Roush 427 & 402 Differences

LudicrousSpeed · #1 (**permalink**) 03-01-2009, 09:18 PM

Hi,

Dont shoot the Noob, but I did a search and couldnt really find answers. I'm looking at several cars with Roush 427's & 402's. What are the differences between the 427R vs. the 427SR or SR w/TW (Twist Wedge Cam?). Same with the 402 series. I've looked at the numbers on the Roush site, But am more curious about the "Intangibles".

What the hell is a twist-wedge cam? When I think of a cam lobe, I think of a lobe profile that resembles the profile of an airfoil.

The 402 & 427R seem to put out the best Nums, but I'm more interested in "Streetability" & would rather have a torky engine than a high HP box.

Also just curious, but have heard "things" about the Roush Webber style FI systems- opinions?

Thanks All

Got the Bug · #2 (**permalink**) 03-01-2009, 10:14 PM

LudicrousSpeed,

The best combination of streetability and torque is probably going to be the SR w/TW (either the 402 or the 427). Plenty of torque and the engine is happy cruising along at low RPMs. Here's a thread that I found with some additional details.

Roush engine ?

twobjshelbys · #3 (**permalink**) 03-02-2009, 09:33 AM

I bought my car at the Barrett Jackson auction with about 500 miles on it. I don't think this car ever ran right. At first I attributed it to just the nature of the beast. The weather hasn't been nice enough to take it out to really look at it but when I had the oil changed a couple of weeks ago we started looking at it and concluded that it was missing on at least one and maybe two or three cylinders. Noone around here will work on this engine so I finally got a contact at Roush and he gave me a couple of places to start, one of which paid off.

Yes, the IR Weber stacks are finicky. They are mechanical coupled and appear to have either gotten out of adjustment or were tinkered with without the proper documentation.

This weekend I "re coordinated" them and things run much better. I was able to get through half of the adjustments they called for (without the computer cable) before running into something they didn't account for. More in my CSX4005LA topic.

Suffice it to say that I concur that it is a finicky system but properly adjusted and tuned will be a rocket sled.

madmaxx · #4 (**permalink**) 03-02-2009, 09:52 AM

I recommend the 427sr/tw. The 427 sr will have the most torque, the 427r will have the most horspower and the 427sr/tw will be the best of both worlds. Same nomenclature used on the 402. I really do not understand the 402 except it is a couple grand cheaper but has same block as 427 (DART). there are three 427's sold for each 402 sold. You cannot go wrong with any of them.

Cashburn · #5 (**permalink**) 03-02-2009, 10:37 AM

Roush has a new IR system on the Tall Deck small blocks. We got our first on Tuesday of last week and should be doing the install sometime next week (owner is swapping out a 402SR T/W for the 427IR). Should know more then.

We actually sold more 402SR/TWs here than 427s, but I think we are against the norm.

vector1 · #6 (**permalink**) 03-02-2009, 11:13 AM

difference between the 402 & 427 would be cylinder size, one based on 4" bore, the other 4.125.

would think the larger bore would make the hp easier by unshrouding the valves plus the xtra cubes.

don't understand the 2000 difference, build costs should be similiar.

Blittleton · #7 (**permalink**) 03-02-2009, 11:56 AM

Mark,

The IR's from Roush will be fickle time to time. I have done several engines both FE's and small blocks. The ones I have completed need to be tweak at or around 1k miles. Is it worth the trouble? You will have to ask yourself that question. All my customers love this setup. They are beautiful and perform very well.

With your quesitons on the 427's or 402's. Here again you have to ask yourself how are you going to drive this car. If you are going to lug around at low RPM in town, you may want to consider the SR/TW version of either of 427 or 402. If you drive more spirited at higher RPM you may want to stay with the "R" version. I perfer the R version because I like to drive a little more aggressive around town or on the highway.

These are my thoughts on this. It may not be for everyone else.

Bill

JWilly · #8 (**permalink**) 03-02-2009, 12:35 PM

I have the 402R and do like the engine a lot. I commented on this in the previous thread so it does not need to be rehashed here (I did have one error in my earkier posting however). I will add, as Bill says above, it does not like lugging around at low rpm's very much. When traveling in stop n go traffic I have to keep it in a low gear (it can do some serious trailer hitch jerking otherwise). ~2000 rpm's seem to be the magic number to stay at or above. I am sure the 427R has the same characteristic.

I do like the 402 and have no plans to replace it. Kinda like the 3 bears, to me this engine is just right for my SPF. Anyway, whatever floats your boat...I think all of the Roush engines are high quality, reliable engines. You can't go wrong.

WildBill1965 · #9 (**permalink**) 03-02-2009, 12:58 PM

If you like to cruise go with the SRTW, plenty of go. The R doesen't like driving around town. Only 25 HP difference!

BRYCE · #10 (**permalink**) 03-02-2009, 04:16 PM

JWilly is right. 2000 RPM,s is the magic number. Mine really bogs down anything less. But the 402R is strong, pulls like a Elephant and gets great mileage on the hiway.

RodKnock · #11 (**permalink**) 03-02-2009, 04:24 PM

I have no idea of what the rod angle ratio is for either engine, but generally, I believe you want the rod angle ratio to about 1.60. Please verify.

twobjshelbys · #12 (**permalink**) 03-02-2009, 04:37 PM

I agree with the 2000RPM for 427IR. After crawling through the adjustments on the throttle intakes (all 8 of them) I finally got it to idle smoothly and it seems happy at about 1200RPM with no load but does want to be about 1800-2000 when in gear.

BRYCE · #13 (**permalink**) 03-02-2009, 04:56 PM

According to the specs, 402r and 427r are very close. Idle is right on at 1200 rpm for mine. Roush makes a great engine. Very happy with mine over close to 8,000 mile

RodKnock · #14 (**permalink**) 03-02-2009, 05:02 PM

Has anyone heard of any issues on the aluminum 351W Dart blocks?

Blittleton · #15 (**permalink**) 03-02-2009, 05:10 PM

I've had a aluminum 402R built. Everything was great as ususal. Roush doesn't keep alot of these blocks on the shelf, so there maybe a wait for them to order one in. I had to wait additional 4 weeks to get my aluminum motor in.

Bill

RodKnock · #16 (**permalink**) 03-02-2009, 05:14 PM

I had heard 2nd hand recently, from someone reliable, that they've discovered some casting issues in the aluminum Dart 351W blocks. Although no warranty problems have surfaced due to this issue.

ERA Chas · #17 (**permalink**) 03-02-2009, 05:55 PM

Quote:

Originally Posted by LudicrousSpeed

What the hell is a twist-wedge cam? When I think of a cam lobe, I think of a lobe profile that resembles the profile of an airfoil.

It means a cam designed to work most efficiently with the "Twisted Wedge" cylinder head design. The cam lobes are shaped as all other cam lobes, but their lift/duration/LSA/CL specs are designed to compliment the head design. The heads have altered (from OE) valve placement, sizes and port runner height. The name comes from the combustion chamber shape.

SP01715 · #18 (**permalink**) 03-02-2009, 07:25 PM

My 434, which is very close to the 427R but with bigger heads and a more radical cam used to have the same issue with the 2000 rpm barrier. I had a guy here in So.Cal. that deals with a lot of these motors swap out my carb to a Holley 4150 HP Series with no choke and billet metering (sp) blocks. Since the swap the car is much more drivable and it dropped the idle down to about 900rpm's. It's a little cold blooded with no choke, but overall it's a much better setup now. It also seems to pull harder on the top end now as well.

LudicrousSpeed · #19 (**permalink**) 03-02-2009, 11:43 PM

Quote:

Originally Posted by ERA Chas

It means a cam designed to work most efficiently with the "Twisted Wedge" cylinder head design. The cam lobes are shaped as all other cam lobes, but their lift/duration/LSA/CL specs are designed to compliment the head design. The heads have altered (from OE) valve placement, sizes and port runner height. The name comes from the combustion chamber shape.

Ahh, Thankyou.
Excellent replies, Thanks guys.

ERA Chas · #20 (**permalink**) 03-03-2009, 07:37 AM

"I've been up & past Mach 1.1, but the Crosswind Landing was much more fun."
-Me

Lude,
Now you can help me understand something: Is that like 820MPH at 10,000 or some fixed altitude level? What was the ride?
Hey, I'm hijacking your own thread!