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5 replies

Feeling uneasy about my camshaft selection.

S sg351cjMember
Hello all, I am new here. I am in the process of helping my father restore his 1971 Mach 1 that has a closed chamber 351 Cobra Jet. I really wanted to build this car right the first time, and I was confident that I was choosing the right camshaft for the engine build until I found this website.

Here are the details. The car currently has 4.11 gears and a C6 automatic transmission. We intend to just drive the car to shows, and occasional spirited driving on the weekend. It's not a race car, and will never see a track. However, we do like to go WOT as well with a little better than stock power.

I am planning to use a Holley Street Dominator Single Plane Intake, and 750 carb. I always figured the 4V loved to breathe, and I assumed the xe284h hydraulic flat tappet comp cam would do the trick. I really thought I could use the stock rockers and simply just upgrade the springs. Well after reading the street cams page on this forum I feel I have made a mistake in buying the camshaft. Since it seems I will need to do a lot more work than expected to make it work. Of course we are planning to completely overhaul the engine, but I want to use as many stock parts as possible.

Camshaft Specs of the hydraulic flat tappet xe284h are:

RPM range: 2500-6500

Valve Timing: 0.006
Lobe Separation: 110°
Intake Centerline: 106°
Duration: Intake 284, Exhaust 296
Duration @ .050" Lift: Intake 240, Exhaust 246
Valve Lift: Intake 0.584, Exhaust 0.588
Lobe Lift: Intake 0.339, Exhaust 0.341


The main reason I chose this camshaft is that I have an xe274hr in my mustang that has a 331 stroker. The car drives perfect on the street with a 5 speed, and makes really good power. So I assumed I could step up to a larger camshaft for the 351 since it's a larger displacement engine.

What I really want to know is how bad of a mistake did I make buying this cam? Am I wrong to assume that the xe284h will work fine with the correct stall converter and 4.11 gears?

Sorry for all the questions, but I just do not know much about 351 clevelands.
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V 4vandproudMember
at first glance, a lot of guys use the XE284H in the same application you have and love it, then there are those that want more and those that have particular criticisms. ticking clicking valve noise is one that the XE cams get quite a bit.

assuming 10.3:1 static CR from the 1971 build, the XE284H makes right at 8:1 DCR, that's like a bullseye for max DCR on pump gas so you have good thermal efficiency. the XE274H pushes the DCR calc to 8.33:1, most consider this a little over the limit and would require drastic spark advance concessions but there are some that consider this still in the max tolerable range, IDK but i wouldn't use it as a target.

cam choice can be very subjective and controversial, you'll get opinions based on fact, personal experience, word of mouth, group consensus and just plain uninformed hearsay. many times when i pry i find out that guys knocking whatever cam it is, that rest of their combo doesn't support that cam choice on multiple fronts. i don't see a deal breaker in the XE284H for your application, are there other cams that will work just as good & maybe better, of course but obviously that going to be true no matter what cam you pick

as far as stock rockers i'm not too sure the stamped Ford units will make the lift of the XE284H, you'll need to upgrade to a decent set of bolt down rollers and verify pushrod length. my understanding is that the Scorpion brand generally requires longer than stock pushrods. if you're willing to change directions to avoid rocker & pushrod work, the '505 cam' is a drop in for stock components

FWIW i'd be more concerned with the intake manifold ...
S sg351cjMember
Thanks for the reply,

Well, my main concern is having to get the heads machined to accept the new rockers. The only machinist near me willing to do it charges about $100 a head. I'm not certain if that is a good deal or not, but I am willing to do whatever is necessary to make the engine right.

I have expressed concerns about the Domninator intake, but it was on the car when we got it. My father is nostalgic for that intake as it was a popular item back in the day. I may be sacrificing 10 or 20 horsepower with the intake on the bottom end even though I am not sure how true that is.

Anyways, I've read a lot about the Cobra Jet Bullet camshaft on these forums. I had already purchased the Comp Cam before I even knew that cam or this site existed. It sounds like that profile may be a better fit as it seems there is no need to machine the heads.

However the 505 camshaft seems to be a good choice as well. I just feel overwhelmed with cam choices really, but if I can find a profile that doesn't require me to machine the heads but still makes better than stock power without sacrificing drive ability, then I'll just exchange the cam.

If anyone has any suggestions I'm all ears. It just seems that most the things I know about Windsors really doesn't apply to Cleveland's.
V 4vandproudMember
$200 sounds like a heck of a deal, almost too good? the thought of handing over a set heads to somebody to cut the pedestals makes me pucker, each head has to be indexed correctly twice, once for the intakes and then again for the exhausts. that's 4 set-ups, yeah $200 is a good deal. then there are guys that have heads where the machinist drilled through to the intake runner and the engine sucks oil through the threads. OK that can be fixed with long reach studs(better than shorter reach), thread sealer and shape the extra threads to the port roof ... fixed ... as long as they got the angles right on all 4 set-ups?

now consider that bolt down rockers don't suffer stud flex and are more stable than stud mount rockers w/o a girdle. common every day stud flex loses HP to stock rockers, all the glossy page ads in chevy-craft don't brag about that

the Street Dominator isn't 'out of the ballpark' to the application, it has reasonable sized runners for decent low speed operation but the open plenum introduces the opportunity to easily over-carb the engine. you may find that the engine has a hard time pulling the secondaries open but you also have some rear gear working in your favor. bottom line obviously the intake will run the engine and if that's what makes Dad happy then that's what it should be
George PGeorge PAdmin.
Scorpion sells adjustable rocker arms that bolt down to the stock pedestals. Scorpion p.n. 3224. That's one way to get around that problem. The other way is to use a cam with no more than 0.530 lift and just use the factory rocker arms.

Return the Comp Cam if you can, otherwise sell it on eBay. Find a cam with wider LSA, less overlap AND less lift. Here's why. A relatively stock engine should be rev-limited to 6200 rpm. As you add lift to the camshaft the engine's horsepower shall peak at higher and higher rpm. A 0.530 lift cam with 60 degrees or less overlap will make peak horsepower around 6200 rpm. Equipping the engine with a cam having more lift will have the engine making peak horsepower ABOVE the rev-limit regardless of how short the duration is. Engines with heads tuned for lower rpm (like your 331) don't have this problem. But this is the nature of Cleveland 4V heads. With the XE cam horsepower will peak around 6600 to 6900 rpm, and will rev to 7000 rpm quite easily. Unless you're willing to do quite a bit of work to the engine, I'd limit lift to 0.530. You'd be able to keep the stock rocker arms too. The engine can make about 400 to 410 peak horsepower with that much lift. The money you'd spend on rocker arms can be spent on a custom cam. I can provide a spec for a custom 0.530 lift cam if you'd like.

The XE cam also has 70 degrees overlap, which will take the bottom end out of the powerband, and there won't be enough intake manifold vacuum for the C6 tans.

The street dominator comes from a period of time (late 1970s) when people were confused, and the aftermarket was grappling to come up with products that people would buy. But your father is certainly entitled to have his nostalgic ideals, and its cool that you're respecting that. Kudos.
Last edited by George P
S sg351cjMember
Thanks for the reply George P,


I would really like to have a spec sheet for that custom .530 cam. That would really relieve a lot of my worries about getting a cam that works. I bought the comp cam from summit racing, and they said they would exchange or refund it. I'm not too sure who I'd need to contact to make a quality custom camshaft though.

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