350 build

[bschiltz]

I picked up a 89' L98 block minus the intake from mobythevan last week and have been looking at cam and intake combos. I'm running a Q-Jet and JTR's headers right now and would like to keep the carb setup and shoot for 350-375 hp and similar torque. For carb'd intakes I have been thinking about an Edelbrock RPM such as: http://www.jegs.com/i/Edelbrock/350/7104/10002/-1/745137

I read that you need to machine out the middle bolt hole, has anyone done this?

 

As for cams, I ran CompCams free cam software thing and thinking Comp's XR264HR or XR258HR or something similar.

 

264HR: http://store.summitracing.com/partdetail.asp?part=CCA%2D08%2D501%2D8&autoview=sku

.050 duration: 212/218

Lift: .488/.495

LSA: 112*

258HR:

http://store.summitracing.com/partdetail.asp?part=CCA%2D08%2D500%2D8&autoview=sku

.050 duration: 206/212

Lift: .480/.488

LSA: 112*

 

 

Anyone have experience with a similar setup? Anything you see that is obviously wrong? I'm open to any and all criticism/ suggestions.

 

Thanks

Ben

[grumpyvette]

what transmission, converter stall speed and rear gear ratio are you matching that engine too?

is it a stock 700r4 like your thread suggests?

have you done a compression test?

at 12:1 its going to run into detonation

you may be at a huge disadvantage using those cams as they are choking off a good deal of your potential hp if matched to some combos

 

ID strongly suggest you read thru these builds and see what the potential real world results will be before dumping money into your build-up so youll see where the money and time is effectively spent, comp cams software is a bit mis-leading as to potential results as the stock heads are far more restrictive than the software assumes, especially if your running the un-touched stock cast iron heads, the aluminum heads have some potential but need work, its a similar set of parts (IE an L98 type sbc 350) even thou its alot lower cpr and a flat tappet cam, Id bet your true cpr is not that high and youll need a cam with more durration if its even close to that

 

http://www.chevyasylum.com/chp/

[Pyro]

wow! 12:1 cr! that is a lot. maybe that is why the hp is kind of high for a little cam and stock heads

[bschiltz]

wow! 12:1 cr! that is a lot. maybe that is why the hp is kind of high for a little cam and stock heads

 

Yeah that's what I was thinking, but that that's the only way I could get the combustion chamber cc even close. You can only edit certain elements in the software. My engine has stock pistons and heads, not high compression. Stock CR is 10-10.5:1 correct? I think I'll re-run that thing with a lower CR tonight.

 

Grumpy-

Yes, I'm running a stock 700R4 from BowtieOverdrives with a 2300 RPM converter. My rear is 3.45 gears. Bryan did a compression test before I bought it and it read 145-155 at 2300' altitude.

[Pyro]

stock cr is more like 9.5:1.

 

the head gasket, piston dishes, piston below deck, and cylinder head cc can all be considered the combustion chamber size.

 

try using about 85cc (10+6+5+64).

 

A 3.54 gear, 2300 stall, 9.5:1 cr would like a cam in the 218 to 224 degree range at 0.050".

[grumpyvette]

1989 vette

http://www.stingray.nu/tips/tech89.htm

 

Cubic Inch 350 - ID/VIN 8

Net HP @ RPM 240 @ 4300

Net Torque @ RPM 335 @ 3200

Comp. Ratio 9.0:1

Bore & Stroke 4.000x3.480

Fuel System TPI - Tuned Port Injection

Valve Lifters Hydraulic

Exhaust NIY

Oil Capacity 4 QT

Oil Pressure @ RPM 50-65 @ 2000

[Pyro]

a 9:1 cr engine with stock heads would do well with intake duration between 206 and 210 and 212 to 218 on the exhaust. a stock converter would be better than a 2300 stall but 2300 is still ok in a light car. if you plan on using a carb then use 108 to 110 lsa.

[bschiltz]

Ok, thanks for all the help. I picked up David Vizard's book "How to build max performance chevy small blocks on a budget" so I'm going to give that a read and look up some more cams.

[bschiltz]

I've read the chapter on cams and valve trains two or three times now and still have a couple questions. He does a great job of explaining the theory behind everything but doesn't explain HOW to determine cam characteristics especially duration. I was searching here on HybridZ and found a post by Pete that says you can use the equation "duration=2*[(overlap/2)+LSA]" to find duration but when I tried it for what I thought was a reasonable overlap and LSA I got a very high duration. Here's what I was thinking:

D= 2 x [(35/2)+108]

D= 2 x (17.5+108)

D= 2 x 125.5

D= 251

That seem way too high, especially with what Pyro was saying above.

Also, he covers lift but doesn't tell how to determine maximum lift. He just says run the most you can. Is .500-.510 reasonable?

Thanks for all your help, I really want to understand the how and why behind this stuff rather than just be told what cam will work.

[dr_hunt]

IMO for your combination if you want to have a little lopey sound and some good power, I'd run isky hydraulic flat tappet grind 201271. It pulls pretty good from about 2K up to about 6K in a 350.

[Pyro]

maybe you are confusing advertised duration and at 0.050" duration.

 

a 206 degrees at 0.050" is typically 252 degrees advertised (seat to seat).

[bschiltz]

You're right. Now that I look at that equation you can tell it will give seat-seat duration.

 

Thanks for the recommendation, Doc. I'll look that one up and keep it in mind. Can you run a hydraulic flat tappet cam with roller lifters? The L98 has hydraulic roller lifters, right?

[dr_hunt]

Oh crap, that's right I forgot you had the l-98. I got lost when you said qjet carb, and not the efi. I was standing in bryans shop and actually looked at the motor. Sorry. If your running carb then you can go with a bigger grind, something in the 220 to 230 range on duration at .050. With a 112 lobe center won't idle too bad. Probably around .500 to .530 lift IMO.

[pparaska]

Yep, that was from Vizard's article: http://www.compcams.com/Community/Articles/Details.asp?ID=-2026144213

Definitely talking about overlap and duration at seat timing, not .050" tappet lift. 251 duration (seat timing) is damned mild in my opinion. I'd be looking at a 262 or 268 duration cam, probably 110 LSA. That's just off the top of my head though!

[dr_hunt]

I agree, that article doesn't take into consideration how light the z really is. 220 to 230 at .050 lift isn't that much of a cam. Kind of like the 350/350 "151" cam from GM which is 224 duration at .050 and .447 lift on a 112 LSA IIRC. These days you can get alot more lift with that duration and subsequently alot more power. Tighter LSA will fill the cylinders better IMO and make more early torque and a more usable powerband on the street.

[pparaska]

I agree, that article doesn't take into consideration how light the z really is. 220 to 230 at .050 lift isn't that much of a cam. Kind of like the 350/350 "151" cam from GM which is 224 duration at .050 and .447 lift on a 112 LSA IIRC. These days you can get alot more lift with that duration and subsequently alot more power. Tighter LSA will fill the cylinders better IMO and make more early torque and a more usable powerband on the street.

 

The biggest problem with that old "151" cam was the incredibly long seat timing. Depending on who you listen to, it was anywhere from 280 to 306 degrees "seat timing" duration. I had one in a 327 with 10:1 SCR and it was a freaking dog. The overlap (seat timing overlap is what really matters IMO) was very large for such a low lift/ low .050 duration. So it had NO low end torque. Came on at 3000 rpm or so like gangbusters though .

 

The newer grinds are much better with more hydraulic intensity for the same 0.050" duration and more lift. I wouldn't put a "151" cam (or copy) in anything, even a restored corvette with a 350/350 engine. I'd put in something with some lope, but a newer, higher intensity design. Probably a 280ish seat timing duration cam with 225 or so .050 duration.

[dr_hunt]

The biggest problem with that old "151" cam was the incredibly long seat timing. Depending on who you listen to, it was anywhere from 280 to 306 degrees "seat timing" duration. I had one in a 327 with 10:1 SCR and it was a freaking dog. The overlap (seat timing overlap is what really matters IMO) was very large for such a low lift/ low .050 duration. So it had NO low end torque. Came on at 3000 rpm or so like gangbusters though ..

 

 

Yeah, that was a re-hash of the Duntov theory of cams for gm heads. The heads didn't have alot of flow at higher valve lifts, so the basis for design is alot of duration to get area under the valve lift curve. Flat tappet designs are acceleration limited unlike hydraulic rollers, but todays designs make more power.

 

The newer grinds are much better with more hydraulic intensity for the same 0.050" duration and more lift. I wouldn't put a "151" cam (or copy) in anything, even a restored corvette with a 350/350 engine. I'd put in something with some lope, but a newer, higher intensity design. Probably a 280ish seat timing duration cam with 225 or so .050 duration.

 

Yup, it's outdated and as I said, not much of a cam. I typically cam even larger than that, I think people tend to be too conservative in cam selection IMO.

[Pyro]

Another thing to consider is the new cam grinds tend to wear out quicker. Yes, the 151 cam is/was a dog, but it was designed by gm to last a long time, so it got slow and low ramps.

 

The xtreme series compcam have very fast ramps but I would not run one with just any motor oil, since the removable of anti-wear additives from most engine oils. So, I tend to stay with the older high energy or magnum series compcams.

[pparaska]

Yup, it's outdated and as I said, not much of a cam. I typically cam even larger than that, I think people tend to be too conservative in cam selection IMO.

 

I do as well. I usually chuckle when reading Chevytalk.com and seeing guys asking if the Xtreme 262 cam is too big for their 350! LoL!

 

I think 225 @ .050 and 270 advertised duration is the bottom of the barrel for any 350 or larger engine. Below that it is just too small. 110 LSA is the max I'd run on a 350.

 

Personally, I'd rather find "too radical" and then back off a bit on a cam than go too conservative.

[dr_hunt]

I do as well. I usually chuckle when reading Chevytalk.com and seeing guys asking if the Xtreme 262 cam is too big for their 350! LoL!

 

I think 225 @ .050 and 270 advertised duration is the bottom of the barrel for any 350 or larger engine. Below that it is just too small. 110 LSA is the max I'd run on a 350.

 

 

 

Personally, I'd rather find "too radical" and then back off a bit on a cam than go too conservative.