbs per cube
wow!! 1.45 lbft/ci na?
pump gas?
not happy dyno?
I'm happy when i get 1.3.

For me aiming for 1.4 would be setting the bar pretty high. I mean 695lb ft of torque from a 496, wouldnt be a walk in the park. 13:1+ a tunnel ram and 2x4s would pretty much be required.
[/quote]

Can't comment on the BBC but at 1.4, 500 lb-ft out of 355 doesn't seem unreasonable.
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Re: Small cams on 106-108 LSA’s

Post by steve cowan »

mt-engines wrote: Sat Nov 21, 2020 12:36 am
steve cowan wrote: Fri Nov 20, 2020 10:20 pm
1.4 -1.45 for pump gas is what people should aim for,very few hit that target.
For a NA unlimited engine EG - pro stock 1.65- 1.67 ft/lbs per cube
wow!! 1.45 lbft/ci na?
pump gas?
not happy dyno?
I'm happy when i get 1.3.

For me aiming for 1.4 would be setting the bar pretty high. I mean 695lb ft of torque from a 496, wouldnt be a walk in the park. 13:1+ a tunnel ram and 2x4s would pretty much be required.
[/quote]
MT - i agree 1.4 is setting the bar high and i agree 1.3 is very reasonable as well,
Hence me saying very few people get there.
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Tony knight (knight engines) Holden engines 308ci - 383 ci most go close to 1.4ft lbs/ci and running our pump gas.
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Re: Small cams on 106-108 LSA’s

Post by dave brode »

Lunati will grind their shelf cams, or custom [you pick lobes] on non shelf tight LSA, same price as their direct price for shelf cams, which is cheaper than summit/jegs etc price.

They just did me a 292/292 - 241/241 [Voodoo 241/249 shelf cam's intake lobe] hyd roller big block cam on a 105*+4, .367" lobe lift, SADI core Gen 6 nose, $265 shipped. The guy didn't like the idea, but he did it. Fwiw It runs good to 5800+ in a stock valved 049 head 460".

Dave
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