Comp XE268 - O/T, Brand X!

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rmchrgr

rmchrgr

Skate And Destroy
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Hopefully this will translate into basic hot rodding 101 and guys won't be annoyed at the Brand-X question. Don't worry, I still eat, sleep and fart Mopar.

Anyway, here's the deal. Sometime in the next few months, I will be tasked with building up my good friend's '68 GTO with the 350-hp 400. It's the original engine - it's never been apart and he says it's tired. He's not Ricky Racer - it will rarely see the high side of 5K and serves as just a weekend/nice weather driver. The Poncho 400 is all about stump-pulling torque, the car grunts pretty well but he's looking for more performance.

I've found the cam I'd like to use but I'm not sure about the drivability - anyone use a Comp Cams XE268? What I'm trying to discern is whether it's too much for that type of application. It is of course a rather big car and has power brakes.

Here's the rest of the combo I'm thinking about: As stated, Comp XE268, stock bottom end, stock iron heads w. 3 angle valve job, mill heads to bump compression a little, (not sure exactly what compression I'm after just yet, probably 9.5 -10:1) Comp valvetrain with basic 1.5 roller-tip rockers, Performer RPM manifold, Holley 750 w. vac. secs., HEI ignition, decent headers with full dual exhaust using 40 Series Flowmasters and a B+M Holeshot converter in front of a rebuilt Turbo 400. Really, just your basic warmed-up muscle car. He wants to fry the tires at will but also wants to enjoy the ride without the temperamental race-car vibe.

I'm debating on whether to use the Holley, I might convince him to go with an Edelbrock carb to take advantage of the smaller primaries, but I think he wants the Holley just to say he has one. No mech. secs. in any event.

The other internal debate I'm having is whether to stay with the stock converter or get the Holeshot or an equivalent. I think the other stuff is matched OK but maybe a little better convertor would help the overall pakcage.

Thoughts on the XE268 cam in relation the rest of the combo please! Sorry for the Brand-X post!
 
There are a ton of guys on here running the XE268, all saying great things about it (lots of torque everywhere, very streetable). Definitely a good choice, along with a host of other fast-ramp cams from other companies.
 
D'oh! I was all self-absorbed in my post. Shoulda used the search field! Seems like a popular cam.

Thanks for the reply though MOPEkidD-3. I guess drivabilty is not too much of an issue. I like what I'm hearing so far.
 
The XE268 should work very nicely with the rest of the proposed combo.

I'd consider running the 1.65 Magnum rockers as well. I believe the cost is still the same.
 
I am running a XE268H in a 360 and it makes great power from 1500 rpm to 6000+, I couldn't be happier with the choice. My car is also a nice weather driver and I seldom run it past 5000 rpm but when I do it goes (a best of 13.7 @ 102 mph).

I have 10.6:1 compression and the cam idles almost a smooth a stock cam at 650 rpm.

In a 400 that cam will act like a smaller cam in a 360 so it still should be a stump puller off idle.
 
rmchrgr said:
it will rarely see the high side of 5K
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I have a couple of buddies that run Tin Indians and I can tell you without equivocation that this is a factual statement - intended or not...! LOL

In all seriousness though, I run a XE268H in the 390 in the wife's Swinger; can't say enough good things about that camshaft for usage in a true street car. NO ISSUES with power brakes.

Ray
 
I had a couple Pontiac's when I was in my early 20's and the 400 is a real stump puller. If I was building what you described I'd go with the 268xe cam too. The factory 350 hp heads are decent flowing heads as cast but a good performance valve job by somebody that knows Pontiac heads would be a real good addition. You definetly want to keep the rev's under 5500 cause Pontiac's had junk rods. They were cast and used 3/8" bolts. Either have them resized using ARP bolts or replace them with good aftermarket rods and have the reciprocating assy. balanced.

With an Air-Gap intake, 750 vac. sec Holley, and set of good headers it should approach 400hp. If you do plan on using headers make sure and get ones that have separate middle tubes. The cheaper headers made for Pontiac's D-port head combined the middle tubes into one larger tube and the flow was pretty unbalanced. When I got my Poncho the headers were real rusty and needed to be replaced. I replaced them with a set of divorced port tube Hookers and it made a big diff on how it ran.
 
I ran that cam in my 64 chevelle years ago in a 350, although i had AFR heads, a moderate converter and 3.73's. I ran 13 flat although more converter and traction would have had me in the 12's easily. Great cam in my opinion but remember that it clicks more than conventional hydraulics - don't overtighten your valves thinking they're loose!!! Good luck!
 
I just sold my 69 lemans two years ago,I still love pontiacs (actually all brands of muscle cars) but its fun to run 12s with a 3.42 gear and 29 in. tire.Anyway I would run the xe268 but imo even better would be the lunati voodoo 268-just a bit more lift.One thing you will notice is 400s have a piss poor deck height,a 400 I rebuilt had some cast repalcements and they were .044 in the hole,now combine that with the small chamber heads and it still was only 8.8 to one so you will need to do your reaearch on pistons.Check out theae guys http://www.pacificperformanceracing.com/ Ken is really cool and this website is great for specific searches to get info http://forums.performanceyears.com/forums/ .As far as the rods they will be fine to 6k with good bolts-although the rods are not great the stock bolts are 90% of the problem.I built several pontiac engines and the last one was a 400 to put in the lemans to sale,it had 8.8 compression,#16 heads that I ported,comp xe 274,stock rockers with crane adjustable nuts,1 5/8 headers with 3in ex.,rpm intake,750 holley,t400 2,800 stall (flash) and 3.42 gears with 29 in. mickey et streets (was set up for a 455 before).This combo ran 12.70s at 107 shifting at 5,500 in a 3700lb. car so your build should meet his desires.I would run a mild stall,problem is pontiacs have so much low end you really need a custom stall built by someone who knows what their doing or you will get too much slippage on the top end,I did find that a reman ls6 12in. chevy convertor works very well,you can get them at any trans shop ect and I paid around $75.It is factory rated as a higher stall and I found it to stall right around 2k on the brake-perfect for a street build-but it has very tight once you give it throttle,I ran a couple ofthese in my car before having a custom 11in. built.Good luck on the build and heres a pic of my old poncho.

lemans.jpg
 
lead69 said:
imo even better would be the lunati voodoo 268-just a bit more lift.

I can go with the 1.6 rockers which will effectively increase overall lift.

One thing you will notice is 400s have a piss poor deck height,a 400 I rebuilt had some cast repalcements and they were .044 in the hole,now combine that with the small chamber heads and it still was only 8.8 to one so you will need to do your reaearch on pistons.

Hmmm... In my research, I've read that the stock comp. ratio for the '68 400 is 10.75! I was surprised. I have yet to figure out exactly what heads are on his car but I'm pretty sure they're original.

I'm thinking tried and true TRW or maybe the KB 167 hypereutectics which seem to work well in a 360, so why not in a 400? I can always deck the block and the heads if necessary.

Check out theae guys http://www.pacificperformanceracing.com/ Ken is really cool and this website is great for specific searches to get info http://forums.performanceyears.com/forums/ .

Thanks. I also found Butler performance, they seem to have everything at good prices.

As far as the rods they will be fine to 6k with good bolts-although the rods are not great the stock bolts are 90% of the problem.

Plan is to use the stock rods and install good bolts, probably ARP. I don't think he's ever been over 5K in that car.

I built several pontiac engines and the last one was a 400 to put in the lemans to sale,it had 8.8 compression,#16 heads that I ported,comp xe 274,stock rockers with crane adjustable nuts,1 5/8 headers with 3in ex.,rpm intake,750 holley,t400 2,800 stall (flash) and 3.42 gears with 29 in. mickey et streets (was set up for a 455 before).This combo ran 12.70s at 107 shifting at 5,500 in a 3700lb. car so your build should meet his desires.

That's a pretty impressive number for low compression and a heavy car!

The headers I'm looking at are the Doug's 1 7/8". They're expensive but as someone stated previously, the cheaper ones have the two ports sharing a tube. Not so good. You can see the difference in pictures. No need to skimp on the exhaust. The guy wants his car to sound mean so good exhaust is key for him.

I would run a mild stall,problem is pontiacs have so much low end you really need a custom stall built by someone who knows what their doing or you will get too much slippage on the top end,I did find that a reman ls6 12in. chevy convertor works very well,you can get them at any trans shop ect and I paid around $75.It is factory rated as a higher stall and I found it to stall right around 2k on the brake-perfect for a street build-but it has very tight once you give it throttle,I ran a couple ofthese in my car before having a custom 11in. built.

Ye Olde Holeshot 2400 is advertised to stall between 2300-2500. Their advertising also staes that "Most street-driven performance cars with 350 foot pounds of torque or more need a 2400 RPM unit." It's the classic street converter. Top end is less of a concern for this build, he mainly just wants to lay rubber in front of his house.

Good luck on the build and heres a pic of my old poncho.

That thing is pretty menacing looking. I dig it.

Thanks for all the info, much appreciated!
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Why do Pontiacs (and I'm assuming Buicks because of the 455 Stage 1 numbers) have so much low end?
 
JFYI: Pontiac lowered their compression in 71 like everybody else did but they did it differently than Mopars. They used the same pistons, deck height, gaskets, etc... but they opened up the head chambers to much higher cc's. I used to know the numbers but it's been so long It's hard to remember but I believe the older heads were around 70 cc's and the newer ones were as high as 100 cc's. Even though you read the compression was rated at 10.75 to 1 it's quite possible their ratings were flawed like Mopars were due to machining tollerances. According to my compression calculator using a stock bore 400 with the piston at zero deck, a .040 thick gasket, 10 cc valve reliefs, and a 70 cc head that only figures up to 10.21 to 1.

BTW: Just for the heck of it I ran a sim on Desktop dyno using flow numbers for the 6X heads (that's the only #'s I have for pontiacs) but used 70 cc chambers with the pistons at zero deck which came out to 10.21 to 1 compression, an Air-gap intake, 750 Holley, big tube headers, and the 274XE cam. It showed 433 hp at 5,000 rpm and 483 ft.lbs of torque at 4000 rpm. Of course Desktop dyno is not all knowing and assumes everything is perfect so unless you spend mega bucks on machining and have it dyno tuned by somebody that knows what their doing it probably won't be that much but it still should have no trouble getting the 400 hp you want.
 
Rmchgr,I dont think you can even buy three tube headers any more,they were phased out long ago (although dougs sells 3 tube),90% of the headers now are all four tube,I ran hooker comps small tube on mine.The 400 compression ratings are similar to the 340 mopar,you will never find a true 10.75 factory,the pistons are too far in the hole and the small chamber heads such as 16s,670s, ect. are all 72 cc,I ccd my piston valve reliefs,measured the deck height ect. to find out I had just under 9.1-and thats with .020 off the heads-but they were just rebuilder stock type pistons.The k.b.s should work great,thats almost all Ken at ppr uses,and they should help the compression,I would stay at 9.5 or less.Also a trick on the rocker arms,get a set of 1.6 ford small ford rockers,the geometry is spot on 9 out of ten times and you wont have the excessive lift of the 1.65 which usually have worse gemoetry.I used ford rockers alot.Thanks for the comment,I wanted a street bruiser:-D!.
 
MOPEkidD-3 said:
Why do Pontiacs (and I'm assuming Buicks because of the 455 Stage 1 numbers) have so much low end?
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400 cubic inches to start with helps allot and they are long stroke, have long rods, and heads that have good low lift flow but not great flow in the higher lifts. Therefore they have good low end torque but don't rev real high cause they can't breath good up high. The 400 Pontiacs aren't really much better than the average 408 mopar. The Buick has 455 cubic inches on it's side so naturally it's a torque monster.
 
fishy68 said:
JFYI: Pontiac lowered their compression in 71 like everybody else did but they did it differently than Mopars. They used the same pistons, deck height, gaskets, etc... but they opened up the head chambers to much higher cc's. I used to know the numbers but it's been so long It's hard to remember but I believe the older heads were around 70 cc's and the newer ones were as high as 100 cc's. Even though you read the compression was rated at 10.75 to 1 it's quite possible their ratings were flawed like Mopars were due to machining tollerances. According to my compression calculator using a stock bore 400 with the piston at zero deck, a .040 thick gasket, 10 cc valve reliefs, and a 70 cc head that only figures up to 10.21 to 1.

Your correct about the heads,the problem is with 400s in paticular the pistons are down in the bore factory (.045-.060),they also have something like 12-14cc valve reliefs,the good h.p. small heads are 72cc,the later heads are all over from 84 to 114,and there are a few early in between heads but they are usually low pefromance press in studs.
Click to expand...
 
lead69 said:
Your correct about the heads,the problem is with 400s in paticular the pistons are down in the bore factory (.045-.060),they also have something like 12-14cc valve reliefs,the good h.p. small heads are 72cc,the later heads are all over from 84 to 114,and there are a few early in between heads but they are usually low pefromance press in studs.
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If that's the case the compression can't be anywhere close to the ratings. That's even worse than Ma Mopar did.
 
That sounds like a nice setup. I had an '84 camaro that we put a mildly built 355 in (350 bored .030 over with the stock 350 crank). Anyhow, we put that cam in there. With the stock 700R4, stock torque converter, and the stock 3.73 posi rear end, it would roast the tires in first and second, and chirp them in 3rd. I think it was pushing the 400hp mark. That cam gives a slight lope to the tune, but only enough to know that there is something not-stock about it.

The only thing I would change about your setup would be the Holley. Edlebrock (IMHO) is far better for reliability and the ease of tuning.

I didn't have any problems with the power brakes at all.
 
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