306 questions

[ManyScalps]

Hello,

My first post. Did not find what I was looking for using the search feature.


I am interested in a high revving 306 - (7,000-7,500 rpm), 400-450 hp.

My concern is how streetable this motor would be? No track use - strickly for street use. I understand Gordon Levy builds these 306s 8,000rpm 500+hp and streetable.

What sort of cam would an engine like this use? Hydraulic or solid roller? Is there such a thing as a streetable solid roller cam? I am concerned about low highway cruises with such a high revving motor - don't want to bog it down with low rpm use.

And what about the torque curve? Will I need lots of revs to get the car moving?

Other options are 331 or a powerful 347, which is very appealing.

Has anyone had any experiences with a high revving 306? Were you satisfied with the low end power? What are your impressions?

Who else builds high revving 306s?

I will also vouch for EFI.

What about de-stroking a motor to build a high revver?

I have yet to drive a 306. I guess like everyone here, I just don't want to be disappointed with the engine selection.


All feedback is certainly appreciated. Thanks in advance...

[blykins]

It wouldn't be very streetable. To get one to rev that high and make power, the cam and head selection need to be a little on the wild side...which would take away all the streetability...hp and torque curves would be at a high rpm....probably around 6800-7000...it would be very lazy around town.

Any particular reason you want a high-revver? Just like the sound? I think they sound awesome...but I'd rather have my power down low.

If you want a 331 or 347 that revs that high, you're looking at incredibly high piston speeds and accelerations....which would probably have a higher wear rate on the piston skirts and rings. You have to build 'em stout to take high horsepower and high revs...I wouldn't put anything less than forged parts...and a 4-bolt block or a main cap girdle.

My guess is that you'd need a flat tappet or a solid roller cam.

There are certainly advantages to the engines that don't rev as high and make power down low....There is a member on here, Hal Copple, that has a stroked 351W that has over 60k miles on it.

[ManyScalps]

blykins,


I have heard that they sound really great (high revving) and pull exceptionally hard up top. I do fancy a stroked 302 (331 or 347) as I feel this would make a better street engine. I am such a novice when it comes to engines and need a reliable motor. I understand that a 351W stroker (408) will give me plenty of power with considerably less stress for a specific power output however, I am not keen on anything other than a stroked 302.

Would a 350-400 hp, 6500-7000 rpm 306 be more reasonable and doable for street use?

[blykins]

You can make anything doable, and what you're willing to live with is one thing...but pure streetability is another. I don't think you would have the streetability that you would want out of that engine. I may be wrong...but the engine is not very large to start out with...and increasing the powerband by that much will really hurt the bottom end quite a bit.

You want me to run some numbers on Desktop Dyno for you? They might give you some good estimates on what you would have to do to get that horsepower at that range.

[blykins]

Here....I worked a little something up for ya....

306 ci
4.030" Bore
3.000" Stroke

AFR 185 Heads, 2.02" I, 1.60" E
10:1 CR
Single plane intake manifold

650cfm carb

Comp Cams Xtreme Energy Hydraulic Flat Tappet Cam
250/256, .554/.558 110LS

Peak HP 411 @ 7500rpm
Peak Torque 348 @ 5500rpm

But....you don't have any power at all until 4500 rpm....and that's 277 hp. The torque there is only 323 lb-ft.

But that's what you face with a small displacement engine. I think it would be easy to build this one....quality parts are imperative. However, streetability????? I guess if you had a real low tranny gear ratio and a real low rearend ratio it wouldn't be that bad.

[Pete Munroe]

You say this a "street mainly" car you are building?

How did you get fixated on "7500 RPM" as the way to go?

If you have to ask...you DO NOT NEED IT!

I have an ERA 289" FIA car with a 65' 289" block, Tremec TKO, 3:55 rear end, 15 inch wheels.

It sees 90% street, 10% open track at Willow Springs and Button Willow race tracks.

I wanted the small 289/302 block as its about 30 ~ 50 pounds lighter than a 351, and in my eye, with the lower deck height, ( if only about 0.80 inches), it looks right in a 289 replica.

Ok, so I got the low weight for optimum handling I wanted...it has aluminum heads, Trick Flow with 2.02 intakes, dual plane aluminum STREET intake, Weiand Stealth, 750 Holley dbll pumper, too big probably...aluminum water pump, aluminum flywheel...not much left to do there short of a aluminum block.

The engine has been stroked...it is at 347"...there is a "girdle" on the main caps...the rods are Eagle, the crank is steel, the pistons Ross forged, the cam is a hydraulic roller, very mild, 224/228, (sort of the Ford Motorsports X cam), but a lot of lift, about 0.55 plus or minus intake/exhaust.

Now, the rotating parts are overkill for my power, but I NEVER wanted to never look at a hole in the block due to missed shift.

The compression ratio came out too high at 10.7, (long story there!), but seems to work with out detonation if you always shift down...should have gotten more cam overlap or less piston, oh well, next time.

( do not do the too high compression for a STREET Engine...!!)

I put a 6000 rpm chip in the MSD to act as a safety valve, it could go to 6500 at least I think even with a hydraulic roller.

But...it has more power than I can use on the street...unless YOU are midnight racing for pink slips...what do you need on the street?

If you are NOT an ACTIVE ROAD RACER, a ACTIVE BRACKET DRAG RACER limited to a certain displacement by rules, or looking for a land speed record, why would you want a high RPM, HIGH HORSEPOWER and LOW TORQUE, life limited engine for the street?

The old saying, "there ain't no replacement for displacement" seems to be true especially for the street.

Ask your self again...what you are going to do with the car?????...how long does it take to DRIVE to the freeway much less an "open track event" for a road race course...?

You could argue that a 331 or 306 would live longer as the piston pin is lower, out of the oil groove, piston speed more reasonable, but if this is a STREET engine, how much time will it be screaming at 5000+?..

As practical matter...a 347 theoretically may last half the time of a stock stroke or 306/331 stroke due to piston speed and ring placement...

I have driven my Cobra about 5500 miles in a year and 5 months...at that rate, its got a FEW years left...and as my skills improve, maybe I will put in a little more cam duration/overlap for power and to kill off the compression ratio, and freshen up everything else at the same time...

Short of a blown cylinder side wall due to side loads, not much to go wrong on an understressed bottom end.

For the STREET, ...TORQUE is what makes it accelerate...from a stop light or a rolling 30 mph...

HORSEPOWER GIVES HIGH TOP SPEED...

Gonna do 140+ to the next off ramp?

The speed limit around here is 70 max, and I have to row the gears for 30 minutes to get to the freeway anyway.

If you are NOT OBSESSED with handling, (like ME!!!)...go with a 351 stroked out to whatever...they seem to do well over 400 inches even on the road race stuff... make LOTS of TORQUE...and you wanted ACCELLERATION?????

.After reading a lot of website posts, magazines, bragging....and living my own automotive dreams, if you GOT TO ASK what you need...you DO NOT NEED the super wazoo 7500 RPM stuff...!

OK, you are gods gift to racing...in a season or two, if you build a GOOD bottom end, you can swap the cam and valve springs, etc. etc. etc. and get your high revving engine without too much trouble.

These cars are light, traction limited, short wheel base squirrels...in a road race situation, they can be a handfull...a lot of the guys here at the web site seem to be very active and experienced amateur/pro racers...I'm not!... but learning!...

So, again, what are you going to USE the car for in its FIRST incarnation...?

Hope this essay doesn't sound condescending, but I think you can have MEGA fun in a 2400 lb car without fantasy power that is a pain to drive in traffic.

Keep posting questions, you will get a million different answers...untill you know what you want to do, and how to get there, don't spend your money.

Pete

[Gordon Levy]

Actually our high rev 306's can be very streetable. We have done a lot of research to make these packages work the way they need to. It does take a solid roller cam to turn that kind of RPM. We have a host of new engine packages listed on our website that were designed for different wants and needs. We will also custom design a package to fit your needs. We design our own cam profiles to optimize what we want out of the engine. We prefer Brodix or Edelbrock heads. They are a much better head for the money that pretty much everything else out there.

[DAVID GAGNARD]

I would suggest you go to a club meeting or cruise or something similar and look at the different set-ups and try to get a ride or two.. Most Cobra guys I know will be more than happy to take you for a ride and some may even let you do some driving.....

I rode in an early FFR some years back,it was a "standard/stock" build,bone stock 30,000 mile plus 302,all the owner did was put a K&N air filter and 3.55 rear gears.... It suprised the hell out of me at what it was capable of doing and it was a strictly street car and got better than 20 mpg.... The owner let me drive it and we went out of town on a little used road.... From a dead stop I ran it thru the gears starting in second gear (first gear was broken) and shifted at a whopping 4500 rpms (not my car,did not want to flog it) and it impressed me quite a bit for the performance considering it was a bone stock 302 GT motor.........

You may find some cars are not as "street friendly" as you would expect and some of the lower hp cars are very fast....

Go for a few rides and then decide what you need for your use............

David

[ManyScalps]

blykins,

Thanks for running the numbers. I agree that 4500 rpm is a bit high for a streetable powerband. 323 ft lbs is plenty for such a light vehicle though once you get it revving.


Pete,

I certainly do appreciate all your input! Tell me, what are your hp and tq specs for your stroker?

Would you opt for more or less power next time?

I understand a high revving 306 is something to be heard! I enjoyed revving my GSX-R 750 and the accompaning sound. I am coming to the realization that a larger displacement motor is going to be the way to go. There will be virtually no track time - 99% street.

I understand Coast High Performance builds a 347 that doesn't use oil. This sounds appealing. A 351 stroker (408) seems overkill to me - 500/500 hp/tq. I like the idea of a 400-425 ish hp/tq motor. It would be nice to to highway cruise or tour with it without searching for a gas station every hour or two.


Gordon,

I will have to talk more with you about your motors. I was unable to find the engine section on your site. I am looking to go with EFI and I understand you are familiar with Motec.

What are your comments regarding a streetable motor for a Cobra? Are you of the line of thinking that says a high torque motor at low rpm is not the way to go? Or are you all for displacement?

By the way, that black with red stripe Cobra in your galley is simply stunning!

Would you say your 306s are poorly suited for the street, meaning they pull poorly at low revs? Is a 331, more suitable? Do you build a 347 that doesn't use oil? For strickly street application, what do you suggest that would give me 400-425 hp and tq?

[Gordon Levy]

The engines are on the website, in the roadster or coupe section under prices. I love the little engines like the 306 and it is very streetable if we build it to be streetable. I am familiar with the MoTeC as well as serveral other systems out there. We still get more power out of a properly set up carb over most EFI systems. For my racing background in these cars, I do like small, high revving engines over big torque engines. They are much easier to drive and control and well generally beat a big engined car in a road coarse. Remember that you are dealing with a car that most weigh under 2500lbs. Having 500lbft of torque at 2000 rpm's and a 90" wheel base is not the safest of cars. They are harder to drive comfortably and when something happens, it will happen quick. Quicker than most can drive through.
I know there are some that don't agree with me. I base my opinions on the cars we have built and race on a regular basis. We have built 700hp cars in both big block and small block configurations and I personally like the small block.

[Pete Munroe]

Scalps,

I just deleted a long diatribe that boiled down to this...if you have to ask...you don't need it.

I am sure Gordon builds great high RPM engines...for road racing, relatively high horsepower, lower torqe engines are good in a Cobra...light car, short wheelbase...high torque engines make a car excessively squirrley in anything but a straight line.

You want a street car, and get good mileage to boot...?

You said a 408 was overkill...I think a small 7500 rpm engine on the street is overkill..the 408 would be very powerfull without expensive hi rev parts, have tons of acceleration due to torque...and you are on the STREET going staight ahead...not road racing.

I do not have any figures on power of my engine...(would the fella with the desk top dyno run the numbers? I will post them...they are pretty much in an earlier post.)

Would love to get some time on a chassis dyno, but a good local that can compentently tune gets about 500/hour, or session? whatever, I would like it, don't need it.

I do NOT need more power...I should have a different cam/compression combo, but will live with what I have...would be easier to get a wilder cam, kill off some compression, pick up more power with more overlap and duration, but I do not need more power.

I have a friend with a ERA 427...427 block, a 428 crank about 454...has good heads, etc...he thinks he should be able to blast past me, but on the street from a rolling start it is hard to see...If I am a little quicker on the pedal, he still has to catch up...and by then we are both jail bait.

Most of what goes on on the street is very subjective...no hard numbers...but torque will snap your neck andyou feel like you are up on power...how you use high rpm on the street is beyond me.

I would build a quality bottom end, and a streetable top end...a year later swap out the cam and heads if you need more power...this is not a full body Galaxie, it is a 2400 lb Cobra.

I spend a LOT of time rowing my up and down the San Diego Freeway through LA at 15 mph...I have a very driveable no problem combo...see my last post for the specs...

Of course there are heads, cams, etc. for more power and RPM, but you are not on the track, ever, you say.

If you want, give me an e-mail and I will have you call me...I can tell you about the STROKER companies and all their BS...I found out the hard way...get a local builder you can see in a 1 hour drive max...the stroker company warranties are total BS.

You will find less is MORE in the Cobra...glad to give you more info get in touch, too much to relate here.

Pete

[ManyScalps]

Gordon,

I found the engine packages on your site. Thanks very much. I would be looking at a turn key FFR and will have to look into importing a Cobra into Canada. I will talk to you more as I get closer to making a decision. That black and red striped Cobra in your gallery really caught my attention...

[ManyScalps]

I found this on Coast High Performance website. It is a dyno chart of a CHP 306 with hydrualic cam. 320 lb-ft tq at 3000 rpm is appealing. Peak tq is close to 400 lbs ft and 460 hp. 6200 rpm looks to be the limit as power falls off. Nothing wrong with these numbers for a 2300 lbs car.

347's, as I understand, won't last as long as a 306/331, because they use oil. Okay, what if a 347 can be built that doesn't use oil? Does this mean they will last as long as a 306/331?








CHP