Well first of all I'd like to say this website is wonderful and wish i would have come across it earlier. I own a 77 vette and am trying to make it fast but still able to keep it streetable. Emissions are a pain but maybe with a little luck the bill in Arizona will pass so I would no longer need to pass emissions!
I have a 700R4 tranny with about a 2500 stall (currently being installed right now)(New to using a Stall so if anyone can tell me how to use it right and any tips that would be great also). I have a decent money source and would like to finish the engine and performance before painting and customizing the rest of the car.
My questions are about my engine performance setup.

Engine Setup:
rebuilt 350 SBC with .03 bore =355 CI
268HE Comp Cam with 1.6 ratio full roller rockers
Flattop Pistons (was told about 10:1 comp total)
ProTopLine aluminum 200cc intake, 64cc chamber heads
Edelbrock Victor Intake Manifold
600 CFM Edelbrock Carb. (1406)
High Voume Oil Pump
Hedmen Headers
True Duel 2.5" Exhaust with cats
Flowmaster series 40 mufflers

Heres my questions:
1. What would a rough estimate on fly power be on this setup?
2. Is there any serious problems with this setup?
3. What would be some worth while improvements for power?

Its a daily driven car but I am looking for a powerful streetrod that will live up to the Corvette name. Before I got the engine rebuilt I took it to the track and ran 16.24 at 83.6 mph (not sure if was original 77 stock engine or was aftermarket) My goal would someday be to arrive in the 13sec range while keep street legal (want to keep up with the stock new vettes)

Any help, tips, tricks would be extremly grateful. Feel free to ask any more questions that would help give me more of an accurate answer. :flag:

Thx,
Brandon

 

First welcome aboard. As far as the stall convertor is concerned, under normal driving just do as you always would with any other automatic. Now when yur at the track and staged up to run, hold your left foot hard on the brake with the trans in gear, apply some throttle to load the engine against the convertor but not so much as to make the car move forward. You just wanna bring the rpm's up against the convertor. Keep yur eye on the tree and when you see the 3rd yellow(dont wait for the green), simultaneously release the brake and push down the throttle. With the 700r4 and its low 1st gear you are likely to have some wheelspin. Launch as hard as you can without wheelspin. For best et you may have to practice a few times with allowing the car to roll out a bit before slamming the pedal to the floor. In that case you could release the brake but hesitate a split second before gunning it. When you release the brake on the 3rd yellow, the car will jump out since you have the engine loaded against the convertor as described above. Practice practice practice. Any wheelspin will be detrimental to yur et.
Up shift points are important too. Depending on how the trans is governed you may need to upshift manualy. Try it in D first and note the upshift points. With you setup, 5500rpm upshift would be good. If the trans wont hold out that long on its own, then upshift manualy.

Yur engine setup looks good. I dont see any outstanding problems with your choices of mods. At the flywheel I would guess 350 to 375 hp on the top end and close to 400ft lbs tq at max tq range. As far as emmisions laws in your area are concerned I dont know. It may be difficult to pass a sniff test with those mods. In some areas its illegal to put true duals on, even if you use two convertors. In those areas you could modify the exhaust, but if its 2-1-2 with on convertor, it must remain that way to be legal.


[Modified by Jvette73, 6:40 AM 3/16/2003]

 

Actually the car came with the true duel setup when I bought it and havent had any problems with the emissions people here in AZ. I did all the engine mods after my last test and my next one is in August, so I'll have a couple months to play around before I have to really worry about it.

How would my engine respond to a high cam if i could get away with the switch. AND what would be better a magnum(280 or 286) or xtreme energy(268/280 or 274/286)? Has anyone had any experience with both kinds who can tell the difference between them in power, idle, etc.

Thx,
Brandon

 

A Forum Member DeskDynoed my combination (see my signature) at 345HP and 409ft/lbs of torque. A somewhat similar set up as to what you want but with a milder (260H) cam. As a suggestion only, dont get too far out there with your cam selection. XE262H or XE268H would be about tops for me but others might have better ideas.........Welcome To The Forum! :D

 

Sounds like you already have a nice combo. A little more cam and maybe a larger carb could get you some more power without hurting drivability much. I agree with Jvette on the hp estimates and I suspect that you are already capable of getting into the 13's.

 

Honestly, for a 355, I would recomend not going above the XE268. Yur using 1.6 rockers to boot. I previously had the XE268 with 1.5 rockers. The cam had great mid-range and some good top end but it did sacrifice bottom end. I switched down to the XE262. Not because I dis-liked the 268 so much that I had to get rid of it, but because it wiped a lobe. So I had to go in there anyway. I could have replaced it with the same. But having direct expierence with it and its sacrifice of bottom end in my 350, and the fact that it didnt have a very comfortable "in gear" idle, I elected to step down to the 262. Overall I like the 262 better. I can rest at a light in gear and it seems comfortable, unlike the 268 which was rumpity enough to coax me into bumping it into neutral at lights. The bottom end is noticabaly better with the 262. This is my expierence with both cams. Remember your chosen rocker ratio is 1.6 so your negitive effects on idle comfort and bottom end will be slightly greater than I expierenced with 1.5 rockers. The 262 pulls hard to at least 5500rpm. unless yur bottom end is gonna be really built for hi po, you dont wanna go much higher than that on a regular basis. The 262 is a nice street cam for performance and a daily driver. Im glad I switched down. Ide also like to note that, in my opinion, cam manufacturers generaly understate the negitive effects on idle quality and bottom end, of thier higher performance cams.

 

Jvette73, I read your article before on how you like the XE262 over the XE268 but the HE268 i have is much more mild than the XE268 you had. There two completely different cams and thats what im trying to find out(exept difference between Magnum, equal lifts, and Xtreme Energy, higher exhaust lift).Even the XE262 has a higher .05 in lift than the HE268.

HE268
Specifications:
* Advertised duration: 268 intake/268 exhaust
* Duration at .050 in. cam lift: 218 intake/218 exhaust
* Gross valve lift: .454 in. intake/.454 in. exhaust
* Lobe separation: 110 degrees
* RPM range: 1,500 to 5,500
* Noticeable idle

XE268/280
Specifications:
* Advertised duration: 268 intake/280 exhaust
* Duration at .050 in. cam lift: 224 intake/230 exhaust
* Gross valve lift: .477 in. intake/.480 in. exhaust
* Lobe separation: 110 degrees
* RPM range: 1,600 to 5,800
* Noticeable idle

XE262/270
Specifications:
* Duration at .050 in. cam lift: 218 intake/224 exhaust
* Gross valve lift: .462 in. intake/.469 in. exhaust
* Lobe separation: 110 degrees
* RPM range: 1,300 to 5,600
* Noticeable idle

280M
Specifications:
* Advertised duration: 280 intake/280 exhaust
* Duration at .050 in. cam lift: 230 intake/230 exhaust
* Gross valve lift: .480 in. intake/.480 in. exhaust
* Lobe separation: 110 degrees
* RPM range: 2,000 to 6,000
* Rough idle
(Data off of Summit Racing)

I'm just looking for an answer for reference reasons, I'm happy with my 268 for a daily driver but if I was ever was to use a higher cam for a racing/weekend warrior type car, would the Magnum or Extreme Energy be the better choice and whats the advantages and disadvantages of both of them with a setup similar to mine.

My cars idle right now is slightly rough but for a corvette it feels like it belongs, even mandatory, and I can easily live with the way it is now, it actually feels wierd to drive a newer car without the idle and a rougher idle would be fine for me.

Question about the larger carb, With a larger carb will I loose some throttle response to get the power or should I not notice much of a difference if installed right?

 

My holley 600 vac sec is working good and im satisfied with it. If I run into some money and get the itch for a but more punch I would probably opt for a Holley 650 DP. A moderated 350 really doesnt need more CFM than that. Smaller throttle bores mean higher velocity of incomming air thru venturies. This is what pulls the gas in. If the CFM rating is to much the velocity will drop and could cause a lean condition.

Sorry I thought you were talkin about the XE268 not the HE. I still stand behind and recomend the XE262. Good lift for good TQ. Reasonable duration for very tollerable manners. Excellant street cam.

 

Oh and yes a carb with a higher CFM will generaly have less bottom end TQ, but will have the potential for better high end rpm power. Its all a matching game. Every part counts to compliment the others. Good idea to do yur homework first.

 

The XE's are a little more agressive than the HE's. The magnum 270 is a pretty big cam. I'd stick with the XE262 or XE268, and if you want a little more go with the XE274(i think). I have an XE262 and love it. It's a little lopy idle, but it's tame and it pulls really good to 5500, i sometimes pull to 5600 but i dont think it helps all that much. But your set up looks stout. If anything call comp cams. Not to dog anyone but they'd probably be able to help more and possilbly grind one specific to your motor

Aaron :chevy

 

:iagree:

 

Thx for the help guys, Maybe It'd be best just call them and have them grind me a cam (hope its not to expensive) but right now and for a while I'm set with my engine setup, want to try to finish cosmetics and customizing before I do any more to the engine.

If anyone else has any comments or past experiences on cams please continue to post your thoughts. So far the XE262/268 has won the majority :)

 

Do the motor 1st. You don't want to ding or scratch new paint when working on it...trust me i learned the hard way :cry

 

Yeah I did try to do all the motor first, thats why I said that it would probably be a long time if I ever change out cams because I dont have the extra money to do another rebuild so soon. Its only been about 2-3000 miles on the engine.
And I think no matter how careful you are eventually something will happen and scratch it whether it be the careless other drivers in parking lots or some kid keying cars.

 

Nah, it usually carelessneess on our part that screws up the paint..seen a friend drop a 7/16 wrench on his hood (6,000.00$ paintjob) after putting on the air cleaner and closing it with the wrench in hand. :eek:

 

looks like a good setup, i might consider switching manifolds to an RPM air gap, to gain a little torque low down, probabely without sacrificing much high end with that setup, i could be wrong. my $.02

 

16.24 at 83.6 mph Yeah, you should be able to beat that! :lolg:

Seriously, it sounds like you have a sweet setup now. I'd opt for a slightly larger carb. :thumbs:

 

One thing you are running a 2500 stall. That is a good idea. Comp Cams says one can run the XE268 without a higher stall. I think they're understating the negitive there. In my expierence the XE268 is too sluggish on the bottom end to run without a higher stall. By the way, what rear gear are you runnin?

 

Your cam & carb are matched now. Set up for 13s now.
Maybe a summary would help. You asked for suggestions, so w/ your "Edelbrock Victor Intake Manifold" & higher stall, you >COULD< run more cam & carb for it as Vetterodder said. CORRECT. Normally w/ a Victor intake one would run more cam & carb to go w/ it.

Your setup is similiar to Jvette73. HE268 is similiar to XE262, so he tried more cam & prefered similiar cam to what you have & said why. CORRECT for him & maybe you.

This is exactly what you should do drive it w/ the new setup & decide what you prefer.
You do not need more carb now. You might want more rear gear w/ the O/D.

:cool:

 

PS Some :cool: of us have been DRAGONSLAYERs a long time.

:cool:

Also, you might want to see 77 Facts on my website.